How long asphalt shingles actually last

Rated life is a warranty term, not a forecast

A shingle sold with a “lifetime” warranty is not a lifetime roof. Those warranties are prorated, cover manufacturing defects rather than weathering, and assume installation exactly to the manufacturer’s instructions and adequate attic ventilation. What a roof actually gives you is closer to the observed bands below.

The four things that shorten it

Heat from below. An under-ventilated attic bakes the shingle from underneath and is the single most common reason a twenty-five-year roof gives fifteen. The code default is 1/150 net free area of the ventilated space; the ventilation calculator checks yours.

Fastening. Nails driven high, driven through the wrong line, overdriven through the mat or underdriven so the head stands proud all shorten a roof by letting the shingle move. The code minimum is 4 per strip.

Trapped moisture. Bathroom and kitchen fans terminating in the attic, or a missing vapour retarder in a cold climate, condense on the deck and rot it under an intact covering.

Impact and abrasion. Hail, overhanging limbs and foot traffic all remove granules, and granules are the shingle’s sunscreen. Once the mat is exposed, the clock speeds up.

Reading the age off a roof

Curling and cupping tabs mean the mat has dried and shrunk. Bald patches with the black mat showing mean granule loss past the point of protection. Granules in the gutter after a normal rain — not the sand-off of a new roof’s first month — mean the same thing. Nail pops, seen as small raised bumps in a line, mean the deck is moving. Any two of those together on a roof past twenty is a replacement conversation, not a repair one.

When repair stops paying

The arithmetic is simple. If the roof has more than about a third of its life left and the failure is local, repair. If it is past two-thirds and the failure is anywhere in the field, every repair is money spent on a roof you are about to remove — and each one makes the eventual tear-off marginally worse. The repair cost guide has the crossover in dollars, and the replacement guide has what the other side costs.