A cold corner of an electrically heated home in Newfoundland.

Background
Mould and mildew have formed on the walls and on the baseboards. While mould and mildew can form indoors when the relative humidity is sustained above 70%, mould and mildew flourish when surfaces are repeatedly wetted by condensation.

Causes
This is a classic case of a cold corner when coupled with a high indoor relative humidity. This often occurs in poorly ventilated homes in a cold climate. Wind chilling of the corner and the movement of cold air through the outboard insulation may have further cooled the corner. The surface temperature in this area is frequently below the dew-point resulting in condensation and the consequential growth of mould and mildew.

Solution
A good exterior wind barrier must be provided to minimise the wind washing that is likely occurring at the corner. Increased thermal insulation levels may also help. These measures will lead to higher interior surface temperatures. Next, the indoor relative humidity should be reduced by providing adequate ventilation, and by reducing or eliminating large indoor moisture sources. For example: green fire wood should be dried outside the building envelope.