There is a smell emanating from a small bedroom

March 2014

Question

A member of our family has recently moved in to her new home. The problem is that there is a strong smell (a bit rancid to be truthful) in a small bedroom. The house was built in the 1960s and it has had two fairly substantial upgrades in recent years. There is a concrete floor and new lino has been laid since she moved in. A dehumidifier was in the room for a while but it did not make much difference. The room is on the ground floor.

The drains in the kitchen which is on the other side of the wall have been treated. At this time the room is unusable. Is there any specialist firm in the west of Ireland who could investigate the source of the smell?

Answer

The problem seems to have occurred since she laid linoleum. If the concrete was recently installed, then there may have been insufficient time for the floor to dry out. Floor coverings should not be laid until the relative humidity (RH) of the floor slab is at or below 80 per cent. In the case of a ground-bearing floor slab, a damp proof membrane (DPM) underneath can restrict drying of the slab. Linoleum, an impervious floor covering, effectively traps the moisture in the floor.

Specialist probes can be inserted to determine the RH and if over a period of time it lowers, then it is drying as the moisture is free to evaporate. A traditional sand cement screed can take 24 hours for every millimetre of thickness to dry, which can be as much as three months for a 75mm screed and even longer if the concrete under is still drying. This criterion is rarely achieved in construction as working programmes do not afford such times. Methods used today to deal with this is to apply a surface damp-proof liquid membrane with levelling compound over the screed before laying an impervious floor covering.

If the floor is old, then it can sweat from moisture trapped under the linoleum sheet. This is common when modern plastic coverings are overlaid on old cold floors. Moisture in the cold slab cannot evaporate due to the impervious floor covering. To resolve this particular problem it is necessary to remove the entire floor covering and thoroughly ventilate the room to allow the floor to dry. A different covering is necessary such as carpet tiles or carpet sheet that will allow the floor to breathe. Laminate flooring may even suffice with a breathable underlay.

You have ruled out drainage, but there could be leaking heating or plumbing pipes in the screed or even a fault in the DPM under the floor. I can only really speculate without knowledge of the upgrade works and local conditions. If the removal of the linoleum and thorough ventilation does not address the problem, I would advise that you contact a local chartered building surveyor and get an inspection carried out.

Jim Drew is a a member of the western region branch of the Society of Chartered Surveyors Ireland