ASK THE INSPECTOR: Lots of reasons for attic and roof leaks

By: Ari Marantz

Updated: February 22, 2014


The most effective measures that homeowners can take to prevent excessive moisture intrusion this spring is to reduce indoor RH and shovel their roofs.

QUESTION: I have been in the roofing business for many years as the owner of Dr. Roof, and I have a concern that I would like to discuss with you and I wish you would share with your readers.

With such an extended period of extremely cold temperatures this winter, combined with the heavy snow loads, we are expecting huge problems with condensation and ice-dam leaks once the temperatures rise above freezing. There has been little to no freeze/thaw cycles this year, which appears to be causing larger-than-normal frost and ice buildup in attics, roof and wall cavities. Once the warmer temperatures hit, this ice and frost will melt, causing what appears to be roof leaks.

With all the home improvements people are doing, like installing new high-efficiency furnaces and new windows, these frost and ice dam problems are getting more frequent each year. Customers call to say their roof is leaking when in fact there is nothing wrong with the roof. The moisture is coming from inside their attics and ceiling cavities, not from outside.

What are your opinions on this?

Norm Gregoire


ANSWER: Problems with attic moisture and relative humidity (RH) is increasing in homes due to furnace upgrades and tightening of building envelopes, but whether that translates into actual leakage can be extremely unpredictable.

For example, moisture issues often occur after chimneys are closed when a high-E furnace is installed, especially when windows are replaced at the same time. But whether this becomes a bigger problem than usual when this winter’s extended cold streak finally ends is yet to be seen.

I get numerous calls every year about this problem occurring in homes with vaulted ceilings and knee-wall attics, where moisture buildup is expected. But some years I also get inquiries from many homeowners who are suddenly faced with water leaking into walls, ceilings or windows even though they’ve never experienced this previously. Sometimes it seems to be related to energy-efficiency improvements, but other times it’s more of a mystery.

Surprisingly, some homes appear to have more attic frost and moisture issues after newer roofing is installed, even when more vents are installed. I can’t say exactly why this occurs, but it may be that the old, worn shingles allowed some moisture to escape, while the new ones are well sealed and trap this moisture in the wood and the attic. This normally causes little concern, other than a large amount of frost visible when someone looks into the attic, as long as attic ventilation is increased to compensate for the new roofing.

Sometimes, the problem can be linked to weather. I vividly remember getting dozens of calls from frantic homeowners a few years ago about leakage in late winter and early spring. There had been unusually warm and wet weather well into November, followed by a sharp drop to sub-zero temperatures for a several months.

My conclusion was that this left many homes with unusually high amounts of moisture trapped in their attics which suddenly froze and then melted quickly during the first thaw.

Even with the unusually large amounts of frost you and I are both seeing in attics this winter, it may not lead to major leakage if the weather gradually warms. As long as we don’t get a very sudden thaw, with temperatures rising from the recent minus-20s and minus-30s to above zero overnight, many homes may be fine. Attic frost should melt slowly, allowing evaporation, if we get a gradual warmup over the next couple of months.

But if we get a very sudden thaw, look out!

The most effective measures that homeowners can take to prevent excessive moisture intrusion this spring is to reduce indoor RH and shovel their roofs. Keeping indoor moisture levels low can often be accomplished by using bathroom and kitchen exhaust fans for a longer period of time, ensuring dryers are properly vented and running furnace fans continuously. Shoveling the roof will reduce the amount of raw material for ice dams and allow the sun to warm the roof deck and slowly melt frost on the underside of the roof sheathing. But safety first. It may be best to leave this job to a properly trained and insured roofer.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the President of the Canadian Association of Home & Property Inspectors – Manitoba ( Questions can be e-mailed to the address below. Ari can be reached at (204) 291-5358 or check out his website at