Hybrid roofs explained Flat roofs Warm and Cold

Link to the abutment vent video
• Venting a badly instal...
Hybrid roofs explained - (Flat roofs)
I'm frequently asked if I install hybrid roofs and do they work.
In this video, I try to explain:
what makes a hybrid roof
how a hybrid roof differs from the standard cold roof or warm roof constructions, which are widely used in the building industry
the different ways you can form a hybrid roof.
A hybrid roof is a mixture of a cold roof and a warm roof construction.
With a cold roof -
If you totally fill the void between the joists with insulation, it's a hybrid roof.
If you don't vent the roof, it's a hybrid roof.
If you don't use any insulation at all, it's a hybrid roof.
With a warm roof -
I'm often asked if some insulation can be put inside the roof and some outside the roof. If you do, it's a hybrid roof. However, if you only place a small amount inside and have at least 3/4 outside this will probably work, but it's still a hybrid roof! You definitely can't have more insulation inside, and less outside that just won't work.
Having different layers of insulation with air gaps under a warm roof will be a hybrid roof, and it may or may not work.
The problem with changing the known buildup of a warm roof or cold roof, is that you need to get it designed. If the design team come back with calculations showing that it will work, who is to say that it won't. But bear in mind that you only get the answers from the data that you enter!
It's easier to think of it like this:
If you stand too close to a cliff edge, you could fall over, so you should always stand well back, in the safe zone.
So why would you design a roof in a way that if the internal humidity or the external temperature were to be just off normal, it could have problems? You always design to stay in the safe zone, because the surrounding elements can change. So don't use a hybrid roof and don't use a cold roof, stay in the safe zone. Always try to build a warm flat roof.

[@farikomike524]

this is probably the best and most clear explanation of this subject, a lot of people will benefit from this for sure 👍

[@SteveRoofer]

Thanks

[@alax5953]

Here here, really appreciate this video Steve.

[@AddictedtoProjects]

I'm so glad KZbin recommended me your video, and that your content makes the topics very accessible! Already queued up your other videos to watch too :)

[@SteveRoofer]

Welcome aboard!

[@jonnorris7564]

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.

[@basilguts1786]

Very clear and well explained,he’s probably a very good tradesman also.👍🏼

[@guyanagold4869]

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

[@arnoldusk]

Truly the best source of information on this subject. Many, many thanks. Let our DIY-project begin !

[@SteveRoofer]

You are welcome!

[@ArcMaple]

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.

[@SteveRoofer]

Thanks

[@ianmarsden8568]

Glad to hear it's helped your understanding of warm & cold roofs. But the video is titled 'Hybrid' roofs and advises getting advice.

[@royfoster7010]

Love this!! Absolutely brilliant!! Steve’s advice has been princess to me! Top man!

[@SteveRoofer]

Great to hear!

[@elliejake11]

Thanks for taking the time to explain this, top man 👍

[@SteveRoofer]

No problem 👍

[@dmbeale]

Great video, well explained. Thank you

[@haroon420]

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.

[@Joneswoodworks]

Great explanation, currently building a home workshop and am glad I found this video just before insulating my roof 👍🏼 thanks 😊

[@SteveRoofer]

Glad it was helpful!

[@plssmellmycheese]

Yes, another well explained vid...as others mention, the cold roof also has issues with penetrations in the VCL for services (cables, downlights, plumbing pipes even)...even if these penetrations to the VCL are well sealed at the time (unlikely to be done perfectly), further down the line someone could very likely (unknowingly) make all sorts of holes in the VCL. (and insulation)...warm roof all the way!👍

[@robertdowd464]

well explained , now I can stop coming up with other ideas 😄, many thanks

[@steveking2401]

Amazing, thanks. Cleared so much up for me

[@Chef1Mat]

now i know why my shed is condensating, excellent explanation thanks.

[@br00728]

Thank you so much for this explication! You should do a video on cavity wall insulation, would love to hear your thoughts on that!

[@Kevin-cy9cv]

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.

[@SteveRoofer]

Glad it helped

[@dannymurphy1779]

Thanks a lot for clearing up a lot of misinformation that can be found elsewhere on KZbin. 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.

[@SteveRoofer]

Glad it was helpful!

[@dominicdoyle2895]

🤯 best explanation ever. Many thanks

[@alexbekele8945]

Only found this today. Can’t wait to binge all videos and actually learn something.

[@SteveRoofer]

Thanks

[@fastlife_tv]

Great video and very informative. 👍

[@andyclarke6105]

Thanks Steve, that was well explained!

[@SteveRoofer]

Glad it was helpful!

[@chasbunn4407]

What a fantastic informative video. Great explanation

[@SteveRoofer]

Glad you enjoyed it!

[@ivanmullen3015]

Excellent presentation

[@kmpeaker3955]

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.

[@SteveRoofer]

have you viewd my vido on this kzbin.info/www/bejne/iHOsf5-MjZWdhcU&ab_channel=SteveRoofer I get them from fixfast.co.uk

[@kmpeaker3955]

@@SteveRoofer cheers steve, it's just understanding the length I need now, and quantity per sheet

[@I-am-not-a-number]

Fantastic content, thanks Steve.

[@SteveRoofer]

Thanks at the moment I'm taking 3 or 4 call a week re hybrid roofs so hopefully this will help people

[@paulbrook2459]

Brilliant, well explained 👍

[@papabear920]

Thank you this is very helpful 👍🏾

[@damdamdam8346]

fab thanks for the direction

[@matthewsaunby9056]

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!

[@jamessilvester9077]

Very well explained, cheers pal👍

[@SteveRoofer]

No problem 👍

[@mrbobo86]

Very informative. Thank you.

[@jethroeast2560]

Great video!

[@KKTR3]

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

[@mojomaze]

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.

[@17071701]

Thanks so much for the detailed explanation!

[@SteveRoofer]

Glad it was helpful!

[@andrisvitus4086]

Wouldn't be better explanation!!! Good Job!

[@stuartandrews4344]

superb video.

[@asm101]

great explanation thank you!

[@vajindertaak3158]

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!

[@SteveRoofer]

Glad it was helpful!

[@klaeLIFE]

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.

[@vajindertaak3158]

@@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.

[@Crooks103]

Brilliant information

[@ricardo-iw9sq]

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 👍

[@kevinreader1548]

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

[@GSRTurbooo]

Great info! Thanks 🙏

[@SteveRoofer]

Thanks

[@MijeongLee-iy6fy]

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.

[@Alite2012]

Nice Video thanks for making it clear

[@SteveRoofer]

No problem 👍

[@DanielPaprocki]

Thx for explanation 😊👍🏻

[@stuartmartin7259]

Great explanation.

[@SteveRoofer]

Glad it was helpful!

[@Jackzuk]

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

[@SteveRoofer]

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

[@mikebarry229]

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!

[@liamflynn141]

Could you possibly give any information on different ways you could run services through a cold roof installation, cheers and happy new year

[@RobindeJongh]

Superb video Steve. As a structural engineer, I'd suggest upping to C24, wider, and closing centres, as you've done at the end of the video. A further step for an ultra thin roof is to use plywood top and bottom to create a stress skin panel.

[@SteveRoofer]

Perhaps we could do sothing on this subject ?

[@RobindeJongh]

@@SteveRoofer I'd be delighted - let's get in touch.

[@gavinbonser3602]

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.

[@stuartbryant8545]

Great video and explained really well. As downlights are an issue in a cold roof constructions could an insulated box be made to insulate above the light?

[@darrenpodger7294]

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. ?

[@1alph1]

great video. many thanks

[@SteveRoofer]

Thank you too!

[@JB-ro7kv]

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! : ))

[@SteveRoofer]

That is awesome!

[@ianmarsden8568]

You mention stuffing full of insulation, but not say what the real world outcome was.

[@ukconstruction]

That was brilliant, well done mate

[@ricos1497]

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.

[@ukconstruction]

@@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!!

[@xMarshy147x]

Awesome vid!

[@SteveRoofer]

Thanks!

[@stephenpearce3880]

Really great content, thanks :-) On a slightly different matter, what's your view on the technique of spraying existing internal pitched domestic loft roofs with that spray foam. I've been given a quote for the work on my house (builts 1999), but I'm cautious about the effect of covering and sealing around the timber struts with potential for sweating etc

[@ggss6420]

Please could you make a video on how to insulate l upstands on a roof light made from OSB3 with CLS frame work on the interior built on top of a warm roof construction made from watching your well explained excellent videos

[@judebrown2672]

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.

[@MrFish1968]

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]

Problem is 80mm is not up to building standards

[@MrFish1968]

@@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.

[@heartfelt111]

This guy knows his stuff.

[@d.beaumont9157]

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.

[@SteveRoofer]

Sounds OK

[@d.beaumont9157]

@@SteveRoofer Thank you for replying much appreciated.

[@CharlieInshawDrums08]

Hey Steve, great video. I have just finished the roof structure on my garage and was planning a cold roof, its just bare OSB3 in the joists at the moment and open at both ends, with notched noggins, but I'm getting a lot of condensation/ sweating when I'm not even in the room. Any idea why that might be? Really appreciate any help you can offer, pulling my hair out trying to understand it.

[@TofuInc]

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.

[@mitch5282]

Do you happen to know where I can find that requirement for my area?

[@logik100.0]

Great video. If your looking for a topic can I ask about a SIP panel hot roof. I'm looking at exposed steels internally holding up a 210mm+ SIP panel. The issue I see is that I want it to be green roof so it will need timbers inside the joints for strength and as I want the steels level the furring's will need to be on top creating a cavity. Not that there will be any air path up but still no idea if it will work. Any pointers to competent engineers appreciated. N London area.

[@ice4142]

Hi Steve, what about spray foam insulation? Really interesting video. I have a detached garage that although recently constructed it was never planned to be insulated and there is very little overhang and no sofits to provide sofit ventilation. During lockdown I have got into woodworking and would like to turn it into a workshop. Could spray foam insulation (professionally done) be used to insulate between the joists and would this stop the leakage of air you might get up to the cold roof deck if you filled the void with PIR?

[@JoeB_BSc]

Hi, what is your opinion of wapl-mounted p.i.v. units for garage conversions please, eg do they work as well as they do with roofspace through ceiling ones in houses please? A very thought provoking video, thanks for posting it.

[@FinbarMagee]

Great description for a late novice like myself

[@SteveRoofer]

Glad it was helpful!

[@stevek6855]

Excellent videos Steve, really informative. I would be most grateful if you could do a video on insulating a shed. You tube is full of nonsense and I can't find a decent video equally I don't have enough understanding myself. We've a basic garden shed, inch and 3/4" studs with shiplap exterior. Loczl shed company trying to sell me polystyrene sheets but mention no air gap. I would like to prevent condensation on the tins of paint/tools etc. Also, I was thinking of replacing the felt with a steel roof with a plastic coating but worried this will make things worse? Can you advise at all? 🤔

[@Scumsuckingpigmonkey]

I'm close to 40 years in the game. Time served Bricklayer, advanced craft, supplementary Studies, O.N.C., L.C.G. (If i paid for it each year) 10 years gas registered Heating Engineer, Director of a heating company 10+ years, SMSTS Site manager, before going back to a "Builder". I've started a dormer loft conversion for my number 2 son. First I have done. I would like to thank you for your clear and informative video. I have the problem of ridge height/ceiling height and building control and asking for a warm roof. However I am confident I can ventilate a cold option. I agree in a perfect world the warm is better. Do you know if the reg change on the 1st of June 2022 regarding insulation has changed the 120mm on retro work? (flat roofs)

[@adamkingdon8063]

Any more videos on hybrid roofs please?

[@williambongo]

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.

[@liammullan2197]

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)

[@terryatkins]

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.

[@SteveRoofer]

No worries

[@welshnutterz]

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

[@terryatkins]

@@welshnutterz that was my general thinking.

[@johna8921]

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

[@stevensexton962]

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

[@peterdorr6190]

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.

[@klaeLIFE]

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.

[@SteveRoofer]

Yes I get lots of people quoting that video

[@coops6621]

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.

[@klaeLIFE]

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.

[@8bitsim]

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.

[@michaelcoles6140]

Would that channel be someone from Leeds?

[@martynmongan9123]

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.

[@ricos1497]

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?

[@martynmongan9123]

@@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!

[@ricos1497]

@@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!

[@MrTurboSAAB1]

@@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

[@mooney0086]

Could you advise of the best solution for a flat roof terrace. Materials etc Thanks

[@Tensquaremetreworkshop]

Great explaination- but where does that top vent on the cold roof (marked 150mm) go to? Do sloping roofs need this?

[@martinhinsley6198]

Thankyou Steve for such clarity on this subject....Question...would different density insulation slabs offer equal U values but with reduced depths? Looking at the various manufacturers data sheets seem to show this might be possible, but I`m still not sure. Your experience and clarity may help me. Cheers

[@SteveRoofer]

I don't think you should go by density but by the manufacturer's specification as there are so many different insulations out there. One thing for sure fix it in position correctly or it wont perform

[@budflanagan1262]

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?

[@SteveRoofer]

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

[@johnmit]

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...

[@SteveRoofer]

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!

[@northeastcorals]

@@SteveRoofer A video on alternatives to chunky timber joists would be great, I've searched KZbin & the internet several times to see if theres any info out there on the subject & not found a thing.

[@SteveRoofer]

@@northeastcorals What would I call that video? as it may be the next on I do

[@northeastcorals]

@@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 👍

[@SteveRoofer]

​@@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"

[@manrajatwal6365]

Hi Steve - thanks for the video. Is there a reason why the warm roof tends to make crack and pop sounds due to heating up and cooling down during the day? My hybrid roof does not have this problem so much.

[@multirole240]

Steve Thank you for an excellent explanation. One question. With a warm roof, what is the result of having the moisture at the dew point, trapped within the insulation.

[@mikebarry229]

Once the moisture vapour reaches its dew point it will be at 100% humidity and begin to condense on any surface at that temperature or lower. In quilt insulation it can condense within the insulation as the temperature reduces, soaking the insulation, making it less effective and increasing the condensation further still. Condensation on timber surfaces will at least lead to mould forming, can soften chipboard, and will eventually lead to rot.

[@IamGaryRichardson]

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.

[@yeekeelam600]

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?

[@keendiy7209]

Hi, what is your view on using a product such as Xtratherm FR/TP for a warm flat roof? Insulation combined with decking would allow us to build a shallower warm roof. Thanks

[@keithbucknall]

Thanks for this video excellent how does that spray foam insulation works?

[@SteveRoofer]

Don't know but i'm not sure I like it I read lots about it gassing off chemicals

[@johnjones2231]

Hi Have you ever used Acrypol liquid rubber system with the fibreglass matting? cheers

[@faz5rock]

Hi Steve, thankyou for the videos, I have learned alot. I am getting a garden room built and unfortunately the builder has done the roof wrong, it's supposed to be a cold roof but they have not left any ventelation gap between the ply and insulation (celotax) and not used a vapour barrier before installing plasterboard. We also have downlights going into the ceiling. I was wondering if there are any ways to salvage this and make right, e.g. using a waterproof paint on the plasterboard, using silicon around the downlights and install a few mushroom vents on top. The garden room will be used frequently and also has a shower. Really gutted I didn't see your channel a couple of week before. Would really appreciate your help with this. Thanks

[@SteveRoofer]

email me all info and photos and let me have a look [e-mail]

[@jamiehalpin9921]

Counter batten your cold roof. Really important especially when it's hard up against an abutment

[@SteveRoofer]

Yes counter battening rarely make a difference

[@jackthomas8185]

Hi I am keen DIYEer - Pls could you address the issue of cold bridging via using long nails to nail top OSB board with insulation under and VCB onto finally 1st Layer of OSB - Would not the very long screw/nail used pierce throught VCB and cause some Cold Bridging - If so how to mitigate the situation as best possible Many Thanks - True Honest Professional Few Are Around & Hard To Find

[@wilbauk]

How would you vapour barrier under new warm over roof on top of bitumen torch on?

[@runzareviews4188]

Couple of questions. I’ve watched a video of a garden office building with 100mm insulation, Is that not enough? Also If using c24 timber and adding more roof joists than normal couldn’t you go even small than 6x2. Something like 5x2?

[@Stratoszero]

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?

[@SteveRoofer]

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.