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Insulation on old sandstone solid wall


I'm trying to insulate an old tenement top floor flat in Scotland. Most of the external walls have lath and plaster with a 50 to 70mm gap to let air circulate around the building (including inside my kitchen...). 

I wonder if I could use wood fiber boards directly on the stone around and below the windows. Sandstone is very porous, do you think this could still work? Which product would work best?

For the rest of the outside wall, I guess I have two options, remove wall paper and paint and stick fiber board on the plaster, before replastering with lime plaster and breathable paint. Could you advise on thickness and products needed?
The second option would be to remove lath and plaster, but then I would need to rebuild a structure to hold the insulation with a gap to allow the building to breath for the other flats. The benefit is that I could get more insulation.

Any thoughts welcome


Topic starter Posted : 13/03/2022 7:14 pm
Chris Brookman
Member Admin

Hi @aldo

You can insulate directly on to the masonry with wood fibre boards but I would not recommend using more than 60mm without reducing the amount of rain water soaking into the exterior. This can be done by rendering, cladding or using a facade impregnating cream.

The can find a spec for the insulation on this page -

I would definitely not try to use insulation over the studs/lath and plaster as you run the risk of getting high moisture levels within the cavity which then causes the decay of the battens. However, unless you have air bricks at the bottom of the wall which are allowing air into the cavity from the exterior, I doubt whether you fixing insulation directly to the walls will have any effect on the other flats in your block.

Hope that helps.

Posted : 14/03/2022 10:19 am

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