Seledek aluminium roof flashings
Seldek flashings are ideal for twin wall flue penetrations through tiled, slated or shingled roofs. You use a Seldek flashing just like a traditional lead flashing. At the centre of the aluminium plate is a flexible EPDM collar which seals the flue pipe penetration and allows for some movement. Because of the EPDM collar you do not necessarily need a storm collar with a Seldek flashing. If your flue pipe has a seamed join in it then you do have to run a bead of silicone around the top of the collar, especially where the collar meets the seam. You should also run a bead of silicone up the seam to the top of the flue pipe to stop any water tracking down the seam of the flue pipe.
The dimension figures given here refer to the external diameter of the twin wall flue. Our workshop twin wall flue system has a wall thickness of 25mm on each side, so the external diameter is roughly 50mm more than the internal diameter. This means that, for example, our 125mm twin wall flue pipe has an external diameter of roughly 175mm so the suitable Seldek flashing is the SDA 102, 110-200MM.
If you are planning on running single skin flue through a roof (and its not the best idea - read more here) then the Seldek is not suitable as the epdm cannot take the high temperatures, you would need a Dektite High Temperature flashing