I’m trying to plan ahead, as my timber frame arrives in a couple of months time.    The architect has specified a 50mm layer of EWI over the timber frame. He originally had a wall make up of 145mm full fill frame (PIR), with an external OSB layer, a breathable membrane, the additional 50mm of polystyrene EWI insulation, then battens, render board and render.   Having read a couple of blogs and posts here was wondering if I could simply use a 50mm thick layer of Rockwool fixed