In short
Cavity walls stay dry because the gap stops rain crossing from the outer leaf to the inner one. When the fill gets wet, whether from driving rain on an exposed wall, a leaking gutter or debris in the cavity, it carries that water across and the inside wall goes damp in patches. The fix is to find why the fill is wet, and where the wall or the exposure was never suitable, to take the fill out.
This is a job for our Cavity wall insulation removal service.
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How a filled cavity goes wrong
A cavity wall is two skins of brick with a gap between them. Rain soaks the outer skin, runs down the inside of it and out through the weep holes, and never reaches the inner skin. Fill the gap and that only holds if the fill stays dry. On a sheltered wall in good order it usually does. On a wall facing the weather, with cracked render, soft pointing, or a gutter that has been overflowing down it for years, the fill soaks up water like a sponge and holds it against the inner leaf. The government's own consumer guide on cavity wall insulation problems exists because this has happened in enough homes to need one.
Norfolk and the Suffolk coast have a lot of exposed elevations, and we see the same pattern from King's Lynn round to Great Yarmouth: the damp is on the wall that faces the wind, and nowhere else.
How to tell it is the fill
- It started after the installation, sometimes years after, as the fill slowly saturated.
- It is in patches, not a tide mark. Rising damp leaves a level line near the floor. Fill-related damp is scattered up the wall, often worse under windows and near the corners where the fill slumped.
- It is on the exposed side. Walk round the house. If only the weather-facing wall is affected, that is the strongest clue.
- Cold spots and mould. Where the fill has slumped and left voids, the wall above is colder than the rest and condensation forms there.
Who pays
Before anything else, find the paperwork. The government guide says to go to the installer first, and if they have gone or will not respond, to the guarantee provider. Most installations carry a CIGA guarantee, which CIGA describe as an independent 25-year guarantee for work by registered installers, and it has a process for registering a concern. Do not sign up with a claims company that knocks on the door; the same guide warns about them specifically.
When extraction is the right answer
Extraction is not automatic. If the fill is wet because of a leaking gutter or a cracked render band, fixing the outside and letting the wall dry may be enough. Where the wall was never suitable, because of its exposure, the width of the cavity, or the condition of the brickwork, no amount of maintenance will keep the fill dry and it has to come out.
When we extract, we open the outer leaf at intervals, draw the fill out with suction and rods, check the cavity is clear with a camera, and then make the brickwork good and repoint the holes to match. You get the photographs from the camera, because a surveyor or a buyer will want to see the cavity is empty rather than take our word for it.
