Case study
Annandale: A Bowing Floor That Was Not Rising Damp
The Property
A house around 140 years old in Annandale, double brick with no cavity, built over a dug-out basement on sandstone bedrock. It had been renovated about two years earlier, including a new damp course and new floors. The owner wanted to turn the basement into a proper office.
Upstairs, a bedroom floor had started to bow. The builder said it was a subfloor damp problem and not his.
Checking the Floor
I went under the bedroom looking for the evidence damp would leave. There was no salt, no sign of rising damp, and the new damp course brickwork was clean. The subfloor was damp, but nowhere near wet enough to bend a floor.
Then I looked at how the floor was fixed. Brad nails instead of screws, gaps between the beams and the sheet flooring, a missed nail and misaligned glue. Timber that was not fully dry when it was glued and fixed had shrunk as it dried and pulled the floor out of shape.
The basement
The basement was a different story. Soil was built up against both sides, and the external damp course sat above the bridged zone. For a room someone is going to work in every day, it needed proper treatment, not a patch-up.
What I quoted for the basement:
- Render removal and grinding the floor, including cracks
- A negative side membrane to the walls
- Injection at the bridging points and above external ground level
- Two subfloor fans and new vents
- External salt and render removal as a separate option
The lesson
A possible cause is not proof. Damp has to leave evidence, and there has to be enough of it to explain the damage. Here there was not, so the floor was a workmanship issue, not rising damp.