In article , Fred
writes
On Sun, 25 Jul 2010 01:05:42 -0700 (PDT), andrew
wrote:

I would have used an insulated plasterboard - something like the Knauf
Thermal Laminate Plus at 27mm total thickness.

That would have been ideal, what a shame I didn't know about it when I
began!

I'll have to phone around to see who stocks 6mm plasterboard tomorrow.
I think only Lafarge make it.

It hardly seems worth the effort to save 3mm.

You could face the insulation with 3mm ply and finish it as you had
planned for the PB, either paint or paper.

If you decide to paint it you can leave it looking like wood or fill the
grain with board filler or even polyfilla to leave a plaster smooth
finish that can be primed then emulsioned. In the latter case it's not a
skim coat you are applying, it is just enough to fill the grain so is
nominally zero thickness.

You could put thinner insulation in the reveals, it would make little
difference to the overall heat loss as the area involved is small but
could help avoid local condensation. To avoid buying a full sheet of
thinner stuff I have sawn small lengths of PIR foam in half depth wise
but you wouldn't want to do a lot of it. You could use a layer or 2 of
polystyrene tiles instead of PIR with some loss in efficacy but I don't
think that's a big issue.
--
fred
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