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top
| Moisture
Problems |
| Why
Does Condensation Occur on Interior Surfaces? |
April 2000 |
Condensation on inside
of window in cold weather.
|
Condensation can occur on any surface that is below the "dew point" of the air
with which it is in contact. The "dew point" is the temperature at which
condensation will occur for a given humidity level.
In most houses in winter, the inner surfaces of the windows are the coolest surfaces in
the home. Condensation will typically appear there before it appears on other surfaces.
Condensation is less likely to occur on interior walls, because they are typically warmer
than "dew point."Occasionally however,
condensation may occur on cold spots such as nail heads, in corners of outside walls where
insulation is reduced, or in confined spaces where the circulation of warm room air is
restricted. In extreme cases, condensation may lead to mildew and the growth of mold. |
What To Do
To reduce or eliminate excessive condensation, the humidity level
must be decreased and/or the ventilation increased.
| To reduce humidity
levels:Turn down humidifiers
Ensure dryers are vented to the exterior
Do not hang clothes to dry inside the house
In extreme cases, operate a dehumidifier.
Dehumidifiers generally are capable of removing 7.5 to 20 litres of water from the air per
day.
|
A household dehumidifier. |
To increase ventilation:
- Operate bath fans when showering or bathing
- Open windows or operate an exhaust fan as soon as
significant window condensation appears, until the source of the humidity is remedied.
- Operate furnace with fan switched on for continuous air flow
- Have range hoods vented to exterior
- In extreme cases, consider installation of an mechanical
air exchanger or Heat Recovery Ventilator (HRV).
|
A typical heat recovery ventilator. |
| If the obvious solutions don’t eliminate
the problem, before investing in a dehumidifier or an HRV, check the structure for other
possible moisture sources. Ensure the appropriate insulation and moisture barriers are
installed in the attic, basement or crawlspace. Check for seepage in the basement. Attic ventilation is normally provided by vent openings in the
soffits or gables and roof. The total area of ventilation should equal one square foot for
every 200 to 300 square feet of ceiling area. Not less than 50% of attic ventilation
should be throught the soffits or gables. Not more than 50% should be through the roof. |
| Moisture
Produced By VariousHousehold Activities: Family of 4 |
Activity
Cooking 3 Meals (per day)
Running dishwasher
Bathing (Shower)
Bathing (Tub)
Washing Clothes (for 1 week)
Drying Clothes Indoors Or With
Unvented Dryer (for 1 week)
Floor mopping (per 100 sq.ft.)
4 Occupants (Respiration - per day) |
Litres of water
1.0
0.5
2.5
1.0
2.013.0
1.5
6.0 |
|
Note: 1 Imperial gallon = 5 litres; 1 US
gallon = 4 litres
|
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