Have you ever noticed water droplets on your window or black staining on the drywall of your walls? Have you ever wondered why the moisture returns around your windows after you have wiped it away?

This type of moisture is from the interior air and is commonly referred to as condensation.

What is Condensation and How Does it Form in My Home?

Condensation occurs in your home when moist air comes into contact with a surface which is at a lower temperature. Moist air contains water vapour — commonly referred to as humidity. Indoors, we can increase humidity through our activities and lifestyle. If a surface in your home is cold enough, the air in the immediate vicinity of the surface will be cooled sometimes causing the moisture in the air to condense or change into a liquid on the surface.

Condensation forms first, on the coldest surfaces of a room, usually on glass surfaces of windows and doors. These surfaces are typically cooled by lower exterior temperatures during the winter months much more easily than the walls which are kept warm by insulation. For example, if it is cold enough outside and/or warm and humid enough inside, condensation may occur on or around your windows resulting in fogging, water or ice on the windows themselves or even a puddle of water on the window frame or sill. Other examples of condensation in your home can include damp

spots or mildew on outside wall corners, closet walls or baseboards. Areas of your home with poor air circulation, such as behind furniture or in a cupboard or closet, can also be susceptible to condensation.

In many instances, condensation moisture simply evaporates back into the air once the surfaces warm up or the moisture source is reduced. An example of this is moisture that condenses on a bathroom window during a shower and quickly disappears shortly after the shower is turned off. However, as a general rule, steps should be taken to avoid condensation problems wherever possible as moisture can lead to damage.

Why Must I Avoid Condensation Problems?

Condensation can cause serious damage to the interior and structural elements of your home or building. If condensation occurs frequently enough and for prolonged periods of time, materials in contact with the moisture may be damaged. Drywall and wood finishes around windows are two examples of materials in your home that can

readily absorb moisture and become damaged if they remain wet for a sustained period of time. If left unchecked, condensation problems can cause:

  • crumbling or soft spots in drywall
  • decay in wood framing or corrosion of steel framing
  • peeling paint
  • damage to the insulation inside the walls, and
  • mould and mildew problems in your home.

Most importantly, taking preventative steps to avoid condensation from occurring in your home will help prevent avoidable and expensive problems in the future. Sources of Moisture in the Home We add to humidity levels in our home through our activities and lifestyle. Water vapour is added to the air in large quantities by our breathing and perspiration, cooking, bathing, cleaning and other daily activities.

How we produce humidity in our homes

  • A family of four can add moisture to the air equivalent to 30 to 40 litres of  water per week
  • Showering, cooking, bathing and washing can add 15 to 20 litres per week
  • Drying clothes indoors can add 10 to 15 litres per week

Source: Natural Resources Canada 


How do I Avoid Condensation Problems?

There are number of steps that you can take to prevent condensation problems from occurring in your home.

1. Reduce the amount of moisture or humidity generated in your home

  • Do not regularly hang large amounts of clothes to dry indoors. Wherever possible, dry your clothes in a dryer with an outside vent.
  • Shut off the humidifier if you are using one.
  • While cooking, put a lid on boiling water — it will also boil faster!
  • Try to have shorter showers. You will save the energy required to heat the water and conserve on water.
  • Ensure the lint trap in your clothes dryer is clean. The lint trap should be inspected and cleaned before each use.
  • As much as possible, try to wash full loads of dishes in the dishwasher.
  • Do not store wood for your fire place indoors.

2. Promote good air circulation in your home

  • Open blinds and drapes so that air can circulate freely over the windows.
  • Direct heat towards exterior walls and windows.
  • Where condensation at window sills is a persistent problem, remove any objects on the window sill such as books, photographs, and knickknacks as they prevent air from circulating and removing the moisture.
  • Move furniture such as sofas and bookcases so they are not touching outside walls. This will improve air circulation around the cooler outside wall and reduce condensation potential.

3. Promote good ventilation in your home

  • Use the kitchen exhaust fan or range hood to remove humidity generated by cooking
  • Use bathroom fans and humidistats (if you have one) while bathing or showering, the exhaust fan should be left running for a period of time after bathing or showering to remove the excess moisture from the bathroom. The exhaust fan should be vented to the outdoors.
  • Some newer homes have a pre-set principal exhaust fan. Ensure that this fan is set to run for two 4-hour periods per day.
  • Open windows periodically and ensure that fresh air intake vents are not blocked.
  • Make sure exterior vent hoods for your dryer, bathroom and kitchen vents are unobstructed
  • Consider upgrading your kitchen or bathroom fans. If you feel that your kitchen or bathroom fans make noise but don’t seem to do anything, you may be right. Some older or cheaper units may not be working effectively.