Hi I'm having a workshop built. Standard construction for Scotland, which is timber kit (CLS timber and OSB ply) then external superstructure of 100mm blockwork and render. 500mm gap between the blockwork and kit. Concrete floor, no heating (possibly an oil-filled radiator when it's brass monkey weather). Between the CLS uprights I'm going to install 70mm PIR board, leaving a 20mm gap at the back between the boards and the OSB. The ceiling will have 100mm boards between the trusses and a cold roof. My question: when I sheet the walls and the ceiling, should I use just normal 12.5mm gyproc or should I use the foil-backed? I know that the foil is primarily a vapour barrier, not a thermal barrier. All walls are external. Many thanks Jim
I assume you mean 50mm gap not 500? I’d use foilback on the ceiling and staple visqueen around all the walls, can use normal board then, though for a workshop I would have thought you’d want to line the walls with ply to be able to fix to?
Many thanks, yes 50mm. Thought about ply on the walls but with 600mm-centre studs I'll fix onto those where I need to. PLus, we're getting a new kitchen so the old units will be going on the workshop. Without visqueen, would you use foil-backed on the walls too?
Yeah, but weigh up the cost first. You’ve obviously got to be fairly neat with your plasterboarding when using foilback, as big gaps between boards defeat the object of using it as a barrier. You'd be better off in my opinion tacking visqueen to the studs, then fixing battens on top of the studs giving you a gap to run cables and pipes, then board over the battens. You could run the services in your 20mm gap between face of stud and PIR board but it’s not ideal, as you’d have to drill and notch the studs to accommodate them. Provided you want the services hidden, of course.
Fair points, thanks. I'm currently planning to run cables behind the PIR boards - 70mm PIR and 95mm CLS studs should give me enough. But I'll look into the visqueen in more details. Thanks again Jim