Fixing insulated plasterboard to vaulted ceiling

[Mark0395]

I’m currently installing lats to attach my insulated plasterboard to and wondered what spacings I should use.
For contexts I have under-boarded the rafters with 100mm insulation. Now attaching lats (1x2) to the rafters through the insulation with 200mm screws.
The insulated plasterboard is 42.5mm.
I have currently gone with 600mm centres but wasn’t sure if that was okay. If noggins are needed what spacing. Or should I go for a smaller spacing between lats

 

[cdbe]

600 will be fine, it's very rigid compared to separates.

200mm screws a bit long for 125mm thickness, would probably do the lot if you binned the battens.

 

[Mark0395]

it’s an old barn so the rafters are twisted and bent. The 120mm screws I had to start with didn’t always hit the rafters through the 100mm insulating. Thanks for the help!