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 begins to melt faster than the attic’s ventilation system can exhaust the accumulated moisture – this is called attic rain.
What can I expect?
Whether or not this results in water leakage into the living space varies with circumstances. Attics are designed to manage small amounts of moisture accumulation. 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.
Is this something my homebuilder could have avoided?
A homebuilder can minimize the indoor air from reaching the attic by ensuring the air and vapour barrier is as continuous as possible, however air leakage into the attic cannot be completely eliminated. Even a small leak can deposit a significant amount of moisture over a long cold spell if the relative humidity of the indoor air is high.
What can I do to avoid attic rain?
During these long cold spells, you can reduce the amount of attic frost by ensuring the humidity in your home is reduced by turning down the humidifier and using either the Heat Recovery Ventilator (HRV) or Principle ventilation fan (PVF). If an HRV is installed in the home, set the control to continuous operation; if there is a PVF, turn on the switch usually located near the thermostat that is labelled “Ventilation”. Doing this also has the added benefit of reducing condensation on the interior surfaces of windows in your home.
However, occasionally, the water from melting frost accumulates faster than it can evaporate out of the attic. When it melts, it runs to an opening that leads to the interior of the home. It may appear as a wet spot on the inside of the ceiling below the attic or as a water leak around a window or at the bottom of a wall. It could also appear on the outside of the house as icicles or moisture on the cladding.
I’ve done all I can but I still have attic rain… what do I do?
Where the integrity of the ceiling air/vapour barrier has not met the requirements of the Construction Performance Guide for New Home Warranty in Alberta, it may be considered a warrantable defect under the Building Envelope coverage of the New Home Buyer Protection Act. If moisture or water enters your home as a result of an attic rain leak, as the homeowner it is your responsibility to a) notify your homebuilder, and b) notify the Program immediately.
While you’re waiting for your home assessment, stay safe. If required, 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 to ensure the switch cannot be turned on. You should not open the attic hatch in an attempt to dry the attic space as this will allow a greater amount of humid air into the attic and exasperate the problem. Do not disturb the ceiling in the location of the leak as doing so may reroute the water away from the area.
For questions on our home warranty products, to notify us of a defect or to file a claim, please contact us at 1 800 352 8240 (toll-free), Monday through Friday from 8 am – 5 pm.
Note: The Program is a warranty provider and not an emergency service company. Claims are prioritized in the order received and will contact the homebuilder immediately. As claim volumes rise, assessment of your home may take up to 60 days.