My solid oak floor is bulging in one spot for no apparent reason

Property Clinic: Something must have recently occurred to increase the moisture content of the wood

Once the cause has been resolved the floor should return to its normal level and the ‘hump’ will diminish, sometimes taking months to disappear

I am living in a purpose-built apartment block, which was completed in 2006. I have been the only owner of the apartment. It is a ground floor, corner apartment which is north facing, with two outside walls and one which borders the hall and stairs of the apartment block. It is also over the garage.

When the apartment was built, it did not include flooring, so I had solid oak floors put down throughout , with the appropriate underlay over the cement floor underneath. A relative did a very precise job and I have had no problems with the floors until recently. In recent weeks, I have noticed that there is a bulge in the floor, a bit of a hump, in the livingroom near the outside wall. It is hard to get a look at in its entirety as it starts under the storage heater. It comes out for about a foot or so and is several planks wide. There aren't any visible signs of water and the storage heater has no water in it as far, as I am aware. I would just like some advice on how to proceed, please. The same floor is throughout the 900sq ft of the apartment bar bathrooms and kitchen and I haven't noticed any similar issues.

All natural timber expands when it absorbs water vapour in the air or water from a leak as you have suspected. Such expansion is greater across the grain of the wood than along it so floating floors as you describe are normally laid lengthwise along the bigger dimension of a room.

Such floors laid over a solid concrete base must be fitted so that there is room for it to move by expansion gaps at the edges so that it can naturally expand and contract with the seasons or as ambient internal conditions change. If the gap is insufficient then as a result of the expansion the floor will rise locally as you describe because it needs more room than is there, sometimes cork strips are inserted to fill these gaps to prevent them being clogged with material that might limit this movement. Normally the supplier will advise the gap required for the area of the room to be fitted or calculated by the installer.


Since your floor has been laid for a number of years without the effect you describe, then something must have recently occurred to increase the moisture content of the wood beyond the tolerances originally allowed or something is blocking the movement space?

Localised condensation

Some factors that can influence such movement beyond the tolerance allowed include: insulation in the ceiling of the garage below has been disturbed or is missing, which could cause localised condensation at the cold spot; pipes within the garage space that may be leaking; a breach of the outer walls, perhaps at higher level allowing water to creep through at the slab level and under your floor unnoticed; fans in bathrooms or kitchens not working properly to remove moisture-laden air.

All these are just some of the possibilities to cause this sudden change in your floor. The remedies might include increasing the tolerance gap at the edges, replacing or upgrading insulation, examining the outer walls and garage space for evidence of water penetration and checking extract fans.

Once the cause has been discovered and resolved then your floor should return to its normal level and the “hump” will diminish, sometimes taking months to disappear.

If you cannot discover the cause then consider having a local building surveyor inspect and advise.

Fergus Merriman is a chartered building surveyor and member of the Society of Chartered Surveyors Ireland,