Humidity and condensation in your home
Humidity is present in every home and building. While some amount of humidity is beneficial, higher concentrations can lead to condensation and mould development. With an increased awareness of the causes and places where condensation is most likely to collect, you can reduce its amount and effects.
Air contains water vapour. The average family produces about 10 litres of moisture a day from activities like cooking, bathing, washing dishes and doing laundry. Condensation is the conversion of the invisible water vapour in the air back into a liquid and occurs when the vapour cools. The temperature at which the vapour begins to condense is called the dew point. Condensation occurs whenever warm, moist air comes in contact with a surface or object cold enough to chill the moisture in the air below its dew point.
As a rule, the coolest visible surfaces in a home in winter or cold weather, will be uninsulated cold water pipes, windows, exterior walls, hinges and locks on exterior doors. It is on these surfaces that condensation usually first becomes apparent. However, condensation may also occur in areas where it is not visible, such as in the attic and in exterior walls.
Condensation on windows may be little more than a nuisance, but condensation on window sills, walls and ceilings can cause paint to peel and promotes mould growth. Hidden condensation can lead to problems that range from mould and mildew to dry rot and damage to the wood-frame structure of the house.
Condensation on windows
Windows are usually one of the coldest surfaces in a house. Condensation forms on a window when warm moist air that contacts it cools rapidly. Like glass, metal is a poor insulator. If a window has a metal frame, condensation can also occur on the frame. Condensation on windows can be reduced and often eliminated by adding inside or outside storm windows or by installing multiple-glazed windows. If you are shopping for new windows, look for ENERGY STAR® labeled windows and sliding glass doors to replace your old ones. ENERGY STAR® windows not only reduce condensation, they also improve your home's comfort. If your windows need to be replaced and are too large, consider replacing them with smaller ones to reduce your heating costs further. Also consider replacing sliding glass doors with insulated doors and outside storm doors. Find out more about ENERGY STAR® qualified doors and ENERGY STAR® qualified windows.
Hidden condensation can occur when warm, moist air migrates into the walls, attic or other interior areas of the structure. Most of the moisture is carried into walls and attics by air leaking through openings for plumbing, piping, electrical boxes and wires, gaps between framing and drywall, attic hatches and other openings. If at some area in the walls or attic the moist air encounters a temperature below the dew point, condensation will occur. If the temperature is low enough, moisture may deposit as ice or frost. If the amount of moisture is small, it may change back into water vapour with a rise in temperature and be carried away by natural air movement. However, large deposits of ice can melt and soak insulation materials, ruin interior and exterior finishes, and lead to structural deterioration.
To minimize problems in attic and wall cavities, it is important to seal these cavities from the interior of the home to minimize the movement of moisture into these areas. It is also important that the cavities are vented to the outside through attic vents and 'breathable' exterior siding. This will allow small amounts of moisture that do get into the cavity to escape.
New housing is required to have a continuous vapour barrier, sealed at all penetrations. This requirement is intended to prevent, or at least severely inhibit, hidden condensation.
The combination of indoor moisture sources, air exchange rates, and cold surfaces will determine how much condensation occurs in the home. Activities such as cooking, washing, or bathing will raise the humidity level in your home and often result in some condensation on windows, walls and ceilings for short periods of time during cold weather. Other than causing some deterioration of the finish on wood frames, sills, or casings, such condensation is harmless. Therefore, moderate, intermittent condensation on windows, walls and ceilings is probably no cause for alarm. However, if windows are consistently wet, or water stains appear on ceilings or walls, prompt action should be taken to avoid further problems such as mould growth. Generally, the quickest and most effective response to a condensation problem is to increase the ventilation of the house. This can be done by means such as:
Controlling humidity in your home
Outdoor air, when heated to indoor temperatures, will generally be dryer than the air indoors. Thus, increased ventilation will reduce the amount of moisture in the air and, as a result, the amount of condensation, but it doesn’t correct the cause. The cause should be located and corrected. The following table lists possible causes of high humidity in the home and suggests ways to control this moisture.
|Causes of High Humidity||Ways to Control High Humidity|
|Cooking, drying clothes, showering and bathing||
|Lack of air circulation||
|Moisture-producing areas such as indoor greenhouses, indoor pools and hot tubs||
|Exposed earth in basements or crawlspaces||
|Outside air supply to heating system is blocked or does not exist||
|No exhaust fans or underutilized exhaust fans||
|No Heat Recovery Ventilator (HRV)||
|Faulty or plugged chimney serving any fuel-fired appliance, such as a furnace or hot water heater||
|New home or large addition||
|Extensive air sealing done to lower fuel consumption and cost||
|Eliminating or blocking off a chimney||
|Flooded basement or crawl space||
|Minor leaks and water
Energy Solutions Centre
206A Lowe St., 1st Floor
Whitehorse, Yukon (Canada)
Phone: (867) 393-7063
Fax: (867) 393-7061