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Showing results for tags 'bitumous membrane'.
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The builder is taking a rest... I've lost trust and am checking everything as it's all down to me now.. The rafters are 200mm. The original spec of the vaulted being was 200mm of sheeps wool, BUT we had to then change to F1 bituminous roofing membrane, non breathable, because of the bats and so was encouraged to change to PIR 150mm and a 50mm gap. Fair enough. However, I need to understand the detailing. On the SE diagram the steels are outside the thermal envelope, except for the one resting on the internal wall. (NB the vaulted ceiling will be the whole area, the diagram is slightly wrong as the design was amended, it seems to me that the vertical steel could go in or out of the thermal envelope). See photo: the steel is bolted to the wooden ‘beam’ of the roof ridge. This means non breathable membrane stops at the top there, so the gap is not contiguous with the ventilation things in the ridge tile. Unless I’m missing something, there’s an 50mm air gap but no actual air circulation. There’s nowhere for the air to be drawn in at the top. Surely non breathable membrane and 'plastic' insulation are a potential problem, even if there is a vapour barrier in the plaster board? I feel it needs air to be drawn over it somehow and not being able to inspect it bothers me. Do I need to change tack and think of a breathable house as its a conversion with all the associated compromises? Steel detail.pdf Steel in situ.pdf
