On Tue, 5 Jul 2011 13:35:42 +0100, TheScullster wrote:

If it was me, I'd simply set a 35mm metal back box into the
existing
wall so that it'll sit flush with (or slightly behind) the front
face
of the plasterboard when it's fitted.

That was my first thought - I like metal boxes screwed to something
solid!

So do it but the times I've used a drylining box on plasterboard the
fix is firm enough but I've always tried to as close to a stud as
possible rather than in the middle of span. The noise as the whole
wall acts a sound board as you plug/unplug/switch is another matter.

But that would cause a cold bridge to the solid/cold/damp outside
wall.

I'm wondereding how the spark is going to deal with fixing boxes to
plasterboard with 50mm of kingspan bonded on the back and running
cables to them behind the 8x4 sheets...

--
Cheers
Dave.