“ROOF” LEAK ON A SUNNY DAY?: Melting Attic Frost May Be the Cause

Q: Earlier this spring I heard a faint drip-drip sound coming from the attic of my 17 year old bungalow. When I opened the attic hatch, I found the edges of the hole to be wet. There’s also lots of frost on the plumbing vent pipe as it goes through the attic. My handyman tells me there’s no need for action. What do you say?

A: If this were my attic I’d certainly do something. The source of the moisture you see comes from indoor air that’s been leaking into your unheated attic space all winter. As this air cools, it loses some of its ability to hold water. This water comes out as liquid or frost depending on how cold the surface involved is. One reason that unheated attics like yours are ventilated is so moisture from wintertime condensation can leave harmlessly as the weather warms up and the summer gets hot. The thing is, air leaks and the resulting condensation are never a good thing. A little leakage is inevitable, but the less the better. The fact that you could hear some water dripping tells me that too much condensation is building up.

Generally speaking, the #1 source of leaked air in attics is the attic hatch. I can see from the photos you sent that it’s insulated on top (that’s good), but it’s also probably leaking air around the edges. The fit looks tight, but the fact that there’s condensation around the edges proves that air leaks are happening. Indoor air could be making its way into your attic through electrical boxes for light fixtures, but attic hatches are typically the biggest culprit. One simple way to ensure a 100% seal around the hatch is by applying peelable caulking to the seam when the hatch is closed. The best stuff is clear and seals well, though it can be peeled off whenever you want.

One other way of tackling this issue is to increase the amount of ventilation area in your roof. Next time you have the roof shingled, have a ridge vent added. Also, it’s not clear in the photos you sent, but your attic insulation might be blocking the free flow of air through the vents at the eaves of your roof. While limiting the amount of leaked air entering  your attic from indoors is one part of the fix, boosting air circulation through the attic is another. Ask your handyman to check that the soffit vents are clear, then have the hatch sealed up.

Understanding Vapour Barriers

Vapour barriers are tricky to understand, but they’re crucial to this whole issue. Even many professional builders don’t have a correct understanding in their minds. Click here for a detailed video tutorial on how vapour barriers work and why they’re necessary in a cold climate.

Posted on March 27th, 2020

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