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Should we insulate a damp bathroom that already has exterior render?

Posted by Jonathan , on Wed 07 Feb 2018 08:26pm

Our Victorian mid-terrace has a problem with condensation in the downstairs bathroom. It's a solid wall brick extension (30s/40s?) so the walls get icy cold in Winter and it is impossible to heat. The cold walls (on 2 sides) mean we suffer heavily from shower steam condensing, ruing the decor and causing mould. I'm exploring options for insulating and improving the room. Ideally I'd like to use internal insulation because it's cheaper than external insulation even if it means going back to brick to get rid of the damaged plasterwork/old tiling etc. I was looking at replacing the extractor with a more powerful model, then lining the walls with waterproof insulated tile backer boards, with floor-to-ceiling tiles to the face. However I've been told by a friend that we should be careful as the exterior of the walls are completely rendered and we risk trapping moisture by not allowing the walls to breathe. Is this advice correct or can we somehow safely insulate the bathroom internally? I think that external insulation is likely to be out of our price range.

Jeremy Griffin

Fri 09 Feb 2018 10:42pm

Hi John you should Thoroseal the walls first up to 1 meter high - this height as rising damp will only rise 900mm due to gravity - once two coats of Thoroseal are applied batton off the walls with 4x2 timber - then insulate between the 4x2 with 100mm Double R insulation. fix a membrane we use 1200 guage over the whole wall and finally plasterboard it - this will give you a warm and damp free wall hope that helps regards Jeremy (Griffin Builders)

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