Ice buildup on interior window

Asked January 7, 2015, 1:02 PM EST

Every winter we get ice build up on our interior windows and when it melts it leaves a wet mess on the sills. See first photo - we had a vaporizer in a small bedroom and woke up to very thick ice covering the bottom. It's never been this bad. We try to dry up the melted ice (when it finally gets warmer) with a towel but it's starting to leave mold in the corners of the sills (see second picture). What can we do to prevent this mess?

Clay County Minnesota

2 Responses

The response somehow got deleted. I am working on it for you It is all about moisture control in your home and the extreme cold surface of the window this winter. Until I respond search our site for moisture control in the home. Additional information is included in a search for Controlling mold and mildew in the home.

Warm air can contain more water vapor than cold air. Each 20 degrees the temporature drops the air's ability to hold moisture is cut approximately in half. When warm indoor air that is over 50% relative humidity and 70 degrees hits any cold surface, like a window, that is below 30 degrees it will go to 100% RH and then loose half of the moisture that it contained on the cold surface. Since that surface is below freezing that condenced water will freeze.

You see this happen every time you have a cold beverage. The glass or mug that contains the iced beverage has water droplets collect on the outside. Those droplets come from the warm, humid air.

To solve your problem you need the manage the moisture in your home and make those window surfaces warmer. Moisture control in your home reqires venting the moisture from kitchen and bathroom activities, checking for leaking plumbing and fixing moisture problems in basement or crawlspace. The indoor humidity should not be lower than mid 50% for comfort.

You can warm the windows with weatherizing or added glazing. Storm windows or the plastic film that comes in the window weatherizing kits are ways to warm that cold surface.

Check our literature on weatherization, home moisture control and mold & mildew contol.