| Quick Answer: A roof that leaks only in winter usually has ice dams pushing meltwater under the shingles, attic frost that melts during a thaw, or worn flashing that lets melting snow seep in around chimneys, vents and skylights. All three are driven by the freeze-thaw cycles common in Gatineau and Ottawa. The lasting fix deals with the cause: attic air sealing, insulation, clear soffit vents and sound flashing. |
Few things are more confusing than a ceiling stain that appears in January when the roof never leaked during summer storms. Rain did not get in, so what changed? The answer is usually snow, ice and the warm, moist air inside your home. Winter in the Outaouais brings deep snow, long cold spells and sudden thaws, and each of those puts a different kind of stress on a roof. This guide explains the most common causes of winter-only leaks, how to tell them apart, and what to do about each one.
What Causes a Roof to Leak Only in Winter?
Winter-only leaks almost always come from water that forms on or under the roof, rather than water that falls on it. Rain runs down a roof quickly. Melting snow sits on the roof for days, and ice can hold that water in place. The main causes are:
- Ice dams: a ridge of ice at the eaves that traps meltwater behind it.
- Attic frost: moist indoor air that freezes on the cold roof boards and melts when temperatures rise.
- Flashing and caulking gaps: small openings that rain runs past but standing meltwater soaks into.
- Wind-driven snow: fine snow blown through vents and into the attic during storms.
Each one leaves different clues, so where and when the water shows up can point you to the cause.
How Do Ice Dams Cause Winter Roof Leaks?
Ice dams form when heat from the house warms the upper part of the roof. Snow there melts, runs down the slope and refreezes at the colder eaves, building a ridge of ice. More meltwater then pools behind that ridge with nowhere to go. Shingles are designed to shed water downhill, not to hold back a pond, so the water backs up under them and drips into the walls or ceiling near the outside walls of the house.
Leaks from ice dams usually appear near exterior walls, around window tops, or in the ceiling close to the edge of the roof. They often show up a day or two into a thaw. You can read more in our guide to ice dams on your roof, including causes, prevention and repair in Gatineau.
Can Frost in the Attic Look Like a Roof Leak?
Yes, and it fools many homeowners. Warm, moist air from bathrooms, the kitchen and everyday living rises into the attic through small gaps around light fixtures, the attic hatch and plumbing stacks. When that air touches the cold underside of the roof, it freezes into a layer of frost. During a mild spell, the frost melts all at once and drips onto the insulation and ceiling. This is sometimes called “attic rain.”
According to Natural Resources Canada’s guide to roofs and attics, moisture can be carried into the attic as water vapour by air leakage, and the best way to prevent ice damming is to seal attic air leaks and insulate well. Ventilation is the second line of defence. In other words, the same attic problems that cause frost also feed ice dams.
Frost-related drips tend to appear in many spots at once, often well away from the outside walls, and they stop when the attic dries out.
Why Does Flashing Leak in Winter but Not in Summer?
Flashing that is slightly loose or has cracked caulking can survive a summer storm because rain moves past it quickly. In winter, snow piles up against chimneys, skylights and walls, then melts slowly. That water sits against the gap for hours or days and eventually finds its way in. Freeze-thaw cycles also widen small cracks each time water inside them freezes and expands.
Leaks around a chimney, skylight or plumbing vent that appear during a thaw are a strong sign that the flashing or caulking needs work. Cossette’s roof repair service covers flashing, caulking, soffit, attic ventilation and waterproof membrane repairs for all roof types.
How Can You Tell Which Problem You Have?
Where and when the water appears gives you the best clues:
- Near the outside walls, during a thaw, with ice along the eaves: most likely an ice dam.
- In several places at once, away from the walls, after a cold snap ends: most likely attic frost.
- Around a chimney, skylight or vent: most likely flashing or caulking.
- After a windy snowstorm, near a roof vent: possibly wind-driven snow.
These are only clues. Many winter leaks have more than one cause, and a roofer who checks both the roof and the attic can confirm what is going on.
Keep a simple note of each leak: the date, the weather in the days before, and exactly where the water appeared. A roofer can use that record to narrow down the cause much faster, especially when the drips have stopped by the time of the visit. Photos of icicles, ice along the eaves and any stains inside are useful too.
What Should You Do If Your Roof Starts Leaking in Winter?
Act quickly, but stay off the roof. Snow and ice make roofs extremely slippery, and falls are a real risk. Inside the house:
- Place buckets or containers under the drips and move furniture and electronics away.
- If a ceiling bulges with water, keep people out of the room.
- Take photos of the damage for your records and your insurer.
- Call a professional roofer.
Cossette Roofing provides 24/7 emergency roofing service across Gatineau, Ottawa, Hull, Aylmer and the Outaouais, 365 days a year. Emergency calls include water infiltration, ice dam formation and snow overload. The crew can apply temporary waterproofing to protect your home until permanent repairs can be made.
How Do You Stop Winter Leaks From Coming Back?
Lasting fixes deal with the cause, not just the drip. For ice dams and attic frost, that usually means sealing air leaks into the attic, improving insulation, and making sure the soffit vents are clear so cold air can flow under the roof. For flashing leaks, it means resealing or replacing the flashing and caulking. Cossette’s residential services include attic inspection and ventilation correction, as well as caulking renewal around chimneys, plumbing vents and skylights.
Fall is the best time for this work. A roofer can still see the whole roof, and repairs can be finished before the first heavy snowfall.
Frequently Asked Questions
Why does my ceiling only get wet when the snow starts melting?
Melting snow sits on the roof longer than rain and can be trapped behind ice at the eaves. That standing water finds small gaps in shingles and flashing that rain would simply run past. Leaks that start during a thaw usually point to ice dams or flashing problems.
Is frost in my attic normal in winter?
Some light frost during a deep cold snap can happen. Heavy frost on the roof boards, or frost that melts and drips onto the insulation, means warm, moist air is getting into the attic. Sealing air leaks and checking ventilation usually solves it.
Should I remove ice dams myself?
No. Climbing on an icy roof is dangerous, and chipping at ice with tools can damage shingles and gutters. Call a professional roofer, who can deal with the ice safely and find out why it formed.
Will a winter leak go away on its own?
The drips may stop when the weather turns cold again, but the cause is still there. Each thaw can bring more water, and wet insulation and roof boards can lead to mould and rot. Have the roof and attic checked as soon as you notice a winter leak.
Does Cossette Roofing do emergency roof repairs in winter?
Yes. Cossette Roofing offers 24/7 emergency service 365 days a year, including holidays, for water infiltration, ice dams and snow overload. Call 819-777-7177 at any time.
Summary
Winter-only roof leaks almost always come from water that forms on or under the roof: ice dams, attic frost or meltwater seeping past worn flashing. Where and when the water appears points to the cause. The lasting fix is to seal attic air leaks, improve insulation, keep soffit vents clear and reseal flashing, ideally in fall. If a leak starts in winter, stay off the roof and call a professional, because Cossette Roofing answers emergency calls 24/7.
Key Takeaways
- Roofs that leak only in winter usually have ice dams, attic frost or worn flashing and caulking.
- Ice dam leaks show up near outside walls during a thaw; attic frost leaks often appear in several places at once.
- Warm, moist air leaking into the attic is a common cause of both frost and ice dams.
- Stay off icy roofs, protect your belongings, and call a professional when a winter leak starts.
- Lasting fixes include air sealing, insulation, clear soffit vents and resealed flashing, ideally done in fall.
Need help with your roof? Call Cossette Roofing at 819-777-7177 or request your free estimate.