Insulation Vapour Barrier

31 Aug 2009
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United Kingdom
We've got a 1930s house, and we've recently realised that there is just a single course of bricks between the hallway and the garage. We think that this is why we've never been able to get the hallway warm in the winter. We don't use the garage to keep a car in are so are happy to loose a bit of space in the garage to insulation.

I was going to put in 100mm slabs of insulation from Wickes, between 4x2 vertical studs 600mm apart and then just have a layer of plywood to finish, but I'm not sure which "side" of the insulation the vapour barrier needs to go.

Is it

Hallway - Bricks - Insulation - Vapour Barrier - Plywood


Hallway - Bricks - Vapour Barrier - Insulation - Plywood

Alternatively, I have seen that you can get Kingspan/Celotex urethane slabs. Would I be able to fix these straight to the wall and not need a vapour barrier at all? And if so, what do I use to fix them?

Is one method "better" than the other? Kingspan seems like it should be less faff and quicker but might end up being more expensive.

Dez :cool:
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Fix 25mm x 50mm tanalised battens (roofing lathe) to the garage wall.

Snug fit 25mm foil backed pir/pur foam board between the lathes. Seal the joints with foil tape.

Screw 75mm foil backed foam boards to the battens. Seal the joints with foil tape.

Screw ply through the inso' sheets and into the battens with some long screws.

Reg's would probably require you use 100mm across the lathes but 75mm will be an improvement. No need for vapour barrier.
Many thanks for the info. I've done some looking around, and the foam boards seem much more expensive that the equivalent "regular" insulation slabs. Apart from being easier as I won't need to worry about a vapour barrier, are the foam boards much more thermally efficient?

If budget determines that I have to stick with "regular" insulation, I've done some more reading that suggests that the vapour barrier goes on the warm side of the insulation, which would mean that I'd need:

warm hallway - bricks - vapour barrier - insulation - plywood - cold garage

Is that right? And if so, is there an easy way of fixing the barrier?

Many thanks again for the help so far....

Dez :cool:
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The foil backed boards are twice as efficient as the woolly stuff. The foil itself acts as the vapour barrier (hence the taping to seal joints)
Another easy way is to just staple up a massive sheet of polythene.

You could ditch the plywood and use insulation backed plasterboard. on the garage wall, solves all problems. Can be dot n dabbed or fixed to battens. You can always overlay this with thin ply for impact protection in the garage.

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