What Causes Window Condensation?


Each winter more and more homeowners become interested in the subject of window condensation. It’s not a happy subject. It stems from bad experiences with window condensation, which range from irritating to downright expensive.

It may strike you as odd, but the growing condensation problems of the nation are caused by progress. Yes, if you have trouble with window condensation it’s probably because you live in a “tight” modern home that you can heat for a fraction of the money it takes to heat the house your parents lived in. And your condensation problems also result from widespread use of several labor-saving appliances that make life easier than it used to be.

This series of posts explains the moisture problems of the “tight” home. It offers suggestions for curing condensation problems in existing homes and provides suggestions for those who are planning a home. While you should build a “tight” home, there are several things you can do to PREVENT excessive moisture when you build.  This will do more to combat this problem than can be done in a home where the problem already exists.

What Causes “Trouble” Condensation?

A little fog on the lower corners of your windows now and then probably doesn’t bother you and shouldn’t. By the time you’ve thought about it a second time it has usually gone away.

What we’re talking about is EXCESSIVE condensation. Condensation that blocks whole windows with fog or frost. Water that runs off windows to stain woodwork… or in serious cases even damage the wallpaper or plaster. If you have this kind of condensation on your windows, you have a good reason worry and a good reason to act.

Don’t worry so much about the windows…where you can SEE the effect of excess humidity. You should worry more about what excess moisture may be doing elsewhere in your home. It may be freezing in the insulation in your attic where it will melt and damage your plaster exactly like a roof leak when warm weather comes. It may be forcing its way out through siding to form blisters under your exterior paint. That means the most expensive kind of a paint job.

It’s natural and easy in such cases to blame the paint or the insulation or the windows. But it’s wrong to blame them.

The real villain is invisible. It’s water vapor…too MUCH water vapor. The best and usually the ONLY way to prevent this trouble is to get rid of excess water vapor. Once you’ve installed modern, high-performance windows with insulated glass, there isn’t very much more you can do to the windows to stop condensation.

In our next post on window condensation, we’ll cover humidity and how moisture gets trapped in tight spaces. Read it here!