Asphalt shingles

Typical lifespan

15–30 years

Installed cost per square

$400–$700estimate

Weight

230–430 lb per square

Fire class

Class A when tested as an assembly

Impact class

UL 2218 Class 1–4 depending on product line

How does asphalt shingles actually work?

An asphalt shingle is a fibreglass mat saturated in asphalt, coated on both faces, and surfaced on the weather side with ceramic-coated mineral granules. The mat gives it tear strength, the asphalt keeps water out, and the granules are the only thing protecting that asphalt from ultraviolet light. Understanding that last part explains almost every failure mode: once granules leave, the asphalt is exposed, it hardens, and the shingle starts curling and cracking. Shingles are laid in overlapping courses from the eave upward so that every joint is covered by the course above, and each one carries a factory-applied strip of sealant that bonds to the course below once the sun warms it. Until that strip bonds, the roof has essentially no wind resistance — which is why a roof installed in cold weather can sit through a whole winter vulnerable, and why the manufacturer's wind rating always assumes a sealed roof.

What drives the cost?

Three things move an asphalt quote more than the shingle does. Pitch, because a steeper roof has more surface than the footprint beneath it and above roughly 6:12 it also needs staging. Complexity, because valleys, hips, dormers, skylights and chimneys are where the labour and the flashing go — a cut-up hip roof and a simple gable of identical area are not the same job. And layers, because tearing off and disposing of two existing coverings costs meaningfully more than one. Decking replacement is the wildcard: nobody knows how many sheets are soft until the old roof is off, which is why it belongs in the bid as a per-sheet price rather than an open "at cost" line.

What separates a good installation from a bad one?

What separates a good asphalt installation from a bad one is almost entirely the parts you cannot see once it is finished. New step flashing woven in piece by piece where the roof meets a wall, rather than a continuous strip of metal or a bead of roof cement. New valley metal. Drip edge at both the eaves and the rakes, lapped in the correct order — under the underlayment at the eave, over it at the rake. Ice barrier where the code requires it. And a fastening pattern that matches the manufacturer's printed instructions, because deviating from them voids the material warranty regardless of how the roof performs. Ask specifically whether flashing is being replaced or reused; reusing it is the single most common way a low bid is reached, and it is invisible the moment the siding goes back on.

Where does asphalt shingles work well?

Best climates: Most of the continental US; mixed and cold climates especially

Worst climates: Sustained high heat with strong UV, which accelerates granule loss and cracking

What maintenance does it need?

Asphalt asks for very little, and most of what shortens its life happens somewhere other than the shingle. Keep the gutters and valleys clear so water leaves the roof instead of sitting against it. Cut back branches that shade a slope, because a permanently damp slope grows moss, and moss holds water against the shingle and lifts the courses as it thickens. Check the pipe boots every few years from the ground with binoculars — the rubber collar splits from UV long before the shingles wear out and is one of the cheapest things on a roof to replace. Above all, get the attic ventilation right, because an under-ventilated attic cooks the asphalt from underneath and is the honest answer to a large share of roofs that only last fifteen years.

What fails first

Granule loss at the exposed surface, then curling at the corners, then sealant strip failure that lets wind lift the tab

When should you choose it?

Choose asphalt when the budget is the binding constraint, when the house is going to be sold inside the next decade, or when you want a covering any local crew can install and repair without specialist skills. It is also the sensible default when the roof geometry is complicated: asphalt cuts and flashes around dormers and valleys far more easily than tile, slate or panel metal, and a complex roof in a difficult material is where installation errors multiply.

When should you think twice?

Think harder if you are staying thirty years and can afford metal, because two asphalt tear-offs cost more than one standing seam roof and involve twice the disruption. Reconsider in sustained extreme heat with strong UV, which ages asphalt faster than anywhere else. And be realistic in severe hail country: an impact-rated shingle helps, but hail is the peril most likely to cost you the roof regardless of what is on it.

What ratings does it carry?

Common mistakes

• Comparing bids on price per square without checking the square count. Two roofers quoting different counts for one roof are not quoting the same job — one measured the footprint instead of the roof surface.
• Accepting an open-ended decking clause. "Additional decking at cost" with no per-sheet number is where surprise money lives.
• Letting old step flashing stay. It saves a few hundred now and costs a wall repair later, and it is invisible once the siding is back.
• Roofing over the existing layer. It hides the deck condition completely, traps heat that shortens the new roof, and many jurisdictions cap the number of layers.
• Scheduling in cold weather without asking about sealing. Below roughly 40°F the sealant strips may not bond until spring, leaving a whole winter of wind exposure.