During periods of extended cold weather, moisture from the living space or outside sources carried by air movement can accumulate on the underside of the roof sheathing and/or on the roof trusses. It may also occur on the attic side of the insulation, in or on the roof vents and on or around the soffits. The degree of frost accumulation is related to the relative humidity of the house air, the rate of air movement into the attic and the length of the cold spell. When the temperature rises above freezing, or the temperature rises and combined with an intensely sunny day, the frost or ice begin to melt faster than the attic’s ventilation system can exhaust the accumulated moisture.
You can stay on top of this with by preventatively managing your relative indoor humidity.
To find out more, check out the attic rain article on the Alberta New Home Warranty Program website.
Last updated on Mar. 28, 2025