Timber decay and woodworm
A new patio has buried an air brick that used to vent the floor void. What timber risk is that, and what rot has it not proved?
The risk is a floor void that no longer gets that air, and no rot has been proved. A new patio has buried an air brick that used to vent under the floor. The survey has recorded the buried vent. It has not seen the joists fail, has not found rot, and has not said the timber is decayed. Suspended timber floors rely on air bricks to keep the void from sitting still and damp. Covering one raises that risk. It does not, by itself, prove that any joist has rotted. The missing vent is the finding.
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?
Air bricks are the planned way moisture and stale air leave the space under the boards. A patio taken up over one of them blocks that opening, so the void behind it ventilates less, especially if it was the only brick on that side. Damp still air is the condition in which wet rot can start at joist ends and wall plates. 'Can start' is not 'has started'. The surveyor did not report opened boards or a probed joist end.
Ask the surveyor whether other air bricks on that void are still clear, and whether any timber was seen at all. Tell the solicitor the defect is a buried vent, not proved decay. A builder can lower the patio or duct the air brick back to open air, which is the ventilation, not a timber replacement. Do not let a timber-treatment quote assume rot the survey did not find. If the boards are to be lifted, that is a separate look.
What should you ask your surveyor?
- Which air brick has the patio buried, and are any others still open?
- Did you see any joist or wall plate in that void?
- Are you recording a lost vent rather than proved rot?
What are the typical next steps?
- Name the buried air brick as lost ventilation to the floor void.
- Do not treat it as proved rot in the timber.
- Restore a vent path before anyone specifies timber repairs.
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 boards spring, has the rot been found?
Not from spring alone. A springy board can be notched, undersized or loose. The survey has not proved rot from the buried air brick, and a lively floor is not that proof. The risk remains the lost vent. The report leaves the buried air brick where it is, without a second finding.
Does one remaining air brick on the far wall clear the void?
It shows some ventilation is left, which the survey can note if it saw it. It does not undo the buried brick, and it still does not prove or disprove rot in timber that was not seen. No extra conclusion about the buried air brick should be read into the wording.