Cembrit's BBA Approved sheathing board, Windstopper Extreme, has a very low vapour transmission resistance, enabling moisture from inside the building to pass through. In consequence, insulation can be placed directly against the inner side of the board. The board resists both rot and fungal growth and can withstand considerable fluctuations in weather and climate conditions. Windstopper Extreme can be left exposed to the elements for up to 12 months before the final façade is installed.