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The colder temperatures are just one of the ‘causes’ of window condensation.
Many condensation problems are caused directly by improvement in building construction. Advanced window and door designs make new homes tighter and less susceptible to drafts. Homes are also built today with superior vapour barriers and insulation that tend to keep the majority of moisture inside the house, instead of allowing it to filter to the outside as it did in older homes.

Below will help explain the problems and causes of condensation and will give you suggestions as to how you can eliminate these problems as much as possible.

Q. What causes condensation?

A. The source of condensation is humidity or invisible water vapour which is present in all but the driest air. When this vapour comes in contact with a surface that is below what is called the “dew point temperature”, the vapour becomes liquid and is called condensation. This process of changing water vapour to liquid occurs on bathroom mirrors and walls after someone has taken a hot bath or shower. It can also occur on windows, as temperatures become cooler, and the inside air contains enough water vapour.

The condensation can occur at any normal temperature, provided the moisture concentration (relative humidity) is high enough. Water on windows is condensation, and can be a problem, the cause / solution usually does not come from windows.

Q. Why does frost or condensation form on the window?

A. The water vapour in the air tries to flow towards drier air and mix with it. This process is called “vapour pressure”. It is not an instantaneous movement, but a definite movement from an area of high vapour pressure to where the air is drier.

In the winter, vapour pressure is very strong in the house because the cold outside air holds very little moisture. This vapour pressure can force moisture easily through most of the materials we use to build our homes: wood, drywall, even cement and brick are susceptible.

Moisture in the bathroom, kitchen and laundry area is absorbed into the warm inside air and then rushes to mix with the drier outside air. The most obvious indication of this is condensation or frost on your windows. The moisture comes in contact with the surface of the window but can not get through the glass or frame. It therefore, condenses to form either frost or water, depending on the temperature of the surface.

Q. What is humidity in general?

A. When air will hold no more moisture, it is said to be saturated. Relative humidity is a percentage of moisture in the air in relation to complete saturation. Example: 100% relative humidity would be rain. 50% relative humidity indoors in the wintertime would be excessively high and dangerous. 10% inside relative humidity would be comparatively dry air.

Warm air can hold more water vapour than cold. Even though inside and outside humidity could be the same in the winter months, the inside air would be holding far more water vapour since it is warmer. Condensation can occur in warm weather, see the following examples:

1. Condensation forms on a glass of water since the surface temperature of the glass is down to the dew point temperature of the inside air.

2. Dew (condensation) forming on grass during the cool nights in summer months.

Q. What are the harmful effects of excess moisture or condensation?

A. If you have condensation on your windows, you have a good reason to worry, and a good reason to act. The problem is not the windows themselves, but what excess moisture may be doing elsewhere in your home.

1. It may be freezing in the insulation in your attic where it will melt and damage your plaster exactly like a roof leak when the warm weather comes.
2. Damp spots on ceilings or warm side surfaces of the exterior walls.
3. Moisture on basement walls and floors.
4. Paint peeling or blistering may result from condensation of moisture in your house. Characteristically, the blisters will contain water and the paint peels down to bare wood. Moisture in the room penetrates the wall until it reaches the underside of the exterior paint. The building materials through which the water vapour has passed are porous while paint is not. As a result, moisture gathers underneath the paint, forms blister, and eventually the paint peels away from the wood.
5. Ice and frost on the underside of roof sheathing boards.
6. Fungus, mould and mildew growth.
7. Delaminating of plywood materials.
8. Loss of “R” value in wall and ceilings. Moisture reduces the effectiveness of insulation. It can reduce the insulation value by over 50%

Q. What can cause excess moisture or high relative humidity which can cause condensation?

A. With energy conservation the main concern today, modern homes are being built with the increased use of “moisture trapping” materials, such as increased insulation in walls and ceilings, use of vapour barriers over insulation; better performing windows and doors so there is less air infiltration and air exchange between the inside and out. This combined with the following sources of moisture, adds to the problem of excessive condensation.

1. Uncontrolled furnace humidifiers.
2. Damp basement walls and floors.
3. Excessive boiling when cooking.
4. Laundry hung up to dry.
5. Bathing and taking showers
6. Large number of plants watered daily.
7. Unvented appliances such as automatic clothes dryers and all gas appliances (water vapour is one of the products of gas combustion).
8. Interior ‘renovations’, as in painting / new carpets / new drywall or wood materials as, all of these products contain moisture that will have to ‘dry out’
9. Crawl spaces without adequate vapour barriers.
10. Cracks or voids in exterior caulking can allow cold, outside air cool inside surfaces of window and doors causing condensation.

Q. Why are new homes more prone to condensation?

A. During the first year after construction, it is likely that a house will have more condensation present because of the massive amount of moisture in the building materials used. It will be a drying out period when the wood, plaster, basement floors, walls and paint finished must dry. When the heating season starts, this moisture will gradually flow out into the air in the home.

The modern insulation and construction that keeps cold air outside, also keeps moisture in. Vapour-seal insulation is designed specifically to stop the escape of water vapour and protect the insulation and your walls from the ravages of water, but at the same time, it adds to the problem of condensation.

We are using superior insulation and vapour barrier techniques, along with superior windows and doors that minimize air infiltration and air exchange between the inside and outside, which all adds to excessive moisture. This is one reason why furnace humidifier should not be used at all during the first heating season. In some instances, a dehumidifier should be used to relieve the house of excess moisture content.

Q. Why is condensation more noticeable the first part of the heating season and directly after winter thaws or winter rains?

A. During the summer, your home has absorbed a great deal of moisture. Condensation will be more noticeable the first several cold spells directly after the heating season. This is because the house is still moist and it will take several weeks of continuous heating to be dried out. Condensation will usually dissipate as the heating season progresses.

A home picks up considerable amounts of moisture during the winter thaws and rains. If a cold spell set in immediately after a thaw or heavy rain, the relative humidity in the home will be at an extreme high, which can cause frost or condensation, unless the humidity level is reduced by moisture transmission to the cold outdoors. This is one reason why frost or condensation can be more noticeable immediately after rainfall followed by cold weather.

Q. Why can frost and condensation be more of a problem after the installation New Windows than before?

A. Before replacement windows are installed, most homes have fairly loose windows that have excessive drafts around them, which automatically reduce the humidity levels within the home. Actually, in many older homes, it is impossible to obtain high humidity levels due to the moisture lost around loose windows.

After the installation of new windows and/or new doors, drafts are reduced to a minimum and the house is sealed far tighter than it has been in the past. The interior moisture cannot escape to the exterior, thus causing higher humidity levels which could not be obtained before. Ways of reducing this excessive moisture are described in the next answer.

Q. What can be done to control condensation and high relative humidity?

A. Any or all of the steps below can alleviate a condensation problem:

1. Recaulk any broken exterior caulking around windows and doors.
2. Shut off furnace humidifier and any other humidifying device in your home.
3. Use kitchen exhaust fans while cooking, or at least close kitchen door to rest of house and open window slightly for ventilation. During and after a bath or a shower, the bathroom should be ventilated with the use of ventilating fans or by opening windows slightly for ventilation.
4. Windows in the laundry room should be open for ventilation when doing the laundry.
5. Large numbers of plants should be concentrated in a sun room or other seldom used room during critical cold weather.
6. Basement floors and walls should be treated with efficient water-proofing.
7. Opening windows slightly throughout the house for a short time each day will allow for humid air to escape and for drier air to enter. The heat loss will be minimal.
8. Never hang up clothes to dry indoors in a house with extreme humidity.
9. Open fireplace damper to allow moist air to escape.
10. Provide vents to outside on all major gas appliances. Also, vent all clothes dryers.
11. Run a dehumidifier if necessary.

If troublesome condensation persists, see your heating contractor about an outside air intake for your furnace, about ventilation gas-burning heaters and appliances, or about installation of ventilating fans. Certainly they will be less expensive than a big repair job caused by the deterioration of the insulation in the walls.
Q. What other factors can contribute to frost and condensation on windows?

A. If the heat within the room is not allowed to warm the window or doors it can become colder and prone to the formation of condensation or frost. On cold winter nights, when drapes and shades are pulled, windows and doors are not allowed to absorb the heat from the room. That is why it is important to position heating registers directly beneath doors or windows.

It is possible to have wintertime humidity levels too high.
High humidity can cause:
• Condensation on windows
• Condensation in/on exterior walls
• Mold and fungus growth
• Swelling of woodwork

The lower the outside temperature, the lower indoor humidity needs to be to prevent condensation. Single-pane windows will have a much bigger problem with condensation than double-pane windows will. Condensation from windows or walls can cause damage and promote mold, don’t let your humidity get too high.

Are your windows fogged up in winter? If so, don’t blame your windows; blame the hot and steamy activity in the house.
While window manufacturers often receive complaints from steamed-up homeowners, condensation has little to do with the quality of the window and everything to do with humidity levels inside the home.

WHAT ? Check for condensation on windows.
WHEN ? During winter
WHY ? When air cools down, it reaches its dew point (the temperature at which condensation forms). The higher the humidity level of air, the higher the dew point. The problem is not bad windows — it’s good science.
Condensation on your windows means the humidity levels in your house are too high. If you’re getting condensation on your windows, you’re likely getting condensation within the exterior wall cavities of your house!

HOW? There are two ways to control humidity levels.

The first is to reduce moisture sources within your house:
• Don’t store firewood in the home.
• Repair foundation leakage problems.
• Turn down or turn off your humidifier.
• Cover any exposed earth floor in a basement or crawl space.
• Cover sump pits.
• Don’t hang laundry to dry inside your home.
• Limit the use of vaporizers or steam generators.

The second way is to ventilate your home:

• Vent your clothes dryer to the outside.
• Use exhaust fans when showering or cooking.
• If you have single glazed windows, the windows should take the blame for part of the problem. The inside surface temperature of this glass is too low. • The solution – storm windows or new windows with double glazing.
• Be sure kitchen and bathroom exhaust fans vent directly outside. Never allow fans to vent into the attic.
• Be sure to insulate any exhaust fan duct, if it runs through a space, such as an attic.

Condensation on the exterior of your glass will happen when it is hot and humid outside, and the inside of your home especially the glass on your windows is cold typically from having your air conditioner on – condensation from humidity will always travel to the coldest surface or dew point. As homeowners we notice this the most on hot humid mornings.

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Serving Halton Region, Halton Hills, Georgetown, Acton, Erin, Milton, Oakville, Rockwood

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