50mm PIR across rafters?

[23vc]

can I screw plasterboard over 50mm celotex using 75mm drywall screws, ie is 25mm into the rafter enough of a fixing? Pretty sure I’ve done it before but can’t remember

 

[Nige F]

12mm board ? that'll give 12 into the joist - should be OK - use plenty of screws

 

[23vc]

Oops Yes sorry 12mm into rafter, thanks

 

[Ian H]

I used 100mm ones from Toolstation.

 

[tomfe]

12mm is not enough, get 100mm or you risk them popping out.

 

[^woody^]

Of course you can do it, but I suspect that is not the question.

12mm in to a rafter is not enough, and whilst 25mm is the minimum for a board fixed direct to timber, with the 50mm insulation it will still allow a lot of flexing and reduced bracing of the rafters by the boards. Probably 40-50mm fixing would be better.

 

[23vc]

Thanks all, I’ll get longer screws

 

[noseall]

We use 100mm, standard. Arm aches after though.
Vaulted ceilings eh.