How long does a roof last?

Those bars are service life, not warranty length. They are different things and the gap between them is where most of the disappointment lives.

A "lifetime" architectural shingle warranty is a material warranty against manufacturing defect, prorated after a short non-prorated window, and it says nothing about the roof lasting a lifetime. Shingles almost never fail from a manufacturing defect. They fail because the asphalt loses volatiles and the mat goes brittle, the granules wash into the gutters, and a wind event finally takes a course off. None of that is a warranty claim.

The number that matters is the second one: the workmanship warranty from the contractor, typically 2 to 10 years, occasionally 25 from a certified installer. Most premature roof failures are installation failures — nails high, nails overdriven, no starter course, valleys done badly, flashing reused. A material warranty does not cover any of that.

Ventilation, first and by a distance. An unvented or badly vented attic bakes the underside of the deck. Shingle temperature on a hot day in a poorly vented roof runs meaningfully higher than the same shingle over a ventilated attic, and asphalt ages on a temperature curve. The rule of thumb is 1 square foot of net free vent area per 150 square feet of attic floor, or per 300 where you have a proper balance of intake and exhaust with a vapour retarder. The part people get wrong is intake: ridge vent with blocked or absent soffit vents does not ventilate, it just gives hot air a hole and pulls conditioned air out of the house. I have seen ten-year-old roofs cooked off a house that had a beautiful ridge vent and insulation stuffed into every soffit bay.

A second layer. Roofing over an existing layer is legal in most jurisdictions up to two layers total, and it costs less because there is no tear-off. It also traps heat against the new shingles, hides the deck condition, and typically costs you a quarter of the second roof's life. It's a landlord's move on a building you are selling. On a house you're keeping, tear off.

Pitch. Water leaves a 10/12 roof and lingers on a 3/12 one. Low-slope asphalt holds moisture and grows organisms; anything below 4/12 needs a doubled underlayment, and below 2/12 asphalt shingles are not a legitimate covering at all.

Salt air and UV. Coastal exposure attacks fasteners and flashing before it attacks the field. In Florida and along the Gulf a shingle roof that would give 25 years in Ohio commonly gives 15 to 18, and insurers there increasingly price on roof age alone. Unprotected steel fasteners near salt spray are a five-year item.

Trees. Overhanging limbs do three things at once: abrasion in wind, constant shade that keeps the surface damp, and a steady drop of debris that dams water at the valleys. The black streaking people call "mould" is *Gloeocapsa magma*, an algae that feeds on the limestone filler in shingles — mostly cosmetic, but it thrives in exactly the shaded damp conditions that are actually shortening the roof.

Foot traffic. Every HVAC service call, satellite install and gutter clean scuffs granules off. It is a small effect that compounds on roofs with rooftop equipment.

Ice dams. In snow country, a warm attic melts snow that refreezes at the cold eave, and water backs up under the shingles. The fix is insulation and air sealing at the ceiling plane, not heat cable. Heat cable is a symptom management tool.

You can date a roof reasonably well from the ground and a ladder, without walking it.

Granules in the gutters, in volume, past the first year: the wear layer is going. Some granule loss is normal on a new roof from handling. Cupfuls a season on a fifteen-year-old roof is not.

Shingle edges that curl up at the corners, or tabs that have gone hard and snap rather than flex when you lift one: the asphalt has dried out. That roof has maybe two to five years, and it will not survive a big wind event well.

Dark patches where granules are gone entirely, exposing the black mat: those spots are now UV-degrading directly.

Nail heads visible on the surface, or shingles lifting in a straight line across the roof: fastener backout or a wind course loss. Repairable, but the repair tells you about the installation.

Any sag in the plane of the roof, or a springy deck underfoot: that is a structural or rot problem and it stops being a roofing conversation. Get someone up there now.

Inside, look at the underside of the deck from the attic on a bright day. Daylight through the sheathing is obvious. What is more useful is dark staining at the nail lines, which means condensation, which means the ventilation problem is already running.

Repair when the damage is local, the field shingles are still flexible, and the roof has more than about a third of its life left. A blown-off course, a failed pipe boot, a chimney flashing that was caulked instead of stepped — all sensible repairs, $300 to $1,200 typically.

Replace when the failure is the material rather than an event. If the shingles snap when you bend them, patching just puts new material next to old material that will fail next season, and matching colour on a weathered roof is a lost cause anyway.

The awkward middle case is a roof at 15 to 18 years with storm damage. That is the point where an insurance claim is worth pursuing, because carriers depreciate roof value hard after 15 years and many now write actual-cash-value roof endorsements rather than replacement cost. Read the roof endorsement on your policy before you need it. In Florida, Texas and the plains states this clause has changed under most people without them noticing.

Pipe boots deserve a specific mention: the rubber collar around plumbing vents typically fails at 10 to 15 years, well before the shingles, and it is the single most common source of a mystery ceiling stain. It is a $150 to $350 fix and worth doing proactively at year twelve.

Spend the money on the parts you cannot see. In order of return: proper intake and exhaust ventilation, ice-and-water membrane at eaves and valleys, and correctly formed step flashing at every wall intersection. Those three cost a fraction of the shingle upgrade and do more for the lifespan than moving from a mid-tier shingle to a premium one.

Upgrade the shingle second. Going from three-tab to architectural is worth it on any roof you intend to keep — better wind rating, thicker mat, and the price gap is about $30 to $60 a square in material. Going from architectural to a designer laminate is mostly appearance.

Then keep the trees back six feet from the roof plane, clean the gutters twice a year, and stay off it.

Two habits worth having: photograph the roof from all four elevations the week it is finished, and keep the material invoice with the lot numbers. Both make a future insurance conversation short.