Insulating inside Solid wall

16 Apr 2006
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United Kingdom
Hi ,
I need a little advice if possible. We are fitting an toilet under the airs of our 1930's detached house. The walls are single brick without cavity. I have removed all the plaster and down to bear brick now. The plaster had mostly blown on the one outside wall and where a cupboard had been fitted within the corner there was a little bit of mould from condensation.
So the one outside wall i would like to insulate from the inside if possible and then plaster the full space.

I have been looking at Duplex plasterboard.
What would be the best method for fixing? I understand we could batten out. If we batten wouldn't the wood also transfer any moisture?
We have a limited amount of space so would rather not reduce the room too much. Any direct experience with this?
Also should i just use an insulation board instead? Should as thermaline? Can this be dabbed?

There is no damp but believe there could be some condensation previously hence the small amount of mould. There was no air circulating in the cupboard tho.
An extract fan will also be fitted and will likely fit a humidity controlled timed fan out of precaution.
I hope to heat this space somewhat as well either electrically or buy a radiator.

Thanks in advance
Last edited:
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Use 25mm thick battens by 50mm wide, which are treated, then screw insulated plasterboard to them. IP is not the cheapest method, but it's the simplest. As it's a toilet, you won't need a humidity fan, just a timer fan.
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28 Jul 2015
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United Kingdom
I'd do similar to doggit, but I'd do the battens, then insulation (foiled both sides) on top, followed by plasterboard.
You get a vapour barrier with the foil, especially if you tape it, when joining boards. You don't get this with insulated plasterboard.
Down, side is it takes around 80mm off the floor space.

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