I am currently finishing off a flat roof dormer internally. The flat roof deck has been constructed using Kingspan roof deck on top of 150mm deep joists. I have some 90mm thick insulation left over from constructing the timber walls and cheeck of the dormer. Can anyone tell me if it is ok to install this 90mm insulation between the joists beneath the Kingspan deck insulation. If it is possible should i push the insulation up to touch the deck insulation or should i leave the 50mm gap between the two? Not sure if this would lead to any condensation problems?