It's time to thank you. I've used your videos to build 2 walls, insulate my garage and tank a wet room. You explain things so well that I understand and can question things in my head. Insulated summer house / office is next which I'm hopping to start in the next month or two. I still bring in the pro's where needed, but understanding what is going on really helps and I think just raises the standards as a whole. Thank you!
Good explanation for people that don't understand the difference. 1 thing that would be better for ventilating the dead spots created by the lantern would be to counter batten the roof the opposite direction of the joist to create a cross flow ventilation throughout the whole roof. Although you increase the deck height by 25mm you get rid of the need for unsightly mushroom vents everywhere 👍
I did wonder when mushrooms kept being mentioned how the neighbours concerned about the height of the roof would like the mass of mushrooms there'll be instead.
Hi lads, You know what, I am level 6 NVQ (not very qualified) site manager, level 3 carpenter and joiner, and intermediate qualifications in Brick laying, plumbing and plastering, (also a fully qualified Locksmith), with 33 years of mud on boots experience, I've forgotten more than most people actually know, but...... I literally LOVE your videos and pod casts, (only found you the other day, so alot of catching up to do),very informative entertaining AND engaging, even if you are shandy drinking Southerners. Keep up the awesome work 👌
Nige Never touch shandy or larger. Give me a pint of best bitter any day. Unfortunately the number of pubs now serving ale are fewer than they used to be.
We know that channel well and he is great. We have used that ventilation detail in the past but, as you may see it would have come up above the parapet wall and upset the neighbour
@@georgeturner6648 Orangery are permitted developments, within certain parameters. Then it's permission from the neighbors. They may of had permission, but then the neighbors changed their mind, and to stop the ball ache of courts and council. Which you may or may not win. Especially if you lose you have to pull it down. Sometimes it's easier in the long run to just go to what's permitted without neighbors consent.
Never really thought about the subject before Roger but in many big old houses they had cellar and attic spaces with air grills below the floor space for the air to circulate. I was lucky when we bought our 300 year old 3 bedroom cob cottage with a thatched roof (cold roof). The 3 foot thick cob walls are build off a rubblestone plinth with no foundations or guttering, the ground is hard clay and stone. There was bad damp when I moved in because the walls were cement rendered and it had been a holiday home for about 15 years which had caused all the damp issues and rotted the timbers on the damp side of the house because I have a hill behind the house whose gable end faces into the hill and in front of that there is a 25 foot deep stone lined well, the water line is about 4 feet below ground, never higher and is only low during summer. Since I put in a French drain along the back side of the house and lime rendered the place we've have no more damp issues. The first floor ceiling is wooden lath & plaster (the walls are reed and plaster), a thick layer of haired course lime mortar and a single layer of thick top coat white lime skim 5 to 6ml thick. Another property of lime walls is they absorb moisture and CO2 and give you better acoustics than cement or gypsum, a friend in nearby Stogursey has plastered his internal walls with clay which has even more amazing qualities. It can be expensive to do but, done well it should last a life time whereas modern builds are designed for about a 40 year life, even a strawbale, single floor structure would last a 100 years. Above this ceiling line is the triangular shaped attic where, between the joists you can see the back of the ceiling and the folded nibs of that 200 year old, haired lime putty mortar and on top of that, between the joists are a few rolls of Rockwool insulation with a 5 foot air space before you see the underside of the straw roof. It's relatively dry. In some of the bigger houses they'd put a thick layer of tamped soil and sand which would be good for the sound proofing and insulation properties. During the night, summer and winter, we sleep with our bedroom window open and during the day, unless somebody is home, everything is shut up. Up the road is an equally old property which has a double-Roman, clay tiled roof, when I climbed up to look there was no roofing felt and it too was dry. As you said on one of your rants, there's no point having an air-sourced heat pump, if the home isn't well insulated inside. I'm house rich and cash poor and can't afford one but I would like a ground-sourced heat pipe, they do work, I would also like some solar panels please. It would help the planet if we all had solar, wind and thermal generating capabilities with storage capacity for any excess power with every home as standard and, if you have a small garden, a compost heap is great for all your organic waste. Ours is barely large enough for the herring bone pipe to the septic tank which is emptied every year (£250) and is cheaper than the mains sewage bill I'm told. We've go no government grants, none available, or help with lower VAT for sustainable buildings, and it was bought to be our family home and so long as it continues to be repaired with like for like materials it should last another 300 years. keep up your interesting topic please, it's healthy when we can all rant.
Ever thought about fitting cross battens running the opposite way to the joists,this creates a continuous air flow of 20mm. No need for mushroom vent. As long as you have.front and rear air soffit/ facia and abutment vents.
Can also set the circular saw to 20mm and cut a notch out the joists. Obviously it slightly weakens the joists but we usually over engineer flat roofs anyway! Iv done it that way before and was really fast and much better than drilling holes as they get clogged easily
@@chriscoulson7684 You're not a structural engineer are you! Notching out the top or bottom of a joist doesn't 'slightly weaken' it - it is the worst place to cut it. The bottom is in tension and the top is in compression - somewhere in the middle on the neutral axis there is no stress.
Very clear and helpful, nice video Rodger! We're always doing these sort of extensions and when the joiner talks to me about hot and cold roofs I'm always bamboozled 😂😂 look forward to see the next video on this project bud!🍻👍
I think i would have gone a cross the 9x2s with tile batten so the whole roof is connected and reduce the number of roof vents. Not only is all them mushroom vents going to cost a lot especially as they have to be built into the roof covering, they will look facking ugly. Good vid Roger 👍
Hi Tony Good idea but we had the deck down and we were going with the warm roof so we didn't want to rip it all up and counter batten. Also the counter batten doesn't give enough cross ventilation on its own. The whole thing is a ball ache and it is all down to a neighbour who said it was O.K and then said it wasn't.
@@SkillBuilder Remember- never ask the question if you don't want the answer. If you have permission for the higher warm roof, go with it, and don't ask the neighbours for their opinion
@@rossbuchanan7632 ...building regs? It sounded to me like there was a veiled mention of the fact that some arch holes can be nay bores. i for one wouldn't like to challenge a regulatíon and have to rip off the roof and then live with the people who opposed me in court. Ridiculous though, that it's a matter of less than a foot.
@@SkillBuilder Had loads of grief with neighbours. Not about height, they just don't like seeing people get on! Can't win, don't even try. Do what's best for you! Just make sure you stay within your rights. They will complain !
Thanks, excellent video! Simple answer - badly installed cold roofs are bloody freezing when the builder who owned your house doesn't air seal between the Kingspan slabs and the joists. It's basically external temperature just above the plasterboard.... 🥶 Also just found out he didn't stick a vapour barrier above the plasterboard either. 🤦♂️🤦♀️😤
Nicely done, I did a little office using warm deck. I stopped the joists at the wall plate, but extended the OSB and 4 inch insulation beyond to create a 200mm overhang. Then sandwiched the edge with 2x4 so I could hold it all together. I only did this to avoid creating an ugly thick fascia that was 300+ tall, instead there's a neat 150mm fascia with the gut attached.
Great videos! I've tried reading most comments so apologies if it's been asked before.. I'm currently starting a new build with a pitched roof. Strangely enough when you search for a warm roof, most videos, info etc. are in the context of a flat roof. Not a great deal of warm roof examples of a pitched although I have seen a handful of insulation companies i.e Kingspan, Tyvek with demo videos and illustrations of this exact setup, though they leave a lot to be questioned, they do show this is a practised method. My main concern really is only a problem when you have a pitch and that is the limited shear strength of the very long screws/insulation fixings that have to sandwich the battens to the rafters with this approx. 100mm of soft insulation board in between that provides no stability to these screws. I hope this makes sense, it's a question I haven't quite seen addressed before, thank you for your time!
Hi Michael You are right to say the focus is on flat roofs but a pitched warm roof is fundamentally the same. The best way to approach it is to counterbatten on top of the insulation in line with the rafters. You can buy stainless steel helical fixings. They are twisted so that stops them bending and they won't pull out. thorhelical.com/product/warm-roof-fixings/ Once you have the counter batten fixed you just batten out the roof in the same way you would on a cold roof.
Thanks so much, just about to build a warm roof for my conservatory. Amazing to see how literally none of these "kits" do not include the ventilation for the cold roof.
Great video Roger explaining the key differences between a warm and cold deck for a flat roof. My comment is on a warm deck. Like a lot of information out there the principle is illustrated by a cross section and details of the layered structure above the joists. For the void between the joists it is always made clear that there must be no insulation between the joists as this will lead to the rising moist air through the ceiling being cooled by the insulation and effectively producing a cold deck but with no ventilation. It would be really good if you could explain the detail to produce the sealing around the perimeter of the void space when an existing old flat roof is being replaced. The joists are above the wall and open to the air when the original fascia is removed. Your video includes at 1:35 'All this area here [between the joists] is warm. It is within the heated area of the house' which is fundamental. I have only found one set of videos by @SteveRoofer describing and illustrating the inclusion of insulation around the perimeter between the existing wall and the underside of the new deck. The principle is clear in CNCD-053. With just a new fascia board and no perimeter insulation the air in the void between the joists will experience some cooling defeating the basic assumption and potentially achieving the worst of all worlds. The wall cavity will be within the void space and this will also add to the cooling effect depending on the quality of the cavity insulation. This is all obvious to me after not much thought but seems to not be fully grasped by the roofing industry when you ask for a quote and for a description of the planned work even by reputable companies.
Great video Roger. I wonder why you didn’t opt for counter batten over the top to negate the need for the GRP mushroom vents? Just pitched a lean to roof and I’ve counter battened and put vented soffit on all three sides.
Just seen this after commenting myself about cross flow ventilation. Would of been a much better way but rach to there own and we all are still learning
Thanks Roger, excellent explanation to a bit of a head scratcher. Am going to replace my old plastic roof on my conservatory and had been trying to weigh up the best way of tackling it but you just explained it in less than 10 minutes!
Great as always Rodger. I have a 15-year-old log cabin. It's perfect inside but a bit dated on the outside. I spend around £100 per year maintaining it as well as the cost of heating. I am about to insulate it on the outside all around and have the products but not 100% sure of which way to have the insulation, membrane etc. I don't want to insulate the inside as I like my LOG cabin. I have 60mm Kingspan sheets (got them cheap so can't change) a breathable membrane, PVC cladding for the walls and box profile sheets for the roof. I was intending to stitch the membrane onto the outside walls then Kingspan held with 2"x1" battens and the pvc cladding onto this. There would be the 1" air gap behind the cladding vented at the top and bottom with mesh to stop wasps etc. The roof is 20mm t&g pine and is felted. The felt needs replacing so was intending on removing this stitch the breathable membrane on top, Kingspan, 15mm OSB then the box profile sheets directly on top. Do I need to change the membrane for a vapour barrier? If so where does it go? Do I need an air gap roof or walls? Any advice would be appreciated as I'm getting conflicting messages on other forums, everybody seems to be an expert
I built a flat roof with cross battens. It was a continuous problem with the boards moving about and cracking the waterproof layers. A butyl membrane would have been ok but the felt I used was a nightmare I seriously regretted not nailing the boards solid and using mushroom vents.
Thank you for sharing that knowledge. In NZ we build a lean to extension with a mono-pitch roof. Plaster board 200mm joists, vapour barrier then corrugated Iron. The Insulation is Pink Batts skillion roof insulation. The insulation had to be specific due to the insulation loft limitation giving allowance for at least a 20mm gap - I now further appreciate what that gap is for. More so it gets me to thinking about flashings and how well they can release water on the inside without letting water in. Hopefully the building codes we built to are correct.
Come see the uk new builds a meter of installation double glazed windows its like being trapped in a oven. ive not closed mt windows all year ... on the inside 30 mm pipes for the plumbing 15 mins to refill a toilet.. but they are alot cheaper than million dollar nz .
@@JONO3679 Sounds like a pressure issue or restricting washers to the toilet water supply? Many 'eco' toilets these days use too little water which can cause more issues - blockages - than having a decent flush volume.
Is it normal on the roof to fit 18mm plywood then osb on top before the grp . Or is this overkill and trying to rectify a problem with the plywood , thanks
Good video Roger. I do a bit of GRP roofing works but our boss gets us to put 100mm on top and 50mm to the under side. When I asked about vapour barrier he said with this system you don't need one.
Roger, firstly great explanation. Can you place a link to the grp mushrooms that you would recommend between the joists, and also the upstand ventilation product you also mentioned please.
Really enjoy watching your videos and on a very steep learning curve as starting from pretty much zero. I am building a warm roof but feel like I need two layers of vapour barriers. My garden room will house tropical plants. It is heated and insulated with 50 to 100mm PIR depending on location. I need to protect the inside of the roof (OSB) from rising moisture and there will be quite a bit of it as I water plants in the room. What's the right solution? I have the Dupont Tyvek membrane and was thinking from inside to outside: Membrane over joists, OSB, PIR, OSB, membrane then finish with felt Hopes that makes sense and look fwd to your opinion. Warmest thanks Jerome
Warm or cold roof, always avoid moist getting in the construction from the warm side of the construction, Make a 100% damp sealing above the plaster board.
I did my flat roof on my lounge 15 years ago. Plaster board, fibreglass, OSB and felt. No sweating, no damp, no problems. Still as good as the day I did it. I can't help but think that a lot of this is snake oil and more money for the men in suits. Great explanation Roger, as always.
My friends house lasted four years due to moisture building up in an unventilated roof space. It is happening all over the place and it is largely due to modern building techniques.
Same principles apply - but there you're keeping the heat out. Check out Matt Risinger's channel as he's rebuilding his home in Austin and super insulated it. There was recent news about the world's most reflective white paint that has the same effect as air conditioning when a house is externally painted with it - could be revolutionary if it comes to marked. Simple answer is a cold roof would be better there as you can use the top of the roof as a rain screen and break a lot of direct thermal transfer between the roof and internal ceiling.
To be honest if you have air con then the vapour is travelling from outside to in. The whole thing is fraught because humidity is higher in the summer. There are some people who say that you should not have a vapour barrier in those situations and just let the moisture drift through
Firstly ,many thanks for all your informative and interesting videos. Two questions please...if I use plaster board with the silver vapour barrier, will vapour still pass through where the sheets are joined...and the second question is could you do a video explaining how to apply a PVC flat roof membrane complete with all the finishing details ?
@@SkillBuilder Thank you for answering my first question. Regarding the flat roof question....it really doesn't matter which material, eg, PVC OR EPDM so long as whatever is used will have a long life span, 25 to 30 yrs...
crazy how the neighbours would be annoyed if the roof was 120mm higher... I would NEVER EVER EVER be that kind of neighbour. Why would they object to 120mm? What difference will 120mm make to them? Crazy! Anyway, thanks for the video! Very helpful
With a cold rood. Could you not put a vapour barrier on the inside of the insulation? In my head that would seem that no moisture would even get to the outside of the insulation/dew point. Therefore, that would make the void and all the ventilation aspects redundant? I don't know if this would work but the implication from a warm roof implies that it could. The only potential issue I see is when installing the plasterboard the screw for attaching are going to pierce the vapour barrier which isn't ideal but I'm sure there would be a way to avoid or mitigate that, if it even is an issue considering the piercing would be filled by the width of the screw.
Where do you put the electrics/extractor tube if the space between the joists is filled by insulation? Is it better to get a warm roof if you don’t have problems with the neighbours?
I have a large flat roof over a kitchen, 75mm fibreglass between the joist with cross ventilation from soffit into the pitched roof void. Its 45 years old and its fine - the fibreglass gets a bit damp in the winter but it always drys out quickly enough. The original chipboard deck failed after 10 years so I re-boarded it with marine ply and had high performance polyester felt laid on top. 35 years later still no leaks. Sometimes low tech works just fine.
I used the 25mm multilayer foil insulation for a warm roof, supposedly equivalent to 225mm of fibre insulation, but adds no more than 40mm with the counter battens. It all seemed to work well. I'm planning an orangery type extension on the house I'm buying.
Hmm. Well, when we build ships we pack the steel against with rockwool hard up. The main issue is stopping the air getting to the steel - or wood - to condense. Given that we have humidity levels at near 100% and a temperature difference of sometimes 90C between machinery rooms and the sea it works fine. I did a roof 12 years ago and used 100mm of Celotex foil backed and sealed it solid so no vapour could reach the OSB and then another 100mm of Rockwool to add even more insulation and fire proofing. No issues at all. As for the plasterboard - I used foil backed and fitted sealed downlighters.
I understand this, but, Why dont you put the vapour barrier down before the fist osb. Is it just because they become damaged and its difficult to install. May be i do not understand it after all.
food for thought. i have two flat roof extensions. both had no air space, both rotted. hopefully the roofer done it right this time. i have edpm roof covers on now.
I am currently doing a garage conversion. Turning it into a salon for my wife it’s having 3/4 inch ply boards on roof 2 layers of under felt and mineral felt for top layer. The under side of the roof (the structure) is all 2x2 timber which leaves me with 50mm void. What would you recommend just add no insulation them add insulated plaster bored maybe ? Thanks
Excellent stuff roger, as a building control surveyor the most common mistake is a warm roof with no decking and VCL below. Happens all the time! Every PIR supplier will ask for an 18mm deck with the VCL
When I've done cold roofs I always put plasterboard with a 25mm backing under the rafters to deal with cold bridging. Do you not think it's really necessary?
Roger, what would the position be if you filled with 225mm insulation so no air gap and then put in well sealed membrane and maybe for good measure the backed plasterboard so in effect an internal warm roof. I know the screws would perforate the membrane but they would be compressed and into the joists.
My thanks to Skill Builder and Roger - now all i need to know about warm and cold flat roofs. Infact my new extension Surrey side of Gatwick a semi-detached and all flats are cold. my new extension will be warm and work to change my current flat roofs to warm but will leave attached neighbours as is. with some magic (in the drawings) for the builder !!
You talk about the warm side sand cold side of the insulation. Where are you located? What if we live somewhere that uses heat half the year and air conditioning half the year? What's the cold side?
Hi Roger, thanks for such a detailed explanation, I finally understand! We are building a cabin in our garden (for us to live in whilst we do our house renovation). The builder has done a cold roof, but not put OSB boards on top. He has a membrane directly above the joists (where the insulation will be), the battens, then our metal roofing will go on top of that. Im a little confused as I thought you would always have boards on top of the roof, but I guess this way you solve the issue of ventilation/allowing vapour to escape? For peace of mind can you confirm you dont need OSB boards on top? Thanks so much!
Apparently in the states they are specifying tissue based pir board insulation when used with a separate vapour barrier. All to do only allowing one vapour barrier. It's constantly changing.
I’m stuck with a cold roof on a extension on a grade 2 listed building. 50mm air gap, 100mm of insulation and then a vapour barrier before the finished ceiling is the system I’ve gone for. Then added extra ventilation on the facias, but the vapour shouldn’t get up into the void to start with.
Nice video. I've got a small extension poorly insulated. I need to insulate it with celotex. I was told to cut to size and slot them into the spaces and there should be enough room for them to breath. I don't there is a vapour barrier, will that be OK? Cheers
Roger for me cold is always the way to go as long as it’s vented properly, around the Sky light/ Lantern you can do a vented upstand where you cut the ply short 25mm and run 50x25 batten vertical and leave the upstand ply 25mm short at the top thus creating enough draw for the air to move, it’s what we always do.
@@denty32 Zero of either. Cold roof needs more work if done correctly and down lights can be a pain. Much easier running out full sheets of materials from above deck. The extra height can look unsightly, that is true. Don't get me wrong, if it works it works.
@@TurinTuramber every flat roof / low pitched roof I get called out to inspect is 99% a warm roof with poorly fitted Vcl. Every one thinks warm roofs are easy to install until it goes wrong. It’s normally a SVP or flue that didn’t get fitted at the time of installation.
@@denty32 On a clear roof like an outbuilding there aren't really any interruptions so goes down super easy. Some roofs are busier than others. Also cold roofs thermal bridge like mad, Roger didn't mention that I think.
Is cross ventilation required for a office outbuilding as its low occupancy, as long as you have good vapour barrier. My office room build has a steel cross beam.
When I put up my extension , It was a cold roof because of the design I wanted. I used foil back pb and foil taped all the underside of the joists to the foilbacked Kingspan so there could be very little chance of any moist air penetrating. Redbrick vents to the front and proprietary vent escape vents to the rear. Hmmmm, forgot about the dead spaces though, gulp ! That said, ten years in and no problems as yet.
I've got a flat roof extension and a lot of heat is lost through that roof. I'm reluctant to start drilling holes and vents. Couldn't you just fix some insulation boards cut into strips against the underside of the sterling boards that are on top of the joists.
I built a garage extension where I didn’t have the height for a warm roof or the joist depth to achieve the required R-Value with venting, so I used Closed Cell Spray Foam. It is allowable under the Canadian Building Code for use in unvented roofs because it acts as a vapour barrier. Pricey though.
In my workshop which is basically a large shed I stapled foil bubble insulation under the roof cladding. Will this cause problems? It's tounge and groove panels only
Brilliantly explained 👍👍 mushroom vents will look rubbish though 😊 cant you just cross Batten above the joist with OSB board above to vent the roof ? This would rise it 2” though .
Hi, thanks for the video. Very informative. I'm part way through the purchase of an edwardian money pit which the wife loves - so hard to say no. The attic above the main living space has already been converted to a bedroom but the attic above the back bedroom and bathroom hasn't been done. It is about 20 meters long and has a pitched roof. I was hoping to fit celotex between the rafters (leaving a 50mm airgap) and then fitting a layer of insulated board to the rafters to improve the thermal insulation (as 50mm celotex won't be that great). This would allow me to board the space out and have a nice bit of storage there. Question is: how to ensure airflow through the air gap behind the celotex on the pitched roof? Thanks.
Great video thank you. We never got planning permission as the size was just shy of 40 sq metres which is allowed in our country. There was a warm roof in the plans, now we have discovered the engineer told the builders we need a cold roof due to height restrictions and no one even told us about this change which i am not happy about at all. The roof is nearly finished now. We live on a height where it gets very windy so I am concerned about whistling through the roof now (we had whistling in the eaves of existing dormer roof until I got foam insulation to block it out) and also cold air through the roof which means increased heating costs for the rest of our lives. Can someone please advise if we can now do anything about this? Seriously concerned :-(
Rodger ... Where does a cold bedroom above a garage sit with this, is it the same principle?. The garage is (very!) well ventilated and dry. I would like to insulate (celotex/Kingspan) below the floorboards, but have seen conflicting views as to how to go about it. Whether vapour barriers are required, and even then that gets confused further if they go directly below the joists or directly below the floorboards. Same with leaving an air gap above the insulation, Seen it done with and without. All a bit confusing, for what seems essentially a (fairly) straight forward job, but paranoid about creating damp / rot?
Really love watching your videos - that are really informative particularly for a novice. I am in currently undertaking a single story rear extension and I was let down but he builder. The flat roof basically was completed with trimmers, joists etc and a GRP layer was pasted on. The roof wasn't insulated so, I got someone else to finish the job and created warm roof on top of the GRP. I asked the roofer to add in a vapour on top of the GRP and beneath the insulation. was that the right thing to do? Will this have a detrimental impact on moisture internally ? Thanks Joanne
Sadly on my cold roof I've only got 120mm to play with in my garden room. If I used 100mm insulation then only 20mm to play with. Better than nothing I guess. Or would you recommend I use 70mm PIR to get the 50mm gap?
If you insulate a warm roof on the inside --> you run the risk of condensation and moisture problems (100% humidity and thus condensation). But you run into trouble much sooner, right? If the humidity level exceeds 70% you increase the risk for mold dramatically. Even in de dry house you get to this level very quickly --> meaning that you can't really insualte a warm roof from the inside. Or what am I missing? Ventilating the in between the roof and the insualtion might be the only option -- but does that not reduce the insulating effect allot?
For cold roofs, why don't you put the vapor barrier on the inside, along the joists? Is this a viable option that's not often chosen because it's a hassle?
That is exactly what you do. From the top down. Roofing membrane (felt) roof deck (OSB) air gap vented across the whole width, Insulation, vapour barrier and or foil backed plasteboard. Do not breach vapour barrier with down lighters.
Why can't you full fill the joists with insulation space but adding a vapour barrier below it, so the warm moistured air can't travel through the insulation?
I have a fairly simple question. With the warm roof design, why do you put the vapour barrier directly beneath the insulation? What would be wrong with putting it under the OSB decking on the joists? I.E. put the vapour barrier on top of the joists, then OSB, then insulation. Would this not be good for keeping that OSB decking dry as well?
@@SkillBuilder Thank you Roger. The more that I have watched your videos, the more I have realised that it's a case of applying common sense, logic, and looking out for any potential cold bridging places where vapour condensation can accumulate and not be released. And also realising that things like insulation and concrete are not necessarily impervious to water. I found the parapet video particularly interesting in regard of the above, and halfway through the video, I could see where it was going.
I always thought that the way to do this (it seems that way in our house) is to put a moisture barrier ie polythene, well taped, no gaps or breaches behind the plasterboard so the moisture is contained there- if the insulation is done to a proper decent standard then the cold should never meet the damp air and turn to water??
You are right about the vapour barrier, Every roof warm or cold should have a vapour barrier. Ordinary polythene is not as impervious to vapour as many believe but it is a good start. Taping all the joins is essential but it is not always done to the letter. After all that trouble somebody cuts holes for downlighters and it is game over.
Thank you for sharing your knowledge. On the warm roof example, would it be ok to insulate in between the joists as well? Assuming drywall is the finished product? Or would that trap the moisture?
It is a very difficult judgement. Sometimes putting in more insulation moves the dew point to somewhere in between. You can get a professional calculation done online that will tell you. I have done it in the past with no problems but the vapour barrier has to be good.
It's time to thank you. I've used your videos to build 2 walls, insulate my garage and tank a wet room. You explain things so well that I understand and can question things in my head. Insulated summer house / office is next which I'm hopping to start in the next month or two. I still bring in the pro's where needed, but understanding what is going on really helps and I think just raises the standards as a whole. Thank you!
Thank you for the message on this fine sunny Easter Sunday.
Such a unique breadth and depth of knowledge from Roger, we are lucky that he is willing to share it with us. Thank you Roger! 🙏
Nice of you to say so, we try.
so unique to the extend that he redefines the dew point at 3:50. He even draws an arrow pointing at the dew
Good explanation for people that don't understand the difference. 1 thing that would be better for ventilating the dead spots created by the lantern would be to counter batten the roof the opposite direction of the joist to create a cross flow ventilation throughout the whole roof. Although you increase the deck height by 25mm you get rid of the need for unsightly mushroom vents everywhere 👍
Exactly!
ALso have to consider how much height the shrooms add and what they look like...
I did wonder when mushrooms kept being mentioned how the neighbours concerned about the height of the roof would like the mass of mushrooms there'll be instead.
Hi lads, You know what, I am level 6 NVQ (not very qualified) site manager, level 3 carpenter and joiner, and intermediate qualifications in Brick laying, plumbing and plastering, (also a fully qualified Locksmith), with 33 years of mud on boots experience, I've forgotten more than most people actually know, but...... I literally LOVE your videos and pod casts, (only found you the other day, so alot of catching up to do),very informative entertaining AND engaging, even if you are shandy drinking Southerners. Keep up the awesome work 👌
Nige
Never touch shandy or larger. Give me a pint of best bitter any day. Unfortunately the number of pubs now serving ale are fewer than they used to be.
Going to be doing a garage to office conversation soon, needed this lessen. Thanks Roger
Also need a spelling lesson
@@NordenEngineering lesson. Sorry teacher.
@@vinnysurti* conversion
😂👍✊
After watching countless videos on youtube once again Roger hits the nail on the head and makes it perfectly understandable. cheers marra
San Francisco, California, homeowners should take note of Roger's sage advice!
A UA-cam channel called Steve roofer shows a good ventilation detail on the flashing, well worth consideration
We know that channel well and he is great. We have used that ventilation detail in the past but, as you may see it would have come up above the parapet wall and upset the neighbour
@@SkillBuilder ...ahhh the poor neighbour, can i picture a forage on the roof, Monty Python style?
Surely you had plans which the neighbours could have objected to before the build commenced?
@@georgeturner6648
Orangery are permitted developments, within certain parameters.
Then it's permission from the neighbors.
They may of had permission, but then the neighbors changed their mind, and to stop the ball ache of courts and council. Which you may or may not win. Especially if you lose you have to pull it down.
Sometimes it's easier in the long run to just go to what's permitted without neighbors consent.
Never really thought about the subject before Roger but in many big old houses they had cellar and attic spaces with air grills below the floor space for the air to circulate. I was lucky when we bought our 300 year old 3 bedroom cob cottage with a thatched roof (cold roof).
The 3 foot thick cob walls are build off a rubblestone plinth with no foundations or guttering, the ground is hard clay and stone.
There was bad damp when I moved in because the walls were cement rendered and it had been a holiday home for about 15 years which had caused all the damp issues and rotted the timbers on the damp side of the house because I have a hill behind the house whose gable end faces into the hill and in front of that there is a 25 foot deep stone lined well, the water line is about 4 feet below ground, never higher and is only low during summer. Since I put in a French drain along the back side of the house and lime rendered the place we've have no more damp issues.
The first floor ceiling is wooden lath & plaster (the walls are reed and plaster), a thick layer of haired course lime mortar and a single layer of thick top coat white lime skim 5 to 6ml thick. Another property of lime walls is they absorb moisture and CO2 and give you better acoustics than cement or gypsum, a friend in nearby Stogursey has plastered his internal walls with clay which has even more amazing qualities.
It can be expensive to do but, done well it should last a life time whereas modern builds are designed for about a 40 year life, even a strawbale, single floor structure would last a 100 years.
Above this ceiling line is the triangular shaped attic where, between the joists you can see the back of the ceiling and the folded nibs of that 200 year old, haired lime putty mortar and on top of that, between the joists are a few rolls of Rockwool insulation with a 5 foot air space before you see the underside of the straw roof. It's relatively dry. In some of the bigger houses they'd put a thick layer of tamped soil and sand which would be good for the sound proofing and insulation properties.
During the night, summer and winter, we sleep with our bedroom window open and during the day, unless somebody is home, everything is shut up.
Up the road is an equally old property which has a double-Roman, clay tiled roof, when I climbed up to look there was no roofing felt and it too was dry.
As you said on one of your rants, there's no point having an air-sourced heat pump, if the home isn't well insulated inside.
I'm house rich and cash poor and can't afford one but I would like a ground-sourced heat pipe, they do work, I would also like some solar panels please.
It would help the planet if we all had solar, wind and thermal generating capabilities with storage capacity for any excess power with every home as standard and, if you have a small garden, a compost heap is great for all your organic waste. Ours is barely large enough for the herring bone pipe to the septic tank which is emptied every year (£250) and is cheaper than the mains sewage bill I'm told.
We've go no government grants, none available, or help with lower VAT for sustainable buildings, and it was bought to be our family home and so long as it continues to be repaired with like for like materials it should last another 300 years.
keep up your interesting topic please, it's healthy when we can all rant.
* Star Wars theme plays *
Ever thought about fitting cross battens running the opposite way to the joists,this creates a continuous air flow of 20mm. No need for mushroom vent. As long as you have.front and rear air soffit/ facia and abutment vents.
Can also set the circular saw to 20mm and cut a notch out the joists. Obviously it slightly weakens the joists but we usually over engineer flat roofs anyway! Iv done it that way before and was really fast and much better than drilling holes as they get clogged easily
Always counterbatten cold roofs for cross flow.job done
@@chriscoulson7684 You're not a structural engineer are you! Notching out the top or bottom of a joist doesn't 'slightly weaken' it - it is the worst place to cut it. The bottom is in tension
and the top is in compression - somewhere in the middle on the neutral axis there is no stress.
Great video explaining in very clear way the difference between cold and warm roofs
Dom, so easy to binge watch your content. Well done to you and Dan. The editing is superb.
Jamie
Very clear and helpful, nice video Rodger! We're always doing these sort of extensions and when the joiner talks to me about hot and cold roofs I'm always bamboozled 😂😂 look forward to see the next video on this project bud!🍻👍
I think i would have gone a cross the 9x2s with tile batten so the whole roof is connected and reduce the number of roof vents. Not only is all them mushroom vents going to cost a lot especially as they have to be built into the roof covering, they will look facking ugly.
Good vid Roger 👍
Hi Tony
Good idea but we had the deck down and we were going with the warm roof so we didn't want to rip it all up and counter batten. Also the counter batten doesn't give enough cross ventilation on its own. The whole thing is a ball ache and it is all down to a neighbour who said it was O.K and then said it wasn't.
@@SkillBuilder Remember- never ask the question if you don't want the answer. If you have permission for the higher warm roof, go with it, and don't ask the neighbours for their opinion
@@rossbuchanan7632 ...building regs? It sounded to me like there was a veiled mention of the fact that some arch holes can be nay bores. i for one wouldn't like to challenge a regulatíon and have to rip off the roof and then live with the people who opposed me in court. Ridiculous though, that it's a matter of less than a foot.
@@SkillBuilder Had loads of grief with neighbours. Not about height, they just don't like seeing people get on! Can't win, don't even try. Do what's best for you! Just make sure you stay within your rights. They will complain !
@@danieljones741
Tends to be, there's max heights your allowed with no permission, anymore you need to consult neighbors.
Thanks, excellent video!
Simple answer - badly installed cold roofs are bloody freezing when the builder who owned your house doesn't air seal between the Kingspan slabs and the joists. It's basically external temperature just above the plasterboard.... 🥶
Also just found out he didn't stick a vapour barrier above the plasterboard either. 🤦♂️🤦♀️😤
Nicely done, I did a little office using warm deck. I stopped the joists at the wall plate, but extended the OSB and 4 inch insulation beyond to create a 200mm overhang. Then sandwiched the edge with 2x4 so I could hold it all together. I only did this to avoid creating an ugly thick fascia that was 300+ tall, instead there's a neat 150mm fascia with the gut attached.
Hi Chris
Nice to see you back. We also do that trick to reduce the fascia height
Highly interesting....more demonstrations would be very much appreciated...thanks
The whole video will show plenty of detail but it is work in progress
Perfect timing. Will be starting on a garage conversion soon and need a new roof. Exactly what I needed. Warm roof it is. Cheers
It really is the best option, I am very uncomfortable with this arrangement
@@SkillBuilder
Whereas in my industry (hard metal roofing) we hate warm roofs because they fail more than cold roofs.
Great videos! I've tried reading most comments so apologies if it's been asked before..
I'm currently starting a new build with a pitched roof. Strangely enough when you search for a warm roof, most videos, info etc. are in the context of a flat roof.
Not a great deal of warm roof examples of a pitched although I have seen a handful of insulation companies i.e Kingspan, Tyvek with demo videos and illustrations of this exact setup, though they leave a lot to be questioned, they do show this is a practised method.
My main concern really is only a problem when you have a pitch and that is the limited shear strength of the very long screws/insulation fixings that have to sandwich the battens to the rafters with this approx. 100mm of soft insulation board in between that provides no stability to these screws. I hope this makes sense, it's a question I haven't quite seen addressed before, thank you for your time!
Hi Michael
You are right to say the focus is on flat roofs but a pitched warm roof is fundamentally the same.
The best way to approach it is to counterbatten on top of the insulation in line with the rafters. You can buy stainless steel helical fixings. They are twisted so that stops them bending and they won't pull out.
thorhelical.com/product/warm-roof-fixings/
Once you have the counter batten fixed you just batten out the roof in the same way you would on a cold roof.
Thank you so much for this advice, I actually introduced a joiner to these fixings who was quite impressed!
Thanks so much, just about to build a warm roof for my conservatory. Amazing to see how literally none of these "kits" do not include the ventilation for the cold roof.
Great video Roger explaining the key differences between a warm and cold deck for a flat roof. My comment is on a warm deck. Like a lot of information out there the principle is illustrated by a cross section and details of the layered structure above the joists. For the void between the joists it is always made clear that there must be no insulation between the joists as this will lead to the rising moist air through the ceiling being cooled by the insulation and effectively producing a cold deck but with no ventilation.
It would be really good if you could explain the detail to produce the sealing around the perimeter of the void space when an existing old flat roof is being replaced. The joists are above the wall and open to the air when the original fascia is removed. Your video includes at 1:35 'All this area here [between the joists] is warm. It is within the heated area of the house' which is fundamental. I have only found one set of videos by @SteveRoofer describing and illustrating the inclusion of insulation around the perimeter between the existing wall and the underside of the new deck. The principle is clear in CNCD-053. With just a new fascia board and no perimeter insulation the air in the void between the joists will experience some cooling defeating the basic assumption and potentially achieving the worst of all worlds. The wall cavity will be within the void space and this will also add to the cooling effect depending on the quality of the cavity insulation. This is all obvious to me after not much thought but seems to not be fully grasped by the roofing industry when you ask for a quote and for a description of the planned work even by reputable companies.
I wish all tradesmen were like you Roger.
Thanks for this. Definitely the clearest and most easy to understand explanation of a cold roof and warm roof on UA-cam.
Great video Roger.
I wonder why you didn’t opt for counter batten over the top to negate the need for the GRP mushroom vents? Just pitched a lean to roof and I’ve counter battened and put vented soffit on all three sides.
We would have counter battened but the deck was down by the time the change of plan came.
Just seen this after commenting myself about cross flow ventilation. Would of been a much better way but rach to there own and we all are still learning
Great vid Roger, nice and simply explained.
Thanks Roger, excellent explanation to a bit of a head scratcher. Am going to replace my old plastic roof on my conservatory and had been trying to weigh up the best way of tackling it but you just explained it in less than 10 minutes!
You are the best! Thank you for the explaining.
Awesome explanation, Thank you. I am considering this for a project and wanted to understand it.
Very interesting subject. Most people wouldn't give it a second thought. But it's important you know in case of dry or wet rot. Thanks rodger👍👍
Interesting stuff Rog , what a massive pain in the area for
5 “ though ! 😳.
Look forward to the build 🧱👍🏽
Excellent stuff. I'll now change what I was going to do with the roof of my new dormer.
This channel is a gold mine of knowledge 👍👍👍 Thanks and thank you for your passion
Great as always Rodger. I have a 15-year-old log cabin. It's perfect inside but a bit dated on the outside. I spend around £100 per year maintaining it as well as the cost of heating. I am about to insulate it on the outside all around and have the products but not 100% sure of which way to have the insulation, membrane etc. I don't want to insulate the inside as I like my LOG cabin. I have 60mm Kingspan sheets (got them cheap so can't change) a breathable membrane, PVC cladding for the walls and box profile sheets for the roof. I was intending to stitch the membrane onto the outside walls then Kingspan held with 2"x1" battens and the pvc cladding onto this. There would be the 1" air gap behind the cladding vented at the top and bottom with mesh to stop wasps etc. The roof is 20mm t&g pine and is felted. The felt needs replacing so was intending on removing this stitch the breathable membrane on top, Kingspan, 15mm OSB then the box profile sheets directly on top. Do I need to change the membrane for a vapour barrier? If so where does it go? Do I need an air gap roof or walls? Any advice would be appreciated as I'm getting conflicting messages on other forums, everybody seems to be an expert
You could simply cross batten between the joists and the OSB to get your cross ventilation, definitely cuts down on mushroom vents
I built a flat roof with cross battens. It was a continuous problem with the boards moving about and cracking the waterproof layers.
A butyl membrane would have been ok but the felt I used was a nightmare
I seriously regretted not nailing the boards solid and using mushroom vents.
Thank you for sharing that knowledge. In NZ we build a lean to extension with a mono-pitch roof. Plaster board 200mm joists, vapour barrier then corrugated Iron. The Insulation is Pink Batts skillion roof insulation. The insulation had to be specific due to the insulation loft limitation giving allowance for at least a 20mm gap - I now further appreciate what that gap is for. More so it gets me to thinking about flashings and how well they can release water on the inside without letting water in. Hopefully the building codes we built to are correct.
Come see the uk new builds a meter of installation double glazed windows its like being trapped in a oven. ive not closed mt windows all year ... on the inside 30 mm pipes for the plumbing 15 mins to refill a toilet.. but they are alot cheaper than million dollar nz .
@@JONO3679 Sounds like a pressure issue or restricting washers to the toilet water supply? Many 'eco' toilets these days use too little water which can cause more issues - blockages - than having a decent flush volume.
Is it normal on the roof to fit 18mm plywood then osb on top before the grp . Or is this overkill and trying to rectify a problem with the plywood , thanks
Good video Roger. I do a bit of GRP roofing works but our boss gets us to put 100mm on top and 50mm to the under side. When I asked about vapour barrier he said with this system you don't need one.
I think you are talking about a hybrid roof there and the insulation on the underside is the vapour barrier. It will have to be well sealed.
Roger, firstly great explanation.
Can you place a link to the grp mushrooms that you would recommend between the joists, and also the upstand ventilation product you also mentioned please.
Really enjoy watching your videos and on a very steep learning curve as starting from pretty much zero. I am building a warm roof but feel like I need two layers of vapour barriers. My garden room will house tropical plants. It is heated and insulated with 50 to 100mm PIR depending on location. I need to protect the inside of the roof (OSB) from rising moisture and there will be quite a bit of it as I water plants in the room. What's the right solution?
I have the Dupont Tyvek membrane and was thinking from inside to outside:
Membrane over joists, OSB, PIR, OSB, membrane then finish with felt
Hopes that makes sense and look fwd to your opinion. Warmest thanks Jerome
A neighbour can effevtively stop 12 cm of additional roof build up? Was there no planning application?
Sometimes it's just about giving the neighbour a concession. Make them feel like you're making an effort. This one's a bit daft though.
Warm or cold roof, always avoid moist getting in the construction from the warm side of the construction, Make a 100% damp sealing above the plaster board.
If you used open web engineered joists then that would help with the dead spot ventilation 👍
Would also be rubbish to insulate
That would mean pulling the building down after it's built
Thank you very much for sharing, Master!
I did my flat roof on my lounge 15 years ago. Plaster board, fibreglass, OSB and felt. No sweating, no damp, no problems. Still as good as the day I did it. I can't help but think that a lot of this is snake oil and more money for the men in suits. Great explanation Roger, as always.
My friends house lasted four years due to moisture building up in an unventilated roof space. It is happening all over the place and it is largely due to modern building techniques.
Look at the thermal values of celotex vs old fashoned inulation rolls.
What would be the best way to insulate if the heat were the other way round. i.e. an air-conditioned house in a hot humid climate?
Same principles apply - but there you're keeping the heat out. Check out Matt Risinger's channel as he's rebuilding his home in Austin and super insulated it.
There was recent news about the world's most reflective white paint that has the same effect as air conditioning when a house is externally painted with it - could be revolutionary if it comes to marked.
Simple answer is a cold roof would be better there as you can use the top of the roof as a rain screen and break a lot of direct thermal transfer between the roof and internal ceiling.
To be honest if you have air con then the vapour is travelling from outside to in. The whole thing is fraught because humidity is higher in the summer. There are some people who say that you should not have a vapour barrier in those situations and just let the moisture drift through
Firstly ,many thanks for all your informative and interesting videos. Two questions please...if I use plaster board with the silver vapour barrier, will vapour still pass through where the sheets are joined...and the second question is could you do a video explaining how to apply a PVC flat roof membrane complete with all the finishing details ?
The edges of the board have foil so the amount of vapour passing through is tiny,
Second question. Are you talking about an EPDM roof membrane
@@SkillBuilder Thank you for answering my first question. Regarding the flat roof question....it really doesn't matter which material, eg, PVC OR EPDM so long as whatever is used will have a long life span, 25 to 30 yrs...
crazy how the neighbours would be annoyed if the roof was 120mm higher... I would NEVER EVER EVER be that kind of neighbour. Why would they object to 120mm? What difference will 120mm make to them? Crazy! Anyway, thanks for the video! Very helpful
Thank you for a very informative and well delivered explanation. Keep up the good work.
With a cold rood. Could you not put a vapour barrier on the inside of the insulation?
In my head that would seem that no moisture would even get to the outside of the insulation/dew point. Therefore, that would make the void and all the ventilation aspects redundant?
I don't know if this would work but the implication from a warm roof implies that it could. The only potential issue I see is when installing the plasterboard the screw for attaching are going to pierce the vapour barrier which isn't ideal but I'm sure there would be a way to avoid or mitigate that, if it even is an issue considering the piercing would be filled by the width of the screw.
Where do you put the electrics/extractor tube if the space between the joists is filled by insulation? Is it better to get a warm roof if you don’t have problems with the neighbours?
I have a large flat roof over a kitchen, 75mm fibreglass between the joist with cross ventilation from soffit into the pitched roof void. Its 45 years old and its fine - the fibreglass gets a bit damp in the winter but it always drys out quickly enough.
The original chipboard deck failed after 10 years so I re-boarded it with marine ply and had high performance polyester felt laid on top. 35 years later still no leaks.
Sometimes low tech works just fine.
Excellent as always!
The GRP mushrooms cost the guts of 70 euro a piece here in ireland. We tend to use them sparingly.
I used the 25mm multilayer foil insulation for a warm roof, supposedly equivalent to 225mm of fibre insulation, but adds no more than 40mm with the counter battens. It all seemed to work well.
I'm planning an orangery type extension on the house I'm buying.
Hmm. Well, when we build ships we pack the steel against with rockwool hard up. The main issue is stopping the air getting to the steel - or wood - to condense. Given that we have humidity levels at near 100% and a temperature difference of sometimes 90C between machinery rooms and the sea it works fine. I did a roof 12 years ago and used 100mm of Celotex foil backed and sealed it solid so no vapour could reach the OSB and then another 100mm of Rockwool to add even more insulation and fire proofing. No issues at all. As for the plasterboard - I used foil backed and fitted sealed downlighters.
So the neighbours would rather see a mushroom field !
This is very useful :) I'm converting my garage to a room and I'll speak to the builder what he plans to do with the moisture issue :D
I understand this, but, Why dont you put the vapour barrier down before the fist osb. Is it just because they become damaged and its difficult to install. May be i do not understand it after all.
food for thought. i have two flat roof extensions. both had no air space, both rotted. hopefully the roofer done it right this time. i have edpm roof covers on now.
I am currently doing a garage conversion. Turning it into a salon for my wife it’s having 3/4 inch ply boards on roof 2 layers of under felt and mineral felt for top layer. The under side of the roof (the structure) is all 2x2 timber which leaves me with 50mm void. What would you recommend just add no insulation them add insulated plaster bored maybe ? Thanks
Excellent stuff roger, as a building control surveyor the most common mistake is a warm roof with no decking and VCL below. Happens all the time! Every PIR supplier will ask for an 18mm deck with the VCL
Thanks James. What would you accept as a VCL? Is 1000 guage polythene suitable? I only ask because the dedicated VCL products cost a fortune.
When I've done cold roofs I always put plasterboard with a 25mm backing under the rafters to deal with cold bridging. Do you not think it's really necessary?
Roger, what would the position be if you filled with 225mm insulation so no air gap and then put in well sealed membrane and maybe for good measure the backed plasterboard so in effect an internal warm roof. I know the screws would perforate the membrane but they would be compressed and into the joists.
My thanks to Skill Builder and Roger - now all i need to know about warm and cold flat roofs. Infact my new extension Surrey side of Gatwick a semi-detached and all flats are cold. my new extension will be warm and work to change my current flat roofs to warm but will leave attached neighbours as is. with some magic (in the drawings) for the builder !!
So rather than seeing a 5 inch higher, nice flat roof - the neighbours can look at a huge number of tiny chimneys. Silly sausages
Yep!
Mouth breathers as AvE likes to refer to.
I was thinking exactly the same. They're moaning about an extra 12 cm in height. Unbelievable!
Surely the mushroom ventilators are about the same height as the extra thickness would have been anyway!
@@timt3813 was wondering that. Can they not complain about that also?
You talk about the warm side sand cold side of the insulation. Where are you located? What if we live somewhere that uses heat half the year and air conditioning half the year? What's the cold side?
Hi Roger, thanks for such a detailed explanation, I finally understand! We are building a cabin in our garden (for us to live in whilst we do our house renovation). The builder has done a cold roof, but not put OSB boards on top. He has a membrane directly above the joists (where the insulation will be), the battens, then our metal roofing will go on top of that. Im a little confused as I thought you would always have boards on top of the roof, but I guess this way you solve the issue of ventilation/allowing vapour to escape? For peace of mind can you confirm you dont need OSB boards on top? Thanks so much!
Really interesting explanation. Jaw on the floor over the 120mm issue. One more brick course on the parapet should sort that out.
Apparently in the states they are specifying tissue based pir board insulation when used with a separate vapour barrier. All to do only allowing one vapour barrier. It's constantly changing.
mmm, in the original warm roof concept you describe the vapour barrier keeps the moisture within the osp, is that good?
If you use a closed cell foam and something like gappo-tape to seal the edges, would you still need the vapour barrier?
I’m stuck with a cold roof on a extension on a grade 2 listed building. 50mm air gap, 100mm of insulation and then a vapour barrier before the finished ceiling is the system I’ve gone for. Then added extra ventilation on the facias, but the vapour shouldn’t get up into the void to start with.
Nice video. I've got a small extension poorly insulated. I need to insulate it with celotex. I was told to cut to size and slot them into the spaces and there should be enough room for them to breath. I don't there is a vapour barrier, will that be OK? Cheers
Roger for me cold is always the way to go as long as it’s vented properly, around the Sky light/ Lantern you can do a vented upstand where you cut the ply short 25mm and run 50x25 batten vertical and leave the upstand ply 25mm short at the top thus creating enough draw for the air to move, it’s what we always do.
If you have the height available, warm roof is so much better.
@@TurinTuramber how many have you had to redo?
@@denty32 Zero of either. Cold roof needs more work if done correctly and down lights can be a pain. Much easier running out full sheets of materials from above deck. The extra height can look unsightly, that is true. Don't get me wrong, if it works it works.
@@TurinTuramber every flat roof / low pitched roof I get called out to inspect is 99% a warm roof with poorly fitted Vcl. Every one thinks warm roofs are easy to install until it goes wrong. It’s normally a SVP or flue that didn’t get fitted at the time of installation.
@@denty32 On a clear roof like an outbuilding there aren't really any interruptions so goes down super easy. Some roofs are busier than others. Also cold roofs thermal bridge like mad, Roger didn't mention that I think.
Is cross ventilation required for a office outbuilding as its low occupancy, as long as you have good vapour barrier. My office room build has a steel cross beam.
When I put up my extension , It was a cold roof because of the design I wanted. I used foil back pb and foil taped all the underside of the joists to the foilbacked Kingspan so there could be very little chance of any moist air penetrating. Redbrick vents to the front and proprietary vent escape vents to the rear. Hmmmm, forgot about the dead spaces though, gulp ! That said, ten years in and no problems as yet.
I've got a flat roof extension and a lot of heat is lost through that roof.
I'm reluctant to start drilling holes and vents. Couldn't you just fix some insulation boards cut into strips against the underside of the sterling boards that are on top of the joists.
I built a garage extension where I didn’t have the height for a warm roof or the joist depth to achieve the required R-Value with venting, so I used Closed Cell Spray Foam. It is allowable under the Canadian Building Code for use in unvented roofs because it acts as a vapour barrier. Pricey though.
That would never pass regulations in the uk. It doesn’t allow anything to breathe! The uk is far too damp for that type of insulation!
A very informative video. Thanks for sharing
Excellent info, thanks 👍🏻
In my workshop which is basically a large shed I stapled foil bubble insulation under the roof cladding. Will this cause problems? It's tounge and groove panels only
Brilliant explanation Roger
Excellent job great explanation 👍
Brilliantly explained 👍👍 mushroom vents will look rubbish though 😊 cant you just cross Batten above the joist with OSB board above to vent the roof ? This would rise it 2” though .
I loved your class but how can I work out around the stairs
Hi, thanks for the video. Very informative. I'm part way through the purchase of an edwardian money pit which the wife loves - so hard to say no. The attic above the main living space has already been converted to a bedroom but the attic above the back bedroom and bathroom hasn't been done. It is about 20 meters long and has a pitched roof. I was hoping to fit celotex between the rafters (leaving a 50mm airgap) and then fitting a layer of insulated board to the rafters to improve the thermal insulation (as 50mm celotex won't be that great). This would allow me to board the space out and have a nice bit of storage there. Question is: how to ensure airflow through the air gap behind the celotex on the pitched roof? Thanks.
Great video thank you. We never got planning permission as the size was just shy of 40 sq metres which is allowed in our country. There was a warm roof in the plans, now we have discovered the engineer told the builders we need a cold roof due to height restrictions and no one even told us about this change which i am not happy about at all. The roof is nearly finished now. We live on a height where it gets very windy so I am concerned about whistling through the roof now (we had whistling in the eaves of existing dormer roof until I got foam insulation to block it out) and also cold air through the roof which means increased heating costs for the rest of our lives. Can someone please advise if we can now do anything about this? Seriously concerned :-(
Rodger ... Where does a cold bedroom above a garage sit with this, is it the same principle?. The garage is (very!) well ventilated and dry. I would like to insulate (celotex/Kingspan) below the floorboards, but have seen conflicting views as to how to go about it. Whether vapour barriers are required, and even then that gets confused further if they go directly below the joists or directly below the floorboards. Same with leaving an air gap above the insulation, Seen it done with and without. All a bit confusing, for what seems essentially a (fairly) straight forward job, but paranoid about creating damp / rot?
Really love watching your videos - that are really informative particularly for a novice. I am in currently undertaking a single story rear extension and I was let down but he builder. The flat roof basically was completed with trimmers, joists etc and a GRP layer was pasted on. The roof wasn't insulated so, I got someone else to finish the job and created warm roof on top of the GRP. I asked the roofer to add in a vapour on top of the GRP and beneath the insulation. was that the right thing to do? Will this have a detrimental impact on moisture internally ? Thanks Joanne
Sadly on my cold roof I've only got 120mm to play with in my garden room. If I used 100mm insulation then only 20mm to play with. Better than nothing I guess. Or would you recommend I use 70mm PIR to get the 50mm gap?
If you insulate a warm roof on the inside --> you run the risk of condensation and moisture problems (100% humidity and thus condensation). But you run into trouble much sooner, right? If the humidity level exceeds 70% you increase the risk for mold dramatically. Even in de dry house you get to this level very quickly --> meaning that you can't really insualte a warm roof from the inside. Or what am I missing?
Ventilating the in between the roof and the insualtion might be the only option -- but does that not reduce the insulating effect allot?
For cold roofs, why don't you put the vapor barrier on the inside, along the joists? Is this a viable option that's not often chosen because it's a hassle?
That is exactly what you do. From the top down. Roofing membrane (felt) roof deck (OSB) air gap vented across the whole width, Insulation, vapour barrier and or foil backed plasteboard. Do not breach vapour barrier with down lighters.
Why can't you full fill the joists with insulation space but adding a vapour barrier below it, so the warm moistured air can't travel through the insulation?
How about an attic sidewall automatic fan to rid the space of moisture?
I have a fairly simple question. With the warm roof design, why do you put the vapour barrier directly beneath the insulation?
What would be wrong with putting it under the OSB decking on the joists? I.E. put the vapour barrier on top of the joists, then OSB, then insulation. Would this not be good for keeping that OSB decking dry as well?
I can't see anything wrong with that idea and it is what I did on my roof. The OSB is on the warm side so no problem
@@SkillBuilder Thank you Roger. The more that I have watched your videos, the more I have realised that it's a case of applying common sense, logic, and looking out for any potential cold bridging places where vapour condensation can accumulate and not be released. And also realising that things like insulation and concrete are not necessarily impervious to water.
I found the parapet video particularly interesting in regard of the above, and halfway through the video, I could see where it was going.
then y did you say above the osb????? @@SkillBuilder
I always thought that the way to do this (it seems that way in our house) is to put a moisture barrier ie polythene, well taped, no gaps or breaches behind the plasterboard so the moisture is contained there- if the insulation is done to a proper decent standard then the cold should never meet the damp air and turn to water??
You are right about the vapour barrier, Every roof warm or cold should have a vapour barrier. Ordinary polythene is not as impervious to vapour as many believe but it is a good start. Taping all the joins is essential but it is not always done to the letter. After all that trouble somebody cuts holes for downlighters and it is game over.
Why not have the moisture barrier below the insulation ?
Between the room lining (plaster board) & the joists/insulation.
You can but it can leak and putting it under the insulation is easy
If the vapour barrier leaks on a warm roof the deck would rot, right? Does that ever happen?
brilliant info - would be nice to see a video showing what it looks like
It will happen but we are in the middle of it right now
Great info for my project I been brain dead for a week same issue cant go to high so the cold deck will be the way forward
We have gone back to the warm deck now because of all those mushroom vents
So if l do a warm room on top l have to put vapour barrier underneath it top of joists then aluminium plaster boards on joists below
Thank you for sharing your knowledge. On the warm roof example, would it be ok to insulate in between the joists as well? Assuming drywall is the finished product? Or would that trap the moisture?
It is a very difficult judgement. Sometimes putting in more insulation moves the dew point to somewhere in between.
You can get a professional calculation done online that will tell you. I have done it in the past with no problems but the vapour barrier has to be good.
Thank you