A Class A fire-rated roof is a roof covering or roof assembly that has passed the most severe exterior-fire tests in ASTM E108 (and its harmonized twin, ANSI/UL 790): the spread-of-flame test, the burning-brand test, and the intermittent-flame test. Class A is the highest of three ratings (A, B, and C). It is the classification most wildfire and building codes call for, and in high fire-hazard zones it is frequently the only rating a building department will accept.
The point that trips up owners, specifiers, and even some installers is this: “Class A” can be earned two different ways. Some coverings are Class A because of the material itself (slate, clay and concrete tile, most modern asphalt shingles). Others reach Class A only as part of a specific tested assembly, meaning the panel, underlayment, deck, and sometimes a cover board were all tested together and listed as a set. Metal panels and fire-retardant-treated wood shakes are the classic examples. Get the assembly wrong in the field and a “Class A product” can end up on a roof that would not pass the test it is credited with.
This guide covers what the standard actually measures, how each common roof covering earns (or fails to earn) Class A, and where code requires it.
The standard behind the rating: ASTM E108 and UL 790
ASTM E108, “Standard Test Methods for Fire Tests of Roof Coverings,” and ANSI/UL 790, which shares the same title, are the two test standards that produce a roof fire classification in the United States. They are technically aligned, so a covering listed to one is generally treated as meeting the other, and code and product listings often cite them together as “ASTM E108/UL 790.” (The older NFPA 256 has been withdrawn; Canada uses the parallel CAN/ULC-S107.)
Important: this is an exterior fire-exposure standard. It measures how a roof resists fire coming from outside and above (an adjacent structure fire, a wind-driven ember shower, a flame front), not how the roof-ceiling assembly resists a fire inside the building. That interior fire-resistance rating is a separate test and a separate number.
The standard defines the three classes by the severity of exposure a covering can survive:
- Class A: effective against a severe exterior fire exposure.
- Class B: effective against a moderate exposure.
- Class C: effective against a light exposure.
A covering that has not been tested, or that fails Class C, is unrated. In wildfire terms, unrated and Class C coverings are the ones fire-safety guidance generally steers homeowners away from.
The three core fire tests, by class
To earn a given class, the roof specimen (mounted on a test deck at the slope for which the rating is sought, with a blower producing a 12 mile-per-hour wind across the surface) must pass the applicable tests at that class level. The three most-cited tests and their pass thresholds are below.
| Test | What it simulates | Class A | Class B | Class C |
|---|---|---|---|---|
| Spread of flame (about a 10-minute exposure) | A flame front traveling across the roof surface | Flame spreads no more than 6 ft | No more than 8 ft | No more than 13 ft |
| Burning brand (a wood crib ignited on the roof) | A wind-blown ember or firebrand landing on the roof | One 12 in x 12 in brand, about 2,000 g (Douglas fir) | Two 6 in x 6 in brands, about 500 g each | Twenty 1.5 in x 1.5 in brands, about 9.25 g each (white pine) |
| Intermittent flame (repeated on/off gas-flame cycles) | Recurring flame contact from a nearby fire | 15 cycles | 8 cycles | 3 cycles |
Across all three tests, the covering must not do any of the following: let flame spread past the class limit, allow the deck to ignite or burn through, expose the deck, produce burning or flaming pieces that fall from the underside, or (for the brand test) let the brand burn through to the underside. A single failure at a given class drops the covering to the next class down, or leaves it unrated.
The two tests people forget: rain and weathering
ASTM E108 also contains a rain test and an accelerated weathering test. These are pre-conditioning steps, and they matter most for any covering whose fire performance depends on a coating or a chemical treatment rather than on the base material. Fire-retardant-treated (FRT) wood shakes are the textbook case: the specimen is weathered first, then fire-tested, so the rating reflects performance after exposure, not just off the truck. The practitioner takeaway is that a treatment-dependent Class A rating is only as durable as the treatment. If a listing requires periodic re-treatment to keep the rating, that condition is part of the rating.
Class A by material versus Class A by assembly
This is the distinction that governs most field decisions. Some coverings carry Class A on their own. Others are listed Class A only as a defined assembly, and swapping any listed component (the underlayment, the cover board, the deck type) can invalidate the rating even though the visible covering looks identical.
| Roof covering | Typical standalone rating | How it reaches Class A | Practitioner note |
|---|---|---|---|
| Slate | Class A | By material (noncombustible) | Rating is inherent; the deck and underlayment still have to be code-compliant. |
| Clay and concrete tile | Class A | By material (noncombustible) | Many listings still require a Class A cap sheet or underlayment, partly to address the open ends and batten cavities under the tile. |
| Asphalt shingle, fiberglass mat | Class A | By material (modern glass-mat shingles) | Older organic-mat (paper) shingles were typically Class C and are largely out of the market; verify the specific product’s listing. |
| Metal panel (steel, aluminum, zinc, copper) | Noncombustible, but not automatically Class A over a combustible deck | Class A over a noncombustible deck, or Class A by assembly using a listed underlayment / thermal barrier over a wood deck | The metal does not burn, but the assembly can fail the brand or spread test at the deck. Do not assume “metal = Class A” on a plywood deck without the listed barrier. |
| Wood shake / shingle, untreated | Unrated to Class C at best | Generally cannot reach Class A | Banned or restricted outright in many wildfire jurisdictions. |
| Wood shake / shingle, fire-retardant-treated | Class B or C on its own | Class A only as a listed assembly (FRT shake plus a Class A cap sheet / underlayment) | Treatment must survive the weathering test; some listings require re-treatment to maintain the rating. |
| Low-slope membrane (built-up, modified bitumen, single-ply) | Varies by product | Class A by assembly (specific membrane, insulation, cover board, and deck tested together) | The rating belongs to the assembly, not the membrane roll. Substituting insulation or dropping the cover board can void it. |
Four practical rules follow from this table. First, noncombustible coverings (slate, tile, metal, and glass-mat asphalt shingles) are the low-friction path to Class A. Second, a combustible deck raises the bar, because the brand and spread tests can fail at the deck even under a noncombustible covering, which is why metal and membrane systems so often rely on a listed barrier. Third, any treatment-dependent rating (FRT wood especially) has durability strings attached. Fourth, if the covering is listed only as an assembly, the field build has to match the listed assembly component-for-component.
Where a Class A roof is required
Roof fire classification is written into the model codes and into wildfire codes. The exact floor depends on the code adopted by your jurisdiction, the construction type of the building, and whether the property sits in a mapped fire-hazard zone. In broad strokes:
- International Building Code (IBC) Section 1505 and Table 1505.1 set the minimum roof-assembly classification by type of construction. Some construction types and occupancies require Class A outright.
- International Residential Code (IRC) Section R902.1 requires roof coverings to carry a Class A, B, or C rating where a fire hazard exists, and lists noncombustible coverings (such as slate, clay and concrete tile, and metal) that are deemed to comply. Many jurisdictions amend the residential floor upward, and in wildfire areas that floor is commonly Class A.
- International Wildland-Urban Interface Code (IWUIC) requires Class A roofing in wildland-urban interface and fire-hazard areas that adopt it.
- California requires a Class A roof covering for new construction in Wildland-Urban Interface Fire Area / Fire Hazard Severity Zones under California Residential Code R337 and California Building Code Chapter 7A, one of the strictest statewide positions in the country.
Because the state-by-state picture is uneven, the same covering can be mandatory in one jurisdiction and optional a county away. For a current state-level breakdown of which states mandate Class A in wildfire zones, see our Wildfire Roof Risk Report. If you are weighing whether the rating is worth it beyond code compliance, our analysis of what post-fire data shows about Class A roofs in wildfires covers the evidence and its limits. Homeowners looking for a plain-language overview of fire-resistant options can start with our guide to fire-resistant roofing.
How to verify a product is actually Class A
A brochure line that reads “Class A fire rated” is a starting point, not proof. To confirm it applies to your roof:
- Ask for the listing number. Request the UL listing (UL 790) or the ICC-ES evaluation report (ESR) that documents the classification, and read the tested assembly, not just the headline.
- Match the deck type. Confirm the listing covers your deck: combustible (wood/plywood/OSB) versus noncombustible. A rating earned over a noncombustible deck does not automatically carry to a wood deck.
- Match the slope. Ratings can be slope-limited. A covering listed Class A up to a stated slope may not be listed above it. Check that your roof pitch falls within the listed range.
- Match every component. For assembly ratings, verify the underlayment, cap sheet, cover board, and fasteners called out in the listing are the ones being installed. Substitutions are the most common way a “Class A” roof ends up unrated in practice.
Common ways a Class A roof stops being Class A
- Installing a metal panel over a combustible deck without the listed underlayment or thermal barrier, on the assumption that metal is inherently Class A.
- Swapping the specified underlayment or cap sheet in a listed assembly for a cheaper or more available product.
- Using fire-retardant-treated wood shakes without the Class A cap sheet the assembly listing requires, or letting the treatment lapse where re-treatment is a condition of the rating.
- Exceeding the slope range in the product’s listing.
- Treating the covering as the whole answer. A Class A roof reduces roof ignition, but wildfire entry through vents, gutters full of debris, roof-to-wall junctions, and attached combustible decks is a separate problem the roof rating does not solve.
Bottom line
Class A is the top exterior-fire classification under ASTM E108 / UL 790, defined by passing the spread-of-flame, burning-brand, and intermittent-flame tests at their most severe levels. Slate, clay and concrete tile, and modern fiberglass-mat asphalt shingles typically reach it on their own; metal, treated wood, and low-slope membranes usually reach it only as a listed assembly. Whether it is required depends on your adopted code and fire-hazard zone. When in doubt, get the listing number and confirm the tested assembly matches what is going on the roof.
Frequently asked questions
What is a Class A fire-rated roof?
It is a roof covering or assembly that has passed the highest level of the exterior-fire tests in ASTM E108 / UL 790, namely the spread-of-flame, burning-brand, and intermittent-flame tests. Class A is the top of three classes (A, B, C) and represents effectiveness against severe fire exposure from outside the building.
Are asphalt shingles Class A?
Most modern fiberglass-mat asphalt shingles are Class A by material. Older organic-mat (paper) shingles were typically only Class C and are largely off the market. Confirm the rating on the specific product’s listing rather than assuming all asphalt shingles qualify.
Is a metal roof automatically Class A?
Not necessarily. Metal is noncombustible, but over a combustible wood deck a metal panel often reaches Class A only as part of a listed assembly that includes a specified underlayment or thermal barrier. Over a noncombustible deck it is generally Class A. The failure mode being tested is the deck igniting under the metal, not the metal burning.
What is the difference between Class A “by material” and “by assembly”?
A by-material rating means the covering itself carries Class A (slate, tile, glass-mat shingles). A by-assembly rating means Class A was achieved only with a specific combination of covering, underlayment, deck, and other listed components tested together. With an assembly rating, changing any listed component can void the rating.
Is a Class A roof required by code?
It depends on your jurisdiction, the building’s construction type, and whether it sits in a fire-hazard zone. IBC Section 1505, IRC Section R902, and the IWUIC set roof-classification requirements, and wildfire codes such as California’s Chapter 7A require Class A in mapped fire-hazard severity zones. Many other areas require only a lower class or leave it to local amendment, so check with the local building department.
Sources
- ASTM International, ASTM E108-20a, “Standard Test Methods for Fire Tests of Roof Coverings” (store.astm.org).
- ANSI/UL 790, “Standard Test Methods for Fire Tests of Roof Coverings.”
- Intertek, “ASTM E108: Fire Tests of Roof Coverings” (intertek.com).
- ICC Evaluation Service (ICC-ES), “ASTM E108 – Fire Tests for Roof Coverings” (icc-es.org).
- International Code Council, International Building Code Section 1505 and International Residential Code Section R902 (roof classification); International Wildland-Urban Interface Code.
- California Building Standards Code, California Residential Code R337 and California Building Code Chapter 7A (Materials and Construction Methods for Exterior Wildfire Exposure).
Cite this article: The Roofing Brief, “Class A Fire-Rated Roofs: What Qualifies Under ASTM E108 / UL 790, by Material,” theroofingbrief.com.