Attic and moisture
Attic Rain in Calgary
Attic rain is condensation, not precipitation. Warm humid air from inside the house leaks into a cold attic, freezes as frost on the underside of the roof sheathing, and accumulates through a cold snap. When a chinook arrives and the attic warms, the frost melts all at once and the water drips through the ceiling. The roof is watertight the entire time.
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- Licence BL272564
- WCB 9892020
- $5M liability
- Free written estimate
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Tell us what the roof is doing
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City of Calgary licence
BL272564
WCB Alberta account
9892020
General liability
$5,000,000
Written estimate
Free, itemised
Calgary gets this more than almost any Canadian city, because Calgary gets more chinooks than almost any Canadian city. A 20 degree swing over a few hours is what turns a winter's worth of accumulated frost into a ceiling stain in an afternoon.
Call 403-700-7542 if water is coming through your ceiling.
01
How to tell attic rain from a roof leak
| Attic rain | Roof leak | |
|---|---|---|
| Timing | During or just after a warm spell in winter | During or just after rain or snowmelt |
| Season | Almost always December to March | Any season |
| Pattern | Multiple spots, often near exterior walls, bathrooms and the attic hatch | Usually one location, repeatable |
| Attic evidence | Frost or water on the underside of the sheathing, wet insulation in patches | A stain trail running down a rafter from a specific point |
| Repeats | Every chinook | Every rainfall |
If the ceiling drips on a sunny plus-8 day in January with no precipitation for a week, the roof is not leaking.
02
What causes it
Three failures have to line up. Usually all three are present.
1. Moist air escaping the living space
Every gap in the ceiling plane is a path. Pot lights that are not airtight-rated. The attic hatch with no weatherstrip or insulation on top of it. Plumbing stacks. Bathroom and kitchen exhaust fans ducted into the attic instead of through the roof or wall. Top plates of interior partition walls that were never sealed.
A single bathroom fan discharging into an attic can put several litres of water vapour into that space per day.
2. Not enough ventilation
The National Building Code requires unobstructed attic vent area of not less than 1/300 of the insulated ceiling area, rising to 1/150 where the roof slope is less than 1 in 6. It also requires the openings to be distributed uniformly on opposite sides of the building, with not less than 25 percent of the required area at the top of the space and not less than 25 percent at the bottom.
The bottom half is the half that gets missed. Roofers add ridge vents or box vents at the top and never check whether the soffits can actually supply air. An attic with exhaust and no intake does not ventilate, it depressurises and pulls more house air in through the ceiling.
3. Blocked or missing baffles
The code requires at least 63 mm of clear space between the top of the insulation and the underside of the roof sheathing, reduced to 25 mm where preformed baffles are installed and extended at least 50 mm above the insulation.
When blown insulation is installed without baffles at the eaves, it packs into the soffit space and closes the intake. This is the single most common cause of attic rain in Calgary homes that have had their attics topped up.
Stop guessing
Get attic rain priced in writing
We look at the roof, photograph what we find, and hand you a scope with a number on it. If a repair is the right answer, we say so rather than quoting a replacement.
Estimates are free and written. Not a range, not a verbal number.
03
What the repair involves
Fixing attic rain means fixing all three, in order.
Air seal the ceiling plane. Seal penetrations from the attic side with foam and fire-rated sealant. Box and seal non-rated pot lights. Insulate and weatherstrip the attic hatch. Duct every bathroom and kitchen fan to the exterior, not into the attic, with insulated duct and a sealed roof or wall termination.
Restore intake. Install baffles at every rafter or truss bay at the eaves. Clear packed insulation out of the soffit space. Confirm the soffit itself is vented and not a solid panel with decorative perforations that were never opened.
Balance exhaust to intake. Add or correct upper vents so the 25 percent top and 25 percent bottom split is real. Mixing ridge vent with box vents on the same attic can short-circuit the airflow so that the ridge pulls from the box vents instead of the soffits.
Restore insulation depth and coverage. After air sealing, not before. Insulating over an unsealed ceiling traps the problem.
04
What it is not
It is not a reason to replace the roof. A contractor who quotes a new roof for winter ceiling drips without going into the attic has not diagnosed anything. Replacing the covering does not change the air leakage, the intake, or the insulation depth. The frost comes back the following winter on a roof that is now three years newer and just as wet.
05
Damage attic rain causes
Wet blown insulation loses most of its R-value and does not recover fully after drying. Sheathing that goes through repeated wetting cycles delaminates. Drywall stains and, past a certain point, sags. Mould growth on sheathing and truss chords follows sustained moisture.
None of that is covered by a roofing warranty, because none of it is a roofing defect.
Cost
What attic rain costs in Calgary
Draft Calgary market rates, 2026. Ranges, not a quote.
| Work | Typical Calgary range |
|---|---|
| Attic inspection and moisture assessment | $200 to $400 |
| Air sealing the ceiling plane | $800 to $2,500 |
| Baffles at the eaves, per bay | $30 to $60 |
| Additional roof vents installed | $150 to $400 each |
| Soffit intake opened up or corrected | $500 to $1,500 |
| Insulation top-up after air sealing | $2 to $4 per sq ft |
The order matters more than the total. Air sealing comes first, then intake and exhaust venting, then insulation depth. Topping up insulation over an unsealed ceiling is the most common attic rain job done backwards: it buries the problem under a foot of new fibreglass and the drips come back the next chinook, at which point the new insulation has to come out again.
Most attic rain calls land somewhere between $1,500 and $4,000 all in. A house with a badly compromised ceiling plane, pot lights everywhere and no soffit intake at all, goes higher.
Our own photographs
Work on Calgary roofs
Every photograph on this site is taken on a job we did. No stock libraries.
Photo neededCeiling stain near an exterior wall, the classic attic rain pattern Photo neededNon-airtight pot light seen from the attic side 
Checkable, not claimed
Credentials you can verify before we set a ladder up
Marku Roofing Repair Ltd. holds City of Calgary business licence BL272564, WCB Alberta account 9892020, and $5,000,000 in commercial general liability through Sandbox Mutual Insurance.
No awards, no rankings, no "best in Calgary". A licence number, a WCB account and a policy limit are things you can check yourself.
More about the companyAnswers
Frequently asked questions
Still unclear? A five minute phone call usually settles it faster than reading.
Ask us directlyIs attic rain covered by home insurance?
Generally no. Insurers treat it as a maintenance and ventilation issue rather than sudden accidental damage. Check your own policy wording.
Will a bigger vent fix it?
Only if the intake is already adequate. Adding exhaust to an attic with blocked soffits makes the depressurisation worse.
Why did this start after I got new insulation?
Because blown insulation installed without eave baffles packs into the soffit and closes the intake. This is the most common trigger we see.
Can I just run a dehumidifier?
Lowering indoor humidity reduces the moisture available to leak into the attic, so it helps. It does not fix the air leakage or the ventilation.
Does a new roof fix attic rain?
No. See above.
Free written estimate
Book it before the next chinook
Freeze-thaw turns a small opening into a large one faster here than almost anywhere else in Canada. Get it looked at while it is still a repair.
Serving Calgary, Airdrie, Cochrane, Okotoks and Chestermere.