Condensation is the fog that forms on the interior or exterior of window and patio door glass when cold weather sets in. This can freeze blocking the view out the window or door, or it can drip on to the windowsill or floor causing structural damage over time. Many people assume that the windows are to blame for this. However, the inside surface of the window is just providing a visible location on which the excess humidity in your home is able to condense. It is important to realize that condensation can be occurring elsewhere in your home that is not as visible as on the window glass. Condensation can be a sign that damage to other parts of your home may be occurring. A few signs of excessive humidity: Dampness in the home that can cause walls and ceilings to discolor Closed areas such as closets and cupboards forming mold or having a musty smell Wood warping Paint on the home’s walls blistering and cracking Water condensing on pipes and window glass


What is condensation and what is causing it to form?

Condensation is water vapor from the air that is deposited on a surface when the humid air near the surface is cooled. The water forms since cool air is not able to hold as much water vapor as warm air.

What is humidity? Humidity is the moisture in the air. It is usually only visible when it is in a concentrated form such as steam vapor or ground fog. Otherwise, all air contains a certain level of invisible moisture

.What could be causing this moisture in my home?

Many of your everyday activities can add more water vapor to the air and raise the relative humidity of your home. The breathing of a family, cooking meals, taking showers, washing dishes and doing laundry will contribute to making the air in your home more humid.

What is air’s relative humidity?

The amount of water vapor that air can hold is its relative humidity and is limited by the air’s temperature. 100% relative humidity occurs when the air contains as much water vapor as possible at that air temperature. When the air contains half that much water vapor it has a 50% relative humidity. As the temperature of the air drops, the maximum amount of moisture it can hold also drops. So when air is 40oF and has 75% relative humidity it contains less moisture than when the air is 80oF and has 75% relative humidity.

Are there ways to tell if there is excessive humidity in my home?

Moisture forming on windows, paint blisters full of water on the home’s exterior, and moist areas on the walls of closets and cupboards that are on an exterior wall are all indicators that your home has a problem with excessive humidity inside.

Are there any health problems that can arise from excessive indoor humidity?

Yes. With moisture condensing on surfaces, molds can begin to grow. Mold growth is evident by a musty smell in the general area of its growth. Some people can have more serious problems ranging from headaches and respiratory problems to allergic reactions from certain types of mold.

What regions of the country are more likely to have condensation occur?

It is more likely to have condensation problems in regions where the average temperature during the winter months is below 35oF. Is excessive humidity damaging to my home? It can damage your home’s ceiling and walls when the frozen moisture thaws in the spring. It can also cause pressure on the exterior surfaces of the house causing blistering of the paint or siding.

How can the humidity go through the wall and what is the effect?

The water vapor in air tries to be equal. Since the air in your home is warmer and contains more water vapor, it tries to have an equal amount of water vapor as the cooler air outside your home. This equalizing is vapor pressure. It will move through porous materials such as cement, wood, plaster, brick and other types of masonry until it reaches a water-tight barrier such as the paint or siding on your home’s exterior wall. It will collect under the watertight barrier and cause blisters in the paint or siding. The water that collects in these blisters on wood surfaces will then start to rot the wood.

Is winter the only time of year that condensation happens?

People with low-E glass in their windows can see condensation on the exterior of the window at other times of the year. Since low-E glass is so efficient, it causes the window to have a lower surface temperature for a longer time during the day. Humid summer days are a good example of this. The warm, humid air outside will form condensation on the outside window glass since the air conditioner is keeping the window glass cool.

How will my home’s age affect my condensation problem?

Homes built years ago were not built to be as tight and energy efficient as homes today. Older homes were built with more porous materials that allow the water vapor to move more easily through the walls. Builders use much tighter materials when building today’s homes to make them more energy efficient. These modern materials and building techniques that are designed to better keep the cold outside, also keep the water vapor inside. This prevents the escape of moisture generated from everyday family activities. The homeowner must rely on mechanical methods of removing the excessive humidity from the air instead.