Edward Thompson
Hi Yvonne it sounds like you are trying to add the membrane to a roof that is already slated!? To work properly the membrane is fitted underneath the tile lathe prior to fitting the slate, there is no point trying to retro fit the membrane as it will not work. Aslong as you leave a suitable gap ( 50mm recommended) between the insulation and the tiles to allow ventilation and prevent condensation you should be fine. Thanks. Ed.
