What might be happening
A failed shower tray seal, waste connection or supply pipe can wet boarding repeatedly without an obvious puddle.
A timber floor can look perfectly ordinary from above while the damage is hidden underneath. The first job is to work out whether the boards themselves are affected or whether the joists and their supports need attention.
What you can look for
Trace the leak with careful checks while the appliance is in use; inspect the subfloor from below if accessible.
You do not need to start taking the building apart yourself. If access is difficult, ask the person inspecting it to explain what needs to be opened up and why. Photographs of hidden defects are useful, especially when you are comparing quotations.
Putting it right
Repair the plumbing or waterproofing defect, allow the area to dry and replace timber that has lost strength.
Be wary of a quotation that deals only with the damaged wood and says nothing about the water or building defect behind it. Once the cause has been dealt with, the remaining timber can be checked and the necessary repairs planned.
When to call someone in
Do not cover damaged floorboards with new tiles or vinyl before investigating what is beneath.
A carpenter or joiner may be right for a local timber repair. If the problem involves a leak, you may need a plumber or roofer first. Where supporting timbers have moved, sagged or seriously weakened, get advice from someone qualified to assess the structure.
Questions worth asking
- Is the problem in the floorboards, the joists or where the joists sit in the wall?
- Can you show me the extent of the damage before any sound timber is removed?
- What caused it, and how will that cause be put right?