Steve, thanks very much. I'm an architect with over 10 years experience in practice and this video is by far the clearest explanation I've ever received on cold vs. warm roofs.
Been building for 40 years and although I had a rough understanding of the mix of ventilation and Insulasion this really brought me up to date, so thanks Steve.
Many buildings particularly on boundaries to comply with permissive developments -walk into the realms of being restricted in height-surely with the move to warm roofs it’s time for those rules to change allowing for that extra 120 mm of external insulation increasing the overall height of the development
Key point to note is continuity between the warm roof and wall insulation. I work as an Approved Inspector an try to advise on all flat roofs being a warm roof (where possible) and where sufficient 25000mm² cross flow ventilation can not be provided to cold roofs. When doing a warm roof, the insulation form the walls must be continued to the underside of the deck or you may as well miss roof insulation off altogether. Continuity of the thermal envelope aids the majority of cold spots and draughts in construction. Great video and comforting to know some tradesmen do care.
Thanks, that was going to be my question. is it basically like a complete box of insulation we're trying to get to, but with a bunch of sticks to hold it all up? What about transition between floor and walls?
@@ricos1497 I suppose you could look at it like that if you are referring to a timber frame building/extension. The floor is a little more tricky as you would generally have a brick/block lower course for damp proofing reasons, but generally the same principles, make sure the wall insulation meets with the floor insulation. On masonry cavity walls the wall insualtion must be continued below DPC, 99% of people don't do this as they think it is a damp risk, it's not!
@@martynmongan9123 once again, thanks! I wouldn't have known that about continuing below dpc, although it makes complete sense. Off to build a high performance shed now!
@@martynmongan9123 I think solid wall and EWI insulation is the best solution,plus thermally insulated foundation all the way down.Potentianlly,you can start building /cavity/ walls on panels from foamglass,that will cancel any cold bridge
Thanks a lot for clearing up a lot of misinformation that can be found elsewhere on RUclips. It is important as a lot of these garden cabins are being used as 'bake off' rooms would you believe. Also the home gym with shower is another popular choice. So I can see many failing unfortunately.
Steve, if you’re ever in Brum, pop me a msg and come around for tea. Really proud of the warm roof built myself using your guidance. Have stopped lots of cowboy suggestions along the way because of your videos. Now that it’s done, I always get ppl advising me to fill the ceiling joists with more insulation to keep it even warmer. I’ve always just said, I’ve built it right and no need to go overboard but now I have a very good explanation on why it’s not right to insulate warm roofs from the bottom.
Thanks for the videos... , I have a flat roof that was added onto the north side of my house with. they stuffed it with fiber insulation and no venting, No question for you but I just wanted to say your videos are demonstrating everything I will need to know to tackle the project.. Thanks again! : ))
I'm so glad RUclips recommended me your video, and that your content makes the topics very accessible! Already queued up your other videos to watch too :)
Excellent content. I hope all of those people building garden rooms realise the popular hybrid roof championed by a particular company is nonsense, especially as they also put in downlighters.
And try suggesting it's not correct! hehe. For what is charged on those rooms he should either offer client a true cold roof and add venting or redesign joist section size and spacing and have a warm deck with maybe a slight reduction in internal ceiling height. Also maybe suggest wall lighting so less impact on the VCL.
Indeed. They normally build with 90mm spare anyway. They could use 50mm of that and add venting. The roof rafters they use are 120x45mm and if the span is 3m they double them up with bolts. They admit to not using span tables. I'm sure it's C16 cls too. It means that dimension spans about 2.2m max. By Making the rafters 170mm they would get better strength and the 50mm vent space.
There's lot of bad information in that garden room video and on that channel, it seems he always thinks he knows best and dismisses any negative comments without actually addressing the issues that get raised. It's a shame that such a lot of people probably go on to replicate those mistakes. Anyway it's good to see someone who knows what they are talking about.
Great explanation! Was planning to build my garden office in April and was going for a cold roof with ventilation, and it never occurred to make a warm one with C24 timbers to keep the height lower. Will go with this as no need fit sections of insulation like in a cold one. I also have seen the garden office videos, which are good, but I would never have risked a hybrid roof. Thanks!
I'm building mine now and have used C24 treated timber for everything where possible. I've been unable to source C24 in certain dimensions so these are C16 but roof is definately C24. After watching Steve's videos and some personal.advice from him I have settled on a warm roof. I saved the height by putting in a concrete floor level with my garden floor so my base starts at zero. Bizarrely I changed my plan half way through so ended up with 150mm hard-core, visqueen, 100mm concrete, visqueen, 50mm PIR, steel rebar reinforcing in 60mm of concrete! The concrete was laid about 9months apart.
@@klaeLIFE Thanks for the tips Khurram, you got a channel that you're posting the build on? I'm going apply for permission to go up to 2.7m. The back wall across all the gardens is 3m so can't see anyone complaining.
I used 80mm Kingspan roof panels for my recent garden room which solves a few of these problems. The 80mm is good for spans of over 2.5 meters, zero thermal bridging, and has finished top and underside which makes for a super quick install.
@@SteveRoofer Well it is good enough for my Garden Room / Office. Plus the obvious lack of thermal bridging it offers, and 80mm is the lowest point, the ridges are 113mm insulated. They do also do 100mm+ roof panels, but I just did not need that for my purpose.
Hi, watched this twice and others of your videos, I'm only building a small 12 x 8 workshop room and I do want it to be good warm and dry, so thanks very useful.
@@ricos1497 Well Rico, I think that Steve is about the only roofer I have ever come across who actually understands the business of ventilation and insulation so well and I would gladly collaborate with him!!
Hi Steve I hope you don’t mind, I’ve emailed you a question with regards to insulating a van. Your videos being such a help in ventilation and insulation has just increased the difficulty and complexity of insulating a steel van.
There is so much debate over this topic but as a builder and van converter I would see the best idea is to insulate with sheeps wool or recycled plastic bottle insulation or similar and let it breath. Vapour barriers etc are only going to trap the moisture that will always get in somewhere
Brilliant video. My kitchen is always cold as its an extension flat roof. 9 degrees on a cold day. I was going to get on top and insulate it until I saw this video. I reckon its warm insulated and only cold as we have large windows and rarely put the heating on. Im glad when the plasterer came we didn't fill the ceiling with insulation as we would have caused condensation especially with all our cooking. Im going to just leave it as is and install a wood burner and heat the room better. Incidentally as we brought the house with no guarantee of the work done (elderly couples old house) are there any tell tale signs I can check to see if it actually is a warm roof. I did notice there was no insulation above the ceiling when the plasterer came but as the house is a bit dodgy can anyone advise please. Without ripping off the roof from the outside I don't really know what roof it is.... I can say with all these storms it's never leaked and has a great run off do at least this is good.
A roofer who understands what the reasons for cold and warm roof designs are. Halleljuah. Never met one in person, including a guy who has been building them for 35 years (he never tired of telling me)
Thank you Steve, that is really clear. I have a 20year old 10x4 cold flat roof with no ventilation and felt on top. I am looking to have it replaced/retrofitted because it's very cold and I get a lot of condensation inside. A roofer told me he will mechanically fix 100m bitumen faced PIR solid insulation to the existing timber. Then apply 3mm underlay felt to that insulation board and then another 5mm granular finish over that. Does that sound right? The rockwool between the joists in the existing roof will remain.
Great video steve. My whole house is flat roofed, I have a 44sqm cold roof retrofitted as seen in your video in the middle example. Its a single ply membrane and has 4 x mushroom vents which each one is supposed to cover 14sqm. My roof is also a roof terrace so the mushroom vents are an eye sore and in the way. When the roofers did it they used rockwall and didn’t install a vapour barrier. A year later i took the old lath and plaster ceiling down to replace with plasterboard and whilst doing this i took all the rockwall out and replaced with PIR between and below the joists, then battened below the pir to hold up the vapour barrier and leave a cavity for electrics and boarded. When i took the old stuff down the deck looked fine in all rooms except the bathroom which had quite bad mould and sweating. Throughtout that 1st year i did have a big hole in the bathroom ceiling, and no bathroom fan. So fan now installed and ceiling replaced as above. I tried to take what i had learned from your videos to install everything as best i could, i dont think it could be worse than the previous setup and only the bathroom was the problem area. Its been a 18months or so since I redone the ceiling and have been meaning to buy a camera that i could tread through the mushroom vent above the bathroom to see if its remained dry there. I don’t use the terrace at the moment but would like to do something with it one day. So was thinking one day i could turn it into a hybrid as mentioned in your video so i can do away with ventilation. Would of liked to of seen a retrofit hybrid example after a retrofit cold installation so the 50mm gap remains. Would like to hear your thoughts on this, thanks
All the info I try to give is whats given to me by the local authorities and building control. As they don't want us to do and we don't do hybrid roofs, I can't comment as don't know
The improvements you have made should have solved the problems with your original roof perfectly, dont change anything else, dont fill the rest of your roof void with insulation and leave the mushroom vents doing their job!
Excellent as ever. you videos have given me the confodence to fit the flat roof on my extension. Alutrix 600 and 18mm OSB top and botom with inuslation in between and then a rubber memebrane on top. just need long enough fixings for it all now.
Just found this, two years later, what a fantastic explanation! I wish I’d seen it three years ago though, because then, when I decided to insulate the main loft, I saw the empty spaces above the 40 year-old cold roof extension, and went and filled them 😱. I think it should be ok though, 🤞🏻as I went and fitted a Nuaire fan unit in the loft, which is always on. However, could I check for moisture in the cold roof, via the small gaps left around the insulation, with a long-reach moisture meter, if there is such a thing?
What a great video explained really clear thank you for your time . I am doing an extension 3mtr x 5mtr block cavity I like the idea of the warm roof but I will be installing it to butt up under eves of single storey , that insulation being 150 plus joists , yet to be configured , that could be tight , I'll have to do slot of measuring may end up with a lower ceiling than existing building , would I be right in thinking this. ?
Hi Steve I had an extension done about 6 years ago, I have pitched roof either end of a flat roof the one end is plaster boarded on the angles for bedroom wall and the other end goes to the original loft space the thing is the builders did a cold roof the building inspector at the time said warm or cold doesn't matter, when I go in the loft the flat roof is mouldy, I have had extra tile vents fitted to get more cross ventilation but still wet, the gap between the bedroom ceiling and the flat roof is about 400 mm with rock wool insulation on the plaster board. The problem I have is if I had a warm roof on but then the pitches are old bitchmen and tile will it still have damp on inside of the loft flat roof under side as there would in theory be different temperature zones thus causing condensation, I have been quoted 4 to 10 k to rip it off and new roof layed, it's say 6m x 4m and I don't want to shell money out if the problem just moves to another place, I did have 2 dehumidifiers running and was pulling 4 to 6 litres a day and then I thought I'm probably making the loft space into a hoover as in sucking more air than I should 🤯, I'm at my wites end. Any help would be appreciated 👍
I spend some time designing my own hybrid roof, doing all the due point calculations and going through a lot of design iterations to see not only what would work, but also to see how robust the design was. The general rule of thumb I had heard was that you start with a warm roof and put half the thickness of the insulation under the deck (so e.g. 120mm above works with 60mm below, i.e. 66/33%, which is only marginally less robust than the 75/25% you quote) and I found it was a good rule in my case as you'd end up with something reasonably robust that wasn't reliant on any additional vapour barriers beyond the normal warm roof one (i still put an additional one in beneath the internal insulation as belt and braces, as for my design that meant either vapour barrier could fail without causing problems). If you start with the cold roof and fill the ventilation gap (or anything with more insulation below the deck rather than above) it becomes an impossible task to end up with anything robust. The vapour barrier beneath the insulation has to be 100% perfect for it to work - all joints perfectly taped and sealed, no downlights or cable penetrations and no second chance on putting screws in to secure the plasterboard/smoke alarms/lights to the roof joists. The smallest hole will result in moisture getting in, condensing in your roof joists and rotting them over time. So while there is a place for hybrid roofs it's limited to warm roofs where you absolutely can't drop the ceiling or raise the roof by 3-6cm, and it has to be carefully designed and very carefully installed. The risks are quite high otherwise...
Yes that about sums things up I have an engineer doing some calculations on some angle irons that are 50 x 50mm that will replace the joists thus giving a slim warm roof. So if that works why are we still using big old chunky timbers!
@@SteveRoofer A video on alternatives to chunky timber joists would be great, I've searched RUclips & the internet several times to see if theres any info out there on the subject & not found a thing.
@@SteveRoofer ah now you’re asking, I might be in to deep 😅. When I’ve searched for videos or info on the subject in the past I’ve usually tried searching something along the lines of “alternatives to timber joists”. Maybe thats similar to what other people will be searching, or I could be way off 👍
Excellent video. Very informative. I would have liked a quick mention of how the warm roof is fixed down. What is stopping the top layer of OSB and your roof from taking off into the sky in the next storm? How do you fix the two sheet layers of the warm roof together without creating a cold bridge?
All of the information is in some of the other videos that I do if you look up firmly broken fixings and how to fix EPDM rapper and how to fit warm roof insulation you'll find the answer to your questions
@@SteveRoofer Thank you Steve. I've now found those videos. Your videos are great. Sorry to criticise. Quick question; what was the name of the special tape that you used on the edges of the PIR to make a good friction fit when using PIR in a cold roof between roof joists?
@@SteveRoofer Hi, I've just come across your channel, really interesting thank you. With Gapotape would that allow you to slide out an insulation panel in future easily enough to inspect your timber?
How do these principles work with deck access? 1974 council built with dwellings below the deck. These lower dwellings their ceilings are covered with batten and foil backed plaster board. The deck is filled with bituminous material. The ceiling is also exposed on the outside: cantilever of approximate 30-5cm. This concrete ceiling that is majority below the deck absorbs the damp air and the guttering leaks and potential dpc failure on the deck wall. Result is an internal ceiling that is wet during winter and most householders are unaware the foil backed plaster board being resistant to moisture and the huge mass of the concrete ceiling above.
Excellent video Steve, I'm hoping to put 100mm kingspan on top to make my garage roof a warm room then 100mm WR3 rockwool underneath to help with the noise of my woodworking tools. I feel this to be a good combination. At the moment my moisture layer is underneath my kingspan.
Steve, in your warm roof build up you don't need any plywood on top of the rigid PIR. This insulation type has sufficient compressive strength to be walked on for maintenance purposes and the like. The extra plywood is an unnecessary additional cost to the customer. I see this being specified on architect J42s all the time... it's wrong. If it were mineral wool, it would be a different story but PIR is the industry standard for flat roofs and you don't need the plywood sandwich.
@@davidd8802 Kingspan TR24 is a rigid PIR board with sufficient compressive strength AND is suitable for torch-on felt. You don't need any plywood above the insulation in a felt warm roof system either. Leave the roofing to the professionals; it amazes me how many people try to DIY their own flat roof extension and end up all sorts of problems. Videos like this aren't all that helpful because to the layman it leaves them with more questions than answers.
In the US there is a table and depending on climate zone there is a set amount of exterior insulation above the sheathing. Any non permeable insulation under the sheathing must be applied directly (aka closed cell spray foam) The inside cavity can also be completely filled with permeable insulation as long as the external insulation requirement is met. The goal is to keep the underside of the sheathing at or above 45*F. It's an excellent way to get a high R-Value in a small roof cavity.
Excellent collection of videos Steven. I've just blasted through A LOAD of them trying to fill some of the gaps in the information I could find on materials websites. The number of times I've found "no info on a topic", or "refer to other element manufacturer" has been very frustrating. You've addressed a lot of those information gaps. I need to replace a porch/mini extension roof so I've been seeking a DIY solution as its so small circa 1300x910. Original roof is simply perched on the side walls only needed 3 joists! Very cold so intend to warm roof it. If you see this and have time then a few remaining questions: a) 2nd ply deck above insulation --> *now* isn't recommended as its an unnecessary point of failure? b) clever PIR with bonded upper deck and no lower deck eg. Eco-Deck --> you've never rated it & it might compress too? (though it might work for me as the porch < 1 sheet! = No joints) c) I can't find anything showing construction of warm roof edges: eg, where insulation stops, edge timbers, barge boards and soffit if overhanging. (I've lots info from pre insulation olden days). Any links that might help? Immense thanks if you have the time to comment. Kevin
This may be a stupid question but I'm going to ask it anyway. We are thinking of building a garden room. As I understand it, garden rooms are not covered by building regs the same way a house is but I believe the maximum height is 2.5m. I also understand that is the reason some people are reluctant to go for a warm roof is to save on height . (so here's the stupid bit, prepare yourselves!!) Our garden is 13m wide and 14 deep from house to back fence. Our plan is to drop the entire area at the back of the garden (so the back of our garden would be 13m wide and 5m deep) by 2 foot and build the garden room in the lowered area. Is the maximum height for the garden room still only 2.5m even though it's now being built 2 foot lower than the rest of the garden? If the construction could then be higher than 2.5m this would easily allow for a warm roof. Be kind gents lol.
Has helped me this! Right at the end of the video, i think this is what I’ll do (warm desk on lower joists) My engineer had already mentioned installing flitch beam in the roof to shorten the span and therefore beam sizes. This way makes total sense to achieve a warm deck but without the 200mm joist. I’ve seen on other videos some comments of using a solvent based adhesive to adhere the EPDM rubber directly to the insulation (tissue backed instead of foil) instead of a waterbased adhesive to the OSB. Would also drop the height by 18mm/22mm. Whats your thoughts/ advice on this?
Great video I like the warm roof is 120mm enough? it seems as though any work has to be 150mm to get to the u value n 200mm for the 0.11 u to future proof. instead of ply could u use cement boards or is their another option water resistant plaster board to gain walking strength
I am building a hybrid roof. My design calls for 2.5 inch insulation on top with the joist pockets filled with closed cell spray foamed. Spray foam is a vapor protection is my understanding. Below the roof joists I will add a 1 inch ridged silver board insulation. My thoughts were that I could reflect heat back towards the interior while covering the bottom of the joist and while adding another vapor barrier layer and to reduce the heat that makes it to the ply layer. Does this work in your opinion?
Extremely hard to insulate a concrete deck. It's the edges you need to run the insulation, not only over the top but down the sides and turn around and come back to the building to totally encapsulates the concrete.
Great video, just a couple of Qs please? 1. Whereabouts is the vapour barrier on your hybrid roof? The last few minutes of the video went just a little quick for my tiny brain to take in. I am interested because I want to add a flat roof garden room to the back of my 1920s bungalow and dont want a big thick roof profile to dominate. 2. How would you treat the insulation around lantern or skylight openings?
That's a lot of information you're asking but basically you always put the vapour barrier on the warm side of any insulation. If you can't get it exactly on the warm side slightly in is okay, but I mean by that if you've got 150 mm of insulation you can put the vapour barrier approximately 50 mm in from the bottom, but no further.
Hi Steve. I have a flat roof with cold roof construction that I'm thinking of changing to hybrid. Could I retain the 50mm insulation and 50mm airspace between the joists under the structural plywood. Remove the existing torch on felt then build the warm roof construction of installing a vapour control layer, 120mm rigid insulation, another layer of structural plywood and then torch on asphalt waterproof member? Would there be any problems of moisture sweating with this?
Yes you can do this why remove the old felt if it is good condition it will be the vapour barrier. If not condition if not in good condition then remove it and use a vapour barrier. Theoretically the reason you can get away with this is because you have far more insulation over the top generally we suggest you have 2/3 above the bath area and one third insulation below however your insulation below is probably not installed that well therefore isn't working that well therefore is weak and will probably work
Hi Steve, thanks for the very clear video. We have a 1940's semi that would have originally had an outside loo and washroom brick wall and solid concrete roof. It is now connected to the house. Can a warm roof system be used on solid concrete as there isn't enough headroom for a cold roof. Thanks.
Great info .I am taking off a felt roof on the first floor as storm damage. Inside is just plasterer board and no vapour barrier as its 20+yrs old i was thinking of putting 100mm of celotex in on top of the plasterboard as only has Rockwell and very poorly done .what should I leave as air gap and is this the right way to do the roof .also was looking at grp or what is the best roofing please
Great video! I’ve a question tho. If you’ve a warm roof like what you showed in min 3:45, and there is then condensation somewhere in the middle of the insulation (where the two temperatures meet), isn’t that a problem for fungus ? Because the condensation is stuck in the insulation?
But depends on the roof, but there's loads of different ways of doing it loads of different things out here. Long is water in six don't get in you can do it whatever way you want to
Great video Steve. Can you answer a question for me please? With your Warm Roof example, for a garage workshop specifically, would you say that the 100mm Kingspan panels create an adequate warm roof "IF" the are fitted and sealed properly? They can easily span 2m without additional structure below and are finished on both sides and technically don't require a vapour barrier since the inner layer doubles as one (again assuming the panels are sealed together properly.
Can someone tell me if SIPS panels will be fine in a garden room with no ventilation on top? so just sips panels, and EDPM glued on the top? Obviously making sure inside of SIPS is seald well etc?? Thanks!
Hello, steve great videos! I would like to use a warm roof on my garden room project but I have height restriction issues. I was wondering if 50mm insulation would be thick enough as all of the warm roofs I see are 100mm plus. Eagerly awaiting your response. Thank you!
Old post I know but might help others with same question. 50mm of PIR will work as a warm roof but you will lose way to much heat and regret it later. For a detached garden room not requiring Building Regulations (so under 30m2 or under 15m2 if timber construction) maybe 100mm might be an acceptable compromise particularly if only occasionally heated. For anything requiring building regs 120mm PIR minimum. If to save height you decide to go for a cold roof, keep a through ventilated 50mm gap over the insulation, and ideally put some of the PIR under the joists as well as between. Total PIR thickness for a cold roof, 150mm if all between the joists, 125mm if at least 25mm of that is under the joists.
@@mikebarry229 125mm between with 50 air gap = 175mm timber minimum, thats a large timber for a roof isnt it. Can a 25m2 garden room be built from timber if its away from a boundry to the rear of a house and not taking up more than 1 third of the available free land? I wanted to build one from timber not blocks.
@@handle1196 under Building regulations (at least England and Wales, not sure about rest of UK) if its detached and more than 1m from the boundary and under 30m2 floor area (so not including walls) single storey and no sleeping accommodation its exempt from Building Regs even if combustible construction, though any drainage (say you wanted a loo) would have to comply. If building an exempt structure you can do what you want but following the guidance in this video is the only sensible thing to do. If you are having a flat roof try to get a warm roof if you can as it's so much better. 125mm of insulation between joists is probably inferior to 100mm over joists in a warm roof. Maybe your flat roof joists wouldnt need to be so deep with a warm roof or perhaps have the joists open on the underside so the headroom doesnt seem so restricted.
I assume you are going down the permitted development route and hence 2.5m height restriction? if so then your options are limited. you certainly wont be able to achieve a proper warm roof design with 120mmPIR. I managed to squeeze a vented cold roof into my design with 100mm PIR and 50mm vent above and building height is 2.485m. If you want to go for planning permission then ask for 2.7m and its all really easy then.
Great video and really useful information, thanks Steve! I’m currently in the process of insulating my new workshop/shed and have opted for a cold roof, leaving plenty of ventilation in my overhanging soffits. I saw your comment about having never seen vapour barrier installed correctly, as I am about to embark on that task in the next week or so do you have any tips of a video explaining the correct process? Cheers!
Hi Steve Fantastic videos Is it possible to have too much ventilation in a cold roof space. I've just had my roof replaced and from what I can see there was no ventilation at all so I'm planning on fitting some air vents into the facia board. With 100mm insulation I've still have a 80mm void and is it ok just to have the vents down one side of the extension the extension is only 3x3m thankyou
@@SteveRoofer thanks for the answer, the reason I am asking is because the way they recommend installing is a hybrid roof, as they say put foil over rafter and then PIR between rafters, leaving an air gap in-between them
You can use whatever you want as long as it gets you to the correct thermal element you want to get to so if you use for instance screwed up newspaper, you would probably need to have a depth of around 1 m. If you use PIR insulation you will probably need a depth of 150 mm, if you use Styrofoam you will probably need 250 mm
Hi, I've got a small extension tiled pitched roof that I'm insulating with kingspan. The rafters are 6x2 and the kingspan is 75mm thick. Should I just double up on the kingspan? Would appreciate any advice from you. Thanks
If you can't ventilate roof system, flat roofs. Keep air from entering in from below Or above, you won't get condensation. Use poly on lower, heated side of assembly. Same concept as exterior walls.
Excellent video thank you! I have had an acoustic engineer recommend 100mm dense wool insulation in the air gap of a warm roof, against the plasterboard though and 100mm air gap up to the warm deck (200mm joists). I wonder what your thoughts are on this design? Thank you
Okay, so this is quite interesting because if you put insulation between the joists on a warm roof you are stopping the warm roof from being warm by blocking the warmth from rising from the rooms below to counteract this. You need to put more information on the warm roof might sound silly, but it's all to do with keeping the vapour barrier above the dew point.
@@877cms the architect is not the person who will know what to do you need an engineer. This is all to do with thermodynamics. The engineer will work out where the dew point will be based on the elements of the buildup of the roof and what's underneath it. some engineers just walk away from this kind of design work because it is pretty complicated. It's more physics. The golden rule that I use based on seeing calculations similar to this is as follows. As long as you have 2/3 of the thermal insulation above the vapour barrier you can have one third underneath.
I am doing an owner builder home with a flat roof and the person drawing the plans mentioned something about the roof not needing vents because they hand the insulation ? Does anyone know what this means:
120mm of PIR insulation should be fine for code. It is isolating better (something like twice as good) than the usual stuff like glasfiber or rockwool. So 200 mm of glasfiber should be matched with 120mm of PIR.
So on a warm roof you have a board insulation then another board. If you were to fill the cavity you would have a board insulation then another board. So what is ot that causes one to sweat and not the other, is it to do with the joists cold bridging?
So what about the walls on a timber garden room, should they be insulated using the same principles? By this i mean should we be having cold walls and warm walls? Should there be insulation over the inside face of the stud walls as well as in inbetween the studs, aswell as maintaining a ventilation gap. After seeing this video, i feel like the walls and roof should be treated in exactly the same way as each other.I notice companys just putting 50mm PIR boards inbetween the studs and plasterboarding.
Excellent question, we shoud be looking at the entire building we call this a building envelope, we shoud think of every component and how they will work together, but ha-ho we don't I would externally insulate all walls do them the same as the roof.
When building a house the insulation is in a cavity with as little thermal bridging as possible. In some countries the entire external of the house is insulated too. With garden rooms the walls have a vent space for the cladding to dry out for rain but not the internal walls. Hot air rises I suppose so it will attack the roof first. I have seen in flats though the walls also get attacked with condensation once the roof is saturated.
Some advice please. The company have installed my summer house and I am currently insulating it for the winter. The roof battens are only 2.5 inches x 1.5 inches. I was looking at using a hybrid roof putting the insulation against the Osb roof, leaving a gap and then vapour barrier before plasterboard. I’m not that confident due to the size of the roof battens my insulation is only 1inch thick. Will this be ok or shall I find an alternative method?
If you have a warm roof 120mm and then 30mm Turing it I to a hybrid should there be a vapour barrier or vapour control barrier above the plasterboard? Do you do jobs in the Midlands?
So I've built my roof but not insulated yet. Basically is 6x2 joists then OSb then EPDM membrane.(shouldve done a warm roof but too late now!). Most likely now go with the cold roof scenario - how does one finish the eaves where the roof joists meet the wall plate? Would you insulate half the height of the eaves (ie same as the ceiling and leave the gap above) or just put no insulation in the eaves? also what's the best solution to downlights in cold roof and vapour barrier? btw its a garden room/shed with no shower etc..
Would closed cell spray foam under the plywood control any vapor with a warm roof with R30 insulation on top. Do you see any problems with that type of hybrid option.
![I.N "HALLUCINATION" | [Stray Kids : SKZ-PLAYER]](http://i.ytimg.com/vi/n5B5q1Hwt_U/mqdefault.jpg)
this is probably the best and most clear explanation of this subject, a lot of people will benefit from this for sure 👍
Thanks
Here here, really appreciate this video Steve.
Steve, thanks very much. I'm an architect with over 10 years experience in practice and this video is by far the clearest explanation I've ever received on cold vs. warm roofs.
Thanks
Glad to hear it's helped your understanding of warm & cold roofs. But the video is titled 'Hybrid' roofs and advises getting advice.
Been building for 40 years and although I had a rough understanding of the mix of ventilation and Insulasion this really brought me up to date, so thanks Steve.
Truly the best source of information on this subject. Many, many thanks. Let our DIY-project begin !
You are welcome!
Only found this today. Can’t wait to binge all videos and actually learn something.
Thanks
Many buildings particularly on boundaries to comply with permissive developments -walk into the realms of being restricted in height-surely with the move to warm roofs it’s time for those rules to change allowing for that extra 120 mm of external insulation increasing the overall height of the development
Key point to note is continuity between the warm roof and wall insulation. I work as an Approved Inspector an try to advise on all flat roofs being a warm roof (where possible) and where sufficient 25000mm² cross flow ventilation can not be provided to cold roofs. When doing a warm roof, the insulation form the walls must be continued to the underside of the deck or you may as well miss roof insulation off altogether. Continuity of the thermal envelope aids the majority of cold spots and draughts in construction. Great video and comforting to know some tradesmen do care.
Thanks, that was going to be my question. is it basically like a complete box of insulation we're trying to get to, but with a bunch of sticks to hold it all up? What about transition between floor and walls?
@@ricos1497 I suppose you could look at it like that if you are referring to a timber frame building/extension. The floor is a little more tricky as you would generally have a brick/block lower course for damp proofing reasons, but generally the same principles, make sure the wall insulation meets with the floor insulation. On masonry cavity walls the wall insualtion must be continued below DPC, 99% of people don't do this as they think it is a damp risk, it's not!
@@martynmongan9123 once again, thanks! I wouldn't have known that about continuing below dpc, although it makes complete sense. Off to build a high performance shed now!
@@martynmongan9123 I think solid wall and EWI insulation is the best solution,plus thermally insulated foundation all the way down.Potentianlly,you can start building /cavity/ walls on panels from foamglass,that will cancel any cold bridge
I had to do a hybrid a few weeks back. But i double counter battened on top of the insulation & ventilated it. Great videos as usual steve
now i know why my shed is condensating, excellent explanation thanks.
Thanks a lot for clearing up a lot of misinformation that can be found elsewhere on RUclips. It is important as a lot of these garden cabins are being used as 'bake off' rooms would you believe. Also the home gym with shower is another popular choice. So I can see many failing unfortunately.
Glad it was helpful!
Thanks for taking the time to explain this, top man 👍
No problem 👍
Very clear and well explained,he’s probably a very good tradesman also.👍🏼
Steve, if you’re ever in Brum, pop me a msg and come around for tea. Really proud of the warm roof built myself using your guidance. Have stopped lots of cowboy suggestions along the way because of your videos.
Now that it’s done, I always get ppl advising me to fill the ceiling joists with more insulation to keep it even warmer. I’ve always just said, I’ve built it right and no need to go overboard but now I have a very good explanation on why it’s not right to insulate warm roofs from the bottom.
well explained , now I can stop coming up with other ideas 😄, many thanks
Thanks for the videos... , I have a flat roof that was added onto the north side of my house with. they stuffed it with fiber insulation and no venting, No question for you but I just wanted to say your videos are demonstrating everything I will need to know to tackle the project.. Thanks again! : ))
That is awesome!
You mention stuffing full of insulation, but not say what the real world outcome was.
I'm so glad RUclips recommended me your video, and that your content makes the topics very accessible! Already queued up your other videos to watch too :)
Welcome aboard!
Excellent content. I hope all of those people building garden rooms realise the popular hybrid roof championed by a particular company is nonsense, especially as they also put in downlighters.
Yes I get lots of people quoting that video
And try suggesting it's not correct! hehe. For what is charged on those rooms he should either offer client a true cold roof and add venting or redesign joist section size and spacing and have a warm deck with maybe a slight reduction in internal ceiling height. Also maybe suggest wall lighting so less impact on the VCL.
Indeed. They normally build with 90mm spare anyway. They could use 50mm of that and add venting. The roof rafters they use are 120x45mm and if the span is 3m they double them up with bolts. They admit to not using span tables. I'm sure it's C16 cls too. It means that dimension spans about 2.2m max. By Making the rafters 170mm they would get better strength and the 50mm vent space.
There's lot of bad information in that garden room video and on that channel, it seems he always thinks he knows best and dismisses any negative comments without actually addressing the issues that get raised. It's a shame that such a lot of people probably go on to replicate those mistakes. Anyway it's good to see someone who knows what they are talking about.
Would that channel be someone from Leeds?
Great explanation! Was planning to build my garden office in April and was going for a cold roof with ventilation, and it never occurred to make a warm one with C24 timbers to keep the height lower. Will go with this as no need fit sections of insulation like in a cold one. I also have seen the garden office videos, which are good, but I would never have risked a hybrid roof. Thanks!
Glad it was helpful!
I'm building mine now and have used C24 treated timber for everything where possible. I've been unable to source C24 in certain dimensions so these are C16 but roof is definately C24. After watching Steve's videos and some personal.advice from him I have settled on a warm roof. I saved the height by putting in a concrete floor level with my garden floor so my base starts at zero. Bizarrely I changed my plan half way through so ended up with 150mm hard-core, visqueen, 100mm concrete, visqueen, 50mm PIR, steel rebar reinforcing in 60mm of concrete! The concrete was laid about 9months apart.
@@klaeLIFE Thanks for the tips Khurram, you got a channel that you're posting the build on? I'm going apply for permission to go up to 2.7m. The back wall across all the gardens is 3m so can't see anyone complaining.
I used 80mm Kingspan roof panels for my recent garden room which solves a few of these problems. The 80mm is good for spans of over 2.5 meters, zero thermal bridging, and has finished top and underside which makes for a super quick install.
Problem is 80mm is not up to building standards
@@SteveRoofer Well it is good enough for my Garden Room / Office. Plus the obvious lack of thermal bridging it offers, and 80mm is the lowest point, the ridges are 113mm insulated. They do also do 100mm+ roof panels, but I just did not need that for my purpose.
Hi, watched this twice and others of your videos, I'm only building a small 12 x 8 workshop room and I do want it to be good warm and dry, so thanks very useful.
Glad it helped
Great explanation, currently building a home workshop and am glad I found this video just before insulating my roof 👍🏼 thanks 😊
Glad it was helpful!
That was brilliant, well done mate
You two should do a livestream zoom call to chat. I'm not sure what about yet, I haven't thought that far ahead. Roofs probably.
@@ricos1497 Well Rico, I think that Steve is about the only roofer I have ever come across who actually understands the business of ventilation and insulation so well and I would gladly collaborate with him!!
Great description for a late novice like myself
Glad it was helpful!
This guy knows his stuff.
Hi Steve I hope you don’t mind, I’ve emailed you a question with regards to insulating a van. Your videos being such a help in ventilation and insulation has just increased the difficulty and complexity of insulating a steel van.
No worries
There is so much debate over this topic but as a builder and van converter I would see the best idea is to insulate with sheeps wool or recycled plastic bottle insulation or similar and let it breath. Vapour barriers etc are only going to trap the moisture that will always get in somewhere
@@welshnutterz that was my general thinking.
Brilliant video. My kitchen is always cold as its an extension flat roof. 9 degrees on a cold day. I was going to get on top and insulate it until I saw this video. I reckon its warm insulated and only cold as we have large windows and rarely put the heating on. Im glad when the plasterer came we didn't fill the ceiling with insulation as we would have caused condensation especially with all our cooking. Im going to just leave it as is and install a wood burner and heat the room better. Incidentally as we brought the house with no guarantee of the work done (elderly couples old house) are there any tell tale signs I can check to see if it actually is a warm roof. I did notice there was no insulation above the ceiling when the plasterer came but as the house is a bit dodgy can anyone advise please. Without ripping off the roof from the outside I don't really know what roof it is.... I can say with all these storms it's never leaked and has a great run off do at least this is good.
A roofer who understands what the reasons for cold and warm roof designs are. Halleljuah. Never met one in person, including a guy who has been building them for 35 years (he never tired of telling me)
Thank you Steve, that is really clear. I have a 20year old 10x4 cold flat roof with no ventilation and felt on top. I am looking to have it replaced/retrofitted because it's very cold and I get a lot of condensation inside. A roofer told me he will mechanically fix 100m bitumen faced PIR solid insulation to the existing timber. Then apply 3mm underlay felt to that insulation board and then another 5mm granular finish over that. Does that sound right?
The rockwool between the joists in the existing roof will remain.
Amazing, thanks. Cleared so much up for me
Great video steve. My whole house is flat roofed, I have a 44sqm cold roof retrofitted as seen in your video in the middle example. Its a single ply membrane and has 4 x mushroom vents which each one is supposed to cover 14sqm. My roof is also a roof terrace so the mushroom vents are an eye sore and in the way. When the roofers did it they used rockwall and didn’t install a vapour barrier. A year later i took the old lath and plaster ceiling down to replace with plasterboard and whilst doing this i took all the rockwall out and replaced with PIR between and below the joists, then battened below the pir to hold up the vapour barrier and leave a cavity for electrics and boarded. When i took the old stuff down the deck looked fine in all rooms except the bathroom which had quite bad mould and sweating. Throughtout that 1st year i did have a big hole in the bathroom ceiling, and no bathroom fan. So fan now installed and ceiling replaced as above. I tried to take what i had learned from your videos to install everything as best i could, i dont think it could be worse than the previous setup and only the bathroom was the problem area. Its been a 18months or so since I redone the ceiling and have been meaning to buy a camera that i could tread through the mushroom vent above the bathroom to see if its remained dry there.
I don’t use the terrace at the moment but would like to do something with it one day. So was thinking one day i could turn it into a hybrid as mentioned in your video so i can do away with ventilation. Would of liked to of seen a retrofit hybrid example after a retrofit cold installation so the 50mm gap remains. Would like to hear your thoughts on this, thanks
All the info I try to give is whats given to me by the local authorities and building control. As they don't want us to do and we don't do hybrid roofs, I can't comment as don't know
The improvements you have made should have solved the problems with your original roof perfectly, dont change anything else, dont fill the rest of your roof void with insulation and leave the mushroom vents doing their job!
Excellent as ever. you videos have given me the confodence to fit the flat roof on my extension. Alutrix 600 and 18mm OSB top and botom with inuslation in between and then a rubber memebrane on top. just need long enough fixings for it all now.
have you viewd my vido on this ruclips.net/video/RBINlVX0jOc/видео.html&ab_channel=SteveRoofer I get them from fixfast.co.uk
@@SteveRoofer cheers steve, it's just understanding the length I need now, and quantity per sheet
Just found this, two years later, what a fantastic explanation! I wish I’d seen it three years ago though, because then, when I decided to insulate the main loft, I saw the empty spaces above the 40 year-old cold roof extension, and went and filled them 😱. I think it should be ok though, 🤞🏻as I went and fitted a Nuaire fan unit in the loft, which is always on. However, could I check for moisture in the cold roof, via the small gaps left around the insulation, with a long-reach moisture meter, if there is such a thing?
Do a search on Amazon for relative humidity monitors. There are some really nice small ones that connect to your phone by Bluetooth really good
Great video, well explained. Thank you
What a great video explained really clear thank you for your time . I am doing an extension 3mtr x 5mtr block cavity I like the idea of the warm roof but I will be installing it to butt up under eves of single storey , that insulation being 150 plus joists , yet to be configured , that could be tight , I'll have to do slot of measuring may end up with a lower ceiling than existing building , would I be right in thinking this. ?
Hi Steve I had an extension done about 6 years ago, I have pitched roof either end of a flat roof the one end is plaster boarded on the angles for bedroom wall and the other end goes to the original loft space the thing is the builders did a cold roof the building inspector at the time said warm or cold doesn't matter, when I go in the loft the flat roof is mouldy, I have had extra tile vents fitted to get more cross ventilation but still wet, the gap between the bedroom ceiling and the flat roof is about 400 mm with rock wool insulation on the plaster board. The problem I have is if I had a warm roof on but then the pitches are old bitchmen and tile will it still have damp on inside of the loft flat roof under side as there would in theory be different temperature zones thus causing condensation, I have been quoted 4 to 10 k to rip it off and new roof layed, it's say 6m x 4m and I don't want to shell money out if the problem just moves to another place, I did have 2 dehumidifiers running and was pulling 4 to 6 litres a day and then I thought I'm probably making the loft space into a hoover as in sucking more air than I should 🤯, I'm at my wites end. Any help would be appreciated 👍
I spend some time designing my own hybrid roof, doing all the due point calculations and going through a lot of design iterations to see not only what would work, but also to see how robust the design was. The general rule of thumb I had heard was that you start with a warm roof and put half the thickness of the insulation under the deck (so e.g. 120mm above works with 60mm below, i.e. 66/33%, which is only marginally less robust than the 75/25% you quote) and I found it was a good rule in my case as you'd end up with something reasonably robust that wasn't reliant on any additional vapour barriers beyond the normal warm roof one (i still put an additional one in beneath the internal insulation as belt and braces, as for my design that meant either vapour barrier could fail without causing problems).
If you start with the cold roof and fill the ventilation gap (or anything with more insulation below the deck rather than above) it becomes an impossible task to end up with anything robust. The vapour barrier beneath the insulation has to be 100% perfect for it to work - all joints perfectly taped and sealed, no downlights or cable penetrations and no second chance on putting screws in to secure the plasterboard/smoke alarms/lights to the roof joists. The smallest hole will result in moisture getting in, condensing in your roof joists and rotting them over time.
So while there is a place for hybrid roofs it's limited to warm roofs where you absolutely can't drop the ceiling or raise the roof by 3-6cm, and it has to be carefully designed and very carefully installed. The risks are quite high otherwise...
Yes that about sums things up I have an engineer doing some calculations on some angle irons that are 50 x 50mm that will replace the joists thus giving a slim warm roof. So if that works why are we still using big old chunky timbers!
@@SteveRoofer A video on alternatives to chunky timber joists would be great, I've searched RUclips & the internet several times to see if theres any info out there on the subject & not found a thing.
@@northeastcorals What would I call that video? as it may be the next on I do
@@SteveRoofer ah now you’re asking, I might be in to deep 😅. When I’ve searched for videos or info on the subject in the past I’ve usually tried searching something along the lines of “alternatives to timber joists”. Maybe thats similar to what other people will be searching, or I could be way off 👍
@@northeastcorals alternatives is a word I like I was thinking of a slim warm roof. I need to think about this! "how to build a slim warm roof"
Excellent video. Very informative. I would have liked a quick mention of how the warm roof is fixed down. What is stopping the top layer of OSB and your roof from taking off into the sky in the next storm? How do you fix the two sheet layers of the warm roof together without creating a cold bridge?
All of the information is in some of the other videos that I do if you look up firmly broken fixings and how to fix EPDM rapper and how to fit warm roof insulation you'll find the answer to your questions
@@SteveRoofer Thank you Steve. I've now found those videos. Your videos are great. Sorry to criticise. Quick question; what was the name of the special tape that you used on the edges of the PIR to make a good friction fit when using PIR in a cold roof between roof joists?
@@w.w.8823 Gapotape
@@SteveRoofer Magic! Thank you! (Couldn't for the life of me remember the name...thought I'd seen it in one of your vids but could not find it again)
@@SteveRoofer Hi, I've just come across your channel, really interesting thank you. With Gapotape would that allow you to slide out an insulation panel in future easily enough to inspect your timber?
How do these principles work with deck access? 1974 council built with dwellings below the deck. These lower dwellings their ceilings are covered with batten and foil backed plaster board. The deck is filled with bituminous material. The ceiling is also exposed on the outside: cantilever of approximate 30-5cm. This concrete ceiling that is majority below the deck absorbs the damp air and the guttering leaks and potential dpc failure on the deck wall. Result is an internal ceiling that is wet during winter and most householders are unaware the foil backed plaster board being resistant to moisture and the huge mass of the concrete ceiling above.
Excellent video Steve, I'm hoping to put 100mm kingspan on top to make my garage roof a warm room then 100mm WR3 rockwool underneath to help with the noise of my woodworking tools. I feel this to be a good combination. At the moment my moisture layer is underneath my kingspan.
Sounds OK
@@SteveRoofer Thank you for replying much appreciated.
🤯 best explanation ever. Many thanks
Steve, in your warm roof build up you don't need any plywood on top of the rigid PIR. This insulation type has sufficient compressive strength to be walked on for maintenance purposes and the like. The extra plywood is an unnecessary additional cost to the customer. I see this being specified on architect J42s all the time... it's wrong. If it were mineral wool, it would be a different story but PIR is the industry standard for flat roofs and you don't need the plywood sandwich.
I agree and Trada say don't put any wood in the build above the VCL, however, try telling people this and everybody thinks it is too soft.
Are you still working for SIG ?
Interesting, very interesting
Interesting. But does that limit your choice of roof finish? I imagine torch-on felt is not an option here, more expensive finish required?
@@davidd8802 Kingspan TR24 is a rigid PIR board with sufficient compressive strength AND is suitable for torch-on felt. You don't need any plywood above the insulation in a felt warm roof system either. Leave the roofing to the professionals; it amazes me how many people try to DIY their own flat roof extension and end up all sorts of problems. Videos like this aren't all that helpful because to the layman it leaves them with more questions than answers.
In the US there is a table and depending on climate zone there is a set amount of exterior insulation above the sheathing. Any non permeable insulation under the sheathing must be applied directly (aka closed cell spray foam) The inside cavity can also be completely filled with permeable insulation as long as the external insulation requirement is met. The goal is to keep the underside of the sheathing at or above 45*F. It's an excellent way to get a high R-Value in a small roof cavity.
Do you happen to know where I can find that requirement for my area?
Thank you so much for this explication! You should do a video on cavity wall insulation, would love to hear your thoughts on that!
Love this!! Absolutely brilliant!! Steve’s advice has been princess to me!
Top man!
Great to hear!
Excellent collection of videos Steven. I've just blasted through A LOAD of them trying to fill some of the gaps in the information I could find on materials websites. The number of times I've found "no info on a topic", or "refer to other element manufacturer" has been very frustrating. You've addressed a lot of those information gaps.
I need to replace a porch/mini extension roof so I've been seeking a DIY solution as its so small circa 1300x910. Original roof is simply perched on the side walls only needed 3 joists! Very cold so intend to warm roof it.
If you see this and have time then a few remaining questions:
a) 2nd ply deck above insulation --> *now* isn't recommended as its an unnecessary point of failure?
b) clever PIR with bonded upper deck and no lower deck eg. Eco-Deck --> you've never rated it & it might compress too?
(though it might work for me as the porch < 1 sheet! = No joints)
c) I can't find anything showing construction of warm roof edges: eg, where insulation stops, edge timbers, barge boards and soffit if overhanging. (I've lots info from pre insulation olden days). Any links that might help?
Immense thanks if you have the time to comment.
Kevin
This may be a stupid question but I'm going to ask it anyway. We are thinking of building a garden room. As I understand it, garden rooms are not covered by building regs the same way a house is but I believe the maximum height is 2.5m. I also understand that is the reason some people are reluctant to go for a warm roof is to save on height . (so here's the stupid bit, prepare yourselves!!) Our garden is 13m wide and 14 deep from house to back fence. Our plan is to drop the entire area at the back of the garden (so the back of our garden would be 13m wide and 5m deep) by 2 foot and build the garden room in the lowered area. Is the maximum height for the garden room still only 2.5m even though it's now being built 2 foot lower than the rest of the garden? If the construction could then be higher than 2.5m this would easily allow for a warm roof. Be kind gents lol.
Thanks Steve, that was well explained!
Glad it was helpful!
Has helped me this!
Right at the end of the video, i think this is what I’ll do (warm desk on lower joists) My engineer had already mentioned installing flitch beam in the roof to shorten the span and therefore beam sizes. This way makes total sense to achieve a warm deck but without the 200mm joist. I’ve seen on other videos some comments of using a solvent based adhesive to adhere the EPDM rubber directly to the insulation (tissue backed instead of foil) instead of a waterbased adhesive to the OSB. Would also drop the height by 18mm/22mm. Whats your thoughts/ advice on this?
Wouldn't be better explanation!!! Good Job!
Great explanation.
Glad it was helpful!
fab thanks for the direction
Great video I like the warm roof is 120mm enough? it seems as though any work has to be 150mm to get to the u value n 200mm for the 0.11 u to future proof. instead of ply could u use cement boards or is their another option water resistant plaster board to gain walking strength
What a fantastic informative video. Great explanation
Glad you enjoyed it!
Counter batten your cold roof. Really important especially when it's hard up against an abutment
Yes counter battening rarely make a difference
I am building a hybrid roof. My design calls for 2.5 inch insulation on top with the joist pockets filled with closed cell spray foamed. Spray foam is a vapor protection is my understanding. Below the roof joists I will add a 1 inch ridged silver board insulation. My thoughts were that I could reflect heat back towards the interior while covering the bottom of the joist and while adding another vapor barrier layer and to reduce the heat that makes it to the ply layer.
Does this work in your opinion?
A great video well explained and clear
This is great, thanks for the info. I have 2 bay windows with a small flat roof above and was wondering if I could just put celotex on top outside.
How does the cold roof vent air when the noggins would be blocking the vent area
If the logins are in the way then you haven't got any airflow so you need to adapt the logins to get the airflow
Great info! Thanks 🙏
Thanks
Brilliant video, what about insulating a concrete deck ?
Extremely hard to insulate a concrete deck. It's the edges you need to run the insulation, not only over the top but down the sides and turn around and come back to the building to totally encapsulates the concrete.
Great video, just a couple of Qs please? 1. Whereabouts is the vapour barrier on your hybrid roof? The last few minutes of the video went just a little quick for my tiny brain to take in. I am interested because I want to add a flat roof garden room to the back of my 1920s bungalow and dont want a big thick roof profile to dominate. 2. How would you treat the insulation around lantern or skylight openings?
That's a lot of information you're asking but basically you always put the vapour barrier on the warm side of any insulation. If you can't get it exactly on the warm side slightly in is okay, but I mean by that if you've got 150 mm of insulation you can put the vapour barrier approximately 50 mm in from the bottom, but no further.
And then electricians come along and cut holes for cables & downlighters in cold roof insulation & vapour barriers.
That's why you go warm roof as well. Lots of space to put ventilation, electricity, etc.
Would sitting roof timbers on a plate on inner leaf and raising outer leaf to reduce height of facia work in a warm roof situation
i would have to look at drawings to see how that would work
Hi Steve. I have a flat roof with cold roof construction that I'm thinking of changing to hybrid.
Could I retain the 50mm insulation and 50mm airspace between the joists under the structural plywood.
Remove the existing torch on felt then build the warm roof construction of installing a vapour control layer, 120mm rigid insulation, another layer of structural plywood and then torch on asphalt waterproof member? Would there be any problems of moisture sweating with this?
Yes you can do this why remove the old felt if it is good condition it will be the vapour barrier. If not condition if not in good condition then remove it and use a vapour barrier. Theoretically the reason you can get away with this is because you have far more insulation over the top generally we suggest you have 2/3 above the bath area and one third insulation below however your insulation below is probably not installed that well therefore isn't working that well therefore is weak and will probably work
Thanks so much for the detailed explanation!
Glad it was helpful!
If I put a vapour layer under joist instead of top of decking in a warm roof is that an issue ?
Excellent presentation
Hi Steve, thanks for the very clear video. We have a 1940's semi that would have originally had an outside loo and washroom brick wall and solid concrete roof. It is now connected to the house.
Can a warm roof system be used on solid concrete as there isn't enough headroom for a cold roof.
Thanks.
Very well explained, cheers pal👍
No problem 👍
Great info .I am taking off a felt roof on the first floor as storm damage. Inside is just plasterer board and no vapour barrier as its 20+yrs old i was thinking of putting 100mm of celotex in on top of the plasterboard as only has Rockwell and very poorly done .what should I leave as air gap and is this the right way to do the roof .also was looking at grp or what is the best roofing please
Any more videos on hybrid roofs please?
Great video! I’ve a question tho. If you’ve a warm roof like what you showed in min 3:45, and there is then condensation somewhere in the middle of the insulation (where the two temperatures meet), isn’t that a problem for fungus ? Because the condensation is stuck in the insulation?
Could you possibly give any information on different ways you could run services through a cold roof installation, cheers and happy new year
hi Steve. Great video. Quick question, how do you make the vents at the top end of the roof? Thanks
But depends on the roof, but there's loads of different ways of doing it loads of different things out here. Long is water in six don't get in you can do it whatever way you want to
@@SteveRoofer thanks for the advice and the reply Steve. Appreciate it
Great video Steve. Can you answer a question for me please? With your Warm Roof example, for a garage workshop specifically, would you say that the 100mm Kingspan panels create an adequate warm roof "IF" the are fitted and sealed properly? They can easily span 2m without additional structure below and are finished on both sides and technically don't require a vapour barrier since the inner layer doubles as one (again assuming the panels are sealed together properly.
definitely yes
Can someone tell me if SIPS panels will be fine in a garden room with no ventilation on top? so just sips panels, and EDPM glued on the top? Obviously making sure inside of SIPS is seald well etc?? Thanks!
Hello, steve great videos! I would like to use a warm roof on my garden room project but I have height restriction issues. I was wondering if 50mm insulation would be thick enough as all of the warm roofs I see are 100mm plus. Eagerly awaiting your response. Thank you!
>>
Old post I know but might help others with same question. 50mm of PIR will work as a warm roof but you will lose way to much heat and regret it later. For a detached garden room not requiring Building Regulations (so under 30m2 or under 15m2 if timber construction) maybe 100mm might be an acceptable compromise particularly if only occasionally heated. For anything requiring building regs 120mm PIR minimum. If to save height you decide to go for a cold roof, keep a through ventilated 50mm gap over the insulation, and ideally put some of the PIR under the joists as well as between. Total PIR thickness for a cold roof, 150mm if all between the joists, 125mm if at least 25mm of that is under the joists.
@@mikebarry229 125mm between with 50 air gap = 175mm timber minimum, thats a large timber for a roof isnt it.
Can a 25m2 garden room be built from timber if its away from a boundry to the rear of a house and not taking up more than 1 third of the available free land?
I wanted to build one from timber not blocks.
@@handle1196 under Building regulations (at least England and Wales, not sure about rest of UK) if its detached and more than 1m from the boundary and under 30m2 floor area (so not including walls) single storey and no sleeping accommodation its exempt from Building Regs even if combustible construction, though any drainage (say you wanted a loo) would have to comply. If building an exempt structure you can do what you want but following the guidance in this video is the only sensible thing to do. If you are having a flat roof try to get a warm roof if you can as it's so much better. 125mm of insulation between joists is probably inferior to 100mm over joists in a warm roof. Maybe your flat roof joists wouldnt need to be so deep with a warm roof or perhaps have the joists open on the underside so the headroom doesnt seem so restricted.
I assume you are going down the permitted development route and hence 2.5m height restriction? if so then your options are limited. you certainly wont be able to achieve a proper warm roof design with 120mmPIR. I managed to squeeze a vented cold roof into my design with 100mm PIR and 50mm vent above and building height is 2.485m. If you want to go for planning permission then ask for 2.7m and its all really easy then.
Great video and really useful information, thanks Steve! I’m currently in the process of insulating my new workshop/shed and have opted for a cold roof, leaving plenty of ventilation in my overhanging soffits. I saw your comment about having never seen vapour barrier installed correctly, as I am about to embark on that task in the next week or so do you have any tips of a video explaining the correct process? Cheers!
Hi Steve
Fantastic videos
Is it possible to have too much ventilation in a cold roof space. I've just had my roof replaced and from what I can see there was no ventilation at all so I'm planning on fitting some air vents into the facia board.
With 100mm insulation I've still have a 80mm void and is it ok just to have the vents down one side of the extension the extension is only 3x3m thankyou
Steve, what is your opinion about multi-foils in the warm/hybrid roof build up ?
I like it however it still has to be installed correctly
@@SteveRoofer thanks for the answer, the reason I am asking is because the way they recommend installing is a hybrid roof, as they say put foil over rafter and then PIR between rafters, leaving an air gap in-between them
@@il1723 You ned to do it the way they tell you
Does the insulation have to be of a specific type or could you also use 120mm Styrofoam boards for example?
You can use whatever you want as long as it gets you to the correct thermal element you want to get to so if you use for instance screwed up newspaper, you would probably need to have a depth of around 1 m. If you use PIR insulation you will probably need a depth of 150 mm, if you use Styrofoam you will probably need 250 mm
Hi, I've got a small extension tiled pitched roof that I'm insulating with kingspan. The rafters are 6x2 and the kingspan is 75mm thick. Should I just double up on the kingspan? Would appreciate any advice from you. Thanks
if yo are puting between the joists you should leave a vented air gap over the top
If you can't ventilate roof system, flat roofs. Keep air from entering in from below Or above, you won't get condensation. Use poly on lower, heated side of assembly. Same concept as exterior walls.
Excellent video thank you!
I have had an acoustic engineer recommend 100mm dense wool insulation in the air gap of a warm roof, against the plasterboard though and 100mm air gap up to the warm deck (200mm joists). I wonder what your thoughts are on this design?
Thank you
Okay, so this is quite interesting because if you put insulation between the joists on a warm roof you are stopping the warm roof from being warm by blocking the warmth from rising from the rooms below to counteract this. You need to put more information on the warm roof might sound silly, but it's all to do with keeping the vapour barrier above the dew point.
@@SteveRoofer thank you, yes it has got me stumped. I am speaking with the architect next week to get his thoughts..
@@877cms the architect is not the person who will know what to do you need an engineer. This is all to do with thermodynamics. The engineer will work out where the dew point will be based on the elements of the buildup of the roof and what's underneath it. some engineers just walk away from this kind of design work because it is pretty complicated. It's more physics. The golden rule that I use based on seeing calculations similar to this is as follows. As long as you have 2/3 of the thermal insulation above the vapour barrier you can have one third underneath.
@@HampsteadBuildersLt thanks Steve I appreciate the guidance, I will look into it! :)
Thanks for explaining this Steve, could you do a video on how a wood burner pipe should be installed on a flat roof hot or cold, thanks.
I thought you couldn’t put anything on top of a warm roof but you have OSB on top, won’t that rot? If not how come?
I am doing an owner builder home with a flat roof and the person drawing the plans mentioned something about the roof not needing vents because they hand the insulation ? Does anyone know what this means:
120mm of PIR insulation should be fine for code. It is isolating better (something like twice as good) than the usual stuff like glasfiber or rockwool. So 200 mm of glasfiber should be matched with 120mm of PIR.
Great explaination- but where does that top vent on the cold roof (marked 150mm) go to? Do sloping roofs need this?
So on a warm roof you have a board insulation then another board. If you were to fill the cavity you would have a board insulation then another board. So what is ot that causes one to sweat and not the other, is it to do with the joists cold bridging?
the board insulation board is above the joists with a AVCL layer at the bottom of the sandwich
What about 50% 50% would that scrape by?
not quite sure what you mean by 50-50 but 50-50 means it's not a warm roof or a cold roof therefore it's a hybrid roof
@@SteveRoofer Sorry I meant if 50% insulation above the deck and 50% below. would a hybrid roof like that work?
@@smellypunks
No, it’s clearly explained why it won’t
So what about the walls on a timber garden room, should they be insulated using the same principles? By this i mean should we be having cold walls and warm walls? Should there be insulation over the inside face of the stud walls as well as in inbetween the studs, aswell as maintaining a ventilation gap. After seeing this video, i feel like the walls and roof should be treated in exactly the same way as each other.I notice companys just putting 50mm PIR boards inbetween the studs and plasterboarding.
Excellent question, we shoud be looking at the entire building we call this a building envelope, we shoud think of every component and how they will work together, but ha-ho we don't I would externally insulate all walls do them the same as the roof.
When building a house the insulation is in a cavity with as little thermal bridging as possible. In some countries the entire external of the house is insulated too. With garden rooms the walls have a vent space for the cladding to dry out for rain but not the internal walls. Hot air rises I suppose so it will attack the roof first. I have seen in flats though the walls also get attacked with condensation once the roof is saturated.
is it vapor barrier no top of 18mm plyboard on warm roof example?
Some advice please. The company have installed my summer house and I am currently insulating it for the winter.
The roof battens are only 2.5 inches x 1.5 inches.
I was looking at using a hybrid roof putting the insulation against the Osb roof, leaving a gap and then vapour barrier before plasterboard. I’m not that confident due to the size of the roof battens my insulation is only 1inch thick. Will this be ok or shall I find an alternative method?
Best you send me some photos and drawings and perhaps I can help
Could you advise of the best solution for a flat roof terrace. Materials etc
Thanks
If you have a warm roof 120mm and then 30mm Turing it I to a hybrid should there be a vapour barrier or vapour control barrier above the plasterboard? Do you do jobs in the Midlands?
So I've built my roof but not insulated yet. Basically is 6x2 joists then OSb then EPDM membrane.(shouldve done a warm roof but too late now!). Most likely now go with the cold roof scenario - how does one finish the eaves where the roof joists meet the wall plate? Would you insulate half the height of the eaves (ie same as the ceiling and leave the gap above) or just put no insulation in the eaves? also what's the best solution to downlights in cold roof and vapour barrier? btw its a garden room/shed with no shower etc..
I have heard that if you have insulation solid right up to the cold roof then no air is there to condense?
You could be right in a way, but building regulations does not approve that so therefore we can't do it
Dew-point gradient graphs are calculated by building services engineers and some architectural technicians.
Would closed cell spray foam under the plywood control any vapor with a warm roof with R30 insulation on top. Do you see any problems with that type of hybrid option.
Probably, however, I don't know much about spray close sell foam