Jake Cole

Hi Steve, Yes, I would probably go for a warm roof next time height allowing. It's a self build, no one else involved. I think I can get the cold roof to work. The screen shot below is what I'm going to do. Breather membrane will go between the rafter raisers and counter batten. Tin will go on as the top and final layer. The design below is what Steve Roofer recommends if working with a cold roof (cross and through ventilation). Cheers, Jake

Cheers Temp, I was expecting to raise the rafters even without OSB as the instructions say to fit membrane with a 10-15mm sag that acts as a drainage channel. That would leave 5mm or less in some places. Might be fine and I'd much rather not have to raise the raters but I'd be concerned that there would be unwanted moisture build up. I wish I knew for sure but I guess one must prepare for the worst.

Thanks @Iceverge, Appreciate some confirmation that it will be OK.

Hi RedBeard, this is my design, no one else involved, just a cacophony of things I've read and researched. I've also already bought the 9mm OSB that I was going to use for roof but that can be used for other things. This would be the build layers with no OSB: 12mm ply Vapour control layer 170mm rafter filled with 150mm PIR board 25mm batten on top of rafter to increase air gap Breather membrane 2x2 counter battens (so I can use 32mm roofing screws and not puncture the membrane unnecessarily). Box profile roofing

Hi Redbeard, thanks for your thoughts on this. RE venting, I plan to leave a 25mm gap on fascia and eaves with insect mesh all the way along. I could not add more insulation for thermal bridging due to budget - not ideal I know. And I've built too much to take down the ply now. What are your thoughts on the need for OSB? I can't see it being much of an insulator. Most people I've asked say it's a structural anti-racking measure, but with the counter battens and 12mm ply ceiling ply, I can imagine it being pretty rigid without the OSB on top of rafters. If I batten at 400mm centres, with box profile roofing, it should be OK to walk on. Thoughts on this appreciated. Cheers, Jake

Looking for some advice on roofing if I may: I’m building a cabin with cold roof in SW UK and concerned about the air gap between insulation and OSB deck. The roof comprises (inside to outside): 12mm Q mark plywood Thick vapour barrier (black DPM) that is fitted best I could but without butyl tape to seal screw holes and stapler holes. 170mm deep rafter filled with 150mm PIR insulation which only gives me a 20mm air gap (50mm is recommended building regs). I messed up the materials order. That’s where I’ve paused building. Roof is 10 degrees single pitch roof Spans 4.2 meters I’ve already ordered 32/1000mm box profile metal roofing sheets High usage holiday cabin I can see 3 options going forward: A) No OSB on top of rafters - just membrane, counter battens then metal roofing Q) is this weather proof enough? Warm enough? Too much airflow? B) OSB fixed to rafters (20mm air gap), breather membrane, cross batten then metal box profile roofing. Gaps on front fascia and eaves for airflow. Q) enough airflow? 50mm is most people's recommendation. C) option B but with battens on top of rafters to lift OSB and increase air flow (cross and through ventilation) Q) is this too much airflow?) Any advice or thoughts much appreciated. I know cold roofs are prone to moisture build up so I want to get this right. Cheers, Jake