Timber decay and woodworm
Decking has been built over the air bricks and the underfloor void was not entered. What air path to the joists is covered?
The air path to the joists is covered by the decking. The deck has been built over the air bricks, and the underfloor void was not entered, so the survey has not shown a clear route for air and has not seen the timbers those bricks should ventilate. Air bricks only work if they stay open to the outside. A deck across them blocks that path. The inspection recorded the cover. It did not enter the void and it did not test the joists.
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?
A suspended timber floor needs air moving through the void so the joists are not left in still, damp space. Air bricks in the outer wall are the usual way in. Decking built over them can close the inlets on that side even while the boards look tidy from above. The surveyor can see the deck and the covered bricks. They cannot see the joist ends without going into the void, and this visit did not. The survey has not certified this deck and it has not measured airflow.
Ask a builder to restore a clear path for air, by altering the deck or by providing vents the deck does not cover, and have the void looked into before anyone calls the joists sound. Tell the solicitor the air bricks are under the deck and were not shown to be clear. Do not assume the floor is decaying, and do not assume it is dry. The survey has not entered it.
What should you ask your surveyor?
- Are the air bricks covered by the decking?
- Was the underfloor void left unentered?
- Is the air path to the joists therefore covered and unverified?
What are the typical next steps?
- Treat the deck as covering the air path to the joists.
- Ask a builder to restore ventilation the deck does not block.
- Have the void inspected before anyone calls the joists sound.
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 room above feels dry, are the joists ventilated?
Not shown. A dry-feeling room is not a view of the void, and the void was not entered. The air bricks are under the deck, so the path to the joists is covered. The survey has not seen the timbers and has not measured air movement. Comfort underfoot does not clear the covered inlets.
Can a few holes drilled in the deck replace a proper look?
Random holes cut in the deck would not be an inspection of the joists. The survey has not designed vents. The air path is covered and the void was not entered. A builder should restore a clear route, and someone needs to see the void before the timbers are called sound.