Timber treatment

Wet rot is far more frequent than dry rot and far less dramatic. It needs persistently wet timber — well above twenty per cent moisture content — and it stays local to the wet area rather than spreading through masonry. Cut off the water and it stops, which is the fundamental difference in how the two are handled.

It shows up wherever timber meets sustained moisture: joist ends built into a damp external wall, floorboards under a long-running leak, the bottoms of door frames, timbers in a poorly ventilated subfloor. The wood darkens, softens, and loses strength while often looking superficially intact under paint.

The structural consequence is what matters. A joist end that has lost its bearing where it enters the wall is a structural defect, not a decorating one, and it will not announce itself until the floor starts to move.

Suspended timber floors were designed to be ventilated underneath, with airbricks providing a through-draught that keeps the void and the joists dry. That system fails quietly and often: airbricks blocked by a new patio or raised border, painted over, rendered across, or covered by an extension that never reinstated the path.

The result is a still, humid void, and timber that sits at a moisture content it was never meant to hold. Clearing and reinstating that ventilation is frequently the highest-value intervention available on an old floor, and it is inexpensive.

Remove the moisture source first — always. Then assess what the timber has actually lost. Where decay is superficial and the member is sound, preservative treatment and improved ventilation are appropriate. Where structural capacity has gone, the timber is repaired or replaced: joist ends cut back to sound material and spliced, or supported off the wall on hangers so new timber is not built back into damp masonry to repeat the same failure.

New and repaired timber is isolated from damp masonry wherever the detail allows, because building fresh wood back into the wall that destroyed the last piece is a common and avoidable way to buy the same repair twice.