After watching countless videos on youtube once again Roger hits the nail on the head and makes it perfectly understandable. cheers marra

Thanks for this. Definitely the clearest and most easy to understand explanation of a cold roof and warm roof on KZfaq.

Very clear and helpful, nice video Rodger! We're always doing these sort of extensions and when the joiner talks to me about hot and cold roofs I'm always bamboozled 😂😂 look forward to see the next video on this project bud!🍻👍

Such a unique breadth and depth of knowledge from Roger, we are lucky that he is willing to share it with us. Thank you Roger! 🙏

Excellent as always!

Interesting stuff Rog , what a massive pain in the area for 5 “ though ! 😳. Look forward to the build 🧱👍🏽

Great vid Roger, nice and simply explained.

It's time to thank you. I've used your videos to build 2 walls, insulate my garage and tank a wet room. You explain things so well that I understand and can question things in my head. Insulated summer house / office is next which I'm hopping to start in the next month or two. I still bring in the pro's where needed, but understanding what is going on really helps and I think just raises the standards as a whole. Thank you!

Great video explaining in very clear way the difference between cold and warm roofs

Thanks Roger, excellent explanation to a bit of a head scratcher. Am going to replace my old plastic roof on my conservatory and had been trying to weigh up the best way of tackling it but you just explained it in less than 10 minutes!

Excellent info, thanks 👍🏻

You are the best! Thank you for the explaining.

Going to be doing a garage to office conversation soon, needed this lessen. Thanks Roger

San Francisco, California, homeowners should take note of Roger's sage advice!

Thank you very much for sharing, Master!

Brilliant explanation Roger

Great as always Rodger. I have a 15-year-old log cabin. It's perfect inside but a bit dated on the outside. I spend around £100 per year maintaining it as well as the cost of heating. I am about to insulate it on the outside all around and have the products but not 100% sure of which way to have the insulation, membrane etc. I don't want to insulate the inside as I like my LOG cabin. I have 60mm Kingspan sheets (got them cheap so can't change) a breathable membrane, PVC cladding for the walls and box profile sheets for the roof. I was intending to stitch the membrane onto the outside walls then Kingspan held with 2"x1" battens and the pvc cladding onto this. There would be the 1" air gap behind the cladding vented at the top and bottom with mesh to stop wasps etc. The roof is 20mm t&g pine and is felted. The felt needs replacing so was intending on removing this stitch the breathable membrane on top, Kingspan, 15mm OSB then the box profile sheets directly on top. Do I need to change the membrane for a vapour barrier? If so where does it go? Do I need an air gap roof or walls? Any advice would be appreciated as I'm getting conflicting messages on other forums, everybody seems to be an expert

A very informative video. Thanks for sharing

What an excellent explanation. Thank you.

Thanks, excellent video! Simple answer - badly installed cold roofs are bloody freezing when the builder who owned your house doesn't air seal between the Kingspan slabs and the joists. It's basically external temperature just above the plasterboard.... 🥶 Also just found out he didn't stick a vapour barrier above the plasterboard either. 🤦‍♂️🤦‍♀️😤

More videos like this Roger 👌🏼

Excellent job great explanation 👍

Thank you for a very informative and well delivered explanation. Keep up the good work.

Learn something new everytime, thank you

Brilliant, thanks, really clear explanation.

Really informative video, Roger.

Highly interesting....more demonstrations would be very much appreciated...thanks

I wish all tradesmen were like you Roger.

Awesome explanation, Thank you. I am considering this for a project and wanted to understand it.

Worthwhile advice!

So well explained!

This is very useful :) I'm converting my garage to a room and I'll speak to the builder what he plans to do with the moisture issue :D

Well that’s another new thing I have learned from you, Thankyou.

learned a lot. That’s why I love this channel. Keep em comin Roger.

Great vid.. very informative

I am about to do this, bloody gold.

I think I would have preferred looking at a flat roof rather than a dozen mushrooms poking out of a roof.

Perfect timing. Will be starting on a garage conversion soon and need a new roof. Exactly what I needed. Warm roof it is. Cheers

Never really thought about the subject before Roger but in many big old houses they had cellar and attic spaces with air grills below the floor space for the air to circulate. I was lucky when we bought our 300 year old 3 bedroom cob cottage with a thatched roof (cold roof). The 3 foot thick cob walls are build off a rubblestone plinth with no foundations or guttering, the ground is hard clay and stone. There was bad damp when I moved in because the walls were cement rendered and it had been a holiday home for about 15 years which had caused all the damp issues and rotted the timbers on the damp side of the house because I have a hill behind the house whose gable end faces into the hill and in front of that there is a 25 foot deep stone lined well, the water line is about 4 feet below ground, never higher and is only low during summer. Since I put in a French drain along the back side of the house and lime rendered the place we've have no more damp issues. The first floor ceiling is wooden lath & plaster (the walls are reed and plaster), a thick layer of haired course lime mortar and a single layer of thick top coat white lime skim 5 to 6ml thick. Another property of lime walls is they absorb moisture and CO2 and give you better acoustics than cement or gypsum, a friend in nearby Stogursey has plastered his internal walls with clay which has even more amazing qualities. It can be expensive to do but, done well it should last a life time whereas modern builds are designed for about a 40 year life, even a strawbale, single floor structure would last a 100 years. Above this ceiling line is the triangular shaped attic where, between the joists you can see the back of the ceiling and the folded nibs of that 200 year old, haired lime putty mortar and on top of that, between the joists are a few rolls of Rockwool insulation with a 5 foot air space before you see the underside of the straw roof. It's relatively dry. In some of the bigger houses they'd put a thick layer of tamped soil and sand which would be good for the sound proofing and insulation properties. During the night, summer and winter, we sleep with our bedroom window open and during the day, unless somebody is home, everything is shut up. Up the road is an equally old property which has a double-Roman, clay tiled roof, when I climbed up to look there was no roofing felt and it too was dry. As you said on one of your rants, there's no point having an air-sourced heat pump, if the home isn't well insulated inside. I'm house rich and cash poor and can't afford one but I would like a ground-sourced heat pipe, they do work, I would also like some solar panels please. It would help the planet if we all had solar, wind and thermal generating capabilities with storage capacity for any excess power with every home as standard and, if you have a small garden, a compost heap is great for all your organic waste. Ours is barely large enough for the herring bone pipe to the septic tank which is emptied every year (£250) and is cheaper than the mains sewage bill I'm told. We've go no government grants, none available, or help with lower VAT for sustainable buildings, and it was bought to be our family home and so long as it continues to be repaired with like for like materials it should last another 300 years. keep up your interesting topic please, it's healthy when we can all rant.

Great info thank you

Hi lads, You know what, I am level 6 NVQ (not very qualified) site manager, level 3 carpenter and joiner, and intermediate qualifications in Brick laying, plumbing and plastering, (also a fully qualified Locksmith), with 33 years of mud on boots experience, I've forgotten more than most people actually know, but...... I literally LOVE your videos and pod casts, (only found you the other day, so alot of catching up to do),very informative entertaining AND engaging, even if you are shandy drinking Southerners. Keep up the awesome work 👌

Great teacher, thx.

Good explanation cheers

My thanks to Skill Builder and Roger - now all i need to know about warm and cold flat roofs. Infact my new extension Surrey side of Gatwick a semi-detached and all flats are cold. my new extension will be warm and work to change my current flat roofs to warm but will leave attached neighbours as is. with some magic (in the drawings) for the builder !!

hi great explanation bang to the point

Very interesting subject. Most people wouldn't give it a second thought. But it's important you know in case of dry or wet rot. Thanks rodger👍👍

Thanks...great video

Brilliant, thank you.

Really love watching your videos - that are really informative particularly for a novice. I am in currently undertaking a single story rear extension and I was let down but he builder. The flat roof basically was completed with trimmers, joists etc and a GRP layer was pasted on. The roof wasn't insulated so, I got someone else to finish the job and created warm roof on top of the GRP. I asked the roofer to add in a vapour on top of the GRP and beneath the insulation. was that the right thing to do? Will this have a detrimental impact on moisture internally ? Thanks Joanne

Great explanation

Great job Nick 👍🏋️‍♀️🤺🤗

Excellent stuff. I'll now change what I was going to do with the roof of my new dormer.

Thanks so much!

Excellent stuff roger, as a building control surveyor the most common mistake is a warm roof with no decking and VCL below. Happens all the time! Every PIR supplier will ask for an 18mm deck with the VCL

great explanation.

Good explanation for people that don't understand the difference. 1 thing that would be better for ventilating the dead spots created by the lantern would be to counter batten the roof the opposite direction of the joist to create a cross flow ventilation throughout the whole roof. Although you increase the deck height by 25mm you get rid of the need for unsightly mushroom vents everywhere 👍

Good explanation.

Thank you!!

Nicely done, I did a little office using warm deck. I stopped the joists at the wall plate, but extended the OSB and 4 inch insulation beyond to create a 200mm overhang. Then sandwiched the edge with 2x4 so I could hold it all together. I only did this to avoid creating an ugly thick fascia that was 300+ tall, instead there's a neat 150mm fascia with the gut attached.

Thank you for sharing that knowledge. In NZ we build a lean to extension with a mono-pitch roof. Plaster board 200mm joists, vapour barrier then corrugated Iron. The Insulation is Pink Batts skillion roof insulation. The insulation had to be specific due to the insulation loft limitation giving allowance for at least a 20mm gap - I now further appreciate what that gap is for. More so it gets me to thinking about flashings and how well they can release water on the inside without letting water in. Hopefully the building codes we built to are correct.

Nice video Skill Builder, well explained! It can be a real headache always thinking about ventilation. Looking forward to seeing the series 👍🏻

the best build channel imo

I think i would have gone a cross the 9x2s with tile batten so the whole roof is connected and reduce the number of roof vents. Not only is all them mushroom vents going to cost a lot especially as they have to be built into the roof covering, they will look facking ugly. Good vid Roger 👍

Top advice !

verry informative

brilliant info - would be nice to see a video showing what it looks like

A KZfaq channel called Steve roofer shows a good ventilation detail on the flashing, well worth consideration

When I put up my extension , It was a cold roof because of the design I wanted. I used foil back pb and foil taped all the underside of the joists to the foilbacked Kingspan so there could be very little chance of any moist air penetrating. Redbrick vents to the front and proprietary vent escape vents to the rear. Hmmmm, forgot about the dead spaces though, gulp ! That said, ten years in and no problems as yet.

Thank you : )

Really interesting explanation. Jaw on the floor over the 120mm issue. One more brick course on the parapet should sort that out.

Thanks so much, just about to build a warm roof for my conservatory. Amazing to see how literally none of these "kits" do not include the ventilation for the cold roof.

I did my flat roof on my lounge 15 years ago. Plaster board, fibreglass, OSB and felt. No sweating, no damp, no problems. Still as good as the day I did it. I can't help but think that a lot of this is snake oil and more money for the men in suits. Great explanation Roger, as always.

Nice one...

I built a garage extension where I didn’t have the height for a warm roof or the joist depth to achieve the required R-Value with venting, so I used Closed Cell Spray Foam. It is allowable under the Canadian Building Code for use in unvented roofs because it acts as a vapour barrier. Pricey though.

crazy how the neighbours would be annoyed if the roof was 120mm higher... I would NEVER EVER EVER be that kind of neighbour. Why would they object to 120mm? What difference will 120mm make to them? Crazy! Anyway, thanks for the video! Very helpful

Built an extension on my house under the new cold roof insulation regulations, resulting in a permanently cold room, took the roof off 18 months later and made it a warm roof, now have a lovely warm room.

👍👌 Good video. Thanks, 👍

Good video Roger. I do a bit of GRP roofing works but our boss gets us to put 100mm on top and 50mm to the under side. When I asked about vapour barrier he said with this system you don't need one.

I used the 25mm multilayer foil insulation for a warm roof, supposedly equivalent to 225mm of fibre insulation, but adds no more than 40mm with the counter battens. It all seemed to work well. I'm planning an orangery type extension on the house I'm buying.

Great video Roger. I used to work at Rose Builders in Colchester and I did actually talk with Dillon on the phone about a possible collaboration a couple of years ago. I now work for myself in Brighton. I always prefer a warm deck roof, avoids any possibility of cold bridging through the joists and allows clear way for any penetrations in the ceiling, downlights, speakers etc. A parapet wall around the perimeter is the nicest look to hide the build up. Keep up the great work. I have a nice project starting in a couple of months. Would be great if you came down to do some filming. Regards. Dave Howells.

I'm surprised the neighbour is even aware of the 'options'. This is what was granted permission, these are the plans and dimensions, and this is what is getting built!

food for thought. i have two flat roof extensions. both had no air space, both rotted. hopefully the roofer done it right this time. i have edpm roof covers on now.

Good vid Roger. RIP Sean Lock. 😞

Warm or cold roof, always avoid moist getting in the construction from the warm side of the construction, Make a 100% damp sealing above the plaster board.

Very good video Roger 👍 My questions 👇 So what is your recommendation for roof construction / insulation for - a warm & humid climate with cool air-conditioning inside - a warm, wet & hot climate with “humidity control with cool air-conditioning inside” - insulating concrete slab roof & concrete walls, in hot & wet climates with cool air-conditioning with water condensing on walls & ceiling What about MVHR, with humidity control, as an addition to air-conditioning Look forward to your reply. It may mean a whole new video, I suppose 👍

very good

I’m stuck with a cold roof on a extension on a grade 2 listed building. 50mm air gap, 100mm of insulation and then a vapour barrier before the finished ceiling is the system I’ve gone for. Then added extra ventilation on the facias, but the vapour shouldn’t get up into the void to start with.

Hi Roger, thanks for such a detailed explanation, I finally understand! We are building a cabin in our garden (for us to live in whilst we do our house renovation). The builder has done a cold roof, but not put OSB boards on top. He has a membrane directly above the joists (where the insulation will be), the battens, then our metal roofing will go on top of that. Im a little confused as I thought you would always have boards on top of the roof, but I guess this way you solve the issue of ventilation/allowing vapour to escape? For peace of mind can you confirm you dont need OSB boards on top? Thanks so much!

lol, perhaps should have told the neighbor "We can avoid putting unsightly shrooms on the roof, if we just build it a little higher!" ;-)

You remind me of Nicko McBrain of Iron Maiden :)) Great presentation, by the way! :)

Hi, Love your video, never watched others that actually put confidence in me. Can I ask a question? I am insulating (cold roof) my workshop but only have 65mm/2.5inch joists. I can either get 30mm or 40mm PIR leaving either a 25mm or 35mm gap for the ventilation. I have soffit vents all the way across and a open channel the other end for ait flow.. Would you go for the 30 or 40mm PIR? is 25mm air gap enough? thanks!

The GRP mushrooms cost the guts of 70 euro a piece here in ireland. We tend to use them sparingly.

What a great video these cold roofs are getting a pain sometimes height problems,vent problems,how much fall changes from place to place then hybrid roofs are coming more common to save height and also different ideas on what vapour barrier to use building inspectors say different things too

Really enjoy watching your videos and on a very steep learning curve as starting from pretty much zero. I am building a warm roof but feel like I need two layers of vapour barriers. My garden room will house tropical plants. It is heated and insulated with 50 to 100mm PIR depending on location. I need to protect the inside of the roof (OSB) from rising moisture and there will be quite a bit of it as I water plants in the room. What's the right solution? I have the Dupont Tyvek membrane and was thinking from inside to outside: Membrane over joists, OSB, PIR, OSB, membrane then finish with felt Hopes that makes sense and look fwd to your opinion. Warmest thanks Jerome

Ever thought about fitting cross battens running the opposite way to the joists,this creates a continuous air flow of 20mm. No need for mushroom vent. As long as you have.front and rear air soffit/ facia and abutment vents.

Apparently in the states they are specifying tissue based pir board insulation when used with a separate vapour barrier. All to do only allowing one vapour barrier. It's constantly changing.

Great explanation! In a conservatory where the roof is plastic and the beams are aluminium, as there’s no wood, would mould still be an issue in a cold roof scenario if you’re using something like recticel for the insulation, is the ventilation still as important?

Brilliantly explained 👍👍 mushroom vents will look rubbish though 😊 cant you just cross Batten above the joist with OSB board above to vent the roof ? This would rise it 2” though .

Great video. Can I ask if kingspan over the top floor ceiling will create moisture or will this be warm air on warm side of insulation? (this is a pitched roof loft so plenty of space above but we were wanting to put green loft boards over the kingspan also

Hmm. Well, when we build ships we pack the steel against with rockwool hard up. The main issue is stopping the air getting to the steel - or wood - to condense. Given that we have humidity levels at near 100% and a temperature difference of sometimes 90C between machinery rooms and the sea it works fine. I did a roof 12 years ago and used 100mm of Celotex foil backed and sealed it solid so no vapour could reach the OSB and then another 100mm of Rockwool to add even more insulation and fire proofing. No issues at all. As for the plasterboard - I used foil backed and fitted sealed downlighters.