Homeowner Insight
It looks like a roof leak. It almost never is. Attic rain is frost that built up inside your attic during a cold snap and melted all at once when a chinook rolled in, and the fix is usually inside the house, not on the roof.
Hello, Gorgeous! It usually shows up the same way: a brown stain spreading around a pot light, or water dripping from a bathroom fan, a day or two after a deep freeze breaks.
The good news is that it is predictable, it is mostly preventable, and the fifteen minutes you spend on it in the fall are worth far more than the insurance conversation you will have in February.
What Attic Rain Actually Is.
Warm, moist air from inside your home leaks up into the attic. When the attic is far below freezing, that moisture freezes onto the underside of the roof sheathing and the tips of the roofing nails as frost. During a long cold spell, the frost keeps building.
Then the temperature jumps. The frost melts faster than the attic vents can clear it, and the water soaks the insulation and drips through the ceiling. The Alberta New Home Warranty Program describes exactly this, and notes that how much frost builds up depends on the humidity of the air in the house, how much of that air gets into the attic, and how long the cold lasts.
That is why Calgary gets it worse than most places. We get long stretches of deep cold, then a chinook that can swing the temperature by thirty degrees or more in a day or two.
The Winters That Made The News
Attic rain is not rare here. It clusters around the big cold snaps.
| When | What happened |
|---|---|
| February 2019 | A month that stayed below freezing almost the whole way through. One Calgary roofing company told Global News it had taken more than 150 attic rain calls in a single week. |
| January 2022 | CTV reported attic rain across southern Alberta after extreme cold was followed by a rapid warm up. |
| January 2024 | Calgary’s high on 12 January was only minus 30.4, the coldest day since 1989. The warm up that followed brought another wave of calls, mostly from homes built in the last twenty years. |
Sources: Global News, 26 February 2019. CTV News Calgary, 11 January 2022. The Weather Network, 14 and 29 January 2024.
Why Newer Homes Get It More.
This surprises people. You would expect the old bungalow to be the problem. More often it is the house that is five or fifteen years old.
Newer homes are built tighter, so the moisture from showers, cooking and a family breathing all winter has fewer places to go. The places it does find are the holes we cut in the ceiling: pot lights, bathroom and kitchen fans, the attic hatch, plumbing stacks, electrical boxes. Natural Resources Canada lists exactly those as the paths vapour takes into the attic.
So the question is rarely “is my roof bad.” It is “how much warm air is getting into my attic, and can the attic breathe it back out.”
What To Do Before The First Deep Freeze.
Check where your bathroom fans go. Bathroom and kitchen fan penetrations are on every official list of where moisture gets into the attic, and a fan that dumps into the attic instead of ducting outside puts it there directly. If you do not know where yours goes, a roofer or insulation contractor can tell you quickly.
Run the fans, and leave them running. During and after every shower, and when you cook. A timer switch is an inexpensive upgrade that makes it automatic.
Watch your indoor humidity on the coldest days. The Alberta New Home Warranty Program recommends 20 to 25 per cent relative humidity when it is extremely cold. A basic hygrometer will tell you where you are. If your humidifier is set high all winter, turn it down before the cold arrives.
Seal the ceiling penetrations. Weatherstrip the attic hatch. Air seal around pot lights and fans. This is also where your heating bill leaks out, so it pays twice.
Make sure the attic can breathe. Natural Resources Canada says heavy frost of 10 mm or more is the sign to check that your vents exist and are not blocked by insulation, and recommends about one square unit of open vent area for every 300 of insulated ceiling.
If it is already dripping, do not open the attic hatch to look. You let in more warm, wet air at exactly the wrong moment.
If It Is Happening Right Now.
Catch the water. Dry what you can. Turn the humidity down and run the exhaust fans. Keep the hatch closed. Then take photos of every stain with the date, and call a qualified contractor to look at the attic once it has stopped. The stains to watch for are around light fixtures, bathroom fans and along the top of exterior walls.
Who Pays For It. The Honest Version.
Home insurance. I am not going to tell you it is covered, because often it is not. The Insurance Bureau of Canada puts it plainly: “A home insurance policy is not a maintenance contract.” Standard policies commonly cover sudden and accidental water damage, while damage that is ongoing or repeated tends to be treated as maintenance. Attic rain sits awkwardly between the two, so read your own policy and call your broker before winter, not during it.
The new home warranty. If your home was built under Alberta’s mandatory warranty, which applies to homes with permits applied for on or after 1 February 2014, you have one year on labour and materials, two years on delivery and distribution systems like ventilation, five years on the building envelope including the roof, and ten years on major structural components. The Alberta New Home Warranty Program says some causes of attic rain are covered and others, like humidity management, are the homeowner’s responsibility. It is decided case by case, so report it in writing, promptly, with your photos.
Ice Dams Are A Different Problem
People mix these up. An ice dam forms on the outside of the roof: snow melts, runs down, and refreezes at the cold eaves, and the water backing up behind it can work under the shingles.
Attic rain starts inside. Both are made worse by warm air escaping into the attic, which is why air sealing and ventilation fix a lot of both. For ice dams, the Insurance Bureau of Canada also points to keeping gutters and downspouts clear and removing heavy snow from the roof edge safely.
If You Are Buying Or Selling This Winter.
Buying. Ask your inspector to look in the attic for old water staining, discoloured insulation and where the bathroom fans are vented. Look at the ceilings around pot lights yourself. If the home is under ten years old, find out how much of the building envelope warranty is left, because that is real value.
Selling. A buyer’s inspector will find old attic rain staining whether or not you mention it. Dealing with the cause before you list is almost always cheaper than negotiating it afterwards, when the buyer has a quote in hand and the leverage to match.
Thinking About A Spring Listing?
The useful conversation is the one you have now, while there is still time to fix things. We will tell you what is worth doing before you list and what to leave alone, and we can point you to trades our clients have used.
Attic rain is one of those problems that feels like bad luck and is mostly physics. Warm wet air, a cold attic, a fast thaw. Take away the first one and most of the drama goes with it.
Related reading: Your September House List For Calgary And Airdrie and Radon In Calgary.
General information for Calgary and Airdrie homeowners, current as of September 2026. It is not insurance, legal or building advice. Coverage depends on your own policy and warranty. Sources: Alberta New Home Warranty Program; Natural Resources Canada, Keeping the Heat In; Government of Alberta, New Home Warranty overview; Insurance Bureau of Canada; Global News; CTV News; The Weather Network.
Disclaimer: This document is not intended to solicit buyers or sellers currently under contract with a brokerage.