If a homeowner in a wildfire-prone area can do only one major hardening upgrade, the roof is almost always the right answer. A burning ember that lands on a Class A roof will usually go out. An ember that lands on an old wood shake roof will usually start a fire. That difference shows up in every post-fire damage survey since researchers started doing them — the Camp Fire (2018), the Marshall Fire (2021), the Palisades and Eaton Fires (2025) — and it is the single strongest signal in the data.

So: what does "Class A" actually mean, what qualifies, and what should you specify when you replace a roof?

The test standard behind the label

"Class A" is a rating from ASTM E108 or its identical twin UL 790, Standard Test Methods for Fire Tests of Roof Coverings. Both standards are used interchangeably, and both define three classes — A, B, and C — based on a roof's performance in three specific tests:

  1. Intermittent Flame Exposure Test. A gas burner is cycled on and off against the roof specimen. The assembly must resist flame spread and not develop sustained flaming underside combustion.
  2. Burning Brand Test. A burning wood brand (the class determines the size — Class A uses a 12 × 12-inch, approximately 2,000-gram brand) is placed on the roof. The roof must resist ignition for the duration of the test.
  3. Spread of Flame Test. A flame is applied to a specimen installed at a specified slope, and the flame spread along the roof is measured. Class A allows no more than a 6-foot spread.

Class A is the most stringent. Class B uses a smaller brand (6 × 6, about 500 g) and allows more flame spread. Class C uses a still smaller brand (1.5 × 1.5, about 9 g) and is the minimum for most standard building codes outside WUI zones. Class A is the baseline for California Chapter 7A, Colorado's new WUI code, and nearly every insurer's hardening checklist.

A critical point that gets lost in most marketing: Class A applies to the assembly, not just the shingle, tile, or metal panel. The assembly includes the roof deck, underlayment, flashing, and the covering itself, installed to the manufacturer's specified details. Swapping out a fire-rated underlayment for a cheaper substitute, or installing a shingle over the wrong deck type, can void the assembly's rating.

Which roof types can be Class A

Most common residential roofing options have at least one Class A product line on the market. What they need to be installed as is another story.

Asphalt composition shingles

The single most common Class A roof in the western U.S. is an asphalt fiberglass composition shingle — what most people picture as a standard shingle roof. Nearly all fiberglass-mat asphalt shingles made today are rated Class A when installed over a code-compliant deck and underlayment. Organic-mat shingles (now rare) historically required additional fire-rated underlayment to achieve Class A.

A typical Class A composition shingle roof replacement runs $15,000–$30,000 on a standard single-family home in the western U.S., depending on size, pitch, tear-off condition, and underlayment upgrade. Expected service life is 25–50 years depending on the shingle tier.

Metal roofing

Standing-seam metal and metal shingles are almost always Class A when installed over a fire-rated underlayment and noncombustible deck. Steel is the most common residential metal; aluminum and zinc are less common but qualify.

Metal roofs $25,000–$60,000+ installed. They shed embers very well — there is literally no fuel on the surface — and they last 40–70 years. For WUI-zone homes with complex rooflines and frequent ember exposure, metal is often the first-choice upgrade despite the cost.

Concrete tile

Concrete tile is Class A in essentially all residential installations. The tile itself is noncombustible, and assembly details include bird-stop pieces at eaves and ridge to close off ember entry points.

Concrete tile roof systems run $25,000–$50,000 and are very long-lived (50+ years). They are heavy (typically 900–1,200 pounds per 100 square feet), and older houses may need structural evaluation before switching from shingle to tile.

Clay tile

Clay tile is also Class A with the right assembly — the same bird-stop and underlayment rules apply. Clay tile is the traditional southwestern roof and carries a premium: $35,000–$80,000+.

Slate

Natural slate is noncombustible and Class A. Rare on ordinary residential work because of cost ($40,000–$100,000+) and weight.

Wood shake

Untreated wood shake is Class C or worse. Fire-retardant-treated (FRT) wood shake can be rated Class B or — with the right assembly — Class A when new. The catch is durability: the fire-retardant treatment loses effectiveness with weathering, often within 10–20 years, and the assembly has to be re-treated or replaced to maintain the rating. Many jurisdictions have banned new wood-shake roofs in WUI zones entirely, regardless of treatment.

If you have an existing wood-shake roof on a house in a fire zone, it is almost certainly the first line item on your hardening priority list.

What makes a Class A roof actually perform in a real fire

The rating is necessary but not sufficient. Real-world post-fire surveys keep showing that roofs fail for reasons that have less to do with the shingle's Class A label and more to do with details around the shingle. The items below are where Class A roofs ignite despite their rating, and are worth specifically asking your contractor about.

Debris in valleys and gutters

Dry pine needles packed into a roof valley are a fuel bed. Embers land in the needles, the needles ignite, and they heat the underlayment and decking past failure. Clean valleys and gutters are part of performing as a Class A roof.

Open ends of tile

Clay and concrete barrel tile have open ends at the eave and ridge. Without bird-stops (noncombustible closures that fill the gap under each tile), embers and burning debris can get up under the tile and ignite the underlayment or felt. Some jurisdictions now require metal bird-stops on all new tile roof installations.

Gutters and gutter debris

A Class A roof with a gutter full of dry oak leaves will burn at the gutter line. Gutters themselves should be noncombustible — steel or aluminum rather than vinyl — and fitted with a 1/8-inch perforated-metal gutter guard.

Roof-to-wall intersections

Where a roof meets a vertical wall (a step-up, a dormer side), the intersection is both a debris trap and a heat-concentration point. Metal flashing, clean sealant, and in some details a noncombustible weather-block are needed to keep this detail protective.

Skylights and roof penetrations

Every penetration in a roof is a potential weak point. Skylights should be tempered glass or listed plastic glazing (per Chapter 7A §708A). Vent pipes, chimneys, and solar mounts need noncombustible flashing and proper sealing. A spark-arresting screen of 1/2-inch mesh or smaller is required on chimneys; some jurisdictions require finer.

Roof-mounted PV systems

Solar PV arrays on a Class A roof generally maintain the Class A rating if the system has been tested as a Class A system (UL 2703 fire classification) and the installation leaves no significant airflow gap where embers can accumulate beneath the modules. Unrated racking can compromise the roof rating. Ask your installer whether the specific PV-and-racking system is listed as Class A in combination with your roof.

What to specify when you replace a roof

If you're replacing a roof in a WUI zone, a reasonable scope looks like:

  • Tear-off to deck (not a shingle-over).
  • Deck inspection and replacement of any damaged sheathing.
  • Class A assembly — specify the exact manufacturer assembly, including underlayment and flashing.
  • Ice-and-water or fire-rated underlayment across valleys, eaves, and all penetrations.
  • Metal drip edge and valley flashing (noncombustible).
  • Bird-stops at tile eaves and ridges (if tile).
  • Noncombustible gutters with 1/8-inch metal gutter guards.
  • Chimney spark arrester to 1/2-inch or finer, per local code.
  • Vents upgraded to 1/8-inch mesh or ASTM E2886–listed ember-resistant products while the roof is open — this is also covered in Ember-Resistant Construction.

Bundling the vent upgrade with the roof replacement is one of the best dollar-for-dollar moves available. You're already paying a crew to be on your roof; the marginal cost to upgrade vents is small, and the combined upgrade checks off two of the most important lines on most insurance hardening forms.

Common misconceptions

"Class A means fireproof." No. Class A means the roof passed specific tests under specific conditions. A Class A roof can still fail when overwhelmed by direct flame, when covered in combustible debris, or when the surrounding components (eaves, vents, gutters) ignite and transfer fire to the roof deck from below.

"Metal roofs are always Class A." Usually, but not always. The rating depends on the underlayment and deck assembly. A steel panel over an untreated wood deck with a non-fire-rated felt may not meet Class A. Always check the assembly listing.

"Class A costs a lot more than Class B or C." Class A asphalt shingles typically cost roughly the same as a Class B alternative in the same tier, because most modern fiberglass shingles happen to be Class A by default. You do not pay a meaningful premium for the rating in the shingle market; you pay a premium for the material category (tile, metal, slate).

The bottom line

A Class A roof is not a luxury feature — in a WUI area, it is the table stakes. The rating is backed by specific, well-established tests; it applies to the whole assembly, not just the top surface; and it only performs in a real fire if the roof's surrounding details (eaves, vents, gutters, bird-stops, penetrations) are done right.

If you're on an aging asphalt shingle, your next roof will almost certainly be Class A by default. If you're on a wood-shake roof in a fire zone, replacement is the single most impactful hardening step you can take, and almost always worth prioritizing over any other upgrade.

For the wider context on where this fits, see What Is Home Hardening, and Why It Matters and Chapter 7A of the California Building Code.

This article is informational and not a substitute for licensed professional advice. Codes, insurance implications, and product availability vary by jurisdiction and carrier. Before committing to significant hardening work, consult a licensed contractor with WUI experience, your local building department, and your insurer.