Attic rain occurs when heat and moisture from everyday activities in the home such as bathing, cooking and doing laundry flow into the attic.   When the temperature drops below freezing, this moisture turns to frost.  If humidity is not controlled in the home, the amount of frost that accumulates can be quite thick (up to 8 inches).   The longer the cold period lasts, the more it will accumulate.  Once the temperature raises above freezing, this can lead to something called attic rain.  

 Typically, when the frost or ice changes to liquid water and then to water vapour, it is absorbed into the air and is exhausted harmlessly by attic ventilation to the outside. It may be absorbed by the insulation or the framing and released slowly. It may pool on the polyethylene at the ceiling and evaporate harmlessly.

How to avoid attic rain

• Ensure your humidifiers in your home are properly set.  Your indoor humidity should be set to below 20 % humidity in freezing temperatures.
• Use your ventilation fans to reduce condensation on the interior surfaces of windows in your home.
• Use your bathroom fans when showering or bathing
• Opening drapes or blinds so that warm air can flow and prevent ice buildup.  
• Wipe away any ice buildup or moisture forming on the windows
• Turn on kitchen fans when cooking
• Ensure air circulation is flowing – open all doors in the house.
• Refrain from air drying clothes in cold temperatures
• Keep your home sufficiently warm – especially at night.

Home Inspection

If you think you may have attic rain, make arrangements for a home inspection. While you’re waiting, you can place containers under the leak to catch the water, dry wet areas and place tape over light switches if water has accumulated or is dripping from lighting fixtures. Do not open the attic hatch to dry the attic space as this will allow a more significant amount of humid air into the attic and exasperate the problem. Do not disturb the ceiling in the leak’s location as doing so may reroute the water away from the area.