Dormer roof insulation (warm deck) 

this is what i noticed first off.

That's what I'm sayin

That's what I'm sayin

The aluminum foil covering the rigid insulation board is a vapour barrier.

@@edmarferreirajunior724 LOOOOOOL no its is 10000% not! this will not pass building control. Also the screws should be in a plastic sleeve to stop bridging. Nice looking but in 1 year the roof will be rotten!!!

Agree u havent put a vapour barrier in u need this warm deck roof. Also the screws u need a special fixing which the screw goes into because of thermal bridging.

@@harrysingh1145 Zinc screws have a very negligible thermal conductivity, besides will allow you to run the EPDM smoothly with no bumps left by the SureFast tube washer.

25mm expansion???

Thanks for the support mate. I agree with everything you've said mate, all your observations are spot on. Thankfully it was very dry and stable when we installed, and the insulation was nice and dry too, but yes, a vapour barrier would have been best. I know that the foil facing of insulation acts as a vapour barrier, but the membrane is different and necessary. On my more recent builds I've done that.

That's a good point. I think there's also an element of not necessarily knowing or understanding the differences between them. If people knew the difference properly, I suspect they would opt for a warm roof in every situation that it's possible to do them.

In terms of loss of head height, it's actually negligible (40-80mm) because on a "cold roof" where the insulation is between the rafters, you need them to be deeper in order to get the same U-value. Because of this you end up spending more time working on them (notching to install and cutting insulation to fit between) and you also have less space as a service void to run your cables and lights. I think that the small loss of head height is definitely offset by speed and ease and the definite increase in insulation levels.

@@OfficeBoyBuilder cheers you explain things very well. Loving this one.

I'm still insulating my cold deck dormer conversion (6.5x5.5m) and my main worry is condensation. I've continuous soffit ventilation across the front face and both cheeks, a 50mm air gap above the 100mm insulation, foam filled any tiny gap due to rafters twisted or a mm or two out, then made sure all wiring was tacked above the 100mm insulation which I then cut a square hole in, fitted Thermahood for 20 spot lights, back filled those with more foam and capped them with a 30mm PIR layer AND THEN under drawn all of that with a 30mm PIR layer and taped all the seams. Building regs also requires a further vapour control barrier so yes, cold decks are an absolute hassle because if you have any breach in your PIR for spots etc, you will have ineffective insulation, risk condensation build up in the structural timber. I'm not a builder, I just learnt all this in a few weeks and redid the whole job I paid professionals to do. It's crazy how many joiners and roofers don't understand their own trade. If I'd have known before undertaking the conversion, I'd have gone for a warm roof too. Cold deck roofs are apparently banned by building control in Scotland? I can understand why. They need to be installed properly and sadly, a lot of traders don't achieve this.

Mate you've literally written chapter and verse what I've done on my loft...! It's a whole ordeal, Vs the simplicity and speed of a warm deck! Ps. Great work going to all that effort. 99% of tradies wouldn't, and 99% of home DIYers wouldn't know to.

@@OfficeBoyBuilder I think a lot of home DIYers do know what to do thanks to channels like steve roofer and others.

As far as I know, there haven't been any issues! The building company I was working for at the time offer a 10 year guarantee on their roofs, so if anything did crop up, it would get fixed.

Yes you're right, I pointed that out to the main contractor that I was subbing for, and he said they never built them like that and it wasn't needed 🙄

@@OfficeBoyBuilder what did it say on your plans or what his the building regs

Building regs vs. what gets signed off are two different things sometimes (sadly!). I didn't see the specifications as I was a subcontracting carpenter.

@@OfficeBoyBuilder Totally wrong.

Occasionally the nails hit a knot in the timbers and get skewed off! It's not deliberately shot at an angle in this instance 🤣

So is the osb on top needed? Or can you also choose to use the rubber roofing directly on top of the insulation?

OSB on top is absolutely needed. Ideally you'd have thermally broken screws to fix it down. But for the structural strength it is most definitely required.

Not sure I fully understand the question...? It's 1200mm thick, and comes in various sheet sizes, but we bought 8x4 foot sheets. In terms of U-values etc. You'd need to check the website because they're quite specific about the conditions needed in order to meet those specs.

@@OfficeBoyBuilder bloody ell 1200mm thick eh, BC must be murder where you are🤣! no worries mate and I can see its 120mm thk quinn therm your using

There are many different ways to do things, so it's not totally wrong...why would you need to ventilate a warm roof? According to the NBS a warm roof doesn't need ventilating...

@@OfficeBoyBuilder Because you have not actually constructed a warm roof. The correct build up for a warm flat roof is as I have stated. I have done 1000s of m2 over the last 36 years and I am qualified in flat roofing and a former Fellow of the Institute of Roofing. Check any major flat roof manufacturers website and they show construction details to back this up.

@@garychue7343 that does make a lot of sense, doesn't seem any benefit putting wood into a space where it can rot. 'If it can't dry it will die!'

@Gary Chue... I'm planning a warm roof project in my garden and all the info I have seen on the planning portals and building regs seem to say nearly the same as you... 18mm osb3 over joists, a good vapour barrier, insulation... and then another layer of 18mm osb3 before putting on the final waterproof layer. Whats the reason/benefit of leaving out the top layer of 18mm osb3 per your suggestion? Also.... one question.... there are gaps between the joists on top of which the warm roof is built-up. What happens with these gaps? Are they blocked and insulated or are they left for air to circulate up and out through the fascia and soffit?

@@jp6975 You can put another OSB layer on top. Some membranes eg fibreglass would need this in place. You can't fibreglass straight onto PIR! Ideally, use thermally broken fixings ie tube washers, along with a vapour barrier and you'll have a good system. Regards to the space in between the joist, do not ventilate- you don't want cold air between the insulation and your living space! But remember to insulate behind the fascia detail (between the rafters) as you'll have a big cold spot there otherwise!