Drylining exterior walls

[Lawrence Zarb]

I am going to dryline my 9 inch solid exterior conservatory walls, and was wondering whether I should use a vapour barrier behind the plasterboard?

[Patrick]

You need a vapour barrier to stop moist air from inside the house/conservatory travelling through the plasterboard and onto the external walls,where it will condense.

If you use dot 'n dab to fix the boards, you're almost certainly going to get damp patches on the wall that correspond to the dabs behind. Use either British Gypsum's Quickwall system or use pre-treated timber to mount the boards. If you do either of these you can then insulate the walls at the same time and do yourself a huge favour. I usually go for Kingspan 25mm boards, which, being foil backed have a VB included. You should also use foil backed plaster boards.

HTH

Patrick

[The Natural Philosopher]

Use foil backed plasterboard. That's good enough. If there is possibility of penetrating damp, arrange for an air gap behind insulation and some air bricking.

Best insulation is Celotex (Kingspan) that has its own vapour barrier built in, you wedge in between the studs with the inner faces level and a gap at the rear, and tape over the whole stud work and insulation joints with aluminium tape. This provides a completely impervious and draughtproof layer. You don't need foil backed board if you use this.

OTOH if the outer leaf is generally free of damp, and can dry outwards well enough, use fold backed board and simply pack the stud work with rock wool.

And empty gap is still not a bad insulator, if you are being cheap and cheerful.

[Lobster]

As it happens I'm doing exactly the above at the moment (remember I posted a query about it a few weeks ago?) - had the BCO round last week to check it all before I applied the plasterboard, and he told me specifically to fit a polythene vapour barrier over the studwork/Kingspan before I boarded over. I did query it but to no avail; anyway the cost/effort of complying wasn't worthwhile - I prefer to save any arguments with Building Control for the important ones!

David

[The Natural Philosopher]

Indeed. BCO is not equal to 'intelligent'

They don't always know the regs, and they don't always understand how to implement them.

stick the ruddy thing up to keep the bastard happy, and as you say, save the arguments for something really expensive.