With a water vapour resistance of 0.03 MN/sg, Klober Permo® air is approved by the NHBC for use is cold roofs without ventilation at or near the ridge. The BBA-certified air-open underlay has consistently proved to be the most breathable available and in independent tests was at least 3 times better than the best performing vapour permeable underlays. This not only helps prevent condensation in the roof space during a building’s critical drying out period but in areas of complex roofs where ventilation is poor. Though there are only two air-open underlays currently available there are marked differences in performance between them.
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