VELUX ETL WK34 0000 Slate Flashing for Fixed Window Slate flashings - ETL VELUX provide a range of flashing options to suit your roof material. For standard installation heights install the brackets at the top and bottom of the frame at the red line level. Flashings for installing one roof window into slate up to 8mm thick. Not for interlocking slate. Roof pitch between 15 and 90. 10 year guarantee. Flashings VELUX flashings integrate with the roof covering to provide a weathertight finish around the window. They are compatible with virtually any type of roofing material, from standard covers such as slate and tiles through to corrugated sheeting or even thatch. Flashings are designed to sit under the roofing materials. The water from the roof is then collected in the built-in guttering system. The gutter overlaps a second section of the flashing to help the water flow smoothly down the side of the window.