How long does a roof last in Calgary?

A widely cited reference is the life expectancy chart from the International Association of Certified Home Inspectors (InterNACHI). It says plainly that a roof's life depends on local weather, building design, material quality and maintenance, and that roofs in areas with severe weather such as hail may have a shorter lifespan. It's a North American reference, so treat it as a baseline for normal wear, not a Calgary forecast.

Many architectural shingles carry a "limited lifetime" warranty, and it's easy to read that as a promise the roof will last as long as you own the house. It isn't. IKO's Canadian warranty states that its warranty periods are not guarantees of the useful lifetime of the shingles, and that how long they keep shedding water depends on roof design, ventilation, weather and exposure.

The structure matters too. For IKO's architectural lines, the first 180 months are an Iron Clad Protection period with non-prorated coverage: replacement shingles plus a reasonable allowance to install them, but not tear-off or disposal. After that, coverage is prorated and pays a shrinking share of replacement shingles, not the labour or tear-off. It covers manufacturing defects, and it lists hail, ice damming and damage from inadequate ventilation among the exclusions. In other words, it's a defect warranty, not a weather guarantee.

Hail can end an asphalt roof in a single afternoon, whatever its age. IBHS notes that hailstones often knock granules loose, and a hard enough hit can crack or tear the shingle. The shingle may not leak that day, but InterNACHI points out that losing granules lets more UV reach the asphalt, which is what breaks it down. InterNACHI also notes that as shingles age they become more brittle and less able to absorb a hailstrike.

That's why the lifespan tables above describe normal wear and not a city like this one. In hail country, the more useful question is often what your roof will do in the next big storm, which is where impact ratings come in.

Sunlight is what slowly wears out asphalt. InterNACHI calls UV radiation the primary force that deteriorates exposed asphalt, and notes that roofs at higher elevations get more of it. The World Health Organization's UV Index guide puts that at about 10 to 12% more UV for every 1,000 m of altitude, because a thinner atmosphere absorbs less. Calgary sits well above sea level at the edge of the foothills, so its roofs get more UV than a similar roof near the coast.

Then there are chinooks. The Canadian Encyclopedia notes that in southwestern Alberta about one winter day in three is a chinook day, and that a temperature rise of 27°C in two minutes has been observed at the start of a chinook. Every swing expands and contracts shingles, flashing and sealant, and every melt that refreezes overnight works water into any gap it can find.

Two roofs with the same shingle on the same street can age very differently, and the reason is usually under the shingles.

One damaged spot usually means a repair. The same symptom across whole slopes usually means the roof is done. Here's what to look for, most of it visible from the ground with binoculars.