The variable performance of vapour permeable underlays ultimately led to the decision by the NHBC and BSI that only air-open membranes can now be used without supporting high-level ventilation.

For roofs needing the highest ventilation performance, Klober Permo air offers not just an exceptional level of breathability, with a water vapour transmission sd-Value of 2736 g/m2/day, but a water vapour resistance which has been independently confirmed to be as low as 0.03 MNs/g.

Permo air has been used to upgrade countless historic buildings and to provide unparalleled performance during the critical drying out period on new builds.

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