Why Does Condensation Form on My Home’s Windows?

window condensation

Every fall and winter, some homes develop window condensation, and it can be a little concerning.  Nobody likes moisture to build up inside their home because it can cause significant damage or even ruin it. Let’s talk about where this window condensation is coming from and how you can stop it from forming.

When you experience “sweaty windows,” it can directly result from the cold air outside your home and the warm air inside meeting one another on a cold pane of glass.  The warm air inside of homes carries humidity, especially if the season is changing, and these are the first few nights of cold weather hitting the area. 

Warm, humid summers leading into warmer than usual autumns can quickly switch to colder, dryer nights.  As windowpanes get cold, the warmer air from inside the house naturally tries to gravitate to the colder, drier air outside the home.

The window condensation that forms can block your view, preventing you from seeing outside.  That condensation can drip onto the windowsill and even down onto the carpet below.  Not good!  On really cold nights, the water can even freeze right on the window.

Suppose you live in an area that gets down to the low 30’s Fahrenheit during December and January. In that case, you are more likely to experience this than others around warmer regions of the country.

How Does Window Condensation Form?

Humidity is water vapor in the air.  Like fog or steam, just on a lower level.  Whether you’re dealing with fog, steam, or indoor air, all of it contains moisture. 

Air can only hold a certain amount of moisture.  And that amount depends on the temperature inside the home.  At 100% humidity, the air has reached a saturation point.  It can’t hold any more water.  At 50% humidity, the air is holding half of its water capacity.  Cooler air can’t hold as much water vapor as warmer air, either. 

Lots of things generate indoor moisture: people doing everyday things in the home, like cooking, bathing, shaving, doing laundry, and working out.  The typical activities of a couple in a home can add up to a gallon of moisture every day to the air inside of a home. 

Learn More:  Moisture Sources in Houses, National Research Council, Canada 

So, is it the windows that cause the condensation?  Well, it’s just like a pitcher of iced tea on a warm sunny day; the difference between inside the pitcher and outside the glass is just the medium.  As I mentioned above, hot air gravitates to cold.  So, warmer humid air is trying to slip through the framing of the windows, glass, walls, and ceiling. You name it!  Windows don’t cause condensation; they provide a cool surface where the water can condense. 

Window Condensation in a 1920s Cottage

Are some houses more susceptible to having their windows sweat than others?  Well, I can tell you on my recent vacation to Yosemite National Park, we stayed in a cottage built in the 1920s.  The room has been upgraded since it was built.  It was nice and cozy, but you could feel cold drafts “coming in” from the edges around the windows and front door.  At the top of this post, you’ll see a photo taken in the cabin, showing the dew forming on the single pane windows and surrounding framing.

Take that cottage and compare it to my house that was built in 2000.  I have never seen condensation form on those windows.  Maybe it’s because the windows are dual pane and the trim is vinyl.  But I can assure you, I’ve personally never been on a service call in the winter where the homeowner of a newer house complained of condensation forming on their windows.  However, I have been to older homes in the Sacramento area that the homeowner has had issues with it.

So, let me ask you this.  Why does almost every bit of information I read about when it comes to window condensation refer to the fact that today’s homes are built tighter than homes built before 1980?  Experts say humidity tends to accumulate in newer, tighter homes and retain it easier than naturally drafty homes built in the old days.  They say this is why newer homes tend to have more humidity issues and sweaty windows than older homes.

I’d love to hear your opinion on this, so leave me a comment down below so we can start a conversation about it.

Window Condensation Can Cause Damage

Excessive interior humidity can be hard on your home because of the types of damage it can cause.  It can damage sheetrock, paneling, and walls (which weakens wood framing and the structure’s integrity).  It can cause the paint to peel from the edges around your window, too. “Sweaty windows” can drip down into window frames, causing dampness and even warping the wood frames.  Nobody wants this.

Is it older homes that seem to build up condensation on windows in the wintertime, or are newer homes?  I can tell you my 20-year-old house has never experienced sweaty windows.  But I have experienced older homes that develop them.

Don’t forget to weigh in, below.

Thanks so much for stopping by, and we’ll see you on the next blog topic.

Don’t miss our video on this topic:  

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