Larger gaps between (insulated) plasterboards

[akist]

I am using 37.5mm insulated plasterboard on the loft space which contains vaulted ceilings and dormer cheeks. It is secured with screws into the rafters/timber frames. The insulated plasterboard is 25mm rigid insulation glued onto a 12.5mm sheet of plasterboard. As I secure it onto the framework//rafters, there is a little bit of play. That is because there is 25mm of "soft" material in between the plasterboard and the timbers.

There are also some gaps (10mm+ in places) where two plasterboards meet, if they have not been cut perfectly. Those gaps are filled in with plasterboard adhesive. Is that a good practice?

 

[Wayners]

I put timber in on joints plus that will give you something to fill against.

Metal foam gun to fill the back 20mm then fill the joint to the surface if you have 10mm gaps