I have just insulated my dormer bungalow using Quinn insulated I have 75mm on top of ceiling timbers and 75 inbetween and 50mm on the slopping bit and I want to put 50mm it insulated plasterboard on it but wanted to know the best options I have been told by quin the aslong as the boards are tight up the vapour Barrier is ok would it be a option to put extra inbetween the 2 50s sorry if this has been coverd before