I'm drawing up building regs for flat roof construction, and had no idea what the difference was between warm and cold deck. Your explanation was simple and uncomplicated. Thank you once again.

The best warm & cold roof video. Thanks

thanks steve - your warm and cold roof videos have been very helpful for me (as part of my surveying qualification). have subscribed to your channel so look forward to other videos in the future.

Great video, Steve. Thanks!

Actually it's becoming a Chartered Surveyor .. which I now am. Still enjoying all your content so thank you for your efforts in uploading them. Good sharing it with some of our assistant building surveyors. We're a firm in Hampshire but do works in London including specing and tendering jobs so good to know you're out there.

Thank you, very interesting and enlightening. Good use of Sketchup too.

thanks for the video clear and concise

So, it seems like a warm roof is really the best way to go. Better insulation, more cost effective and less disturbance to the interior of the home/building. I'm sold.

Thank you Steve, most informative. Its made my decision so much easier. Dave

Nice works Steve.

I understand the benefit of a warm roof but nobody talks of the expense of heating all that wood, the air between and possibly previous layers of roofing felt etc. It'd be interesting to see a thermal image of a ceiling under a warm roof an hour after the heating comes on. Going to have a look into how much heat / time, a specific quantity of wood takes to warm by 1 degrees. A lot of people only warm a room for a few hours a day which would make the problem worse.

Very informative video. Thanks.

Cheers Steve. Really great video.Wonder if you could help me with any advantages the roof types have when dealing with condensation risks?

Good video. However, you have not shown what happens on the the three ends with the fascia boards

Hi Steve, I’ve watched a lot about cold and flat roofs now. I’m making a shed with a flat roof and planning a typical cold roof construction with 150mm joists, bottom deck, 50mm services space, 50mm insulation, 50mm vent space and finally top deck. My question is - if I placed a vapour barrier on the underside of the insulation, as you would do with a warm roof, then could I just place the top beck onto the insulation, removing the need for a ventilation space? If not, why does this principle work with a warm roof and not a cold roof - ultimately, with the vapour barrier preventing moisture ever reaching the top deck. And if not, where does the moisture go when you have a warm roof with vapour barrier- surely it stays in the room?

Hello. Thank you for this excellent video. Can a cold roof be cost effectively be changed into a warm roof ? Thanks

Thanks for not showing the hot roof FLIR shots. That makes the whole video redundant. Usually in a comparison there is a comparison not just someones word for it.

thanks for reply

Hi Steve. I have a small extension (2.5 L X 3.6 W). The flat roof is shot to bits including the joists (genuinely horrendous I have pictures if you want to see). I have on both outer walls concrete block walls including the garden door wall and then the house wall is a brick wall. Can I resin fix wallplates on both external concrete block walls then run the joists across (including frame for flat roof light not lantern) or do I have to put wallplate on brick wall and door wall? I am going for the warm roof design. Thanks alot, James

I've a old flat roof that needs replacing. It's a cold roof but don't know if it's ventilated. Was going to get it done the same as it is now but after watching this a warm roof would be better. Trouble is it's 2 storey side extension flush with the front of the house and about half way front to back. The flat roof just sits under the house hip roof. The extra height would mean the house hip roof would need some adjusting, ie cutting of tiles/ hip etc. Would this be possible or should i stick to a cold construction...Thanks

If i decide to make a retrofit over an cold existing flat roof and transform it into a warm roof , would the vapour barrier still be effective if it goes over the existing felt ( it's in good condition ) and then the insulation ? Thank you

Is it possible to incorporate a skylight using warm roof construction

Kind of in depth. Simplified though..i understand this

Thanks what surveying course have you taken ?

How do you get over not having a big fascia

Yes but make sure you insulate the up-stands of the skylight or they may sweat

I am turning a 10'x24' screened porch attached to a 2 story 1875 built home, into a heated room. it has true cut 2x4 rafters that I was planning on sister joisting milled 2x8 to the existing non-milled 2x4 roof joists. The lower end is currently screened and I want to add 6" insulation in the ceiling leaving 1-1/2" air gap. How would you vent the top end of the porch roof …? This is in the North East (USA) where we have on average a foot of snow on the roof throughout the winter.

Hi Steve, I have watched your video on cold roof construction I know that the warm roof construction is better and easier and stop cold bridging, however I do not have a height problem with my extension and can only do a cold roof , do you have a video that reduces the chances of bridging on a cold roof and would it be better to use the better quality sticky vapour barrier. Thank you

Unless the area between the joist is air tight then warm roof construction is a waste of time, as an electrician I regularly fit downlights and find a howling cold draught coming out of the hole I've cut in the ceiling

Hi Steve, my builder is recommending a cold deck flat roof, howeve, he is adamant that ventilation should only be at the front of the extension all along the fascia, and does not need to be at the back, I've tried explaining, but he is saying that's the way he's done it for over 20 extensions, would very much appreciate your advice. Thanks in advance.

I'm looking to do a warm roof because I'm having big problems with condensation, I'm going over a fiberglass roof, will i have to take most of the rockwool out of the joists from the inside for the condensation problem to stop or could it be left there, PS I think there's too much rockwool in the joists anyway

What about the sides of the roof or joist how do you insulate them.

Hi Steve, if changing from a cold roof to warm roof is it OK to leave existing insulation between the joists? Second question if you want to be able to walk on the warm roof I take it you would overboard the insulation with OSB is this fitted with adhesive too? Many thanks Joe

Having watched many of your excellent videos, I decided on a cold roof because of thermal bridging issues. I must disagree with a comment made at the end of this video based on theoretical knowledge only i.e. no access to thermal imaging equipment. The joist hangers would still be a source of thermal bridging on a warm roof because the wall they are attached to is an external one. As hot goes to cold, the room heat would travel into the plasterboard, then the joists, then the joist hangers and then to the brick and then out to atmosphere. The house extension I have constructed has 150mm of XPS insulation in between the joists, 50mm of EPS insulation underneath the joists, an unvented 50mm air gap and then the plasterboard. There is also no thermal bridging from the block walls as they are all covered with 50mm EPS bonded to the wall and then bonded to the plasterboard with PU adhesive. In my opinion, this is about the only way you can cut thermal bridging to its minimum value with todays construction methods. Just as a FYI, I chose XPS because its LTTR (Long Term Thermal Resistance) figures remain fairly constant after decades of use whereas PIR boards e.g. Celotex, Kingspan etc start dropping from the day you buy them and start to match XPS/EPS after 5 years or so. In short, in less than a decade, your U values would NOT pass todays building regulations. On the plus side for XPS it has twice the compressive strength as PIR boards, not affected by water and is cheaper in the long run.

Seems that warm roofs are significantly better than cold roofs. If that is the case, is it also true that most of your clients opt for warm roofs? Or do they still mostly go for a cold roof?

I'm a smoker. I open the window even in the middle of winter.