Venting a cold roof view asks for help
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- Опубліковано 30 вер 2024
- This customer was going to go for a highbred roof; however, after doing some investigations, he found that this was not the way forwards and decided to go for a cold fat roof. Unfortunately, he hadn't built in the ventilation for the cold roof, and he asked my opinion on how to vent the roof how that the timberwork is in place.
Luckily there are still options open to him and adding ventilation to the flat roof from inside the building is posable. Bouse this is a shed or outhouse, there shoud not be that much moister in the air; therefore, the ventilation isn't as critical as it would be if this was a domestic building and there was a kitchen or bathroom under the roof.
Just a thought in this situation, could the customer not have added some roof battens to the top of the timberwork with say 25mm gaps to allow airflow in all the roof compartmentalisation? Double / treble them up at the back with the wider timber arrangement. Then vent through the facia.
My old 1911 house has air vents on the outside walls and air vents on the inside walls and a roof space where any air is free to move inside and out...Ventilation is always the key
Counter battens and vented soffits would have worked, shame the covering has already been applied!
What do you mean?
Hi Steve. Once spot lights are put into the ceiling it would no longer be airtight. How would you get around a situation like this please
Go and have a look at my video on installing down lighters into a cold roof. Your point is exactly right you just can't do it
Hello, I´ve been watching a couple of your videos today which I find very interesting. I´m in California, what we propose here is a combination of eave ventilation with ventilators. We leave 1 inch gap for air circulation. The insulation R30 comes in between the roof rafters. The problem for the contractors is basically two: they need to slope the deck min 1/4":12" for drainages, then we have to provide the structural shear transfer from the plywood to the rafters and all the way down to the foundation (for earthquakes). So, the nailing is part of the calculations. Steve would you please let me know which one of your videos would be more enlightening for these two issues, I mean to avoid interruptions of the cross ventilation with min slopes. Thank you for your videos, I've sent the link to one of the contractors.
Good evening Steve
I’m doing a cold roof early next year. Could you please tell what is the correct AVCL.
Many thanks Steve 👍
Hi Steve - Some garden office builders are doing these 'hybrid' roofs with 5 by 2 timbers filled with 100mm PIR and no ventilation on account of the 2.5m height rule on outbuildings with a flat roof. Do you regard this as a compromise too far or might it be OK if the building only has 'light use' and no bathroom. Might it be OK if the vapour barrier is very well sealed say??? Or is this just a bad idea???
Definitely a bad idea as its very costly if it goes wrong. You never know what the building may be used for in the future. I've never seen the correct AVCL ( air vapour control layer) added to the underside of a cold roof.
An online Archetecter magazine Archeitecer today recently published an excellent article (I'll add the link below) It talks about hybrid roofs and the best practice.
Best practise it to stay away from them.
If you think that you are designing something that is extremely close to having interstitial condensation happen, you don't fix the insulation correctly and use the wrong AVCL or use the correct one and don't install it correctly; it's not going to work.
Conclusion build a robust building that can take small mistakes, misdemeanours.
architecturetoday.co.uk/roofing-in-detail-hybrid-roofs-best-practice/
ua-cam.com/video/EZFcHcxbFbE/v-deo.html
Same question I was going to ask , is this practise efficient?
Hi Steve if you're possibly happy giving out flat roof ventilation advice I really could do with a professionals opinion? 👍
STEVE - Couldn't you just put up heavy duty polythene as a vapour barrier ??
Not really it has to be the correct kind of plastic and it also has to be sealed in a tight
Hi Steve love the videos very informative. I would love to get some advice from you on the design of my flat roofs. Please get in touch if you can find the time. Thanks Chris
This is a great explanation, thanks for this.
Hi Steve, I'm in a bit of a similar dilemma myself.
I am doing research in the leadup to redoing my flat roof. Currently it's a vented space, about 2-3' high with zero insulation and not accessible. My climate dictates that I need about a foot and a half/18" of insulation.
Am I correct that with my large vented space as it is right now, I could get away without having to vapour barrier/air seal from the interior since there will be considerable room for air flow on the cold side of the insulation? Or would you still recommend placing the insulation/vapour barrier above the decking?
What ever you do you always put a vapour barrier on the warm side of any insulation regardless if you have ventilation you're trying to stop moisture from rising into the area above the more you can stop rising the less you have to get rid of
@@SteveRoofer our national building code says oil paint or vapour-blocking latex is sufficient. Do you agree?
I love watching your videos and hearing your advice. Thanks so very much
Thanks for watching!
Fit cross battens for good ventilation over roof area batten will only add 25 mm to height
Yes, that is the key because you've not only get cross ventilation. You get through cross ventilation which is from all directions
Hi Steve, we are getting a new hip roof replaced. I'm unsure how much ventilation I need for three bed semi detached hip roof . I wanted to get vented ridges, two vented roof tiles on each three sides of the roof, fascia vented strips too. But where do we install the vented redland 49 roof tiles? Should they be near the ridge or third way down or in the middle? Also how many vent ridge to we need?
So can anyone submit a question and photos for your opinion? I have a question and like some suggestions on my garage flat roof. It's hard to know what is the right thing to do.
Hello, loving the videos I was wondering what your opinion on William Griffin garden rooms is as he does not leave an air gap in the roof and claims he’s been back to 1-2 year old builds that do not have moisture build up nor any mould/damp.
Thanks!
You need to look at my video on hybrid roofs, and that will answer your question
I would have laid the joists on top of the block work with a good overhang and then put sofit vents in all the way around.
Very educational video thank STEVE THE ROOFER (Bob builder of Roofs)
Hi Steve I’m building a garden room for my self and haven’t got the height for a warm roof
So looks like it will be a cold roof ventilation shouldn’t be an issues as I will cross batten and use vented soffits on all sides.
My question to you is there a way for having Downlights without causing any future problems.
I’ve only really done warm decks in the past on loft conversations so height hasn’t been an issue
Thanks nathan
Anyone know if there's a "rough" price per M2 for a cold roof? Been quoted £2500 for a 4m x 3m cold roof, EPDM covering. I was going to do it myself but baby is due in a month and I can't spare a weekend 😔
So downlighters are basically a non starter if the vapour barrier is to be air tight?
Hi Steve, would you give your outlook on the Galvanised steel frame outbuildings and making them airtight with external thermal cladding, worth it or go wooden frame?
Age old problems here. One big plus is that it will be low occupancy.
Whack a high rate extraction fan in, and crack a window.
Hi steve, how regular should counter batterns be placed when venting a cold roof, many thanks, Matt
Steve- would cross battoning work across the roof joists to allow air flow between each joist as the air can simply flow over the joist? Great vids btw
yeah cross battening is definitely the way to go
Hi Steve, I've got a grp flat roof above a indoor swimming pool. Grp> osb floor> 3" ferrings filled with 3" cellotex> ferrings screwed to 8" joists filled with 5" cellotex pushed right up to the 3" cellotex. My concern is if I place a vapour barrier below the joists now will any moisture between the timbers cause fungal or bacterial growth?
Depends on the moister content up there, I would carry out measurements and drop the RH before doing anything
I’ve been looking for a video like this for ages. In the process of a loft conversion and after loosely storing flooring up there I noticed moisture build when moving the board about due to there being no air gap between them an insulation. The roof dose not have any insulation .
That's a strange way to have laid out your roofing timbers! I would have just run them all from the rear to the front of the building and used some Simpson adjustable joist hangers for those that come in to the angled part at the front.in face I wouldn't even have had the perimeter timbers that you have hung them off you would have been better sitting them on a wall plate as it would make it much easier to get good airflow flowing right through. You should have consulted with a joiner mate,we don't mind giving out a bit of free advice.
Yes but thats the way the man did it
I think there is a case of over complication here, this is not a living space, ie sleeping, cooking, washing machine, drying clothes so the venting is not as important as in a living space.
I agree and wrote about this in the explanation of the video. whist the roof is still open from beneath its worth adding as much ventilation as possible
Hi Steve. I never hear anybody talk about (assuming all other advise is followed correctly) applying a coating of varnish as an additional step on the underside of the plywood on a cold roof. Do you think this would be helpful to delay damage from moisture just in case? Anybody else?
problem with doing that is you will be stoping any moisture penetrating the deck and escaping that way but if its vented at both ends then I cant see a. problem
Hi, I am looking for a help, how can get in touch with you? Similar problem
Email me with all the info and your phone number steve@londonflatroofing.co.uk
Hi Steve. I am impressed by your insight into condensation into cold flat roofs. Do you have any knowledge of the conservatory solid roofs, so called "warm roofs" I have fitted a few and am experiencing condensation under the ply boarding and under the metal tiling. To be honest the manufacturers are unhelpful to say the least. Any advice would be helpful.
send over info to info@londonflatroofing.co.uk
I'm in a similar position
Building control have told me to have a hybrid roof
Completely fill the joist with 150mm PIR
Seal around any areas with gaps using expanding foam
Foil tape all joists
Then a further 25mm of PIR
Its a flat roof that was a garage now a bedroom
So method mentioned above would close all the ventilation off
All wiring for lights & sockets run through the joists a new lowered ceiling of 100mm below the joist will be constructed and plasterboarded
Will this be enough 😔
uilding control shoud never tell you how to do something. If they do, they are responsible for the design. They shoud tell you that they disagree and ask you to go and get it designed.
So will it work yes if you can keep the Relative humidity inside down and the control the outside and inside temperature to a pint where interstitial condensation doesn't happen. And of course, you cant do that
Thanks for the reply Steve
I want it done properly please advise
How it should be done correctly
The roof is not tilted at any angle for water to drain away, will it be a rubber EPDM on the surface and will the lack of a pitch angle enhance the speed of damage to the roof as moisture will be retained longer?
The roof has a 1 in 60 fall 👍👍
Also the roof is tiny to be fair.
Hi steve i have a brick shed that i need to build the roof for soon but i will have a sauna cabin placed inside should i be going down the route of warm roof them? And what do you recommend as the minimum pir for this
Yes warm roof 100mm and more if you can
@@SteveRoofer excellent thanks for the reply and your extensive attention to detail its great to learn from 👍
Insulate tight, ventilate right
Yes very good saying
Would the cost of replacing a roof due to damp/condensation issues outweigh the money you save on energy bills when heavily insulated?
If you worked out how much was saved from the roof I would expect it would take about 100 years to pay for itself but good question. Building control also looks at retrofit works using the same thought processes if the cost of updating the thermal element of a roof cannot be saved within ten years it's not worth doing. ( this info is based on old dater don't know if this is still true but you have to look at this equation )
@@SteveRoofer Thankyou for the information 👍
Hi, Love your video, never watched others that actually put confidence in me. Can I ask a question? I am insulating (cold roof) my workshop but only have 65mm/2.5inch joists. I can either get 30mm or 40mm PIR leaving either a 25mm or 35mm gap for the ventilation. I have soffit vents all the way across and a open channel the other end for ait flow.. Would you go for the 30 or 40mm PIR? is 25mm air gap enough? thanks!
25mm will work and I would go for 40mm
@@SteveRoofer Thank you! I was going to go for the 30mm PIR but after your comments I will go for the 40mm PIR. Was so worried about not leaving enough air gap, its a 10 x 16ft workshop FYI on the off chance that changes your advice?
@@davidalleeson2120 The most important think is for you to have a good airtight AVCL (air vapour control layer) under it all
@@SteveRoofer 100%, thanks Steve 🙂
Is that a single skin of blockwork, if so internal walls are going to be wet even with a good render
We don't know if he is going to insulate from the inside also the external wall cladding is open so I Don't think he will have a problem
Crazy not to do this in timber frame. It's a small space so would benefit from thinner walls.
On cold roof construction always counter batten on top of firings with 2 x 1 tile lath , vent soffit, and use mushroom type vents in roof . No problems .hope this helps . Richard .
That is a way of doing it but you will need more than mushroom vents
It’s pretty obvious as people just don’t understand flat roofs! I don’t know why you keep promoting cold roofs as they’re clearly inferior to warm roofs! To the amateur your advice looks looks, but professionals just see right through you.
I haven't seen him promoting cold roofs, just answering questions on them. From watching his videos, I very much got the impression that warm roofs were the majority of his work.
@@ricos1497 If you spend the whole video talking about something, clearly you are promoting it whether you realise it or not. More should be said in the videos to dissuade people from using cold roofs, rather than comments about how they should be constructed/corrected. Don’t get me wrong the videos are OK, but for me they are full of inaccuracies.
@@subzero3054 well if you were to watch this video in isolation, you might get the impression that Steve was suggesting that cold roofs were preferred, but not if you watch, say, his latest ten videos where he states/implies on numerous occasions that warm roofs are preferred and the comments are full of examples of him saying similar. He's been given an example here from a viewer, asking for help. It would be deeply unhelpful to tell him that he's done it completely wrong and that he should start again with a warm roof, you have to work with what you're given. Especially as it's basically a shed, and we're not told if there are any height restrictions or something else that may have prevented warm roof construction. You say "inaccuracies" without pointing to any? Can you tell me what those are? Bearing in mind this is a video of a completed roof done by someone else, not his own work. How would you have corrected the errors made in its construction?
@@ricos1497 I disagree. People have to face up to facts if they’ve done it wrong, making the best of a bad job isn’t in my opinion the right way to go about work and explains why as an industry there are so many problems. Construction is full of cowboys and people who just don’t know what they’re doing, had this builder paid for the correct advice at the start this could have been avoided. I just don’t see the point of the videos when it’s clear what the faults are.
With regards to inaccuracies, in one video he said he doesn’t recommend bonding insulation boards as they have a silver face, yet there are other boards in available that have different facings where adhesives can be used for example kingspan TR27, so why not say this or doesn’t he know. A fully bonded warm roof will allow less vapour to pass through as you’re not puncturing the VC or adding fixings which could potentially be a cold bridge.
In one video he states he overlays the insulation with 18mm OSB, in this video the waterproofing layer has been installed directly onto the insulation.
Pretty sure if I watched all the videos I’d find countless more! I just feel these type of videos are dangerous as certain people will thing if they just drill a few holes in the joists then everything will be OK, when it most certainly will not. Every small extension will have its own issues, particularly ones with rooflights in the middle or that adjoin a pitched roof. In these cases if the design is not right at the start it’s going to take a lot of work to correct if the design has not been carried out correctly.
@@subzero3054 none of what you're saying justifies your original comment ("see through you"), which bordered on accusing him of being dishonest or suggesting he was promoting something for personal gain. He's been asked to critique a particular cold roof construction by a viewer, which he's done. It's helpful for those who think that they can do these things themselves (the person who built this) to see that they are not tackling something easy that requires no thought. Nobody in their right mind would tell this person to rip off their shed roof and start again, even if that would be the perfect solution (I agree with you that it would). An extension is a different matter of course. Again, your points are minor points of contention that you can reserve for individual videos and nothing to do with this one, your simply moving the argument. I have no doubt Steve would happily concede to some of your points in a subject that has so many possibilities if you were to put them to him. You're approach was to question his overall integrity and his motives, which I think was unjustified. It is possible for people to be wrong about something whilst simultaneously trying to help them.
Counter batton eh air flow ?