Attic Rain in Calgary: Why Your Ceiling Drips When It Isn't Raining
Attic rain is frost that builds up on the underside of your roof sheathing during cold snaps, then melts and "rains" inside your attic when temperatures swing back up. The cause isn't your roof - it's warm, humid air from your living space leaking into the attic, freezing against the cold wood, and waiting for a chinook.
In Calgary, where January can jump from −30 °C to +10 °C in a day, attic rain drenches more ceilings than actual rainstorms do. I'm Gjin Bajraktari, the founder - February calls about "mystery leaks" are half my winter.
What Causes Attic Rain - The Actual Mechanism
Attic rain follows a four-step chain, and every step has a fix.
- 01
Humid indoor air escapes upward
Showers, cooking, humidifiers, even breathing push moisture into your house air. It rises and slips into the attic through gaps - pot-light housings, the attic hatch, bathroom fan ducts, plumbing stacks, and wire penetrations.
- 02
Moisture freezes on the sheathing
During a cold snap, the underside of your roof deck can sit at −25 °C. Humid air touching it deposits frost, layer upon layer, sometimes for weeks.
- 03
A chinook melts it all at once
Calgary's signature warm wind can raise temperatures 20+ degrees in hours. The accumulated frost melts far faster than it can evaporate.
- 04
Water soaks insulation and drips through ceilings
It shows up as stains around pot lights and bathroom fans - the exact spots where the warm air escaped in the first place.
Newer Calgary homes get it worse, not better: tighter building envelopes hold more humidity, and high-efficiency furnaces don't pull air up the chimney the way old ones did.
Attic Rain vs. Roof Leak: How to Tell
Timing gives it away - and because we're roofers, we won't sell you an attic-sealing job when your flashing is the real problem.
It's probably attic rain if…
- It appears during a thaw after a deep freeze - often under a clear blue sky.
- Stains cluster near bathroom fans and pot lights.
- There's frost on nail tips and damp insulation in cold weather.
It's probably a roof leak if…
- It appears during or right after rain and snowmelt.
- Water tracks from valleys, chimneys, or vents.
- It follows weather, not temperature swings.
How We Fix Attic Rain
The permanent fix stops warm air from reaching the cold deck - then flushes and dries what's already there. We work the causes in order:
Inspection first
We examine the attic (frost patterns, insulation, duct routing), measure ventilation, and check indoor humidity sources. You get photos of what we find - most homeowners have never seen their own attic.
Seal the air leaks
The permanent fix is stopping warm air getting up there: sealing the attic hatch, pot lights, and penetrations, and making sure bathroom and kitchen fans duct through the roof, not into the attic.
Fix the ventilation
Balanced intake (soffits) and exhaust (roof vents) flush residual moisture before it freezes. Blocked soffits - usually stuffed with insulation - are the most common defect we find in Calgary attics.
Manage indoor humidity
In deep cold, your house should run around 25–30% relative humidity. Turn humidifiers down at −20 °C, run bath fans 20 minutes after showers. Free advice - no equipment purchase needed.
Top up damaged insulation
Wet insulation loses R-value permanently. We replace damaged sections once the source is fixed - never before, or you're insulating a rain cloud.
What Attic Rain Repair Costs
Sealing and ventilation corrections are among the cheaper roofing-related fixes - typically far less than homeowners fear after seeing water pour through a light fixture. The expensive version is the one that waited: saturated insulation, mould remediation, and drywall replacement multiply the bill several times over. We quote the fix in writing after the inspection.
Is attic rain covered by insurance?
Often not - and this surprises people. Many insurers classify attic rain as a preventable moisture/maintenance issue rather than sudden accidental damage, and some Alberta policies exclude it explicitly. Coverage varies, so check yours - but prevention costs a fraction of remediation, and you can't count on a payout.
Related: roof inspection and skylight condensation, a related winter complaint.
Attic Rain Questions
What is attic rain in winter?
Who do you call for attic rain - a roofer or an insulation company?
How do I prevent attic rain?
Can attic rain damage my roof itself?
Does APEX charge for attic rain inspections?
Ceiling stains after a chinook?
Get a free attic inspection with photos - we'll find the air leaks and ventilation faults feeding the frost, and quote the fix in writing. Call (403) 999-7877.