Cottage Q&A: Wet windowsill fix

A hand wiping a wet windowsill with a green cloth By mady70/Shutterstock

When we checked on our cottage this winter, I noticed that condensation had puddled on the windowsills. Can we prevent this from happening? The cottage is not heated through the winter, and we do not regularly use it.—Margaret Robinson, via email

You know the science: if warm, humid air inside the cabin meets the cooler surface of a window in winter, condensation forms on the glass.

It’s possible that the air inside warmed up because of the sun. “You could envision how passive solar heating of a cottage could create moisture deposition problems inside,” says Don Fugler, a building scientist in Ottawa.

But, more likely, says Darrell Paul, the managing director of Qualistat Building Performance Consultants in Olds, Alta., is that the condensation is an after-effect of the last time you were at the cottage—when we assume you turned on the heat and then engaged in other humidity-producing behaviours: cooking, showering, and breathing.

In either case, the best way to prevent condensation is to increase ventilation to the cottage. Simple enough while you’re there. Trickier while you’re not. Almost anything that allows outside air into the cottage will help; the problem is “How do you do that safely, in a way that animals won’t get in?” says Fugler. If your chimney is covered by a pest screen, you could open the damper; you could leave a few windows partially open, covered with hardware cloth; you could also install new openings in the cottage, such as fresh air-intake ducts.

If you have reliable power, a small fan—either rated for continuous use or triggered by a humidistat (it responds to relative humidity)—is an alternative.

This article was originally published in the Winter 2017 issue of Cottage Life magazine.

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