Plasterboard over insulation leaving a void

[mickthetree]

Hi there
Insulating our extension with 150mm foil backed boards between the rafters, but due to some obstructions they will stick out past the rafters. We then plan on screwing 50mm insulation backed plasterboard over this. There will therefore be a void where the rafters are. Does this need to be filled? Quick sketch of a cross section to hopefully help explain the above.

 

[foxhole]

You cut around obstruction. ? So no voids

 

[mickthetree]

yeah my drawing probably doesn't explain it entirely. They are actually trusses rather than just plain rafters and the cross bracing that passes through them is quite substantial.

Hopefully this helps