Why is there condensation on the interior of my windows?

Condensation happens when cold dry winter air hits the exterior of a window, at the same time that warm humid air inside your home comes in contact with the interior of the window. Regardless of the window manufacturer, or whether the window is made of wood, vinyl or aluminum, humidity can cause condensation on the inside of any window, if the conditions are right.

Window condensation can sometimes block your view and can cause droplets of water to drip onto your floors. When temperatures drop below freezing, the condensation can sometimes create frost or even ice on the inside glass. While it is natural to blame the windows, they are not to blame. Window condensation is simply the result of excess humidity inside your home.

Condensation is usually temporary and can be managed by making adjustments to reduce interior moisture, unless the condensation is between the window panes. This occurs when the seal between the glass panes is broken or when the desiccant inside the window is saturated.

With double pane windows, the insulating air space in between the glass panels maintains consistent temperature and reduces heat lost. Most windows today have two seals: an inner seal to protect against moisture and corrosion, and an outer seal to protect the strength of the window. The seals hold a spacer in place, which is usually a tube containing water absorbing chemicals known as a desiccant, as previously noted.

Insulated windows can withstand all types of weather, including severe cold and hot temperatures, and humidity, however as windows age beyond their designed life span, the seals begin to break down and can cause condensation to enter between the panes. Typical causes of this type of condensation are the result of water retention in the frame or improper drainage around the window. Seals can also be broken when there is direct exposure to sunlight, as the more sun your window gets the more heat will build up, causing the panes to expand and contract and eventually weaken. Once the seal is broken, moisture begins to form between the panes, giving your window a milky, foggy appearance.

If you have windows with single-pane glass, consider replacing them with windows that have at least double paned glass with a low e-coating and argon gas filling. This is not guaranteed to eliminate condensation, but it will at least reduce it significantly. Laboratory testing shows that these types of windows allow about 37% relative indoor humidity without condensation when the temperature outside is 0 degrees Fahrenheit, and 70 degrees inside. Older single pane windows only allow about 12% relative indoor humidity at the same temperatures – lower than the typical humidity levels found in a desert.

There are many things that generate indoor moisture. Perspiration and breathing of the occupants of a home adds moisture into the air. So does cooking, bathing, showering and doing laundry. The normal daily activities of a family of four can add more than 18 gallons of water a week into the air in their home, greatly increasing interior relative humidity.

Relative humidity is the measure of the amount of water vapor that air can hold at a certain temperature. The warmer the air, the more moisture can be retained. The cooler the air, the less moisture can be retained in the air. When humidity reaches 100%, the water vapor precipitates out of the air as rain and snow. Some of the signs that there is excess humidity in your home are peeling paint, rotting wood, buckling floors, deteriorated insulation, mildew and even moisture spots on ceilings and walls.

Excess interior humidity can be destructive to a home, and can damage sheetrock, paneling and window sills. It can penetrate walls and wood framing, and cause the seals of double paned windows to be compromised.

Condensation typically occurs in the winter, but can also form on the outside of windows on hot, humid summer days when your air conditioning on the inside has cooled the interior glass – creating the reverse effect.

Homes built prior to the late 1970s were not built as weather tight as those in later years. With the recent emphasis on energy efficiency and improvements in the construction industry, modern techniques and materials are creating much “tighter” homes. Unfortunately, the by product of these advances is an effect that locks moisture inside.  Without adequate provisions for ventilation, this excessive moisture builds up in the home and produces condensation.

The recommended indoor relative humidity levels for our region is between 35% to 40%, when temperatures are about 10 to 40 degrees Fahrenheit. When you see excess condensation on your windows, that means the relative humidity is too high inside your home.

To reduce the humidity in your home, make these adjustments:

1)     Lower the humidifier humidistat (humidifier controller) to 35%.

2)     Leave room doors open to allow good air circulation.

3)     Make sure the louvers in your attic or crawlspace are open and that they are large enough.

4)     Run your kitchen exhaust fans when you are cooking to remove the condensation from the air and cover pots when boiling water or other liquids.

5)     When showering, make sure that your exhaust fan is on or your window is ajar to allow the moisture-soaked air to vent outside the room.

6)     Crack open you’re a couple of windows for about 15 to 30 minutes once a week to allow for fresh arid air to enter your home.

7)     Open your fireplace damper to allow humid air to escape your home.

8)     Store firewood outside of your home.

9)     In severe cases, purchase a dehumidifier to remove the humid air mechanically.

Gas and electric furnaces reduce humidity with dry heat during winter operation. Air conditioning lowers the moisture level in the air as it cools. Keep registers open and unblocked to allow good air flow, and have the systems inspected and serviced regularly to make sure they are functioning properly. This will help maintain proper humidity levels in your home to avoid condensation on your windows.

John Kolbaska, President      The Men with Tools Home Remodeling

(347) 815-4151    www.themenwithtools.com