dampness – BIG

We have a cottage built on a slope. The unfinished basement floor is always damp, which results in high humidity levels inside the cottage, as well as a musty smell. We’re looking for a way to reduce the humidity and get rid of the smell. Would covering the basement floor in plastic sheeting and topping it with fine gravel be a solution?—Mieke Foster, via email

Yes, it would be a solution. But it might not be the best solution if you don’t figure out what’s making the basement damp in the first place and fix that problem before covering the floor.

Moisture can get into basements in all kinds of sneaky ways, but an obvious one, given that the cottage is on a slope, is that surface water is draining into the basement through “the inevitable cracks in your basement walls,” says Kim Pressnail, an associate professor emeritus in civil and mineral engineering at the University of Toronto. If that’s the case, yay for you! “Surface rainwater is often the easiest to control,” he says. Use topsoil and gravity; regrade around the perimeter of the cottage so that the ground slopes away from the walls instead of towards them. Create a “one in 12 slope—the soil drops one centimetre for every 12 cm from your cottage,” says Pressnail. “That will more than do.” And make sure that your eavestrough downspouts are directing water well away from the building.

Is the cottage below the water table? Then both rainwater and groundwater could be getting in through those basement wall cracks. “Water also may be entering through the walls because they’re in contact with moist soil,” says Pressnail. “It’s known as ‘capillary wicking.’ The soil moisture can ‘wick’ through your masonry or cast concrete below-grade walls and evaporate into the interior basement air.” Or, water may be evaporating up from the unfinished floor. “It’s like a soggy cracker,” says Pressnail.

So much water! These issues are more complicated to diagnose and treat, and you’ll probably need expert help (from, for example, a contractor). But once you get rid of the moisture source, “the musty smell should gradually diminish,” says Pressnail. “Operating a dehumidifier in the basement during the warmer months may help.”

The article was originally published in the June/July 2022 issue of Cottage Life magazine.

Got a question for Cottage Q&A? Send it to answers@cottagelife.com.

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.

Got a question for Cottage Q&A? Send it to answers@cottagelife.com.