Thanks for your help - the insulation was boards that went in between the joints. On top of the boards went the felt and then on top of the felt the batoning and then the tiles.
The insulation had silver stuff on top if that is any help lol! and I think the roof plaster boards could have...
I know this must have been covered to death, but wondered if anyone had any ideas. We have recently had a 3 metre extension across the back of our 1960s semi detached house. It has a pitched tiled roof with two velux windows in and vents at the bottom of the roof behind and just above the...