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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