Timber decay and woodworm
A cellar beam shows cuboidal cracking and the surveyor did not probe every joist. What does that cracking pattern suggest, and what replacement has it not specified?
Cuboidal cracking suggests brown-rot decay in that cellar beam, the pattern in which the wood breaks into cube-like blocks. It suggests that kind of decay in the beam that shows it. It does not name the species for certain, because more than one brown rot can leave that pattern, and it has not specified which joists to replace. The surveyor did not probe every joist. The survey recorded the cracking it saw. It has not written a renewal schedule and has not said the whole cellar floor must be renewed.
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?
Brown rots, including dry rot, consume the timber so that it shrinks into cubes and loses strength even where the surface still roughly holds its shape. Seeing that pattern on a cellar beam is a serious local note. It is not a licence to list every joist as condemned. The joists that were not probed might be sound, partly decayed, or worse than the beam, and the visit did not decide. The suggestion stays on the cracking: brown-rot decay in the member that shows it, with the rest unchecked.
A timber specialist should probe the beam and the joists the surveyor could not, and only then say what needs to come out. Tell the solicitor there is no replacement schedule in the home survey. The report has not specified a steel and has not specified a new floor. Damp in the cellar is part of why the rot could establish, so the specialist should also say where the moisture is coming from. Do not prod the cracked beam apart on a viewing.
What should you ask your surveyor?
- Which beam showed cuboidal cracking, and which joists were not probed?
- Have you described the pattern as brown-rot decay without naming a single species as proved?
- Is any replacement left unspecified because the rest was not probed?
What are the typical next steps?
- Read the cracking as brown-rot decay in that beam, not as a full schedule.
- Ask a timber specialist to probe the joists the survey left unprobed.
- Do not replace the cellar floor until that extent is known.
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 cubes are only on the surface, is the beam still full size?
Surface cracking does not prove the core is sound, and the survey did not measure the remaining section. Cuboidal cracking suggests brown rot in that beam. It still has not specified a replacement. Asking about it again later still leaves this surfacecube point outside what the survey decided.
Does cuboidal cracking always mean dry rot and a whole-house strip?
No. The pattern suggests brown rot, which includes dry rot but is not a species test, and the surveyor did not probe every joist. Nothing in the note orders a whole-house strip. The home survey itself did not pursue this wholestrip question any further than the visit.