Reining in the occurence of attic rain

A thin ribbon of water trickles through a vent from the ceiling into your living room. Adjacent a greying patch seems to grow on the ceiling drywall. You are perplexed. “This house isn’t even a year old, what is going on?”

You probably have a case of Attic rain (also known as Frozen Attic Condensation). This phenomenon is caused when humid air collects in the attic and then when the plummeting temperatures (typically found in Alberta), cause the air to form frost. Then, in the event of rapidly warming temperatures (a chinook for example) this frost then pools and drips into the ceiling.

This phenomenon can occur in new homes because modern homes are much more airtight than those of their predecessors. Those older homes naturally contain a bit more draft allowing warm air to escape and so the occurrence This phenomenon can occur in new homes because modern homes are much more airtight than those of their predecessors. Those older homes naturally contain a bit more draft allowing warm air to escape and so the occurrence of frozen attic condensation is generally non-existent even while the escaping air incurs extra cost. New homes, however, are much more energy efficient. In the same way, because these homes have seals that are much tighter, warm, moist air from bathrooms or kitchens that may collect in the attic becomes trapped. This then can convert to snow and ice as a result of extreme temperature drops. This effect seems surprising in new homes, but the reality is that no home is 100% sealed and there is always some condensation in the air, meaning that even simple negligence in restoring the seal on the attic hatch can have compounding effects.

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Avoid the situation:

In general, run your bathroom exhaust fans after bathing or doing laundry, and ventilation fans and range hood fans while and after cooking to avoid humid air collecting in attic spaces.

Then, ensure proper ventilation throughout your home by doing these three things:

Do not overly use your humidifier. The humidifier settings in winter are lower than in summer and the relative humidity becomes significantly less with every 5-6 degree change outdoors. That said, the relative humidity in your home, even in summer, should never be above 40%. If the relative humidity in the interior of the home is too high, the moist air will actually make you feel colder. Certainly, if frost is forming in your attic you should turn your humidifier down. Here is a helpful guide to help gauge:

When the Outdoor Temperature Is (deg. C):The Relative Humidity Should Be:
-7 to 4< 40%
-12 to -7< 35%
-18 to -12< 30%
-23 to -18< 25%
-29 to -23< 20%
-29 or below< 15%
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Please note that you can email if you have lowered the humidity and any issues still persist.

Ensure roof vents on the exterior of your home are clear of ice, snow and debris. The pipes that siphon air in and out of the home can easily become blocked. Make sure to frequently do a quick check of these pipes at the exterior of your home after a heavy snowfall.

Keep the attic hatch closed. Check that this is properly shut and the seal is firm because even a little bit of air flow can contribute to the attic rain problem. Also check the attic frequently in winter and after drastic temperature changes to inspect whether this problem is occurring in your home. Another tell-tale sign of too much humidity is ice or water collecting at the bottom of your window sills in main living spaces.

If Frozen Attic Condensation occurs:

In the event that you do notice water in a light fixture, do not turn the light on. Instead, turn off the breaker to the light and call for service. Then wipe up water from floors, carpet and furniture. Similarly check your attic frequently in winter.

In some cases, re-caulking around bathroom vents and light fixtures can help avoid the passage of humid air into the attic, something that may be attended to during a service call. In general, however, to avoid this incidence, include frequent surveillance as part of your regular home maintenance during the winter, to ensure there is no unwanted frost build-up.

As you adapt to your new home, you will discover the right balance of humidifier and ventilation to keep you adequately warm and have optimal air flow. New homes have whole-house ventilation systems that exchange all the air inside the home with the outside air to ensure that moisture is removed. This ventilation system is called the HRV and is required to be on when you want airflow. It is very inexpensive to run and helps create a home and atmosphere that sufficiently breathes.

Feature Image Courtesy of Kevin Flemming with Calgary CTV News


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