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Insulation boards on damp walls?

Postby drewster » Tue Dec 27, 2022 9:17 am


We are refurbishing our house and have been advised by an architect friend to put insulation boards on all exterior walls - it's a cold house. I'm concerned this will trap damp within them though and reduce breathability.

The house is an Edwardian semi with pebbledash - i don't think the damp we can detect (significant) is rising. Though i can't find articles saying so exactly, I suspect it could be shot render trapping damp from rain and/or poor drainage and hampered air bricks.

If we put insulated plasterboard up, will this trap the damp within the walls? And so what if we do?! And i assume that insulated plasterboard will effectively be watertight? Will it allow the walls to breathe at all?

I've googled compatibility but can only see articles relating to exterior insulation.

Also, our architect friend recommends prohibitively expensive 65mm insulation board to meet new building standards; this would also make the stairs very narrow. Would we be best stripping walls of all plaster then dotting and dabbing on the exposed brick to "gain" 30mm of space and/or breathability?

Many thanks.
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Simply Build It

Postby stoneyboy » Sat Dec 31, 2022 11:17 pm

Hi drewster,
Sealing your internal walls with insulated plasterboard will trap moisture and will make the walls wetter as internal moisture is attracted to the colder external walls.
Suggest you coat the rendered walls externally with a waterproof paint, instal dehumidifers to remove internal dampness and extract moisture from all moisture generating rooms.
It will probably take one summer to dry out the house internally.
Regards S
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