I am contemplating turning my loft into a cinema room. My loft is a 'L' shape being 9m x 10m x 5m in lengths. My first objective is to seal and insulate the roof area. I was thinking of getting in a company like www.warmroof.co.uk to sprayseal the roof area with foam but quotes of close to £5,000 are putting me off. If I am to go the DIY route and insulate the roof myself what do I need to do? I can attach foil backed plasterboard from wickes to the rafters but I don't know what I need between the foil back of the plasterboard and the tile in the roof. Any suggestions will be much appreciated.