What might be happening
The outside edge of a suspended timber floor is often where the joists enter the masonry. That makes it an important place to look when a floor drops close to a wall.
Joist ends built into damp masonry can decay out of sight, leaving the visible part of the joist apparently sound.
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
Inspect the wall/joist junction and subfloor conditions, including air bricks, ground levels and gutters outside.
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
A sound repair may require replacement bearings or engineered support and correction of moisture entering the wall.
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
A significantly dropped floor can be unsafe. Ask for structural assessment before lifting large sections or loading the area.
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?