A guide for understanding & fixing interior moisture problems.
Condensation often occurs during colder weather when moist air inside the home comes into contact with cooler surfaces. The moisture in the air can condense into water droplets or even frost. The risk of condensation increases as the weather gets colder and/or the inside humidity rises.
For windows, doors and skylights, condensation can form:
Condensation occurs on cold surfaces when three conditions happen at the same time: too much moisture in the air, inadequate indoor-outdoor air exchange (ventilation), and the availability of cold surfaces for moisture to condense on.
Moisture is continually released inside every home — 10 to 50 litres (2 to 10 gallons) every day. In a heating season lasting 200 days, with windows and doors typically closed up, 2,000 to 10,000 litres (400 to 2,000 gallons) of moisture can be trapped inside.
If condensation is infrequent (once or twice a winter), briefly opening two windows on opposite walls or running the kitchen or bathroom exhaust fan usually solves it. If it's a persistent problem, consider installing a controlled mechanical ventilation system, ideally one with a heat recovery unit and humidity control.
Relative humidity (RH) is the amount of water vapour in the air, expressed as a percentage of the maximum the air could hold at that temperature. RH is measured with a hygrometer, an inexpensive gauge similar to a thermometer, and runs from 10% to 100% — drier air has a lower reading, moist air a higher one.
Dry air can cause a dry nose and throat, dry skin, and an increased risk of catching a cold. In the home, low humidity can damage wood and drywall, shrink wood floors, and even put a piano out of tune. A humidifier can help — keep it clean and change filters regularly per the manufacturer's instructions, and choose one sized for the area it will cover.
Excess moisture can stain ceilings and walls, peel paint and wallpaper, and create a breeding ground for mold, rot and insects. Basements, bathrooms, kitchens and laundry rooms tend to run higher in humidity. Newer, energy-efficient homes — built to seal tightly against heat loss — can be more prone to trapped moisture and window condensation as a result.
In double or triple-pane windows, a seal around the perimeter keeps an insulating gas fill (such as argon) locked between the panes, helping keep your home cooler in summer and warmer in winter.
Condensation between two layers of glass usually points to one of two things: on larger windows, the glass surfaces can flex and briefly touch, producing a ring-shaped condensation pattern in the centre of the window; or the seal separating the panes has failed. In both cases, this is typically covered under the manufacturer's warranty.
Defective windows do not cause condensation. Because glass has a lower surface temperature than any other surface in your home, your windows will be the first place you notice condensation. Some degree of condensation will always be a natural occurrence with your windows.
During construction, a tremendous amount of moisture is introduced into a new home — from curing concrete, framing lumber, drywall joint compound and paint — that takes time to dry out. This moisture usually dissipates after the first heating season, but in extreme cases it can take up to two years.
This happens with very energy-efficient windows and is a temporary condition that will disappear on its own.
The black substance is mold. Mold spores grow on moist surfaces, which is a clear sign that the relative humidity in your home is excessive and increased ventilation is needed.
A 50/50 water and bleach mixture can be used to kill mold spores. On wood components, once the water/bleach mixture has dried, lightly sand the surface to restore its appearance, and seal any exposed wood promptly since raw wood absorbs moisture quickly.