January 17, 2015
Since Trim deck and Clip lock roofing have flat and wide troughs, the flashing supplied with the VELUX skylight can not be used.The most reliable way is using a custom flashing and a so called dry pan.
A dry pan is a flashing that attaches to the top of the custom flashing of the VELUX unit and goes all the way up to the ridge cap of the roof.
As water runs down the trough of the sheet it would hit the back of the skylight and build up there. The dry pan flashing acts like a diverter which prevents the water channeling in the trough and guides it around the skylight and off to the sides minimising the build up and pressure on the back of the window.