Attic Rain

What is it, and what causes it?

Attic rain occurs when warm, moist air sneaks into the attic, freezes during cold weather and then melts during warm spells, leaking water into the home. 

Ice and frost buildup from condensation in the attic is inevitable, and nothing can completely prevent attic rain from happening. This is something that naturally occurs with the drastic temperature swings from our Alberta winters. 

With good airflow in an attic, a small degree of attic rain shouldn’t be a problem for many homeowners because the moisture that drips into the insulation will evaporate naturally. It becomes more of a problem when extra moisture is released into the attic and then finds its way back into the home.

Common telltale signs are water stains on the ceiling or water dripping through a ceiling fan or ceiling lights. Leaks like this may not be because your roof is compromised but instead could be due to inadequate ventilation and insulation in your attic.

Another type of drip occurs with skylights. The metal and glass surfaces of skylights tend to be considerably colder than the rest of the house, especially when the outside temperatures are very cold for an extended period of time. These combine to create condensation on the edges of the skylight, which then melts when it warms up. A common but short-term fix is simply placing a towel under the drip.

Unfortunately, attic rain can be more common in newer as more energy-efficient homes that do a better job trapping warm air and moisture. Older, poorly insulated homes tend to have hot attics.  Because of extensive and expensive heat loss into the attic, it can get quite warm up there, and it will “burn off” frost before it has time to build up.  This heat is not a cure all, as it can do significant damage to your roof sheathing and shingles.

As far as solutions go, there isn’t a one-size-fits-all, especially with something that happens infrequently.

How to Mitigate Attic Rain Damage

Almost all condensation issues must be addressed in the attic. So check out your attic periodically to see what is going on up there. This is a good time to see if all your fan hoses from the house are properly connected to roof vents to prevent moist air from escaping into your attic. 

Anticipate cold weather and avoid using your humidifier; use your stove hood exhaust fan whenever cooking, and leave your bathroom fan running an extra 15-20 after you shower.

Air ventilation is key to removing moist air from your attic. Are your soffits blocked by insulation? Some homes may need updating by adding more ventilation in accordance with the existing building code. 

Older attics may have a compromised vapour barrier or none at all.  Inspect your vapour barrier and seal holes with insulation tape or spray foam.

Upgrade your insulation.  If you have a very low level, it will promote more heat loss into the attic, carrying more moisture with it.

If you come across anything questionable, take some images and send them to your local roofing or insulation company, to evaluate.