Roof and attic ventilation in Calgary
Air in low at the eaves, out high at the ridge. How attic ventilation works, why it matters through a Calgary winter, and when to have it looked at.
What roof and attic ventilation is
A ventilated attic lets outside air move through the space under the roof. Fresh air comes in low, through vents in the soffit under the eaves. It leaves high, through the ridge or through roof vents near the peak. Warm air and moisture rise and go out with it.
Intake and exhaust need to be in balance. Too little intake starves the exhaust vents, and vents that are blocked by insulation or paint do nothing. Insulation and sealing the ceiling below matter as much: ventilation works best when less warm, damp air from the house reaches the attic in the first place.
Why it matters in a Calgary winter
Warm, damp air from the house leaks into the attic. In a cold snap that moisture can freeze as frost on the underside of the roof, then drip into the insulation when it thaws.
Heat that gets into the attic also warms the roof deck, so snow melts from underneath. The meltwater runs down to the cold eaves and refreezes there, which is how ice dams build. Calgary's freeze-thaw swings make that cycle worse.
In summer, an attic with poor airflow can run far hotter than the air outside. Ventilation does not promise a result on its own, but a balanced system helps the roof shed heat and moisture.
Signs of a ventilation problem
- Ice dams and long icicles at the eaves, or snow that melts off in patches while the neighbours' roofs stay covered.
- Frost, damp insulation or dark staining on the rafters and roof sheathing when you look into the attic in winter.
- A musty smell in the attic, or mould on the underside of the roof deck.
- Ceiling stains or drips that appear in cold snaps and thaws, not only after rain.
- An attic that feels much hotter than outdoors in summer.
- A bathroom or kitchen fan that vents into the attic instead of outside.
Warranty
15-year workmanship warranty on qualifying projects, plus the manufacturer's limited warranty on the shingles.
Shingle makers set ventilation requirements in their installation instructions, and a limited warranty can depend on them. The warranty paperwork for your shingle has the details.
How ventilation work is priced
Ventilation work is priced with the roof job it goes with, after a free look at the roof and attic.
On a replacement the instant estimate shows a price range, plus GST. A free inspection confirms it.
How a ventilation check runs
1.Tell us what you see
Ice at the eaves, frost in the attic, a stain, a smell. Photos help.
2.We inspect
Roof and attic together, tracing moisture and heat to where it comes from.
3.One written price
Any ventilation work is quoted with the repair or replacement it belongs to.
Roof and attic ventilation questions
Does my attic need ventilation in a Calgary winter?
In most cases, yes. A ventilated attic stays closer to the outdoor temperature, which helps keep frost from building up under the roof and helps limit ice dams. Ventilation works alongside insulation and a sealed ceiling, not instead of them.
How do I know if my attic is poorly ventilated?
Common signs are ice dams and long icicles at the eaves, frost or damp insulation in the attic in winter, a musty smell, staining or mould on the roof sheathing, and an attic that feels far hotter than outdoors in summer. A roof and attic inspection can confirm the cause.
Can poor ventilation cause ice dams?
It can contribute. Ice dams form when heat escaping into the attic melts snow on the roof and the meltwater refreezes at the cold eaves. Ventilation, insulation and air sealing all play a part, so no single fix is certain to stop them.
What is the difference between intake and exhaust vents?
Intake vents sit low, usually in the soffit under the eaves, and let outside air in. Exhaust vents sit high, along the ridge or as roof vents near the peak, and let warm, damp air out. The two need to be in balance for air to move through the attic.
Does attic ventilation affect my shingle warranty?
It can. Shingle makers set ventilation requirements in their installation instructions, and a manufacturer's limited warranty can depend on them. Our workmanship warranty is 15 years on qualifying projects. The manufacturer's limited warranty is separate.
Can you look at my attic ventilation?
Our inspections cover the roof and the attic, and the estimate is free. When you book, tell us about any ice dams, frost or damp you have seen.
More answers on the main FAQ page.