Air tight flashing should be secured internally, to form a barrier against warm and humid air, as any moisture on the surface of the insulation greatly reduces its thermal insulation properties. For this reason, to avoid any air gaps the roof window opening has an XDS air tight flashing. This ensures a flush fit between roof window and sheeting. The sheeting is pushed into a groove specifically made in the window’s frame. The air tight flashing is made of polythene.
The flashing should be chosen in accordance with the size of the window.
