Timber decay and woodworm
A new deck covers the air bricks to the suspended floor and the joists were not seen. What ventilation of the void is blocked?
The ventilation of the underfloor void is blocked, at the air bricks the new deck covers. Those bricks are the inlets that should let air through to the space under a suspended floor. A deck built over them closes that path. The joists were not seen, so the survey has not described their condition, and it has not measured the air in the void. Covering the bricks is what was visible from outside. The report has not said the timbers are decayed. It has said the ventilation into that void is obstructed by the deck.
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?
Suspended timber floors rely on air moving through the void so the joists and the boards are not sitting in still, damp air. Air bricks in the outer wall are the usual way in. A new deck that lands across them, or buries them behind boards, stops that flow at the face of the wall. The surveyor could see the cover. They could not see the joists, because the floor was not opened. Blocked inlets are the finding. The condition of the hidden timber is not.
Ask a builder or a timber specialist how the deck can leave the air bricks clear, and do not open the floor solely on this note unless someone advises that. Tell the solicitor the void ventilation is blocked and the joists were not seen. The survey has not diagnosed rot, and it has not designed a new deck. Clearing the bricks is the first physical point. Any view of the joists would be a later inspection, not a result already in the report.
What should you ask your surveyor?
- Which air bricks does the deck cover?
- Is underfloor ventilation blocked there, with the joists unseen?
- Was the void itself left uninspected?
What are the typical next steps?
- Treat the deck as blocking ventilation to the underfloor void.
- Ask how the air bricks can be left clear.
- Do not claim the joists were inspected.
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 floorboards feel firm, are the joists ventilated?
Firm boards underfoot are not a view of the void. The joists were not seen, and the air bricks are covered by the deck, so the ventilation of that void is blocked at the wall. Stiffness on the day does not move air under the floor. The survey has not diagnosed decay. It has recorded the covered inlets.
Does the report tell you to bore new holes through the deck?
No. The report says the existing air bricks are covered and the joists were not seen. It does not set out new holes, and it did not design the deck. How to restore a path into the void is for someone looking at this deck. Do not open the boards merely because the note mentioned air bricks.