A note about the screenshots and the channels I referenced. The garden room guru is a great guy and one of the best UA-cam channels out there for self builders. As are the channels by Ali Dymock and The DIY guy, in fact all the channels I noted. That isn’t going to get in the way of what I’m showing here and doesn’t change my analysis in the video. It also doesn’t prevent me from recommending the channels noted to self builders, home improvers and competent DIYers. Construction has to be an iterative process where we can focus on the weak points and find better ways of doing them. UA-cam comments is a great way of understanding this, so to hear both sides, you might want to scroll through the comments.
Great video - really useful content. Just a suggestion, the constant rotating and zooming of the 3d drawings is quite hard to watch and hard to follow. Still images would be fine. The drawn animations work very well though.
Only watched 5 minutes of this and was just about to post exactly the same comment, as much as I want to learn about this subject the constant zooming in and out ( at speed) is making me nauseous.
Yes, would greatly help to slow the graphic movements. I paused & backed up several times as I watched, in order to study the graphics. This start-pause-start cycle made it tricky to glean all the information.
Very informative and well described. I have over 20 years of experience with grp from a manufacturer/specifier point of view. EPDM is probably the way to go. Grp is fatally flawed on a flat roof. Although I have never had a failure of a roof I have installed, there are too many parameters for your average roofer to comprehend. I have inspected more poorly installed grp roofs than is acceptable. I also take issue with moisture barriers. The roofs I have seen fail catastrophically are the ones installed with moisture barriers. The roof may have a small leak. The home owner is blissfully unaware as the moisture is held in the roof buildup. It will spread throughout the whole roof and no-one knows until it's too late. A simple repair has turned into a major refurbishment of the roof. I haven't seen a roof without a MB affected by condensation, so I will never be convinced it should be used.
I am a retired Architect. I completely agree, the OSB below the membrane always seemed a bit dodgy. I always thought it was done to give more support when walking over the roof, but had not considered the cost of the glue. Of course although glue more expensive, so is the extra layer of OSB. Although your method is more foolproof, if the VCL is good enough, and can resist screws penetration, the fact that the rubber is slightly permeable should make the OSB on top ok. One of the calculations that should be done is checking the build up of moisture during winter months doesn’t exceed that that gave evaporate during summer.
As a retired architect, I assume you've seen a few things. Have you come across a rotten top OSB deck due to condensation when there was a VCL? Genuinely interested in gathering some evidence.
@ haha…you got me there. I didn’t come across any, but from my technical training, I woke wary of this top OSB layer. You see this detail from major manufacturers, who should know what they are doing. But I think I recall they used a fully bonded system, so no screw holes to compromise the VCL
Making a build project fool proof is my key... You may get away with one build shortcut, but two or three in the same area leads to a failure. Plus my recommendation for UK home owners is to always have and use quite extractor fans + use a dehumidifier to reduce the amount of moisture testing the effectiveness of the VCB and layers above...?
Very informative video thank you, there are currently so many conflicting techniques regarding warm/cold roofs. They all make for interesting viewing though. Unfortunately the link to the restricted height option isn't working for me, I can't seem to find it in your video list either. Thanks again
Well finally someone who talks sense. I thought I was going mad seeing how wrong these roofs are built here in Ireland. If I may ask what is your take on installing the vapour barriers under a tile roof? Do you recommend pulling it taught or leaving some slack so the membrane sags between the rafters? I was taught to allow some slack so any rainwater making it past the tiles can flow down freely instead of stopping at each and every furring strip...
Hi. Yes I would lay it slack like you say. I think you mean breather membrane rather than vapour barrier? The vapour barrier is on the warm side of the insulation. Thanks for your comment.
Exactly this, me too. Have seen plenty of bad cold roofs, contractor rushing, forgetting to properly ventilate. No evidence of someone pulling up a roof and it's rotted due to evaporation. All due to water ingress from above.
Thanks, good video. The more people that are aware of the potential problems, the better. I regularly see poorly designed and detailed roofs. Some can cause trouble soon after construction. Sad really, as it often costs much the same to do properly. As houses are better insulated and are less draughty, cold bridging is a growing problem.
Great video , and also completely correct on the stubborn point of view of many builders. Uk construction industry at the tradesman level has so much ground to make up in comparison to the european counterpart. Not a surprise when you look at the general attitude to new technologies vs "how we've always done it".
We seemed to have perfected most things in Victorian times and mostly have been working backwards since the amount of old buildings I've taken apart where the timbers are in perfect condition speaks for itself heat and ventilation are the key also much healthier for the inhabitants of the buildings
Interesting video but the dew point should be calculated so it’s in the center of the PIR and that’s why you can have a OSB top deck without fear of it rotting.
I think you’re talking about about the “calculated” dew point which you can determine by defining a couple of variables. You are correct in that it can be in the centre of the PIR, especially in a warm roof. That’s not what I’m talking about in the arguments I’m making. I just tried to keep it simple to avoid confusing jargon. I may make a follow up video to go into the detail of what you’re saying versus what I think is also the case. Thanks for your comment.
@@build-better-things isn’t that the whole point? You’re saying it will rot with certainty while it’s actually in theory, same as, in theory the moisture will not rot your ply in your construction.
The principles apply to peaked and pitched roofs as well, but I didn’t know that until I started paying attention. After the spray foamers came and insulated my attic roof. I haven’t a clue if there was any sealant or member sprayed to the underside of the roof decking before applying the foam. 😅
wow the value of this information is just insane.. I'm going to scour your channel for insulation and moisture solutions for the basement. I tried to find what software you use in the comments but to no avail..
Great video, i have an art deco house all flat roofs and parapets and was shocked how little roofers know about this or choose to ignore it, i get stuck as i get quotes and i know more about the theory than all of them after doing extensive research, my issue is my lack of skill to do it myself, id hap pily try a garden room by the house is another beast, the expense of a tin roof alone makes me want it done correct 1st time….Is the height restriction video out yet as i couldnt find ut
@@Jackzuk The University of Greenwich's Chartered Surveying course related on day one "building is an art, not a science". Books will only get you half way.
Another superb video. Thank you for being so generous with your advice and providing detailed rationale behind each construction detail. In the process of a timber extension build myself and benefitting a lot from your videos.
Please excuse me if this is a daft question. I was totally onboard following your explanation and it made perfect sense, until you mentioned that air pockets between the rubber and the insulation are not a problem as the rubber is slightly permeable and air bubbles will eventually flatten out. So why would this permeability allow the air out of air pockets but trap moisture from the condensation below? Please be gentle in your response, there is every possibility I've misunderstood something. :)
Hi. This permeability will allow some trapped moisture to slowly breathe through beneath the membrane, but it won’t if there’s 18mm of OSB sitting on the cold side above the insulation and the localised vapour areas, where the moisture will get trapped within. It’s a good question and my fault for not explaining it well.
Thank you for the great video and I agree with your explanation. Unfortunately I am very worried as I have done more then 50 flat roofs with 18mm wbp on top of the firrings, vlc “alutrix” on top of the plywood, 150mm ecotherm (very well done, fill and seal all the joints) then 18mm tongue and groove OSB mechanical fixed with the “ plastic washers “ then finished with Flexi tec resin 2020 (very expensive material) and I have provided 10year warranty to my clients. Your explanations make sense, but I don’t know what to do with all the roofs that I have done and also with the others that we already have booked. I find it very difficult to use tissued face insulation (no plywood on top) when you have a lot of parapet detail, box gutter detail, skylight upstand, when the flat roof will be used as a balcony, or air source heat pump will be installed on top, etc…. Any suggestions? All the best
@@AgronIlirBilla why would you trust more the author of this video instead of your experience? Have you seen a top layers of a warm roof with VCL rot? Also, would you reckon it would be easier and cheaper to replace the existing top layer of OSB or the bottom one?
@@OmegaLok Me again. Yes, in answer to your question, I have seen rot in a warm flat roof with a VCL. Indeed, I have worked on a number of schools in which whole buildings have had to be demolished and replaced for that very reason. If I say that the plywood on the outside (not OSB) under the single ply membrane was rotten...........It's incredibly difficult to get ply to rot, but it rotted in this build-up. There was an extant vapour barrier. If you can control the moisture in the building properly, which inevitably means a mechanical ventilation system, then the issue seems likely to go away. I fit them in every building I design. But there are millions of houses around the world with OSB or ply sheathing, and without a MVHR system. They're all in danger.
@@MikeAG333 Sorry I am not convinced about a warm roof simply because you say: "whole buildings have had to be demolished" and "There was an extant vapour barrier." and that indicates to me full timber framing with OSB on the outer shell of the walls + membrane (i.e. you're not talking about a warm roof). I've seen this membrane lapped incorrectly several times on UA-cam (Izzy the Bricky had a video), i.e. top section tucked under the bottom section. I've also seen how my contractor incorrectly lapped the DPC over the DPM, me correct the issue, and building control signing off and then describing in their report that I've correctly put the DPC over the DPM... I just can't logically think that condensation will rot a warm roof outer layer of OSB when I compare the other mistakes where water will literally flow into an envelope and rest there forever.
@@OmegaLok Well, I didn't make myself as clear as I thought I had. Yes, it was a warm roof, and yes, there was a vapour barrier. One can't post drawings on UA-cam or I'd sketch the build-up for clarity. The principle of my point is that OSB is also a vapour barrier, and putting a vapour barrier on the outside of a timber construction, be it wall or roof, is a very poor idea in any place where the building is heated. I'm sure you could probably get away with it in a building that is never heated (and which has decent ventilation), but that's not much of Britain, Europe, or North America. Oh, and I have never claimed that the OSB would rot. It will get mouldy ......sorry......it DOES get mouldy, but it's the framing which is at risk from the interstitial condensation, not the OSB (although, as I said, some of the ply in the schools I talked about had turned to compost).
Hi. Great question. I deliberately avoided talking about the “calculated” dew point because I don’t think it’s relevant to what I’m talking about and it’s not something many might understand. It’s just very hard with the choices of information to focus on in the time you have in ten minutes of video. I’d make a specific video on it but I’ve tried similar before and the interest isn’t there.
Fair point, good to keep the info concise. I agree it's good to keep the details robust and allow an easy way out for moisture. You can never guarantee a perfect installation of a VCL so a theoretical dew point can become slightly irrelevant anyway. I always try to specify details that still work even if they are installed on a Friday afternoon. Cheers.
With the target U value being reduced to 0.11 there is currently a problem of how to buy PIR thick enough to be able to construct such a roof with doubling up the insulation. This poses two possible issues 1) A highly theoretical opportunity for condensation between the two sheets of PIR and 2) Screwing down possibly 240mm of insulation. The first I think is probably not a problem but interested in thoughts and both and also availability of insulation material to meet the new target.
Your point 1, if you are using foil backed insulation, which many builders continue to do, you will have trapped condensation where the two foils butt against each other, regardless of your vapour barrier. Your point 2, I would be aiming for 120 between joists, and around 150 over the top, to get around a theoretical 240mm sheet. You raise an excellent point on the new u values, and I suspect manufacturers will find new ways of increasing the lambda effectiveness, such as KingSpan’s newer phenolic batts.
I'm a lowly DIY'er, half way through his first warm roof (a mere 4 square metres). I did consider gluing the rubber directly to the insulation, but in the end I went with a 9mm OSB3 layer beneath the EPDM because that's what the majority of people seem to recommend, and I wanted a roof that I could walk on to get access to the gutters etc. Have I made a horrible mistake ? Time will tell, I suppose. I tried very hard to leave no gaps in the vapour layer (= Alutrix), and I deliberately chose OSB3 because it can apparently tolerate humid conditions. Kingspan claim that their phenolic insulation ("Kooltherm") is also vapour resistant, so perhaps that will help too. I hope it won't end up worse than the cold unventilated felt roof I replaced, which had the consistency of soggy Wheetabix. Fingers crossed.
I wouldn’t call it that. If the roof fails, hopefully you can peel it off, along with the old OSB, it’s not a huge exercise nor cost to adhere new rubberto, using a new 20mm layer of tissue faced over your old insulation to keep the depth almost the same. Humidity is a site specific thing, so you might be OK. Just wait and see.
Hi, great video - thanks. Is it possible to apply final layers to say rockwool flexi or such. I'm ocd about fire proofing and toxic fumes with kingspan and it's ilk. Is some form of more non-rottable layer or support system be available to walk on after installation? Cheers
Hi. Which way are you worried about fire proofing. Starting inside and spreading out presumably? Surface spread of flame is one of the main issue with flat roofs. I’m just not 100pc clear on your question. Can you word in a different way? S Thanks.
I mean that if I only wanted to insulate with rockwool and not pir, then it seems a cold roof is my only option as the load bearing capacity on a warm roof is not sufficient for walking on and such in comparison to pir?
Yes that is correct. You need to ventilate between the insulation and the timber deck. But you also must remember, mineral wool is less than half as efficient as PIR, so you’re not going to be even close to the efficiency of rigid.
Thanks for this. Difficult to get a 100% visual on what you were trying to show as the gold standard. So it's Breathable membrane, osb, insulation and then epdm?
I think it’s osb then vapour control layer on the warm side, then insulation. This keeps the osb in the warm area meaning it does not get cold enough for the vapour in the air to condense on. A breathable membrane lets vapour through so not what you want because that takes the moisture through and as the temperature decreases as you travel through the insulation eventually you get to the dew point and moisture will condense out. Breathe membranes are for where you want vapour to escape but at the same time be waterproof. I.e. above a 50mm air gap in a cold roof below tiles.
No breathable membrane. OSB then vapour barrier, then insulation, then EPDM. Sorry if I wasn’t clear. You only use breather membrane where you have a ventilated cavity on the cold side of the membrane.
Jerry thanks for yet another great informative video. Just in time as I'm in the planning phase of adding an open plan kitchen dinner leading onto the rear garden. I'm going to pass your video onto the architect so they can spec the construction drawings accordingly. It might not go down well, but I'm the paying customer :)
Thank you too. I’ll be interested if you come back with their comments. Construction industry is a sea of conflicting information sometimes, that’s why I over do it with the analysis.
9:12 could you please link to your other video? I can't fight the video you are referring to. Thanks for this video, I live in Belgium and unfortunately, we have the same "I have been doing this for 20 years and never had any issue" builders. The problem with these kind of builders is that they got in the craft by "doing" not "understanding".
I’m going to embark on building a garden building possibly next year and have seen a lot of what you showed in your vid, so it was helpful to get a bit more info on it. just fully renovated our home and have had numerous crappy experiences with tradespeople. A good few of them have come across as entitled and have wanted to get in and out with maximum return while providing bad quality work. It’s refreshing when I come across one who actually seems to care. I had a chat with a guy that has a decorating company in Windermere area and he said that most domestic trades don’t seem to realise they’re in a service industry and that how you deal with customers and the quality of your work matters. I couldn’t agree more. That’s why I’ll build my own garden building, then I don’t have to put myself through dealing with them again.
@eddiemcboofin1917 It probably is. I’ve filmed a couple of different ways and need to get some time to make up a vid. Thanks a lot for taking the time to comment.
Great video and just binged a few others (inc french drain which im looking to do with my cellar and a external sump pump). I also one day want to build a garden room with solar, given the weight, how would you construct this kind of roof?
I’ve planning a solar installation at the moment, flat roof using EPDM, fixings for rail system through the membrane and insulation and into the joists. I hope I will post it here at some point but maybe next year.
Interesting video. Lots of conflicting info on flat roofs. I think most are doomed to fail simply because of a lack of pitch and water lying on it. But one simple question. What is the method if your not using rubber? What about fibreglass(not dryseal) and torch on felt?
It’s more just to avoid anything that can rot, such as timber product, on the cold side of the insulation, not part of a ventilated void, and still under the outer membrane. I just happened to be using EPDM because I understand the technology. If your roof membrane requires a timber sub strata, and you’re attempting a warm roof, ie not a cold roof, then I’m saying I think it’s a significant weakness, and I hope I’ve shown why.
If the vapor barrier is merely laid out and taped I would be inclined to put some silicone sealant in the tip of each screw: 1. As a lube to prevent windup of vapor film around the screw; and 2. To seal around the screw. + Somewhere in the matrix there needs to be an deliberate path for pressure release in a rain protected area since one is creating two sealed diaphragms, maybe along the edge under a rain cap in a dry area. You do not want changes if barometric pressure lifting the membrane, and you want any residual chemical fumes to vent outdoors.
What about when sips panels are used? The foam is completely bonded to the osb when the panels are formed in the factory so no moisture can pass through.
Interesting. To my horror my 20 year old lead roof had erupted on a warm roof construction , the LSA now state that they no longer recommend this. I had initially thought the lack of vapour barrier was the main cause. I have added Allutrix to the sub deck then refitted the insulation on top followed by OSB and primer finally layered with ResTech . Im now concerned about moisture forming. Everyone tells you something different!
Great video. My only comment is that cold roofs will always create condensation in the cold roof void and its the ventilation that will dry this out. Water vapour doesnt magically waft out the vents and then condense outside. Ps i have 40 years in construction surveying design and inspection. Pps people are still building cold roofs for some mad reason.
Thanks. That makes me feel good. I missed out several points (eg exact position of dew point, difference between roof and wall) just because there isn’t time in a ten minute video, hopefully they’ll have some questions.
Thank you for a very useful explanation! I have a question also: is a vapor barrier any use in conjunction with a sealed hard isolation panel of which the seams are taped? Am I wrong in thinking no vapor can get through taped PIR panels anyway?
Taping is not perfect but close enough. I don’t tape the boards because I don’t think foil insulation should be used in a warm roof, but you’ll see in these comments many arguing otherwise. If you have an effective vapour barrier below, that’s really all to focus on. Appreciate it’s tricky with the conflicting info but all I can do is show my analysis and conclusions like in the video. Best of luck with it.
Your general rule that any moisture will condensate on the cold side of the insulation or inside the insulation itself is the simple but effective rule. That is the most important thing to consider when deciding on how to assemble any wall or roof. Thank you
Also on your own video of you installing a roof, it looks like your vapour barrier is just loose laid? We usually prime the deck then install the vapour barrier and seam roller all over laps ?
Yes, you need the warm roof to do the opposite for your summers, never insulation between the joists, always over the top to prevent thermal bridging from outside to in. Those joists just act like radiators in summer if they’re not insulated, and you’re air con will have to be on far more.
@@build-better-things Oh, bit surprised at that answer as I doubt roofs are being made like this down here. They are often more like the cold roof design. Great to know, thanks.
Ventilated cold roof space (insulation at base of roof void) is also ok, but warm roof is best. The faster the air moving created by the negative pressure, the more likely the thermal gain is going to be weakened by air movement over the structural members.
Though I think you raise interesting points I think you are incorrect on your main point about the top layer of OSB. I’ll happily keep doing it this way with the blessing of building control. Dew points.
Hi and thanks for your comment. Yes I’m just trying to make the arguments the way I see them, but if you have a way that’s working for you, that is great too.
Having resigned myself to doing a flat roof on my planned renovation's extension to save a bit of cash(I can DIY this, I don't trust myself to DIY pitched slate lol) I wonder, can this advice be applied with GRP/fibreglass? I like the idea of being able to walk on the roof for future maintenance of outside walls without stressing about puncturing the surface as I would with EDPM, but all the GRP videos I've seen have been adamant that you *must* adhere down to OSB sheet or, at worst, rough-sanded plywood.
this is what my builder says too i challenged him when we did grp on our dormer and relented to his advise and guidance by the grp people. time will tell.
There are a number of reasons why I would avoid GRP and one of those reasons is the requirement to bond into timber. You can’t bond directly into insulation.
We are. Make no mistake about that. This video has a staggering amount of inaccuracies. Don't forget that at the end of the video he calls himself a novice which not only speaks volumes but could also be the only true thing he says.
@@Mr_A_Builders Anyone with any sense will realise you, with lots of actual knowledge and experience are correct As opposed to someone with no qualifications, no experience no examples to back up his claims, and what “he thinks” is correct
You're absolutely right. But TR27 is useless. We tried a warm roof with no OSB. TR27 ended up with dents in it every time we stepped or kneeled on it. The fibre facing peeled off at the edges. I need a solid roof that I can put ladders on, not one made out of sponge cake. So I ended up solvent gluing 12mm OSB to the TR27 and then solvent gluing the EPDM to that. Really didn't want to, and I know I'm going to have to replace the roof in 10 years because the OSB will rot. Kingspan/other manufs need to come up with a decent product with a hard deck. Until then we will keep installing OSB because it's the only practical option.
I have not had the same problem, although I use the Resista insulation rather than KingSpan and it’s always very firm to walk on, and you can’t peel the face at all. However, for your specific needs, I think you need to be considering an inverted roof, or integrating a raised deck system similar to if you were adding solar , if you’re putting heavy point loads on, or regular foot traffic , regardless of whether I think it will work with Resista. Your use case is not really what the system is designed for, to be fair to the manufacturers .
I'm shocked. I've been following some of the pro builders you've highlighted in this video and regarded them all as sound sources to watch for good building practices. I built a garden room following a well known channel. I used a liquid adhesive to glue the EPDM down to a wooden roof deck. The saving grace is that I've kept the garden room uninsulated as it is used as a workshop. However, I am now going to rethink/replan the roofing of our single story house extension. In your video the EPDM of your garden room shows all the tube washers. Is this permanent since I don't want upstairs to look down on a spotty roof. I had understood EPDM to be the best modern solution, but if it looks ugly its a no - which probably means fiberglass is the only alternative ?
You could keep exactly what you have done, but do a cold ventilated roof. Which means the top face of the insulation is 50mm below the inside face of the roof deck and it will work well. You do need to ventilated that 50mm void.
@ the extension is in the planing stage. I was just making the point that i had assumed the way other pro builders have shown on UA-cam was correct. Your explanation is excellent and causing me to replan what I eventually end up doing with the extension roof. Warm roof feels like the right way to go but 100% want to get the roof covering and insulation right and lasting a lifetime. My main concern was whether the epdm after correct install shows no signs of fixing points beneath it? It’s this type of aesthetic detail that is just an important where a roof is visible (unlike most garden rooms).
@phil7309 yes you’ll see the washers below like you can in my video, towards the end. However if you took more time laying them out neatly it probably would look ok. Personally it doesn’t bother me the way it is but you might not like it.
Please please please do yourself a massive favour and don't change your plans based on this video, there are massive problems with it. What other channels do you follow that you refer to?
@@onlyidiotsrespond I’m not an expert so I try to learn from those wiser and with real experience to inform my decisions, ideally so I don’t need to rectify a problem caused by an assumed right way to build something. Certain jobs need to be done correctly and a roof is one of those. So after listening to this video I will be researching this more and making sure I am 100% happy with the way I will eventually insulate and build my roof.
Actually I’m not sure. I always thought you needed to renew it after quite short periods. I also think you might need to torch onto a timber sub strata so cold ventilated roof might be best. I’m no expert on felt however. Best of luck with it.
@@build-better-things Thanks for coming back so quick. Yes I think it does need renewing from time to time, but should last a good while - perhaps not as long as best case well laid/prep'd GRP/Rubber. This is to do with an 'already built' outbuilding around 3 years ago, did have OSB sheet under and over PIR. I'll inspect at some point as I'm interested in deterioration of the sheet. Thanks!
As long as you have an air gap, ideally 50mm but dependant on the depth of your joists / insulation and that air gap needs to be pulling air through it by good use of vents. Then your suggested makeup is ok
@@build-better-thingsbut you didn't do it in practice. What's the point in telling everyone how best to do it when you don't do it yourself? Honest question, with all the conflicting information within this video...please be honest...do you know what you're doing/talking about?
I was wondering how this might apply to a sloped warm roof design? I asked our architect for a warm roof on our extension (Which has both a sloped and flat portion), but after the calcs they wanted to put 100mm of Celotex on top of the rafters and 100mm of Celotex between the rafters with 50mm of ventilation above the insulation for the pitched portion for some reason stating it was still a warm roof somehow. For the flat roof they specified 18mm ply over 200mm Celotex, but specified no ply between the insulation and rafters. I might ask the inspector directly if we can just do 200mm on top for the pitched roof instead, and build it up as you've suggested.
A sloping roof is different because the opportunity is there for a ventilated void, using the battens and counter battens which take the tiles, and therefore the option of a breather membrane. I’ve made a video about it elsewhere on the channel.
Thank goodness I'm not the only one saying this. I've been banging on about it for years. OSB should be on the INSIDE of insulation, if it's anywhere. The good old US of A is going to have a massive issue with their walls in the next few years, as they've been making thjis fundamental mistake for decades. Oh, and I'm an architect.
Thanks. I guess you have many more climates to consider compared to the smaller European geographies. Scotland has slightly different energy legislation and therefore different make ups, for example, than England, but it’s a relatively small area.
@@OmegaLok We are seeing evidence of failure. Lots of it. But what we haven't seen is any large-scale research or reports, academic studies, or proposals for revised "codes", as the Americans call them. Houses are just repaired on an ad-hoc basis, and the failures blamed on poor workmanship, or leaky gutters, or somesuch.....but if you pull off the outer skin and OSB on almost any 20+ year old house in the parts of the USA where winter heating is a thing, you'll find mould on the inside of the sheathing board, and damage to the framing.
Not happy as i have just recently completed a warm roof with 18mm OSB on top of PIR then got 1.6mm EDPM on top. But your information seems sound and logical. Is there any actions i can take to improve / avoid early rot in the top OSB ? (Minor not major reconstruction). PS - Could not find the height restriction video you referenced.
If you've used a VCL I would not worry so much. There is simply no evidence of a top deck rotting if there is a VCL. The only thing I find on youtube is: ua-cam.com/video/6NWrYG2G2Ho/v-deo.html and surprise surprise they did not use a VCL. All other examples are pitched cold roofs with improper ventilation or water ingress
@@OmegaLokthere is zero evidence in this country providing all stages are correct and installed correctly. Absolutely zero. If anyone would like to prove me wrong please do so!
Hi. If you read my bio on the channel, you’ll find it, and I go over it in some of my videos. However, qualifications are less relevant than the arguments and the data I’m putting forward, which you’re welcome to dispute so we can enjoy a conversation. Qualifications are nice, physics is best. Physics doesn’t care about your qualifications.
@ I’m not disputing anything, “however qualifications are less relevant than arguments” however argument require facts not opinions Especially when handing out public advice
Absolutely. If I’ve got things or facts wrong, I hope you can let me know. I put a lot of work into these videos but it’s very hard to be perfect. Especially on a subject like this which has a load of “it depends” about it.
So just to clarify you have no roofing background, no qualifications no real "on the tools experience" by which i mean how many flat roofs have you done?
@@build-better-things Your are making the assumption the dew point is on the bottom of the OSB, this is not correct on a warm roof, this is the whole point of a warm roof, this does not happen In fact, in a warm roof, the Dew Point happens within the PIR insulation and moisture-tolerant boards, away from the roof timber, so there are no moisture spots in the roof space causing condensation issues. There is a very good technical web site which explains this in detail it’s detail library
The OSB is often a “standard detail” that’s all. I am sure a builder would happily leave out that additional task with a simpler build up. I certainly will do so with my own. What do you think about those one way breathable membranes to avoid trapped moisture?
They are great, but they only work with a ventilated cavity. For example, a wall or sloping roof with tiles on battens. For the examples I describe, not feasible.
I'm not a builder or a roofer. Last year, I built a 5m x 5m extension for my sister. I went to an architect (a good one) for how to build the warm roof...and it wasn't the way you do it. Halfway through, I had issues with digging out for the slab (solid concrete from many years ago), so I consulted a surveyor who suggested a raft slab. But my point is that for £500 cash, he also included drawings for the roof...and again, it was the same as the architect's design...which is the way you say NOT to do it...timbers-OSB-Celotex-vapour barrier-OSB-EPDM. Forgot to add... As I have never built anything, I was running everything past Building Control, and they were very happy with it - even came up to see the roof halfway through construction. I'm not getting at you personally, just saying that an architect, a surveyor, and BC, all suggested the above method I used, and that you don't recommend.
Hi and thanks for sharing. If you read the comments here, you’ll see several people saying I’m wrong, (some throwing insults etc) and that OSB under the membrane is a fine thing. I’ve explained in the video visually with my reasoning why it’s an awful solution, you are welcome to disagree, but I hope you get the same level of detailed explanation and analysis from your architect or builder as to why OSB and foil are a good thing on the cold side in a warm roof set up.
Hi. Yes it’s safe to walk on, but just like with an OSB sub strata, sensible with the kind of footwear, avoid anything that can damage / nick the membrane etc. For Solar, you need to design the loadings in the joists for the additional weight plus the wind uplift, and then it’s down to your choice of fixings locations for the rails, and whether they pierce the membrane. For a green roof, I would be considering an inverted roof, rather than a warm roof.
It’s easier to think about these things in terms of the u value, and work backwards from that. You can find the list of u values for each element, eg roof, walls, floor, and one you have it, you visit one of the manufacturer’s online u value sites, and see what insulation options are there. I would never put quilt in between the joists for thermal reasons because it performs poorly. Sometimes acoustics are relevant but then you need to allow separation and some ventilation. Really easier to draw than describe.
I’m currently designing a warm roof, and like you point out everywhere shows a top deck of wood material. This bothered me for the reasons you lay out, if the wood on the cold side can’t breathe it’ll rot. I’m planning a GRP roof, but I think it would still be best to have a top deck to do so. What are your thoughts on a rather unconventional method of using something like an xps tile backer board for top deck before GRP?
Yes, I guess if you’re set on GRP, that’s an option, but the point is, you want the dew point (where it condenses) to occur toward the outside of the rubber, so it just evaporates away. Even with a synthetic board, which won’t rot, you’ll still have trapped condensation, since the dew point will happen someways into that board and the “dew” has nowhere to go.
@@SlayerLaw There is simply no evidence of a top deck rotting if there is a VCL. The only thing I find on youtube is: ua-cam.com/video/6NWrYG2G2Ho/v-deo.html and surprise surprise they did not use a VCL. All other examples are pitched cold roofs with improper ventilation or water ingress
@@OmegaLok Thanks for the additional input. That roof did seem to be poorly constructed! It seems logical if the VCL is working correctly it should be ok. I will keep researching
You attach a fascia with the top face flush with the sub strata (eg top of insulation) and leave the membrane hanging over by about 80mm. Then you attach a 2 piece gutter trim and friction fit to secure the rubber. You can see it towards the end of the video in the roof with the black corrugated cladding.
Can an existing cold flat roof with a bitumen/felt covering be over boaded with insulation WITHOUT a vapour barrier? Will the bitumen felt be a vapour barrier?? Many thanks
In theory, bitumen in these compounds when combined with the fibres of felt is not breathable. In reality, if the roof has been exposed for a while, it may still keep the water out, yet let vapour permeate. However the problem you have is around the edges, where the envelope must be continuous with whatever the vertical vapour barrier is, that junction is going to be difficult with two different materials.
@@build-better-things when was the last time anybody received a response as quickly as that! Thank you. Shooting from the hip, if the rubber membrane excess/over lap is glued to the felt on the side of the roof.... Would that work? Also any advice or a video of attaching rubber membrane to an existing wall?
That’s just asking for trouble sounds like something a cowboy builder would try and pull off No self respecting builder or roofer would contemplate this
Do you think a 45mm air gap will be enough on a garden room above insulation it’s 3m span wall to wall with shower in. I know the regs say 50mm but iv currently got 45mm was going to do hybrid but then realized iv got enough space almost to do cold roof. Thanks for any help.
Hi. A few millimetres is ok in that situation. . The other issue with both cold roofs and hybrid to consider is the vapour barrier and things like lighting. I will release an Ina few days about how I think it’s best to do a hybrid roof. Thanks for your comment.
@ thank you for quick reply really appreciated, ye I’m not planning on putting recessed lights in for that reason I don’t want to many holes/week points in the vapor barrier so I’m just going with a single light in the middle. Thanks again
With this method, how would i go about fixing down a prefab upvc skylight, where the instructions say to screw it down to the top deck of OSB, before applying the EPDM? Im a diy'er doing a flat roof extension myself, with no experience, so any help greatly appreciated.
Good question. I’d always fix into the trimmers around my opening, but you can also fix under the insulation into the warm OSB deck using window brackets which sometimes come with the kit. Hard to explain, easy to draw.
OK - how do you protect the EPDM from birds pecking/scratching at it? I've got what sounds like pigeons wearing hobnail boots thumping around on my roof! It's felt/gravel at the moment, but needs replacing as it's a badly insulated cold roof install (previous owner was a builder, allegedly) - lots of gaps around the PIR and no VPL above ceiling!
The only time I’ve seen a problem with birds pecking at the membrane is when there is creases in it. I don’t know why, but it seems to attract them. It’s actually very easy to sort, using a repair kit. If you don’t have that problem, then I’m not sure.
Hi. Part of the worry for me is that if you have impermeable surfaces, be they foil, polythene or OSB, under the surface of the outer membrane, on the cold side of the insulation, given we are not in a vacuum and that no vapour barrier is perfect, you are creating perfect conditions for interstitial condensation. I just would never go there whether for my own or someone else’s when I can eliminate the issue entirely. There’s several people commenting here who disagree with me, a few of them are going out of their way to reply and repeat all over the place saying I’m wrong, so you might want to read all the comments and make your own mind up. Great building construction is as much about mitigation as anything else, I think the science is sound, but you can always disagree with me. Thanks for the comment.
Yeah in Arch Tech collage (a couple years ago since I graduated) we were thought to apply the roofing membrane finish directly onto the insulation when detailing as you specified in this video. I watch alot of the channels you screen grabbed (+ others) who all do the 2nd OSB layer on the cold side of the insulation & I always wondered why they would add such an unnecessary layer to the roof assembly. Now I know! 😅
I've just installed my rubber roof as per the old way. Its on my shed/garden room. As it will be low occupancy with trickle vents i am hoping it will be ok?
I didn’t go into trickle ventilation in there video due to time. If you’ve got OSB under your membrane, then ventilation will definitely help you with vapour control. People tend to close the vents in winter for obvious reasons, that’s why I don’t talk about it much. The fact you’re asking the question, and it’s not going to have much vapour generation will work in your favour.
You are making the assumption the dew point is on the bottom of the OSB, this is not correct on a warm roof, this is the whole design of a warm roof, this does not happen In fact, in a warm roof, the Dew Point happens within the PIR insulation and moisture-tolerant boards, away from the roof timber, so there are no moisture spots in the roof space causing condensation issues. There is a very good technical web site which explains this in detail it’s detail library
Yes, thank you! Please comment again with the technical info source you mention. Because I've designed the 'flat' roof of my house currently under construction, after exhaustive research about this very condensation issue, and determined my roof deck's underside should be perfectly protected b/c of the critically-correct R-value proportion --- specific to my climate zone --- I'll be using of between-the-joists batts (i.e. UNDER the roof sheathing) and foamboard (EPS) on TOP of my sheathing. In other words, while this UA-cam person is clearly extremely knowledgeable about bldg. science, the REAL issue here is WHERE IN YOUR ROOF SANDWICH IS THE DEW POINT? Also BTW, I'll be stapling & taping a 'smart' vapor barrier to the underside of the joists, btwn. them and the ceiling sheetrock.
EPDM rubber is permeable and allows water vapour to escape, albeit slowly, yet reasonably. If a solvent based adhesive is used it will certainly cause a hindrance to that. Unless one builds a hermetically sealed inner roof/insulation surface (a practical impossibility, essentially, at best an expensive and needless endeavour) water will always condense at a cold point. The amount of water available to condense in a building /given area of it should be lower than the amount which can reasonably escape, and unless the building has big issues with damp/condensation then there should be no issues with the boarded roofs depicted. If there is any issue, it will be down to remedial works being needed on the rest of the building. In a climate like Britain's, screws into wood will cause negligible heat loss. I've built numerous buildings and many, many EPDM roofs all over the UK and Scandinavia, as well for myself and which I monitor and experiment with - never an issue, and i have often used the OSB top boarding method. I hope the feedback is useful to people.
Appreciate your experience, welcome to disagree here and give your reasons, and keep doing it the way you have always done it. Your experience and your comments will help everyone decide. My view remains…..Timber composite on the cold side is unnecessary and it can rot, as is using foil in roof insulation, and I’ve given my arguments why in the video. Thanks.
@build-better-things thanks for your reply. I totally agree about not using foils and it's so important to think through air movement and the building design as a whole, carefully. As i'm sure you know, but in case it helps others, it's common that people reduce ventilation 'reduce drafts and heat loss' by closing vents/windows and sealing gaps etc. As an old Swedish engineer friend put it 'any building design has to take into consideration the trade-off between insulation and air flow'. If it feels cold, it probably needs to be insulated better, and reducing/changing air flow without considering its effects can cause a lot of damage. (I appreciate that's verging on being off topic and rather general, sorry).
Hello! Hope you're well. A couple of our viewers have brought this video and it's contents to our attention so I thought I'd check it out. Disappointingly it seems that you have intentionally misrepresented contents of our videos to fit the narrative of yours. Some of the things you say when visually representing Mr A Builders are extremely misleading at best and at worst completely untrue. As mentioned this is extremely disappointing as I really can't see how I've misunderstood what you've said in relation to our content. We all need ideas for videos but it's a shame that you have appeared to go down this particular, unethical route. I'm looking forward to your response, should you give one, I can guess what it's going to be but we shall see. I think it's only fair that should we have a conversation about it, of which I'm more than willing to have, that it's done in 'public' and not private so other people (let's not get too ahead of ourselves, no one else will care!) can read, get involved and make their own minds up in regards to your integrity. Take care.
From. Someone who watches both channels, do you disagree with this method? Or are you just arguing the idea because he has used a still picture of your channel? Just interested to know!
@@seunakin6961hello, hope you're well. Our main concern is that whilst he is showing clips/stills from our content his commentary appears to explain things that we are doing that we certainly aren't. It seems to be incredibly disingenuous. As mentioned in my previous comment he's changing the narrative of our videos to fit his. Naughty naughty!
@Mr_A_Builders Fair enough and I understand your point. I will continue to watch your content as I find it extremely educational. Keep up the great work
Thanks for taking the time to comment. You say misrepresented, untrue, unethical and you mention my lack of integrity. But you don’t give any examples from my arguments and reasoning of what makes you think that, not one, you just get stuck in and make it personal, which is just the way it seems to be these days online, from those in the Trade in particular, when you question something they’re doing. I’m happy to have a conversation, the aim for me is to help self builders wade through the conflicting info, and make the best choices. For what it’s worth, I think yours is a fine channel, always positive and generous with your knowledge.
I never understood all these 'water based' products for outdoor applications. This also goes for paint. Solvent based makes more sense to me. Rain will not slowly dissolve it.
Left slightly confused by this video. If you glue your EDPM directly to the PIR then the same moisture that you say rots the top layer of OSB now has nowhere to go as EDPM will not allow moisture through. Also, if you have put a vapour barrier under the EDPM then surely you have eliminated the moisture getting through anyway.Would welcome any replies.
Hi. I thought I did say EPDM has a slight breathable element to it. The trapped moisture will permeate slowly through it. It won’t do that if it’s stuck within 18mm of impermeable OSB or within some air within below a layer of foil on the cold side. The vapour barrier is just a retarder and I can’t rely, on it so I’m designing out the quality control issues. You raise some great questions, even if I’m totally wrong, why take the risk, when there’s no difference in cost?
@@build-better-things - Thank you for getting back so quickly. I'm currently making a decision on which way to go with this on my own extension. You are correct that EDPM is slightly breathable but it won't allow moisture to pass through as you say (not according to the data I'm reading). Personally I think the real solution to this is to deal with the problem at source and condition the air first. This could be achieved using an appropriate air-conditioner, heat pump or dehumidifier. But now I'm increasing my costs. Meanwhile, I'm going to say a big thank you for putting your videos out there I've certainly learnt from them and put a lot of what you say into practice.
You've got a few issues here, pal. 1. You're referencing other channels that dont contain what you say they do. 2. You've got the dew point wrong which undermines your entire point. 3. You ahow a confusing diagram that shows the VCL in completely the wrong place 4. You have absolutely no evidence for anything you say, not even a link to an article. 5. You say you're a novice but offer consultation services! How does that work? 6. You advise to go against manufacturers recommendations. I could go on but surely thats enough? This is a shoddy, ill conceived poorly researched argument that you felt the need to discredit other UA-camrs videos to make. I will be amazed if some of them don't get in tiuch with you, even try to get it taken down. Unbelievably bad.
My thoughts exactly… guys got a lot of misinformation in his videos and some very silly references to other guys that clearly know exactly what they’re doing and have done for many years
@Telferroofing spot on mate. I checked out one of the channels he slags off, Mr A Builders and do you know what? There isn't a warm deck roof with an EPDM covering on it! Not a single video on the entire channel. This clown accuses them of doing something they simply haven't done. And that's just one of the points. This video should be taken down.
Timber on the cold side is not great, timber composite is worse, as is using foil in roof insulation, and I’ve given my arguments why along with solutions in the video.
@@build-better-things you haven't addressed a single point from the above but instead down graded the entire point of your video to "not great". Seriously mate, you need to sort this. Having this opinion is fine but you've dragged other UA-camrs into it and from what I can see lied about their videos. As mentioned above Mr A Builders does not have a rubber roof on a warm deck video on their entire channel and you say they do. That's the same for the Garden Room Guru, one of the other videos you've shown. I've noticed in one of Mr A's posts that they say maybe you should donate to their fund raising as way of the an apology. You do need to reach out to them if you haven't already.
PSS: The vapour barrier in your video looks like a laminated polythene foil product as it looks lose laid (not stuck to the base deck with bitumen). These products are not sufficient and regardless of whether you’ve used an upper layer or not, condensation will occur between the roof membrane and the insulation because you have failed to prevent rising vapour due to an inadequate vapour barrier. Ok that condensation will have no OSB to rot, but it will reduce the life of your roof to exactly the same extent by delaminating your membrane bond to your tissue faced TR27 insulation. Good points regards mechanical fixing, but in terms of thermal performance it doesn’t matter what roofers toss about with on top of the insulation. The key is stopping warm vapour holding air from inside the building rising through the structure as it will condense if it’s allowed to meet a cold surface whatever you do on top.
As long as the insulation is fully supported underneath then the insulation can’t go anywhere , fine for light traffic. Tapered insulation is perfect, take the minimum thickness eg lowest point to calculate your u value
I have zero building experience, and am coming from this with probably complete misunderstanding, but if the EPDM stops the moisture getting out, and it sits on and rots the OSB, what happens if you don't have the OSB? Does it not sit on the insulation? That doesn't or can't rot?
If you’re using EPDM, there is a breathable aspect to the compound where the trapped moisture con dissipate slowly on top of the tissue faced of the insulation and directly under the membrane. Instead it’s trapped in the OSB and never gets out.
@@russellwheeler2760 the EPDM membrane is a breathable monomer. It does allow a fairly slow but reasonable egress of water. It's an excellent material to work with.
@russellwheeler2760 that doesn't really add up in practice - even small gaps allow air movement and dissipation of moisture. Permaroof, based in the UK have excellent videos on best practice usage of EPDM freely available on their website - they're Firestone distributors and have decades of US and international, other climates experience to draw on, as well as the UK.
It should be, but architects are as guilty of builders of getting this detailing wrong. Building regulations are just checking for compliance, they’re not there to check the design, although many do end up being helpful. Planning permission has no relevance for roof makeups, just appearance and size.
I'm pretty sure this is a flawed theory as the warmth never gets to the top sheet of osb and vapour can't get there because there is a vapour barrier and the actual PIR is a vapour barrier in itself. if anything the sheet underneath the vapour barrier is the one that's going to get vapour on it but it has breathable materials underneath plasterboard etc. I wouldn't use water based anything but also we use rolls of resitrix so I don't think it's ever coming off.
Thanks. The warmth is always going to transfer, it’s just a question of speed. It’s the moist air that causes the problem in localised spots where there’s the inevitable vapour barrier weaknesses, fixing gaps, poor edge treatment residual air vapour, and joints which, over time, causes the problem as the small amounts of moisture collecting have nowhere to go. Even if you dismiss all of that, my point would still be, why include foil insulation and all that timber composite top decking when you can just bond direct and get rid of the potential failure completely.
Omitting OSB on top makes the roof way way more likely to be damaged by footfall, ladders, people just carrying out routine maintenance/decoration etc in the future. Stop being silly.
If the membrane’s going to fail because of footfall, it’s going to fail, regardless of whether it’s an OSB or synthetic sub strata and it’s obvious you’ve never walked on the latter, or you wouldn’t have written such nonsense. For your ladder, even for your OSB sub strata , shouldn’t you be using a spreader plate sir? You say “silly”…..you seem to be desperate to have OSB below your membrane, so …..go for it.
Never liked rubber roofs snd wouldn’t use them on domestic jobs either, I use grp system flexitec, and were possible warm roof applications, if not possible cold roof system with crossed battening to ensure good air circulation, and good vapour barrier.
Thanks a lot for your comment. What’s the sub strata you use on it? I focused on EPDM on the video because that’s the material that a lot of small general builders and most self builders tend to use.
@@AN-vt3kl with all due, "I never liked" isn't much of an argument. EPDM allows water to egress and is far more environmentally friendly that GRP and any other membrane or coating system I can think of, has far greater longevity (accelerated wear and weathering tests well over 100 years), is elastic to allow for movement and can even be reused.
@@build-better-things most times its 18mm t/g osb 3 boards, also can use 8x4 osb boards if no access for smaller boards but in that case a lot more work to seal the joins prior applying matting.
@@gurglejug627 in my experience there is a reason cheap isn't good, I would agree edpm ok for sheds garden rooms etc. but not for extensions, loft conversions but each to their own.
@AN-vt3kl that's not an argument it's a baseless and odd opinion - i speak from vast experience. The price has nothing to do with the quality of material or of suitability for any job.
I don’t rate it, but I would also say, I’m not an expert in the technology of it. As i understand it, you have to bond to timber sub strata so it’s horrible for warm flat roofs. Cold ventilated roofs perhaps.
A note about the screenshots and the channels I referenced. The garden room guru is a great guy and one of the best UA-cam channels out there for self builders. As are the channels by Ali Dymock and The DIY guy, in fact all the channels I noted. That isn’t going to get in the way of what I’m showing here and doesn’t change my analysis in the video. It also doesn’t prevent me from recommending the channels noted to self builders, home improvers and competent DIYers. Construction has to be an iterative process where we can focus on the weak points and find better ways of doing them. UA-cam comments is a great way of understanding this, so to hear both sides, you might want to scroll through the comments.
Great video - really useful content. Just a suggestion, the constant rotating and zooming of the 3d drawings is quite hard to watch and hard to follow. Still images would be fine. The drawn animations work very well though.
Only watched 5 minutes of this and was just about to post exactly the same comment, as much as I want to learn about this subject the constant zooming in and out ( at speed) is making me nauseous.
Yes, would greatly help to slow the graphic movements. I paused & backed up several times as I watched, in order to study the graphics. This start-pause-start cycle made it tricky to glean all the information.
The author should respond to your comment, which is very constructiive advice. He responded to many other posts - it's like he doesn't agree with you.
This is the author, Sir. Thanks for the comments. I’ll take that feedback into account for the next one.
@@build-better-things Yes please do, find a view and leave it there if you can. Have a wonderful week and thanks for sharing. Charles
Very informative and well described. I have over 20 years of experience with grp from a manufacturer/specifier point of view. EPDM is probably the way to go. Grp is fatally flawed on a flat roof. Although I have never had a failure of a roof I have installed, there are too many parameters for your average roofer to comprehend. I have inspected more poorly installed grp roofs than is acceptable. I also take issue with moisture barriers. The roofs I have seen fail catastrophically are the ones installed with moisture barriers. The roof may have a small leak. The home owner is blissfully unaware as the moisture is held in the roof buildup. It will spread throughout the whole roof and no-one knows until it's too late. A simple repair has turned into a major refurbishment of the roof. I haven't seen a roof without a MB affected by condensation, so I will never be convinced it should be used.
Thanks a lot for the comment. Interesting to read your experience. There’s a few commenting here they will never use EPDM.
Appreciate the video but your graphic display jumps around without clearly showing the problem layers, it’s so confusing. Just something simple.
Agreed. Three arrows, and three roating images - can't make out a darned thing.
@dommoore7785 Yes, I’ve mentioned already in other comments many times I’ll try to do it better next time for you.
I am a retired Architect.
I completely agree, the OSB below the membrane always seemed a bit dodgy.
I always thought it was done to give more support when walking over the roof, but had not considered the cost of the glue.
Of course although glue more expensive, so is the extra layer of OSB.
Although your method is more foolproof, if the VCL is good enough, and can resist screws penetration, the fact that the rubber is slightly permeable should make the OSB on top ok. One of the calculations that should be done is checking the build up of moisture during winter months doesn’t exceed that that gave evaporate during summer.
As a retired architect, I assume you've seen a few things. Have you come across a rotten top OSB deck due to condensation when there was a VCL? Genuinely interested in gathering some evidence.
@ haha…you got me there. I didn’t come across any, but from my technical training, I woke wary of this top OSB layer.
You see this detail from major manufacturers, who should know what they are doing. But I think I recall they used a fully bonded system, so no screw holes to compromise the VCL
Making a build project fool proof is my key... You may get away with one build shortcut, but two or three in the same area leads to a failure. Plus my recommendation for UK home owners is to always have and use quite extractor fans + use a dehumidifier to reduce the amount of moisture testing the effectiveness of the VCB and layers above...?
im on almost 4 years doing commercial roofing and osb below the membrane sounds absolutely bananas
@@markthomasson5077Hello. Genuine question...why does it "seem a bit dodgy" to you when you have evidence to the contrary?
Good advice!!
I am building a shed/workshop next year and will follow this method!
Very informative video thank you, there are currently so many conflicting techniques regarding warm/cold roofs. They all make for interesting viewing though. Unfortunately the link to the restricted height option isn't working for me, I can't seem to find it in your video list either.
Thanks again
Well finally someone who talks sense. I thought I was going mad seeing how wrong these roofs are built here in Ireland. If I may ask what is your take on installing the vapour barriers under a tile roof? Do you recommend pulling it taught or leaving some slack so the membrane sags between the rafters? I was taught to allow some slack so any rainwater making it past the tiles can flow down freely instead of stopping at each and every furring strip...
Hi. Yes I would lay it slack like you say. I think you mean breather membrane rather than vapour barrier? The vapour barrier is on the warm side of the insulation. Thanks for your comment.
Hi, yes @@build-better-things i meant the breather on the cold side. Thanks for confirming.
Do you have a buildup for Felt and Fibreglass finishes?
Can you show me an example of a failed "deck on top of the insulation"? Just intrested to see it with my own eyes.
Exactly this, me too. Have seen plenty of bad cold roofs, contractor rushing, forgetting to properly ventilate. No evidence of someone pulling up a roof and it's rotted due to evaporation. All due to water ingress from above.
Thanks, good video. The more people that are aware of the potential problems, the better. I regularly see poorly designed and detailed roofs. Some can cause trouble soon after construction. Sad really, as it often costs much the same to do properly. As houses are better insulated and are less draughty, cold bridging is a growing problem.
Thank you for your insights Alan.
Another smashing video on flat roof construction - thanks for sharing
Absolutely brilliant video! I wish the 3d renders moved a little slower, but this was great. Thank you
I appreciate that! I’ll try and make the speed a bit more comfortable in the future.
This is a great video. Very thorough and well-explained. I will watch this a few times before I add a new addition. Thanks.
Thanks a lot. Really appreciate the comment.
Great video , and also completely correct on the stubborn point of view of many builders. Uk construction industry at the tradesman level has so much ground to make up in comparison to the european counterpart. Not a surprise when you look at the general attitude to new technologies vs "how we've always done it".
Thanks a lot. I’m not trying to be critical of others’ efforts . Just want to look at the science and use it to make us all do it better.
Yes, doing it wrong for a long time (Normalized Deviance) does not make something correct.
We seemed to have perfected most things in Victorian times and mostly have been working backwards since the amount of old buildings I've taken apart where the timbers are in perfect condition speaks for itself heat and ventilation are the key also much healthier for the inhabitants of the buildings
Interesting video but the dew point should be calculated so it’s in the center of the PIR and that’s why you can have a OSB top deck without fear of it rotting.
I think you’re talking about about the “calculated” dew point which you can determine by defining a couple of variables. You are correct in that it can be in the centre of the PIR, especially in a warm roof. That’s not what I’m talking about in the arguments I’m making. I just tried to keep it simple to avoid confusing jargon. I may make a follow up video to go into the detail of what you’re saying versus what I think is also the case. Thanks for your comment.
@@build-better-things isn’t that the whole point? You’re saying it will rot with certainty while it’s actually in theory, same as, in theory the moisture will not rot your ply in your construction.
I’m saying that I’m mitigating against that possibility. Having a composite on the cold side provides no mitigation.
At last someone that actually knows and understands the warm roof theory, and why it actually works
stumbled across your channel today - very glad i did! so much useful information crammed into your vids in a fuss free style.
subscribing! cheers!!
The principles apply to peaked and pitched roofs as well, but I didn’t know that until I started paying attention. After the spray foamers came and insulated my attic roof. I haven’t a clue if there was any sealant or member sprayed to the underside of the roof decking before applying the foam. 😅
wow the value of this information is just insane.. I'm going to scour your channel for insulation and moisture solutions for the basement. I tried to find what software you use in the comments but to no avail..
Hi. I made a video about the software and my workflow earlier which you can see. Thanks for your comment.
I imagine coming back to this . thanks
Great video, i have an art deco house all flat roofs and parapets and was shocked how little roofers know about this or choose to ignore it, i get stuck as i get quotes and i know more about the theory than all of them after doing extensive research, my issue is my lack of skill to do it myself, id hap pily try a garden room by the house is another beast, the expense of a tin roof alone makes me want it done correct 1st time….Is the height restriction video out yet as i couldnt find ut
@@Jackzuk The University of Greenwich's Chartered Surveying course related on day one "building is an art, not a science". Books will only get you half way.
Another superb video. Thank you for being so generous with your advice and providing detailed rationale behind each construction detail. In the process of a timber extension build myself and benefitting a lot from your videos.
Thank you very much!
Please excuse me if this is a daft question.
I was totally onboard following your explanation and it made perfect sense, until you mentioned that air pockets between the rubber and the insulation are not a problem as the rubber is slightly permeable and air bubbles will eventually flatten out. So why would this permeability allow the air out of air pockets but trap moisture from the condensation below?
Please be gentle in your response, there is every possibility I've misunderstood something. :)
Hi. This permeability will allow some trapped moisture to slowly breathe through beneath the membrane, but it won’t if there’s 18mm of OSB sitting on the cold side above the insulation and the localised vapour areas, where the moisture will get trapped within. It’s a good question and my fault for not explaining it well.
Good video thanks for posting . Agree with other commenters have drawings static non rotating
Yes I’ll take the feedback in. Thanks for the comment.
Thank you for the great video and I agree with your explanation.
Unfortunately I am very worried as I have done more then 50 flat roofs with 18mm wbp on top of the firrings, vlc “alutrix” on top of the plywood, 150mm ecotherm (very well done, fill and seal all the joints) then 18mm tongue and groove OSB mechanical fixed with the “ plastic washers “ then finished with Flexi tec resin 2020 (very expensive material) and I have provided 10year warranty to my clients.
Your explanations make sense, but I don’t know what to do with all the roofs that I have done and also with the others that we already have booked.
I find it very difficult to use tissued face insulation (no plywood on top) when you have a lot of parapet detail, box gutter detail, skylight upstand, when the flat roof will be used as a balcony, or air source heat pump will be installed on top, etc….
Any suggestions?
All the best
@@AgronIlirBilla why would you trust more the author of this video instead of your experience?
Have you seen a top layers of a warm roof with VCL rot?
Also, would you reckon it would be easier and cheaper to replace the existing top layer of OSB or the bottom one?
@@OmegaLok Me again. Yes, in answer to your question, I have seen rot in a warm flat roof with a VCL. Indeed, I have worked on a number of schools in which whole buildings have had to be demolished and replaced for that very reason. If I say that the plywood on the outside (not OSB) under the single ply membrane was rotten...........It's incredibly difficult to get ply to rot, but it rotted in this build-up. There was an extant vapour barrier.
If you can control the moisture in the building properly, which inevitably means a mechanical ventilation system, then the issue seems likely to go away. I fit them in every building I design. But there are millions of houses around the world with OSB or ply sheathing, and without a MVHR system. They're all in danger.
@@MikeAG333 Sorry I am not convinced about a warm roof simply because you say:
"whole buildings have had to be demolished"
and
"There was an extant vapour barrier."
and that indicates to me full timber framing with OSB on the outer shell of the walls + membrane (i.e. you're not talking about a warm roof).
I've seen this membrane lapped incorrectly several times on UA-cam (Izzy the Bricky had a video), i.e. top section tucked under the bottom section.
I've also seen how my contractor incorrectly lapped the DPC over the DPM, me correct the issue, and building control signing off and then describing in their report that I've correctly put the DPC over the DPM...
I just can't logically think that condensation will rot a warm roof outer layer of OSB when I compare the other mistakes where water will literally flow into an envelope and rest there forever.
@@OmegaLok Well, I didn't make myself as clear as I thought I had. Yes, it was a warm roof, and yes, there was a vapour barrier. One can't post drawings on UA-cam or I'd sketch the build-up for clarity.
The principle of my point is that OSB is also a vapour barrier, and putting a vapour barrier on the outside of a timber construction, be it wall or roof, is a very poor idea in any place where the building is heated. I'm sure you could probably get away with it in a building that is never heated (and which has decent ventilation), but that's not much of Britain, Europe, or North America.
Oh, and I have never claimed that the OSB would rot. It will get mouldy ......sorry......it DOES get mouldy, but it's the framing which is at risk from the interstitial condensation, not the OSB (although, as I said, some of the ply in the schools I talked about had turned to compost).
This guy has no qualifications no experience
It’s all what he thinks ignore this
Steve roofer is a far better site on UA-cam he will keep you right
Can you share your opinion on internal wall insulation systems such as SWIP please?
I'd be interested to hear your thoughts on calculated dew point.
Hi. Great question. I deliberately avoided talking about the “calculated” dew point because I don’t think it’s relevant to what I’m talking about and it’s not something many might understand. It’s just very hard with the choices of information to focus on in the time you have in ten minutes of video. I’d make a specific video on it but I’ve tried similar before and the interest isn’t there.
Fair point, good to keep the info concise. I agree it's good to keep the details robust and allow an easy way out for moisture. You can never guarantee a perfect installation of a VCL so a theoretical dew point can become slightly irrelevant anyway. I always try to specify details that still work even if they are installed on a Friday afternoon. Cheers.
With the target U value being reduced to 0.11 there is currently a problem of how to buy PIR thick enough to be able to construct such a roof with doubling up the insulation. This poses two possible issues 1) A highly theoretical opportunity for condensation between the two sheets of PIR and 2) Screwing down possibly 240mm of insulation. The first I think is probably not a problem but interested in thoughts and both and also availability of insulation material to meet the new target.
Your point 1, if you are using foil backed insulation, which many builders continue to do, you will have trapped condensation where the two foils butt against each other, regardless of your vapour barrier. Your point 2, I would be aiming for 120 between joists, and around 150 over the top, to get around a theoretical 240mm sheet. You raise an excellent point on the new u values, and I suspect manufacturers will find new ways of increasing the lambda effectiveness, such as KingSpan’s newer phenolic batts.
I'm a lowly DIY'er, half way through his first warm roof (a mere 4 square metres). I did consider gluing the rubber directly to the insulation, but in the end I went with a 9mm OSB3 layer beneath the EPDM because that's what the majority of people seem to recommend, and I wanted a roof that I could walk on to get access to the gutters etc. Have I made a horrible mistake ? Time will tell, I suppose. I tried very hard to leave no gaps in the vapour layer (= Alutrix), and I deliberately chose OSB3 because it can apparently tolerate humid conditions. Kingspan claim that their phenolic insulation ("Kooltherm") is also vapour resistant, so perhaps that will help too. I hope it won't end up worse than the cold unventilated felt roof I replaced, which had the consistency of soggy Wheetabix. Fingers crossed.
I wouldn’t call it that. If the roof fails, hopefully you can peel it off, along with the old OSB, it’s not a huge exercise nor cost to adhere new rubberto, using a new 20mm layer of tissue faced over your old insulation to keep the depth almost the same. Humidity is a site specific thing, so you might be OK. Just wait and see.
Plenty award winning excellent builders on UA-cam have done the same don’t worry
@@macsmith6216👍
Hi, great video - thanks. Is it possible to apply final layers to say rockwool flexi or such. I'm ocd about fire proofing and toxic fumes with kingspan and it's ilk. Is some form of more non-rottable layer or support system be available to walk on after installation? Cheers
Hi. Which way are you worried about fire proofing. Starting inside and spreading out presumably? Surface spread of flame is one of the main issue with flat roofs. I’m just not 100pc clear on your question. Can you word in a different way? S Thanks.
I mean that if I only wanted to insulate with rockwool and not pir, then it seems a cold roof is my only option as the load bearing capacity on a warm roof is not sufficient for walking on and such in comparison to pir?
Yes that is correct. You need to ventilate between the insulation and the timber deck. But you also must remember, mineral wool is less than half as efficient as PIR, so you’re not going to be even close to the efficiency of rigid.
Thanks for this. Difficult to get a 100% visual on what you were trying to show as the gold standard.
So it's
Breathable membrane, osb, insulation and then epdm?
i was thinking the same. trying to watch the video again to see if i missed the detail.
I think it’s osb then vapour control layer on the warm side, then insulation. This keeps the osb in the warm area meaning it does not get cold enough for the vapour in the air to condense on. A breathable membrane lets vapour through so not what you want because that takes the moisture through and as the temperature decreases as you travel through the insulation eventually you get to the dew point and moisture will condense out.
Breathe membranes are for where you want vapour to escape but at the same time be waterproof. I.e. above a 50mm air gap in a cold roof below tiles.
No breathable membrane. OSB then vapour barrier, then insulation, then EPDM. Sorry if I wasn’t clear. You only use breather membrane where you have a ventilated cavity on the cold side of the membrane.
@davideyres955 that’s right. Thanks for your comment.
Jerry thanks for yet another great informative video. Just in time as I'm in the planning phase of adding an open plan kitchen dinner leading onto the rear garden. I'm going to pass your video onto the architect so they can spec the construction drawings accordingly. It might not go down well, but I'm the paying customer :)
Thank you too. I’ll be interested if you come back with their comments. Construction industry is a sea of conflicting information sometimes, that’s why I over do it with the analysis.
9:12 could you please link to your other video? I can't fight the video you are referring to. Thanks for this video, I live in Belgium and unfortunately, we have the same "I have been doing this for 20 years and never had any issue" builders. The problem with these kind of builders is that they got in the craft by "doing" not "understanding".
I can’t either but would love to watch it
5:00 I have been doing it this way for years . . .
Yea . . . We drove without seat belts and used leaches for years also.
Thank you so much for sharing such important topic. Please avoid moving the images so much. Give time to the brain to get what is what. Thank you.
Thanks. Guilty of speeding up to fit it in. I’ll slow it down for next one.
I’m going to embark on building a garden building possibly next year and have seen a lot of what you showed in your vid, so it was helpful to get a bit more info on it. just fully renovated our home and have had numerous crappy experiences with tradespeople. A good few of them have come across as entitled and have wanted to get in and out with maximum return while providing bad quality work. It’s refreshing when I come across one who actually seems to care. I had a chat with a guy that has a decorating company in Windermere area and he said that most domestic trades don’t seem to realise they’re in a service industry and that how you deal with customers and the quality of your work matters. I couldn’t agree more. That’s why I’ll build my own garden building, then I don’t have to put myself through dealing with them again.
Thank you very much. I really appreciate that comment
@@build-better-thingsmaybe a vid about types of garden room foundations? It's an equally contested area of building lol
@eddiemcboofin1917 It probably is. I’ve filmed a couple of different ways and need to get some time to make up a vid. Thanks a lot for taking the time to comment.
Great video and just binged a few others (inc french drain which im looking to do with my cellar and a external sump pump). I also one day want to build a garden room with solar, given the weight, how would you construct this kind of roof?
I’ve planning a solar installation at the moment, flat roof using EPDM, fixings for rail system through the membrane and insulation and into the joists. I hope I will post it here at some point but maybe next year.
@ Excellent 👌 This is good news! Love your detail and the logical explanation behind stuff. Subbed and will continue watching 🙏
Interesting video. Lots of conflicting info on flat roofs. I think most are doomed to fail simply because of a lack of pitch and water lying on it. But one simple question. What is the method if your not using rubber? What about fibreglass(not dryseal) and torch on felt?
It’s more just to avoid anything that can rot, such as timber product, on the cold side of the insulation, not part of a ventilated void, and still under the outer membrane. I just happened to be using EPDM because I understand the technology. If your roof membrane requires a timber sub strata, and you’re attempting a warm roof, ie not a cold roof, then I’m saying I think it’s a significant weakness, and I hope I’ve shown why.
If the vapor barrier is merely laid out and taped I would be inclined to put some silicone sealant in the tip of each screw: 1. As a lube to prevent windup of vapor film around the screw; and 2. To seal around the screw. + Somewhere in the matrix there needs to be an deliberate path for pressure release in a rain protected area since one is creating two sealed diaphragms, maybe along the edge under a rain cap in a dry area. You do not want changes if barometric pressure lifting the membrane, and you want any residual chemical fumes to vent outdoors.
What about when sips panels are used? The foam is completely bonded to the osb when the panels are formed in the factory so no moisture can pass through.
Interesting. To my horror my 20 year old lead roof had erupted on a warm roof construction , the LSA now state that they no longer recommend this. I had initially thought the lack of vapour barrier was the main cause. I have added Allutrix to the sub deck then refitted the insulation on top followed by OSB and primer finally layered with ResTech . Im now concerned about moisture forming. Everyone tells you something different!
Hi can you link to your 2.5m height restriction video?
My IT skills are terrible. I’ll get it up asap
Likewise haven't been able to find it. This channel is a fantastic resource as an undergraduate architect
Great video. My only comment is that cold roofs will always create condensation in the cold roof void and its the ventilation that will dry this out. Water vapour doesnt magically waft out the vents and then condense outside. Ps i have 40 years in construction surveying design and inspection. Pps people are still building cold roofs for some mad reason.
Thanks. Yes you definitely need ventilation and need to understand how the placement of the vents creates the movement to deal with the moisture.
Because some people are restricted because of height
I'm making our Part 1's (and a few Part 2's) watch this.
Thanks. That makes me feel good. I missed out several points (eg exact position of dew point, difference between roof and wall) just because there isn’t time in a ten minute video, hopefully they’ll have some questions.
Thank you for a very useful explanation! I have a question also: is a vapor barrier any use in conjunction with a sealed hard isolation panel of which the seams are taped? Am I wrong in thinking no vapor can get through taped PIR panels anyway?
Taping is not perfect but close enough. I don’t tape the boards because I don’t think foil insulation should be used in a warm roof, but you’ll see in these comments many arguing otherwise. If you have an effective vapour barrier below, that’s really all to focus on. Appreciate it’s tricky with the conflicting info but all I can do is show my analysis and conclusions like in the video. Best of luck with it.
Your general rule that any moisture will condensate on the cold side of the insulation or inside the insulation itself is the simple but effective rule. That is the most important thing to consider when deciding on how to assemble any wall or roof. Thank you
Also on your own video of you installing a roof, it looks like your vapour barrier is just loose laid? We usually prime the deck then install the vapour barrier and seam roller all over laps ?
I said in the video, I’ll talk about the vapour barrier another time.
@ the vapour barrier is the most important element?
I said in the video, I’ll talk about it in another video.
I follow "Steve the Roofer" from the UK - He knowa his stuff on flat roofs
Yes, he does.
Love the science based approach. Would this be ok in warmer climates? (Melbourne, Australia - does get a winter, but a warmer summer).
Yes, you need the warm roof to do the opposite for your summers, never insulation between the joists, always over the top to prevent thermal bridging from outside to in. Those joists just act like radiators in summer if they’re not insulated, and you’re air con will have to be on far more.
@@build-better-things Oh, bit surprised at that answer as I doubt roofs are being made like this down here. They are often more like the cold roof design. Great to know, thanks.
Ventilated cold roof space (insulation at base of roof void) is also ok, but warm roof is best. The faster the air moving created by the negative pressure, the more likely the thermal gain is going to be weakened by air movement over the structural members.
Though I think you raise interesting points I think you are incorrect on your main point about the top layer of OSB. I’ll happily keep doing it this way with the blessing of building control. Dew points.
Hi and thanks for your comment. Yes I’m just trying to make the arguments the way I see them, but if you have a way that’s working for you, that is great too.
👍 Appreciated
Having resigned myself to doing a flat roof on my planned renovation's extension to save a bit of cash(I can DIY this, I don't trust myself to DIY pitched slate lol) I wonder, can this advice be applied with GRP/fibreglass? I like the idea of being able to walk on the roof for future maintenance of outside walls without stressing about puncturing the surface as I would with EDPM, but all the GRP videos I've seen have been adamant that you *must* adhere down to OSB sheet or, at worst, rough-sanded plywood.
this is what my builder says too
i challenged him when we did grp on our dormer and relented to his advise and guidance by the grp people. time will tell.
There are a number of reasons why I would avoid GRP and one of those reasons is the requirement to bond into timber. You can’t bond directly into insulation.
Avoid grp. Simple. 3-layer felt, done properly, is still relevant.
Interesting video, thanks for sharing. What software are you using to draw your examples?
Hi. I use sketchup.
Called out by Mr_A_Builders, so who’s correct
We are. Make no mistake about that. This video has a staggering amount of inaccuracies. Don't forget that at the end of the video he calls himself a novice which not only speaks volumes but could also be the only true thing he says.
@@Mr_A_Builders
Anyone with any sense will realise you, with lots of actual knowledge and experience are correct
As opposed to someone with no qualifications, no experience no examples to back up his claims, and what “he thinks” is correct
@@macsmith6216I'm with you two, and so should everyone else. This video is as close to complete nonsense y6ou can get!
You're absolutely right. But TR27 is useless. We tried a warm roof with no OSB. TR27 ended up with dents in it every time we stepped or kneeled on it. The fibre facing peeled off at the edges. I need a solid roof that I can put ladders on, not one made out of sponge cake. So I ended up solvent gluing 12mm OSB to the TR27 and then solvent gluing the EPDM to that. Really didn't want to, and I know I'm going to have to replace the roof in 10 years because the OSB will rot.
Kingspan/other manufs need to come up with a decent product with a hard deck. Until then we will keep installing OSB because it's the only practical option.
I have not had the same problem, although I use the Resista insulation rather than KingSpan and it’s always very firm to walk on, and you can’t peel the face at all. However, for your specific needs, I think you need to be considering an inverted roof, or integrating a raised deck system similar to if you were adding solar , if you’re putting heavy point loads on, or regular foot traffic , regardless of whether I think it will work with Resista. Your use case is not really what the system is designed for, to be fair to the manufacturers .
What do you think about the hibrid roof that have a layer of insulation at the top of the rafters and then additional insulation above?
Hi. I think it’s a better solution, maybe the only solution, for when there’s a height restriction.
Plenty of information on the net about Hybrid roofs, non of it good
I'm shocked. I've been following some of the pro builders you've highlighted in this video and regarded them all as sound sources to watch for good building practices. I built a garden room following a well known channel. I used a liquid adhesive to glue the EPDM down to a wooden roof deck. The saving grace is that I've kept the garden room uninsulated as it is used as a workshop. However, I am now going to rethink/replan the roofing of our single story house extension. In your video the EPDM of your garden room shows all the tube washers. Is this permanent since I don't want upstairs to look down on a spotty roof. I had understood EPDM to be the best modern solution, but if it looks ugly its a no - which probably means fiberglass is the only alternative ?
You could keep exactly what you have done, but do a cold ventilated roof. Which means the top face of the insulation is 50mm below the inside face of the roof deck and it will work well. You do need to ventilated that 50mm void.
@ the extension is in the planing stage. I was just making the point that i had assumed the way other pro builders have shown on UA-cam was correct. Your explanation is excellent and causing me to replan what I eventually end up doing with the extension roof. Warm roof feels like the right way to go but 100% want to get the roof covering and insulation right and lasting a lifetime. My main concern was whether the epdm after correct install shows no signs of fixing points beneath it? It’s this type of aesthetic detail that is just an important where a roof is visible (unlike most garden rooms).
@phil7309 yes you’ll see the washers below like you can in my video, towards the end. However if you took more time laying them out neatly it probably would look ok. Personally it doesn’t bother me the way it is but you might not like it.
Please please please do yourself a massive favour and don't change your plans based on this video, there are massive problems with it. What other channels do you follow that you refer to?
@@onlyidiotsrespond I’m not an expert so I try to learn from those wiser and with real experience to inform my decisions, ideally so I don’t need to rectify a problem caused by an assumed right way to build something. Certain jobs need to be done correctly and a roof is one of those. So after listening to this video I will be researching this more and making sure I am 100% happy with the way I will eventually insulate and build my roof.
Really interesting. Thanks
Interesting video, thanks. Out of interest, with a warm deck with torch felt over, what's that like for reliability? Asking for a friend 🙂
Actually I’m not sure. I always thought you needed to renew it after quite short periods. I also think you might need to torch onto a timber sub strata so cold ventilated roof might be best. I’m no expert on felt however. Best of luck with it.
@@build-better-things Thanks for coming back so quick. Yes I think it does need renewing from time to time, but should last a good while - perhaps not as long as best case well laid/prep'd GRP/Rubber.
This is to do with an 'already built' outbuilding around 3 years ago, did have OSB sheet under and over PIR. I'll inspect at some point as I'm interested in deterioration of the sheet. Thanks!
Best of luck with it
OSB, water based glue and EPDM is okay on a cold roof with insulation between joists?
As long as you have an air gap, ideally 50mm but dependant on the depth of your joists / insulation and that air gap needs to be pulling air through it by good use of vents. Then your suggested makeup is ok
what are you doing on the four 150mm cut edges - surely vapour will get in there much more than through epdm or osb ?
I don’t understand what you mean. Can you explain it in a different way so I can respond?
@@build-better-things theres vapour barriers top and bottom but not at the 4 sides of the kingspan, or is there?
I describe how that works in detail in the early part of the video, photos of typical installation along with a diagram.
@@build-better-thingsbut you didn't do it in practice. What's the point in telling everyone how best to do it when you don't do it yourself? Honest question, with all the conflicting information within this video...please be honest...do you know what you're doing/talking about?
@@DICEGEORGEit's not there is it. Hello said one thing, did another and trying to tell you that you don't understand!
I was wondering how this might apply to a sloped warm roof design?
I asked our architect for a warm roof on our extension (Which has both a sloped and flat portion), but after the calcs they wanted to put 100mm of Celotex on top of the rafters and 100mm of Celotex between the rafters with 50mm of ventilation above the insulation for the pitched portion for some reason stating it was still a warm roof somehow. For the flat roof they specified 18mm ply over 200mm Celotex, but specified no ply between the insulation and rafters. I might ask the inspector directly if we can just do 200mm on top for the pitched roof instead, and build it up as you've suggested.
A sloping roof is different because the opportunity is there for a ventilated void, using the battens and counter battens which take the tiles, and therefore the option of a breather membrane. I’ve made a video about it elsewhere on the channel.
@@build-better-things Thank you, I'll have a look at that video.
Thank goodness I'm not the only one saying this. I've been banging on about it for years. OSB should be on the INSIDE of insulation, if it's anywhere. The good old US of A is going to have a massive issue with their walls in the next few years, as they've been making thjis fundamental mistake for decades. Oh, and I'm an architect.
Thanks. I guess you have many more climates to consider compared to the smaller European geographies. Scotland has slightly different energy legislation and therefore different make ups, for example, than England, but it’s a relatively small area.
@@build-better-things I'm English.
Ah. Ok sorry I just assumed.
@@MikeAG333 if they’ve been making this mistake for decades, isn’t it about time we see some evidence of failure?
@@OmegaLok We are seeing evidence of failure. Lots of it. But what we haven't seen is any large-scale research or reports, academic studies, or proposals for revised "codes", as the Americans call them. Houses are just repaired on an ad-hoc basis, and the failures blamed on poor workmanship, or leaky gutters, or somesuch.....but if you pull off the outer skin and OSB on almost any 20+ year old house in the parts of the USA where winter heating is a thing, you'll find mould on the inside of the sheathing board, and damage to the framing.
How good is good old-fashioned fibreglass at sticking to the roof insulation?
Not happy as i have just recently completed a warm roof with 18mm OSB on top of PIR then got 1.6mm EDPM on top. But your information seems sound and logical. Is there any actions i can take to improve / avoid early rot in the top OSB ? (Minor not major reconstruction). PS - Could not find the height restriction video you referenced.
If you've used a VCL I would not worry so much. There is simply no evidence of a top deck rotting if there is a VCL. The only thing I find on youtube is: ua-cam.com/video/6NWrYG2G2Ho/v-deo.html and surprise surprise they did not use a VCL. All other examples are pitched cold roofs with improper ventilation or water ingress
@@OmegaLokthere is zero evidence in this country providing all stages are correct and installed correctly. Absolutely zero. If anyone would like to prove me wrong please do so!
Are you an architect or a builder, what is your qualifications
Hi. If you read my bio on the channel, you’ll find it, and I go over it in some of my videos. However, qualifications are less relevant than the arguments and the data I’m putting forward, which you’re welcome to dispute so we can enjoy a conversation. Qualifications are nice, physics is best. Physics doesn’t care about your qualifications.
@
I’m not disputing anything, “however qualifications are less relevant than arguments” however argument require facts not opinions
Especially when handing out public advice
Absolutely. If I’ve got things or facts wrong, I hope you can let me know. I put a lot of work into these videos but it’s very hard to be perfect. Especially on a subject like this which has a load of “it depends” about it.
So just to clarify you have no roofing background, no qualifications no real "on the tools experience" by which i mean how many flat roofs have you done?
@@build-better-things
Your are making the assumption the dew point is on the bottom of the OSB, this is not correct on a warm roof, this is the whole point of a warm roof, this does not happen
In fact, in a warm roof, the Dew Point happens within the PIR insulation and moisture-tolerant boards, away from the roof timber, so there are no moisture spots in the roof space causing condensation issues.
There is a very good technical web site which explains this in detail it’s detail library
The OSB is often a “standard detail” that’s all. I am sure a builder would happily leave out that additional task with a simpler build up. I certainly will do so with my own. What do you think about those one way breathable membranes to avoid trapped moisture?
They are great, but they only work with a ventilated cavity. For example, a wall or sloping roof with tiles on battens. For the examples I describe, not feasible.
I'm not a builder or a roofer. Last year, I built a 5m x 5m extension for my sister. I went to an architect (a good one) for how to build the warm roof...and it wasn't the way you do it. Halfway through, I had issues with digging out for the slab (solid concrete from many years ago), so I consulted a surveyor who suggested a raft slab. But my point is that for £500 cash, he also included drawings for the roof...and again, it was the same as the architect's design...which is the way you say NOT to do it...timbers-OSB-Celotex-vapour barrier-OSB-EPDM.
Forgot to add...
As I have never built anything, I was running everything past Building Control, and they were very happy with it - even came up to see the roof halfway through construction.
I'm not getting at you personally, just saying that an architect, a surveyor, and BC, all suggested the above method I used, and that you don't recommend.
Hi and thanks for sharing. If you read the comments here, you’ll see several people saying I’m wrong, (some throwing insults etc) and that OSB under the membrane is a fine thing. I’ve explained in the video visually with my reasoning why it’s an awful solution, you are welcome to disagree, but I hope you get the same level of detailed explanation and analysis from your architect or builder as to why OSB and foil are a good thing on the cold side in a warm roof set up.
just brilliant
On the roof mentioned with no OSB ontop of the insulation, is it safe to walk on and is it suitable to hold solar panels and a green roof?
Hi. Yes it’s safe to walk on, but just like with an OSB sub strata, sensible with the kind of footwear, avoid anything that can damage / nick the membrane etc. For Solar, you need to design the loadings in the joists for the additional weight plus the wind uplift, and then it’s down to your choice of fixings locations for the rails, and whether they pierce the membrane. For a green roof, I would be considering an inverted roof, rather than a warm roof.
@build-better-things thank you very much for the information
What if you have a roof made of SIP paneels?
Is it a good idea to add a layer of insulation roll between the joist of a warm flat-roof?
It’s easier to think about these things in terms of the u value, and work backwards from that. You can find the list of u values for each element, eg roof, walls, floor, and one you have it, you visit one of the manufacturer’s online u value sites, and see what insulation options are there. I would never put quilt in between the joists for thermal reasons because it performs poorly. Sometimes acoustics are relevant but then you need to allow separation and some ventilation. Really easier to draw than describe.
Never, do that, plenty of sites with technical drawings and the reason behind it
I’m currently designing a warm roof, and like you point out everywhere shows a top deck of wood material.
This bothered me for the reasons you lay out, if the wood on the cold side can’t breathe it’ll rot.
I’m planning a GRP roof, but I think it would still be best to have a top deck to do so.
What are your thoughts on a rather unconventional method of using something like an xps tile backer board for top deck before GRP?
Yes, I guess if you’re set on GRP, that’s an option, but the point is, you want the dew point (where it condenses) to occur toward the outside of the rubber, so it just evaporates away. Even with a synthetic board, which won’t rot, you’ll still have trapped condensation, since the dew point will happen someways into that board and the “dew” has nowhere to go.
@ thanks for the super quick response! There is so much mixed information available it hard to know what is best.
@@SlayerLaw There is simply no evidence of a top deck rotting if there is a VCL. The only thing I find on youtube is: ua-cam.com/video/6NWrYG2G2Ho/v-deo.html and surprise surprise they did not use a VCL. All other examples are pitched cold roofs with improper ventilation or water ingress
@@OmegaLok Thanks for the additional input. That roof did seem to be poorly constructed! It seems logical if the VCL is working correctly it should be ok. I will keep researching
How do you do gutter with this type
You attach a fascia with the top face flush with the sub strata (eg top of insulation) and leave the membrane hanging over by about 80mm. Then you attach a 2 piece gutter trim and friction fit to secure the rubber. You can see it towards the end of the video in the roof with the black corrugated cladding.
Can an existing cold flat roof with a bitumen/felt covering be over boaded with insulation WITHOUT a vapour barrier? Will the bitumen felt be a vapour barrier?? Many thanks
Top question.👍 I've heard it can, but would appreciate this chaps response.
In theory, bitumen in these compounds when combined with the fibres of felt is not breathable. In reality, if the roof has been exposed for a while, it may still keep the water out, yet let vapour permeate. However the problem you have is around the edges, where the envelope must be continuous with whatever the vertical vapour barrier is, that junction is going to be difficult with two different materials.
@@build-better-things when was the last time anybody received a response as quickly as that! Thank you. Shooting from the hip, if the rubber membrane excess/over lap is glued to the felt on the side of the roof.... Would that work? Also any advice or a video of attaching rubber membrane to an existing wall?
Could you cover the felt with DPM sheet first?
That’s just asking for trouble sounds like something a cowboy builder would try and pull off
No self respecting builder or roofer would contemplate this
Good info. hampered by to much unnecessary "jump cuts"
What’s a jump cut?
Do you think a 45mm air gap will be enough on a garden room above insulation it’s 3m span wall to wall with shower in. I know the regs say 50mm but iv currently got 45mm was going to do hybrid but then realized iv got enough space almost to do cold roof. Thanks for any help.
Hi. A few millimetres is ok in that situation. . The other issue with both cold roofs and hybrid to consider is the vapour barrier and things like lighting. I will release an Ina few days about how I think it’s best to do a hybrid roof. Thanks for your comment.
@ thank you for quick reply really appreciated, ye I’m not planning on putting recessed lights in for that reason I don’t want to many holes/week points in the vapor barrier so I’m just going with a single light in the middle. Thanks again
With this method, how would i go about fixing down a prefab upvc skylight, where the instructions say to screw it down to the top deck of OSB, before applying the EPDM? Im a diy'er doing a flat roof extension myself, with no experience, so any help greatly appreciated.
Good question. I’d always fix into the trimmers around my opening, but you can also fix under the insulation into the warm OSB deck using window brackets which sometimes come with the kit. Hard to explain, easy to draw.
Great info - any way you can share your 3d sketchup model
OK - how do you protect the EPDM from birds pecking/scratching at it? I've got what sounds like pigeons wearing hobnail boots thumping around on my roof!
It's felt/gravel at the moment, but needs replacing as it's a badly insulated cold roof install (previous owner was a builder, allegedly) - lots of gaps around the PIR and no VPL above ceiling!
The only time I’ve seen a problem with birds pecking at the membrane is when there is creases in it. I don’t know why, but it seems to attract them. It’s actually very easy to sort, using a repair kit. If you don’t have that problem, then I’m not sure.
Hi mate if there was another vapour barrier under the 2nd osb would that stop if rotting basically wrapped the insulation like a parcel
Hi. Part of the worry for me is that if you have impermeable surfaces, be they foil, polythene or OSB, under the surface of the outer membrane, on the cold side of the insulation, given we are not in a vacuum and that no vapour barrier is perfect, you are creating perfect conditions for interstitial condensation. I just would never go there whether for my own or someone else’s when I can eliminate the issue entirely. There’s several people commenting here who disagree with me, a few of them are going out of their way to reply and repeat all over the place saying I’m wrong, so you might want to read all the comments and make your own mind up. Great building construction is as much about mitigation as anything else, I think the science is sound, but you can always disagree with me. Thanks for the comment.
Very Interesting. thanks
Yeah in Arch Tech collage (a couple years ago since I graduated) we were thought to apply the roofing membrane finish directly onto the insulation when detailing as you specified in this video. I watch alot of the channels you screen grabbed (+ others) who all do the 2nd OSB layer on the cold side of the insulation & I always wondered why they would add such an unnecessary layer to the roof assembly. Now I know! 😅
I've just installed my rubber roof as per the old way. Its on my shed/garden room. As it will be low occupancy with trickle vents i am hoping it will be ok?
I didn’t go into trickle ventilation in there video due to time. If you’ve got OSB under your membrane, then ventilation will definitely help you with vapour control. People tend to close the vents in winter for obvious reasons, that’s why I don’t talk about it much. The fact you’re asking the question, and it’s not going to have much vapour generation will work in your favour.
You are making the assumption the dew point is on the bottom of the OSB, this is not correct on a warm roof, this is the whole design of a warm roof, this does not happen
In fact, in a warm roof, the Dew Point happens within the PIR insulation and moisture-tolerant boards, away from the roof timber, so there are no moisture spots in the roof space causing condensation issues.
There is a very good technical web site which explains this in detail it’s detail library
Yes, thank you! Please comment again with the technical info source you mention. Because I've designed the 'flat' roof of my house currently under construction, after exhaustive research about this very condensation issue, and determined my roof deck's underside should be perfectly protected b/c of the critically-correct R-value proportion --- specific to my climate zone --- I'll be using of between-the-joists batts (i.e. UNDER the roof sheathing) and foamboard (EPS) on TOP of my sheathing. In other words, while this UA-cam person is clearly extremely knowledgeable about bldg. science, the REAL issue here is WHERE IN YOUR ROOF SANDWICH IS THE DEW POINT? Also BTW, I'll be stapling & taping a 'smart' vapor barrier to the underside of the joists, btwn. them and the ceiling sheetrock.
EPDM rubber is permeable and allows water vapour to escape, albeit slowly, yet reasonably. If a solvent based adhesive is used it will certainly cause a hindrance to that. Unless one builds a hermetically sealed inner roof/insulation surface (a practical impossibility, essentially, at best an expensive and needless endeavour) water will always condense at a cold point. The amount of water available to condense in a building /given area of it should be lower than the amount which can reasonably escape, and unless the building has big issues with damp/condensation then there should be no issues with the boarded roofs depicted. If there is any issue, it will be down to remedial works being needed on the rest of the building. In a climate like Britain's, screws into wood will cause negligible heat loss. I've built numerous buildings and many, many EPDM roofs all over the UK and Scandinavia, as well for myself and which I monitor and experiment with - never an issue, and i have often used the OSB top boarding method. I hope the feedback is useful to people.
Appreciate your experience, welcome to disagree here and give your reasons, and keep doing it the way you have always done it. Your experience and your comments will help everyone decide. My view remains…..Timber composite on the cold side is unnecessary and it can rot, as is using foil in roof insulation, and I’ve given my arguments why in the video. Thanks.
@build-better-things thanks for your reply. I totally agree about not using foils and it's so important to think through air movement and the building design as a whole, carefully. As i'm sure you know, but in case it helps others, it's common that people reduce ventilation 'reduce drafts and heat loss' by closing vents/windows and sealing gaps etc. As an old Swedish engineer friend put it 'any building design has to take into consideration the trade-off between insulation and air flow'. If it feels cold, it probably needs to be insulated better, and reducing/changing air flow without considering its effects can cause a lot of damage. (I appreciate that's verging on being off topic and rather general, sorry).
Hello! Hope you're well. A couple of our viewers have brought this video and it's contents to our attention so I thought I'd check it out. Disappointingly it seems that you have intentionally misrepresented contents of our videos to fit the narrative of yours. Some of the things you say when visually representing Mr A Builders are extremely misleading at best and at worst completely untrue. As mentioned this is extremely disappointing as I really can't see how I've misunderstood what you've said in relation to our content. We all need ideas for videos but it's a shame that you have appeared to go down this particular, unethical route. I'm looking forward to your response, should you give one, I can guess what it's going to be but we shall see. I think it's only fair that should we have a conversation about it, of which I'm more than willing to have, that it's done in 'public' and not private so other people (let's not get too ahead of ourselves, no one else will care!) can read, get involved and make their own minds up in regards to your integrity. Take care.
From. Someone who watches both channels, do you disagree with this method? Or are you just arguing the idea because he has used a still picture of your channel? Just interested to know!
@@seunakin6961hello, hope you're well. Our main concern is that whilst he is showing clips/stills from our content his commentary appears to explain things that we are doing that we certainly aren't. It seems to be incredibly disingenuous. As mentioned in my previous comment he's changing the narrative of our videos to fit his. Naughty naughty!
@Mr_A_Builders Fair enough and I understand your point. I will continue to watch your content as I find it extremely educational. Keep up the great work
@@seunakin6961appreciate that mate, thank you. Take care.
Thanks for taking the time to comment. You say misrepresented, untrue, unethical and you mention my lack of integrity. But you don’t give any examples from my arguments and reasoning of what makes you think that, not one, you just get stuck in and make it personal, which is just the way it seems to be these days online, from those in the Trade in particular, when you question something they’re doing. I’m happy to have a conversation, the aim for me is to help self builders wade through the conflicting info, and make the best choices. For what it’s worth, I think yours is a fine channel, always positive and generous with your knowledge.
I never understood all these 'water based' products for outdoor applications. This also goes for paint. Solvent based makes more sense to me. Rain will not slowly dissolve it.
You would paint the exterior of your house in a solvent based paint?
Left slightly confused by this video. If you glue your EDPM directly to the PIR then the same moisture that you say rots the top layer of OSB now has nowhere to go as EDPM will not allow moisture through. Also, if you have put a vapour barrier under the EDPM then surely you have eliminated the moisture getting through anyway.Would welcome any replies.
Hi. I thought I did say EPDM has a slight breathable element to it. The trapped moisture will permeate slowly through it. It won’t do that if it’s stuck within 18mm of impermeable OSB or within some air within below a layer of foil on the cold side. The vapour barrier is just a retarder and I can’t rely, on it so I’m designing out the quality control issues. You raise some great questions, even if I’m totally wrong, why take the risk, when there’s no difference in cost?
@@build-better-things - Thank you for getting back so quickly. I'm currently making a decision on which way to go with this on my own extension. You are correct that EDPM is slightly breathable but it won't allow moisture to pass through as you say (not according to the data I'm reading). Personally I think the real solution to this is to deal with the problem at source and condition the air first. This could be achieved using an appropriate air-conditioner, heat pump or dehumidifier. But now I'm increasing my costs. Meanwhile, I'm going to say a big thank you for putting your videos out there I've certainly learnt from them and put a lot of what you say into practice.
How can you on the roof with your method?
You've got a few issues here, pal.
1. You're referencing other channels that dont contain what you say they do.
2. You've got the dew point wrong which undermines your entire point.
3. You ahow a confusing diagram that shows the VCL in completely the wrong place
4. You have absolutely no evidence for anything you say, not even a link to an article.
5. You say you're a novice but offer consultation services! How does that work?
6. You advise to go against manufacturers recommendations.
I could go on but surely thats enough?
This is a shoddy, ill conceived poorly researched argument that you felt the need to discredit other UA-camrs videos to make. I will be amazed if some of them don't get in tiuch with you, even try to get it taken down. Unbelievably bad.
My thoughts exactly… guys got a lot of misinformation in his videos and some very silly references to other guys that clearly know exactly what they’re doing and have done for many years
@Telferroofing spot on mate. I checked out one of the channels he slags off, Mr A Builders and do you know what? There isn't a warm deck roof with an EPDM covering on it! Not a single video on the entire channel. This clown accuses them of doing something they simply haven't done. And that's just one of the points. This video should be taken down.
Timber on the cold side is not great, timber composite is worse, as is using foil in roof insulation, and I’ve given my arguments why along with solutions in the video.
@ you said it’s wrong not “not great”
@@build-better-things you haven't addressed a single point from the above but instead down graded the entire point of your video to "not great". Seriously mate, you need to sort this. Having this opinion is fine but you've dragged other UA-camrs into it and from what I can see lied about their videos. As mentioned above Mr A Builders does not have a rubber roof on a warm deck video on their entire channel and you say they do. That's the same for the Garden Room Guru, one of the other videos you've shown. I've noticed in one of Mr A's posts that they say maybe you should donate to their fund raising as way of the an apology. You do need to reach out to them if you haven't already.
You dont have any examples to back up your point then?
PSS: The vapour barrier in your video looks like a laminated polythene foil product as it looks lose laid (not stuck to the base deck with bitumen). These products are not sufficient and regardless of whether you’ve used an upper layer or not, condensation will occur between the roof membrane and the insulation because you have failed to prevent rising vapour due to an inadequate vapour barrier. Ok that condensation will have no OSB to rot, but it will reduce the life of your roof to exactly the same extent by delaminating your membrane bond to your tissue faced TR27 insulation.
Good points regards mechanical fixing, but in terms of thermal performance it doesn’t matter what roofers toss about with on top of the insulation. The key is stopping warm vapour holding air from inside the building rising through the structure as it will condense if it’s allowed to meet a cold surface whatever you do on top.
Wont the insulation deform if its walked on? Would this be ok with tapered insulation to create the fall
As long as the insulation is fully supported underneath then the insulation can’t go anywhere , fine for light traffic. Tapered insulation is perfect, take the minimum thickness eg lowest point to calculate your u value
@build-better-things thank you
I have zero building experience, and am coming from this with probably complete misunderstanding, but if the EPDM stops the moisture getting out, and it sits on and rots the OSB, what happens if you don't have the OSB? Does it not sit on the insulation? That doesn't or can't rot?
If you’re using EPDM, there is a breathable aspect to the compound where the trapped moisture con dissipate slowly on top of the tissue faced of the insulation and directly under the membrane. Instead it’s trapped in the OSB and never gets out.
@@russellwheeler2760 the EPDM membrane is a breathable monomer. It does allow a fairly slow but reasonable egress of water. It's an excellent material to work with.
@@gurglejug627 ah ok, both replies make sense. And the OSB is not breathable because of the "glue" in the board, shown in the video
@russellwheeler2760 that doesn't really add up in practice - even small gaps allow air movement and dissipation of moisture. Permaroof, based in the UK have excellent videos on best practice usage of EPDM freely available on their website - they're Firestone distributors and have decades of US and international, other climates experience to draw on, as well as the UK.
I can't find your video about maximum 2.5 metre
Why isn't this being captured on drawings by architects and before being approved by planning?
It should be, but architects are as guilty of builders of getting this detailing wrong. Building regulations are just checking for compliance, they’re not there to check the design, although many do end up being helpful. Planning permission has no relevance for roof makeups, just appearance and size.
I'm pretty sure this is a flawed theory as the warmth never gets to the top sheet of osb and vapour can't get there because there is a vapour barrier and the actual PIR is a vapour barrier in itself.
if anything the sheet underneath the vapour barrier is the one that's going to get vapour on it but it has breathable materials underneath plasterboard etc.
I wouldn't use water based anything but also we use rolls of resitrix so I don't think it's ever coming off.
Thanks. The warmth is always going to transfer, it’s just a question of speed. It’s the moist air that causes the problem in localised spots where there’s the inevitable vapour barrier weaknesses, fixing gaps, poor edge treatment residual air vapour, and joints which, over time, causes the problem as the small amounts of moisture collecting have nowhere to go. Even if you dismiss all of that, my point would still be, why include foil insulation and all that timber composite top decking when you can just bond direct and get rid of the potential failure completely.
Omitting OSB on top makes the roof way way more likely to be damaged by footfall, ladders, people just carrying out routine maintenance/decoration etc in the future. Stop being silly.
If the membrane’s going to fail because of footfall, it’s going to fail, regardless of whether it’s an OSB or synthetic sub strata and it’s obvious you’ve never walked on the latter, or you wouldn’t have written such nonsense. For your ladder, even for your OSB sub strata , shouldn’t you be using a spreader plate sir? You say “silly”…..you seem to be desperate to have OSB below your membrane, so …..go for it.
TBH in these ever wetter climates, I have to question why anyone thinks that a flat roof is a sensible option. Sooner or later it's gonna leak.
Never liked rubber roofs snd wouldn’t use them on domestic jobs either, I use grp system flexitec, and were possible warm roof applications, if not possible cold roof system with crossed battening to ensure good air circulation, and good vapour barrier.
Thanks a lot for your comment. What’s the sub strata you use on it? I focused on EPDM on the video because that’s the material that a lot of small general builders and most self builders tend to use.
@@AN-vt3kl with all due, "I never liked" isn't much of an argument. EPDM allows water to egress and is far more environmentally friendly that GRP and any other membrane or coating system I can think of, has far greater longevity (accelerated wear and weathering tests well over 100 years), is elastic to allow for movement and can even be reused.
@@build-better-things most times its 18mm t/g osb 3 boards, also can use 8x4 osb boards if no access for smaller boards but in that case a lot more work to seal the joins prior applying matting.
@@gurglejug627 in my experience there is a reason cheap isn't good, I would agree edpm ok for sheds garden rooms etc. but not for extensions, loft conversions but each to their own.
@AN-vt3kl that's not an argument it's a baseless and odd opinion - i speak from vast experience. The price has nothing to do with the quality of material or of suitability for any job.
Hi, so what are your views on grp
I don’t rate it, but I would also say, I’m not an expert in the technology of it. As i understand it, you have to bond to timber sub strata so it’s horrible for warm flat roofs. Cold ventilated roofs perhaps.