Is my Calgary attic too hot in summer?

A Calgary attic that hits 60°C or more on a hot July afternoon is running too hot, and that heat is doing real damage to your roof from the inside out.

What an Overheated Attic Does to Your Roof

Shingles are designed to shed water and resist hail, but they rely on a reasonably stable temperature underneath. When attic air stagnates at extreme heat, the underside of the sheathing cooks, the adhesive strips on shingles soften and lose grip, and the shingles themselves age faster. In Calgary's climate, that same attic that bakes in July will also drive ice dams in January if it is warm enough to melt snow at the eave. Both problems share the same root cause: not enough ventilation moving air through the space.

The National Building Code, 2023 Alberta Edition, sets the minimum at 1 square metre of net free vent area for every 300 square metres of insulated ceiling area, with at least 25% of that venting at the top (ridge or high on the slope) and at least 25% at the bottom (soffits). If your soffits are blocked by insulation pushed to the eave, or your ridge vent is undersized, the math fails and heat builds up. On low-slope roofs or roof-joist construction the ratio tightens to 1 in 150.

Signs your attic is not venting properly: the attic feels like an oven within an hour of sunrise on a warm day; you find frost or condensation on the sheathing in winter; shingles are curling or granules are collecting in the eavestroughs faster than expected; or your upper-floor rooms are noticeably harder to cool than the rest of the house.

The fix usually involves two things together. First, make sure soffit vents are clear and unobstructed, which you can check from inside the attic with a flashlight. Second, confirm that ridge or upper vents are adequate and not blocked by debris or a poorly installed cap. Adding a powered attic fan can help in extreme cases, but most building scientists prefer passive ventilation (balanced soffit-to-ridge airflow) because it works year-round without a motor to maintain.

Insulation matters too. The City of Calgary's guidance on ice dams points to improving attic insulation as the first step, because a well-insulated attic floor keeps conditioned air in the house and unconditioned air in the attic, which is exactly what you want. If the insulation has been pushed aside at the eaves or is compressed, a roofer or insulation contractor can correct it when the roof is next opened up.

One Calgary-specific note: if your house was built before 1990, have a professional check whether any existing insulation or roofing materials contain asbestos before anyone disturbs them. Alberta OHS requires that removal be handled by trained workers and the waste taken to an approved facility.

A roofer doing a roof inspection, typically $150 to $400 for a paid report, can assess vent placement and count, check whether the soffit baffles are in place, and flag any sheathing damage caused by heat or moisture. If you are already planning a re-roof, this is the right moment to correct the ventilation, since adding vents during a tear-off costs far less than cutting them in afterward. Like-for-like re-roofing in Calgary needs no building permit under Alberta's Permit Regulation, but if structural changes to the roof framing are involved, check with the City of Calgary.