Attach stud wall ceiling plate to plasterboard?

[simplyben]

I am building a stud wall on a mezzanine floor which has a plasterboarded and painted vaulted ceiling. Where the wall needs to go I can't find any joists through the plasterboard to attach the ceiling plate so was wondering if I could just attach the ceiling plate to the plasterboarded with some heavy duty fixings.

Would that be ok or are there any other things I could try?

 

[oldbutnotdead]

It'll be a bit wobbly and noise transmission may be excessive. Have you tried a stud finder on the ceiling? Oh hang on, vaulted ceiling so the boards are fixed to the rafters...which probably run parallel to your proposed wall. And potentially insulation between rafters and plasterboard. If the rafters are parallel to proposed wall you could cut into the plasterboard and insert noggins (but that may compromise any insulation between/under the rafters).
Or fix some inch ply to the 2 rafters nearest your wall (through the pb/insulation)

 

[simplyben]

Thanks @oldbutnotdead
I've found the rafters and you're right, proposed wall runs between them. Think I should be able to get some noggins in there but if not, will go with your ply suggestion.