Filling gaps between joists and a party wall (Victorian terrace)

12 May 2022
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United Kingdom

We live a late Victorian terrace property with shared floor joists between ours and our neighbours. There are large gaps in the party wall that the joists pass through. There are big gaps between the wall itself and the joists (between 1" and 4") and we're getting a lot of the neighbours smoke into our kid's bedroom.

As a short term fix I'm thinking I could use expanding foam to fill the gaps and block out at least some of the smoke.

My concern is how much pressure is expanding foam able to exert on the surrounding brick and mortar. Could it , theoretically cause damage to the party wall itself - which is already in a very poor state. Lots of loose mortar, cracked and slipped brick work.

My other thought was whether to seal the floors instead. Perhaps use a membrane under the joists, then a later of mineral wool then a top later of membrane, perhaps running behind the skirting.

This sort of thing:


The floorboards are gappy but there's carpet and underlay over the top. Smoke is still seeping through. It's pretty unpleasant.

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I'm afraid I can't see your image.
I have had exactly the same problem in my Victorian terrace.
Although as well as the funny 'smoke' smell from next door, rats were coming through as well! :confused:
Gaps were filled with wire wool and expanding foam.
So far, no rats, but the smell has found a way through to a different part of the house :mad:

If you can, fill the gaps with foam and seal the floorboards! :)
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You need to clean dust, cobwebs etc out first, a small brush and powerful builders vac will do it

You can get a pink fire-resistant grade of foam which I think is worthwhile. Spray water first to help it grip and set.

If the gaps are bad you can pack mortar into them first, this will also reduce noise and keep out rodents.

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