hi guys ive just took down the plasterboard on the ceiling of the extension due to building work and seems theres been a leak at some point and the rockwall 150mm seems to have held the water like a sponge anyway when the building works done i was thinking of using 75mm polystyrene sheets and foiled bubble stapled to the joists would you think this will be better than rockwall for thermal insulation as celetex is a bit out of my budget