Please note no ventilation is required with this product. Permo air is the most breathable air open low resistance underlay on the market. It is the ideal solution where there is a high risk of condensation forming in the roof space. Features Air open & vapour permeable. Over 13% more breathable than any other air open underlay on the market. Lowest vapour resistance of all breathable membranes. Being both air open & vapour permeable further minimises the risk of condensation forming, particularly during the drying out period of a building. No ventilation required. Hydrophobically treated. Type LR underlay. Strong 3 layer material. 15 year guarantee. Recyclable. UV stable for 4 months. Batten spacing 350mm. Superior nail tear strength. Suitable Cold and warm roof applications.