Class A roof: what it means and how to get one

Class A is the top rating in ASTM E108 / UL 790, the standard fire test for roof coverings. To earn it, a roof assembly has to resist flame spread, not generate burning brands when exposed to flame, and not let flames burn through to the deck after sustained exposure.

There are three classes — A, B, and C — plus unrated. Class A is the only rating that gives a home meaningful protection in a wildfire. California Building Code Chapter 7A requires a Class A roof on new construction in wildland-urban interface (WUI) zones for exactly this reason, and most Western US states have adopted similar requirements.

The test is rigorous: the assembly is exposed to direct flame, burning brands, and intermittent flame in a controlled lab. A Class A roof has to hold up under all three exposures, with documented limits on flame travel, brand generation, and burn-through.

Post-fire investigations by IBHS, NIST, and CAL FIRE consistently find the same thing: when one house in a destroyed neighborhood survives, it almost always has a Class A roof. The roof is the largest horizontal surface on a home and catches more wind-blown embers than any other part of the structure.

A Class B or unrated roof — wood shake, old wood shingle, some lightweight materials — can ignite from a single ember landing in dry debris. Once the roof goes, the rest of the home almost always follows, because the attic is now open to the sky and fire spreads laterally through the rafter bays.

Conversely, a Class A roof denies embers their primary opportunity. Even if embers land in a roof valley full of pine needles, a well-detailed Class A assembly will not ignite at the deck. Combined with clean gutters and screened vents, this single upgrade is the largest single move you can make on your home's wildfire survival.

Standing-seam metal roofing. Long-lived (50+ year service life), low-maintenance, excellent ember resistance, and light enough that most reroofs don't require structural reinforcement.

Concrete and clay tile. Heavy but extremely durable; common throughout California. Note that under-tile underlayment is part of the rating — replace it whenever you replace the tile.

Slate. Premium and Class A by default. Expensive but essentially permanent.

Class A composition (asphalt) shingles. The most affordable option — look for the explicit "Class A" label on the bundle. Just being "fiberglass" or "architectural" is not enough; the bundle must call out the Class A rating.

Wood shake and wood shingle. Banned in many California WUI areas because they ignite from embers and then throw burning brands onto neighboring roofs, spreading conflagrations from house to house.

Old organic-felt asphalt shingles past their service life — curled, cracked, or missing granules. Even if originally Class A, the rating depends on intact granules. A 25-year-old roof with bare felt showing is no longer Class A in practice.

Lightweight panels and unrated metal sheeting sold for sheds and outbuildings. Fine for a shed; not adequate for a primary residence.

Tar-and-gravel built-up roofs and most rolled-roofing products without explicit Class A certification. Many of these are Class B or unrated.

Class A is an assembly rating. The covering, underlayment, and sometimes the deck all factor into the test. When you re-roof, ask the contractor to confirm in writing that the full assembly is Class A, not just that the shingles are. A Class A shingle on a substandard underlayment can lose the rating in practice.

Equally important: no gaps at the roof edge, ridge, valleys, or where two roof planes meet. Embers find the same gaps that birds and leaves do. A Class A roof with open ridge gaps is still a vulnerable roof — birdstop, metal flashing, and properly closed ridge vents are part of the system.

Penetrations matter too. Plumbing vents, satellite mounts, antenna brackets, and skylight curbs all need to be properly flashed and sealed. A perfect Class A field with an open skylight curb is still an opening for embers.

"I want a Class A roof assembly per ASTM E108. Please specify the covering, underlayment, and any required interlayment in the bid, and confirm the assembly's Class A listing."

"Include metal birdstop at the eaves, sealed ridge vents, and proper flashing at all valleys and penetrations."

"Replace any damaged sheathing before re-roofing."

"At the chimney, install a noncombustible cap with 1/8-inch spark-arrestor screen."

"Provide the manufacturer's documentation showing Class A listing for the specific assembly used."

Keep the documentation with your home records — many insurers will ask for it during underwriting in wildfire zones.

If your roof is Class A: clean it. Sweep needles and leaves off, clear the gutters, and check for any lifted shingles, missing granules, or open gaps along the ridge and edges. A Class A roof buried in pine needles is a roof full of fuel.

If your roof is not Class A and is near end of life: get bids that specify a Class A assembly. The cost difference between Class A composition and unrated/older Class B roofing is typically 5–15% — small compared with the survival difference.

If your roof is wood shake: prioritize replacement. Check whether your county or insurer offers a wildfire-mitigation rebate (many do), and check whether your jurisdiction has banned wood-shake replacement (many have).

Either way, schedule the gutter clean and a visual inspection every spring before fire season and every fall after leaf drop.