Moisture and Air Quality Problems

Moisture is continually being released inside your home: 10 to 50 litres (2 to 10 gallons) every day. In a heating season lasting 200 days, when your home is typically closed up, 2,000 to 10,000 litres (400 to 2,000 gallons) of moisture can be trapped. A cord of wood stored in your home, for example, can release more than 270 litres of moisture. Excess moisture can result in moisture problems, which can lead to air quality problems.

Moisture Problems

Moisture problemsThere are two types of moisture problems — leaks and condensation. This publication focuses on condensation problems.

When warm, moist air comes into contact with a surface that is too cold, moisture condenses. The water and frost that you see collecting on windows is a visible example.

Condensation may also be collecting in your attic, and inside the exterior walls.

Over time, if the air in your house is too humid, the result may be damage to the house structure, your possessions and possibly your health. Controlling humidity in your home is the best step to preventing mold problems.

Leaks from roofs and plumbing often cause moisture problems in homes. This topic is dealt with more extensively in other CMHC publications. See the related CMHC publications listed at the bottom of this Web page for more details.

Air Quality Problems

Air quality problemsThe air you breathe in your home should be clean (i.e. as free from pollutants as possible). For your health and comfort, your home should have an exchange of air between the indoors and outdoors. Without the air exchange, your home can accumulate moisture, mold can become a problem, and you can experience poor air quality.

Mold growing in your home can release mold spores, toxins from mold, and moldy odours.

Harmful chemicals can be released from synthetic fabrics, furnishings, and household products. Additional contributing sources of indoor air pollutants are cigarette smoke, burning candles, or improperly maintained or vented combustion devices, such as gas or propane cooking stoves, furnaces, water heaters, wood stoves and fireplaces.

The exchange of stale air with fresh air reduces potential air quality problems.


Condensation occurs on cold surfaces. It results from:

  • excessive moisture production:
    • ventilating with warm outdoor air during spring and summer can cause lots of condensation in basements;
    • from inappropriate use of humidifiers;
    • by evaporation from showers, washing dishes and clothes, cooking, aquariums, standing water, people, pets and plants;
    • in damp basements;
    • from earth floor basements or crawlspaces.
  • inadequate ventilation with outdoor air:
    • air inside the house is not exchanged with outdoor air (in general outside air in cold weather will help dry the air inside the house).
  • cold surfaces due to:
    • inadequate heat or insufficient heat provided to areas of the home (i.e. spare bedroom heat blocked off if the room isn’t used regularly, unheated basement);
    • wide swings in inside temperature (i.e. thermostat setbacks, uneven heat distribution from use of wood stoves, unheated room);
    • poor air circulation within a room due to furnishings against the exterior walls;
    • poor quality windows or heat blocked by blinds or drapes;
    • poorly insulated walls and ceilings.
  • cool basement surfaces in summer.


Reduction of moisture is the priority:

  • remove moisture sources;
  • reduce basement moisture entry;
  • discontinue use of humidifiers; and
  • use a dehumidifier in the basement during fall, spring and summer.

Keeping surfaces warm is the next priority:

  • upgrade windows with energy-efficient ones;
  • keep walls and ceilings warm through adequate insulation;
  • provide sufficient heat to all indoor areas in your home.

Adequate ventilation, good air circulation and maintaining adequate heat throughout your home are important and effective methods to help prevent moisture problems.

Find the Moisture Level in Your House

The amount of moisture in the air is normally measured as its relative humidity.

  • A relative humidity sensor (hygrometer) can measure the moisture level of your home.
  • Hygrometers can be purchased at your local hardware or building supply store.
  • In very cold weather, a level of 30 per cent or lower may be needed to prevent window condensation.
  • In the winter heating season, the relative humidity should not exceed 45 per cent.
  • Upgraded, energy-efficient windows can support a higher level of relative humidity without condensation occurring.
Carol Ireland

Carol Ireland

Sales Representative
CENTURY 21 Millennium Inc., Brokerage*
Contact Me

Blog Archives