Variable performance of vapour permeable underlays prompted the NHBS and, ultimately, the BSI to require supporting high level ventilation for such products.
By contrast, air-open underlays may still be used unsupported and for roofs needing the highest standard of ventilation performance, Klober Permo® air offers an exceptional level of breathability. It provides the ideal solution where there is a high risk of condensation forming in the roofspace, particularly during the drying out period of new builds.
Permo air has a water vapour transmission sd-Value of 2736 g/m²/day and water vapour resistance as low as 0.03 MNs/g, both of which have been independently confirmed by the BRE. The hydrophobically treated underlay is BBA and IAB-certified for cold and warm roof application, has high tensile strength and offers exceptional nail tear resistance. It has also been used to upgrade countless historic buildings and is fully recyclable.