Spray foam and lenders
Spray foam continues across the party line in the loft. What fire and moisture separation has that foam not been tested for?
The foam has not been tested for fire separation or for moisture separation at the party line. Spray foam continues across the party line in the loft, so the visible barrier between the two roofs is interrupted or covered by the foam. The survey can record that continuity. It has not fire-tested the party wall, has not sampled the foam, and has not shown that moisture can or cannot cross. A home survey does not carry out those tests. The separation the party wall was there to provide has not been demonstrated once the foam runs through.
Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.
What is the fuller explanation?
Party walls in lofts are often a block or brick leaf that should be seen closing the roof space between neighbours. Foam sprayed across that line hides the leaf and can link the two voids. Whether that creates a fire path or a moisture path is exactly what was not tested. The surveyor should describe the foam crossing and the fact the wall head could not be confirmed clear. They should not invent a fire rating or a dryness certificate.
Tell the solicitor the foam crosses the party line, and ask what the lease or the titles say about the party wall if this is a divided building. Raise the fire and moisture question with a specialist who can see the wall head, not with a reinterpretation of the survey. Inform the lender in the same plain words. Do not scrape the foam away yourself to peek. The survey has flagged an untested separation.
What should you ask your surveyor?
- Did the foam run across the party line, and was the wall head hidden?
- Which fire or moisture test was not done at that line?
- Have you avoided giving the party wall a pass because the loft looked tidy?
What are the typical next steps?
- Record that spray foam crosses the party line and was not tested.
- Do not claim a fire or moisture separation that was not demonstrated.
- Ask a specialist to consider the wall head, and tell the solicitor.
Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.
Also asked about this
If the neighbour's loft has no foam, is your side cleared?
No. The neighbour's roof is theirs. Foam on your side that crosses the line is still untested for fire and moisture separation. Their bare rafters do not test your party line. Your party line remains untested even with their roof bare.
Does a blockwork line glimpsed in one place prove the whole leaf?
A glimpse is only a glimpse. It does not show the leaf wherever foam covers it, and it is not a fire test or a moisture test. The survey has not demonstrated separation along the run. The crossing foam is still untested.