One of the most common problems I hear about is “leaky windows”. It seems like everybody’s got them—why do you suppose those replacement window companies are always phoning you during your dinner looking for your business?

Once the temperature starts to drop, many people start finding their windows are fogged up or covered in condensation—sometimes it’s so bad there’s water pooling on the windowsill or floor.  So why do we care about a bit of water pooling on our windowsills in the winter? Is that such a big deal? Yes, it can be.

Mould is one reason--it can grow anywhere that it has enough heat, a food source--and moisture. Moisture can also cause structural damage, like rot and rust, as well as damage to surface finishes.

Where does all the moisture in your house come from? It can get in through your roof--if you have a leak--or through your basement’s concrete walls and floor. Remember, concrete is porous, and water can move through it from the soil outside. But, most of the moisture in your house comes from you—from your shower, your cooking, your washing machine, your dishwasher, your breath.

When people find they’ve got sweaty windows, the first thing they do is call in a replacement window company, and spend a lot of money putting in new windows. That might make sense, but I’ve seen these problems with new windows too. So what causes wet windows, and what can you do about it

Condensation happens when the warm air inside your house hits a cold surface—like the glass in a single pane window.  Newer windows are double glazed, and usually have an inert gas—like argon or krypton--in between their panes, which provides some insulation and reduces the chance of condensation.

Between the two panes of glass there should be an airtight seal.  If the seal is cracked, you’ll get condensation in between the two layers of glass – usually on the inside surface of the outside pane of glass.  That’s because the outside pane is the coldest surface.

If you have a cracked seal, you probably do need to replace your windows. But, if they seem fine, and you still have condensation on your windows, the reason is probably air leakage—somehow there is air movement between the warm area inside your home and the cold world outside. That’s not what we want—ideally we want to make sure there is an envelope around your home, keeping the warm air in and the cold air out.

How do you get air leakage around your windows?  I see it all the time--they weren’t properly installed and insulated. Cold air gets in and around the window and creates condensation.  It’s easy to check by carefully removing the interior trim and looking to see how much insulation there is--or isn’t. Then spray in some low-expansion foam—but make sure you read the directions carefully. If you use the wrong type of foam, or use too much, your windows won’t work properly.  Adding some insulation is a lot cheaper than replacing your windows, so try that first.

There are other possible causes for condensation on the inside of your windows:

1. If you have a new home that was built within the last 2 years it is possible that your wood framing is full of moisture. Have you ever seen a new development being built where they cover the piles of framing with tarps to keep the rain and snow off? No, I didn’t think so! That wood will soak up moisture, and will continue to let that excess moisture out until it is dry—go figure—and that will be happening within your walls.

2. It might be that your home is very well built, and as a result is too airtight. Think about it--try to blow into a bottle—you can’t. With the weak exhaust fans that are installed in many homes’ bathrooms (minimum code again), you will be lucky if even the slightest amount of air gets expelled. Poor air movement in your home will cause condensation. So, open a window just a crack downstairs and install stronger, better quality exhaust fans. These exhaust moist air from inside your home and replace it with dry, fresh air from outside.  This will help you create some air movement. You may also want to look into a Heat Recovery System (HRV).

3.  It is possible that you have a problem with your H.V.A.C. (Heating, Venting and Air Conditioning). For that you should contact a qualified Heating Contractor.

If you control the moisture in your house, and make sure your windows are properly installed and insulated, you can get rid of your wet window problems.