The following is an excerpt from the booklet Moisture and Air, Householder’s Guide distributed by Canada Mortgage and Housing Corporation (CMHC).
The advice contained herein is oriented primarily toward owners of single-family homes. Moisture and air problems in multi-level buildings differ somewhat from those that
affect smaller structures - nonetheless, they are a significant factor affecting various components within the building. Signs of moisture damage described here may also be seen in
multi-level buildings, and the causes and remedies needed to address these conditions may be similar. Therefore, some, if not all, of the following information may be useful to condominium owners and management.
This advice is offered for information purposes only – if you are experiencing problems of this nature, always consult with a professional contractor
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Moisture and air quality problems are a significant cause of property damage in the typical Canadian home.
Many household problems can be solved if a householder changes certain practices, performs maintenance or minor repairs and has a professional contractor make major repairs.
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MOISTURE PROBLEMS
If the air in your house is too moist, your house structure and your personal possessions may be damaged.
When warm moist air comes into contact with a surface that is too cold, it releases condensation. The water and frost that you see collecting on windows is a visible example. Condensation may also be soaking into your roof sheathing, exterior walls and insulation, where hidden leaks are releasing humid house air to the outside.
Over the long term, the result may be damage to the house structure.
AIR QUALITY PROBLEMS
Stale air is a health hazard. For the health of everyone in your home, your house (like you) should breathe properly. If it doesn’t, the air in your home can become polluted with harmful chemicals released from synthetic fabrics, furnishings, household products, cigarette smoke and improperly maintained or vented combustion devices, such as cooking stoves, furnaces, water heaters, wood stoves and fireplaces.
Moisture is continually being released inside a house: 10 to 50 litres or 2 to 10 gallons every day. In a heating season lasting 200 days, that adds up to 2, 000 to 10,000 litres (400 to 2,000 gallons) of moisture!
Find the moisture level in your house.
The amount of moisture in the air is normally measured as its relative humidity.
Purchase a relative humidity sensor (hygrometer) at your local hardware store or building supply store. Inside your house, the relative humidity should be brought down to approximately 45% during the winter heating season. In very cold weather, a level of 30% may be needed to prevent window condensation.
Upgraded windows can support a higher level of relative humidity without condensation occurring.
If you reduce the amount of moisture released in your house each day, you can reduce ventilation and save energy.
A WET OR DAMP BASEMENT, ESPECIALLY IF HEATED, MAY GENERATE MUCH MORE MOISTURE THAN ALL OTHER FAMILY ACTIVITIES COMBINED.
MOLD AND MILDEW
Problems
Mold and mildew fungi can cause:
unsightly stains;
damaged paint wood, drywall and fabrics;
allergies; and
illness
Some symptoms
Musty smells
Green or black marks on the inside surface of outer walls or ceilings
Stains in carpets
Mildew on drapes and backs of furniture
Prevention
Fungi (such as the wood rot, mold and mildew varieties) require high humidity levels to survive.
Some fungi require condensation to start growing. Certain fungi actually generate moisture and then continue growing even when condensation stops.
TO AVOID MOST MOLD AND MILDEW PROBLEMS, KEEP MATERIALS DRY
Clean-up methods
Mold and mildew on surfaces can be cleaned up with a solution of one part chlorine bleach in four parts of water.
When applying:
- ventilate well;
- use gloves;
- let stand 10-15 minutes;
- rinse well; then
- keep surfaces dry.
Mold and mildew-stained fabrics should be removed and discarded.
MOISTURE PROBLEMS IN YOUR HOME?
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TYPICAL SIGNS
- Excessive condensation on windows
- Rotting window sills and door jambs
- Damaged gypsum board
- Mold and mildew in corners of interior surfaces of outside walls
- Mold and mildew in closets
- Moldy drapes, carpets or furniture near outside walls
- Cracked or bulging ceiling
Bathrooms
- Condensation on toilet tank and bathroom fixtures
- Mold and mildew between ceramic tiles
- Musty smells from inside walls
- Water dripping from vents
Kitchens
- Moisture under sinks or kitchen counters
- Peeling paint or curling tiles
- Mold in cupboards
- Doors difficult to open and close
PROBABLE CAUSES
- Excessive moisture gains in basement or crawl spaces
- Excessive boiling of food
- Household washing: dishes, floors, clothes, etc.
- Operation of humidifiers
- Inadequate ventilation with fresh air
- Poor air circulation between rooms or within a room
- Cold surfaces due to ineffective insulation
- Large air leaks at electrical fixtures, window frames, etc.
- Closed drapes
- Closed doors
- Bedroom temperature much lower than in other rooms
- Furniture too close to outside walls
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PRACTICAL SOLUTIONS
- Caulk basement floor to wall joint
- Moisture seal basement walls and floors
- Don’t let liquids and food simmer uncovered more than necessary
- Operate vented exhaust over range when cooking
- Close bathroom door when using shower or bathtub and turn on fan
- Dry very wet clothes or bath mats and towels in a vented electrical dryer or hang outside to dry
- Caulk sinks and fittings to counters
- Discontinue use of humidifiers and unvented heaters
- Use moisture-proof paint and wallpaper in water-use areas
- Install a balanced ventilation system – and use it regularly
- Circulate air between rooms
- Trim cupboard and closet doors, or install louvred doors so that air can circulate
- Trim bottom of bedroom door to create a gap, or leave the door open
- Properly insulate cold surfaces
- Seal large air leaks
- Open drapes
- Keep furniture away from outside walls
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HIGHLIGHT SUMMARY
CAUSES
Condensation occurs on surfaces because they are too cold for the amount of moisture present in the indoor air. That results from:
- excessive moisture production;
- by ventilation with muggy warm and humid outdoor air (a common climatic problem in spring or fall and in coastal areas);
- by evaporation from wet floors, dishes, cooking, people, plants and damp basements; and
- from inappropriate use of humidifiers
- inadequate ventilation with outdoor air
- inadequate circulation of indoor air
- unusually cold surfaces because of:
- insufficient glazing layers in windows;
- inadequate insulation levels in ceilings and walls;
- cold air penetrating insulation (a typical cold-climate winter problem); or
- a cool basement in summer
SOLUTIONS
Reduction of excess moisture production is the first priority:
- Control evaporation
- Keep the basement dry
- Discontinue use of humidifiers if window condensation is common
Keeping surfaces warm is the second priority:
- Window glazing should be appropriate to the climate (triple glazing in cold regions)
- Well-insulated walls and ceilings keep indoor surface temperatures high; but
- cold outside air must be prevented from penetrating insulation (wind barriers, attic air deflectors, etc.)
A reasonable ventilation rate, plus good circulation of indoor air, are important and effective methods to help prevent all indoor air quality problems.
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