Condensation Leaks

Apart from a winter leak that may sometimes rear its head as a result of an ICE DAM, there is another type of winter leak that some homeowners experience due to… CONDENSATION.

Here’s what and how it can happen…

We have a string of cold (freezing) days; often in combination with a blanket of snow. Snow is an effective insulator. More on that later.

We live our daily lives… cooking, showering, laundry, socializing, perhaps even cranking up the heat to counter the cold weather outside.

Now, we all know that air is laden with moisture. In fact, the warmer the air, the greater the volume of moisture air can hold. Think rain forest. We also know that warm air rises and (naturally) travels to any area that is cold.

Our attics are cold in winter. They’re designed and built that way. The Ontario Building Code mandates air/vapour barriers & insulation for the sole purpose of containing warmth inside our homes to keep us comfortable while preserving energy.

But what if all that warm air wasn’t contained in our living spaces and air was escaping? What if, for example, there was a breach in the air/vapour barrier? Perhaps there are recessed pot lights in the ceiling that are not air tight? Perhaps a bathroom exhaust fan vents into the attic? Perhaps a faulty reno job from the past or sub-standard workmanship from the homes original construction? All very common.

Let’s go back to a “string of cold (freezing) days.” Imagine now, warm air on a continuous migration escaping into a cold attic. That warm air (overtime) becomes saturated. Eventually, it condenses into liquid water. Condensation takes the form of ice / frost that settles on any building component inside the attic. Uninsulated steel girders, ducts, electrical boxes etc are the worst. The longer the stretch of consecutive freezing days… the greater the build-up. Remember how a blanket of snow is an effective insulator? Snow contributes to keeping the attic cold. No outside help here to raise the attic temperature limiting the formation of ice / frost.

Imagine now a rise in temperature. Snow begins to melt. As it warms up, so does the temperature inside the attic. And now, you have a roof leak. Or so it seems.

But, the ROOF is not leaking. Moisture intrusion to the homes interior is coming from inside the home, the attic. Condensation leaks cannot be underestimated. It can cause severe damage. It can also act slowly, revealing moisture stains or blisters to the drywall. And, no roofing product will prevent it. Ventilation may help but the real solution is getting to the cause; control air movement. That’s Building Science 101.

If your roof does not leak during the severest downpour of rain & only during winter, it is powerful evidence that the problem is related to condensation.

It’s not surprising homeowners jump to the conclusion that it’s a roof leak. After all, it can’t be seen and it’s coming from above. With luck, this article will help you ask the right questions…

Does the roof need to be repaired or does an internal environmental issue need to be corrected?

  • Tim Mulroy