If the foundation walls, slabs and earth floors appear dry yet the space seems damp, this might indicate that moisture is wicking through the foundations and evaporating faster than it can accumulate.

To test for this, cut a sheet of plastic about 1 m (40 in.) square and tape it to the concrete walls and slab. For earth floors, hold down the edges with sand or sticks. After a day or two, check the plastic. If condensation formed on the top of it, this indicates high interior moisture levels. (See details in Control of moisture flow and Ventilation and combustion air.)

Carefully remove the plastic and note any condensation on the bottom of the plastic or wetting of the concrete or soil. Condensation formed under the plastic indicates moisture movement from the ground into the home as well as the possibility of radon emissions.

To reduce the movement of moisture into the home from the foundations, apply a moisture barrier (see Crawl spaces) or have the interior or exterior concrete sealed or waterproofed.

iii) Cracks

If the basement has an active crack (i.e. one that gets bigger or smaller), seek professional help to determine if the situation requires structural repairs.

iv) Radon

Radon may be present in all homes, with and without humidity and moisture problems (see Health and safety considerations, for more information).