Timber decay and woodworm

Plywood has been laid over a bouncy floor. What can the survey say about the boards underneath?

Almost nothing, if the plywood was not lifted. The survey can say the floor feels excessively springy and that a sheet covering hides the boards, but it cannot call those boards rotten, beetle-eaten or sound. Spring under a new layer is a reason not to take the surface as the structure. A home survey does not take up a fixed overlay to prove the timber.

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?

People overlay plywood because boards are worn, gappy or springy, or because they want a smooth base for a finish. The overlay can itself be well fixed and still conceal edges that have lost their bite on the joists. The Property Care Association’s concern with floors is damp timber, decay and insect damage where the wood is still structural. None of that is visible through a screwed sheet. A bounce tells you the floor is lively. It does not name the cause: undersized joists, notching, a lost sleeper support, or decay. The inspection should not pretend to choose.

Ask the surveyor whether any board edge was visible at a pipe boxing or a lifted corner, and what that one place showed. One edge is one edge. Do not let a seller say the new plywood “sorted the rot” unless the rotten timber was replaced, which the overlay does not prove. Do not strip the sheet before completion unless the seller agrees. If you need to know, the instruction is to lift enough covering to see boards and, if needed, joist ends. Until then the report’s honest line is that the structural timber was concealed and the floor was springy.

What should you ask your surveyor?

Was any original board visible, or only the plywood?
Where was the bounce, and did you see a cause?
Are you reporting a concealed floor, not a diagnosed rot attack?

What are the typical next steps?

Do not pay to treat insects or rot in boards nobody has seen.
Do not accept the overlay as evidence that the structure was repaired.
If the bounce is serious, arrange a look underneath or from lifted sheets, with the seller’s agreement.

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

Is a squeak the same as a rotten joist?

No. Squeaks are often boards moving on nails. Ask whether the surveyor found softness or only noise.

Does chipboard instead of plywood change the point?

No. Any fixed sheet that hides the boards leaves the boards uninspected. Name the sheet you saw.