Wrong size plasterboard for studs and noggins - preventing cracks

I am boarding out a new loft and had to buy the smaller 1800mm x 900mm plasterboards as there was no way to get the larger boards up to the room.

However the builder (who completed the shell of the loft for me, while I am doing all internals) has built 400mm stud centres on walls, with noggins halfway up ie. designed for 2400mm x 1200mm plasterboards...even though he told me to order the smaller plasterboards as he never uses the larger ones!

There's Celotex in between the studs and also on top of the studs. Same for the flat and pitched roof - Celotex in between joists/rafters and another layer underneath them.

For the walls I'll be fitting the plasterboards horizontally in a brick pattern, which means short edges will be on studs but long edges will be unsupported. I am worried about cracks forming on these unsupported edges.

There's also no noggins in the pitched roof rafters and only one noggin in the middle of the flat roof joists (also all 400mm centres), which has 3.3m long ceiling joists.

Adding noggins in the walls/ceilings at this stage not really an option as insulation is already snuggly fitted, foamed edges etc.

My only thought is to use gripfill/drywall adhesive on any unsupported plasterboard edges (so they are glued to the Celotex), in both the walls and ceilings.

Would this prevent cracks?

Many thanks

 

To add, the plasterboards I have are all 12.5mm thick and all walls and ceilings will be skimmed

 

it’s not ideal and sounds like a bodge. just add more timbers if you can.
a loft is subject to more movement and temperature variations as it is , and most will invariably end up with a crack or two.
don’t compromise it by cutting corners.
all board edges should land on a timber.
better to use more boards than bodge it.