Read MoreEach year, cold weather brings mysterious moisture issues to many Canadian homes — problems that seem puzzling but are important to address. If you have strange leaks in your ceiling when it’s not raining, or mysterious patches of mold forming on walls, you need to understand what’s probably going on and how to remedy the
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Each year, cold weather brings mysterious moisture issues to many Canadian homes — problems that seem puzzling but are important to address. If you have strange leaks in your ceiling when it’s not raining, or mysterious patches of mold forming on walls, you need to understand what’s probably going on and how to remedy the situation. Even some professionals are stumped by these things.
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The hidden culprit is wintertime condensation. With no possible source of water from outdoors, and no broken pipes leaking, that leaves one source of moisture that’s hard to understand — the heated air inside your home.
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Warm air can hold a surprising amount of moisture, but as it cools its capacity drops sharply. This is the fundamental dynamic that leads to puzzling moisture issues during cold weather, and air leakage is the second half of the puzzle.
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If the air barrier is even slightly incomplete, warm indoor air inevitably migrates into wall and ceiling cavities during cold weather. Even a small flaw in the air barrier can allow this, and as this air cools as it makes its way to exterior surfaces of your home from the inside, it deposits airborne moisture that can turn liquid. Here’s how . . .
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Let’s say the air inside your house is 22C with 50% relative humidity. The air is holding only half as much moisture as it can at that temperature. That’s what “relative” humidity means. It’s relative to temperature. But if that air is allowed to enter the cooler structural areas of a building envelope, that air will cool off and lose some ability to hold moisture. At 12.5C, for instance, that same air will be at 100 per cent relative humidity simply by virtue of the fact that it has gotten colder. Any further cooling forces excess moisture to condense into droplets within insulation, wood framing and anything else nearby. This is the source of mystery moisture, and extended periods of cold weather makes this moisture accumulate in surprising ways.
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When it’s cold enough, this expelled moisture freezes instantly inside walls and ceilings. The longer the cold spell lasts, the larger this frost accumulation becomes. And when the weather finally does turn warm, all that frost melts, leaving you with strange leaks, often on a sunny, warm day. In one extreme example, a contractor came to me for advice on an exterior wall of a new house where gallons of water leaked out from under baseboards in the spring. Yes, gallons. This is extreme, but it shows the dynamic of air leakage and internal frost accumulation. So, what can be done?
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The key is preventing indoor air from seeping into any part of your home’s exterior envelope. This is why plastic sheets are installed on the warm side of fibre-based insulation during construction, but many times breaks around light fixtures, plug outlets, attic access hatches and other elements are behind the condensation issue. Cathedral ceilings are especially prone to condensation. Unlike ventilated attics that let moisture escape to the outdoors above the insulation, cathedral ceilings offer no such relief. That’s why I hear from puzzled and distraught homeowners with wet cathedral ceilings every winter and especially spring.