By The Roofing Brief Team. Last reviewed: October 2026.
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. The 2021 IRC Section R902.1 (as adopted in the Seattle Residential Code) spells out the deemed-to-comply list: brick, masonry and exposed concrete roof decks are Class A outright; metal sheets and shingles, copper, clay or concrete tile and slate are Class A on noncombustible decks; and over a combustible deck only copper sheets of at least 16 ounces per square foot and slate over underlayment are deemed Class A without a product listing.
The deck under a listed product matters too. Per UL’s code-authority bulletin on Class A, B and C roof ratings, prepared roof coverings such as asphalt shingles are tested over 3/4-inch wood sheathing or 3/4-inch plywood unless the instructions say otherwise, and where instructions allow a 1/2-inch minimum, 15/32-inch plywood or 3/8-inch OSB qualifies only with a certified underlayment between deck and shingle.
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 (The older NFPA 256 has been withdrawn; Canada uses the parallel CAN/ULC-S107.)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, run to ASTM E119 / UL 263 and expressed in hours rather than as Class A, B or C.
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. UL’s bulletin states the hierarchy plainly: a Class A assembly may be used wherever Class A, B or C is required, a Class B assembly wherever B or C is required, and an unrated assembly is not suitable for any application requiring a class unless a code specifically allows it.
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, 5 inches per foot by default per Intertek’s ASTM E108 summary, with a blower producing a 12 mile-per-hour wind across the surface) must pass the applicable tests at that class level. The burner runs at 1,400°F for Classes A and B and 1,300°F for Class C, and the spread-of-flame exposure lasts 10 minutes for Classes A and B and 4 minutes for Class C, per ICC-ES. 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. Per ICC-ES, the rain conditioning runs six decks through 12 one-week cycles of 96 hours of water exposure and 72 hours of drying at 140°F before two decks each go to the intermittent-flame, burning-brand and flying-brand tests, and treated wood shakes are tested with the air current raised from 12 to 18 mph. 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. IRC R902.2 adds a manufacturing rule: fire-retardant-treated shakes and shingles must be pressure-impregnated by the full-cell vacuum-pressure process under AWPA C1, with each bundle labeled with its fire classification.
ASTM E108 / UL 790 test parameters by class
| Parameter | Class A | Class B | Class C | Source |
|---|---|---|---|---|
| Burner temperature (spread, intermittent, flying brand) | 1,400°F ± 50°F | 1,400°F ± 50°F | 1,300°F ± 50°F | Intertek ASTM E108 summary |
| Spread-of-flame exposure | 10 minutes | 10 minutes | 4 minutes | ICC-ES ASTM E108 page |
| Burning brand | One brand, 12 x 12 x 2 1/4 in | Two brands, 6 x 6 x 2 1/4 in | Twenty brands, 1 1/2 x 1 1/2 x 25/32 in | Intertek ASTM E108 summary |
| Brand wood | Dry Douglas fir | Dry Douglas fir | Dry non-resinous white pine | ICC-ES ASTM E108 page |
| Brand ignition flame | 1,630°F ± 50°F | 1,630°F ± 50°F | 1,630°F ± 50°F | ICC-ES ASTM E108 page |
| Wind across the deck | 12 mph (18 mph for treated shakes) | 12 mph | 12 mph | Intertek; ICC-ES |
| Default test slope | 5 in per ft | 5 in per ft | 5 in per ft | Intertek ASTM E108 summary |
| Rain conditioning (when water can affect fire performance) | 12 one-week cycles: 96 hours water, 72 hours drying at 140°F | ICC-ES ASTM E108 page | ||
Class A by material versus Class A by assembly
This is the distinction that governs most field decisions. UL files Class A, B and C products under separate certification categories: Roofing Systems (TGFU), Prepared Roof-covering Materials (TFWZ), Fire-retardant-treated Wood (TFXX), Prepared Roofing Accessories (TGDY) and building-integrated PV (QHZK), and a TGFU listing names the deck, any slope limit and the required barrier boards or ply sheets. 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. Note the code’s narrower view of tile and metal: IRC R902.1 deems them Class A only on noncombustible decks, so on a typical plywood house deck the product or assembly listing is what carries the rating. Thatch is not in the table; for that material, see our guide to Class A synthetic thatch and thatched roof rules.
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. UL’s bulletin gives two reference points: the IBC requires at least Class B roof coverings on Type IA, IB and IIA buildings, and buildings the International Wildland-Urban Interface Code assigns to Class 1 ignition-resistant construction need Class A roof assemblies. 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 Class A, B or C roofing, listed to ASTM E108 or UL 790, in jurisdictions designated by law and wherever the edge of the roof is less than 3 feet from a lot line. Its exceptions deem brick, masonry and exposed concrete decks Class A, metal, tile and slate Class A on noncombustible decks, and only 16-ounce copper sheets and slate over underlayment Class A over combustible decks. Many jurisdictions amend the residential floor upward, and in wildfire areas that floor is commonly Class A.
- Solar on the roof (IRC R902.3 and R902.4): building-integrated PV used as the roof covering must be listed for fire classification to UL 7103, and rack-mounted PV systems to UL 2703, with Class A, B or C required under the same 3-foot lot-line and designated-area triggers.
- International Wildland-Urban Interface Code (IWUIC) requires Class A roofing in wildland-urban interface and fire-hazard areas that adopt it.
- California requires Class A roofing for new construction in mapped Fire Hazard Severity Zones, one of the strictest statewide positions in the country. For permits from January 1, 2026, that requirement sits in the 2025 California Wildland-Urban Interface Code (Title 24, Part 7), Section 504.2 (roof assembly); the code relocated the former California Residential Code Section R337 and California Building Code Chapter 7A provisions into its Chapter 5, per the California Building Standards Commission’s State Fire Marshal rulemaking file. Older permits and documents may still cite Chapter 7A or R337, and local amendments can be stricter. For how this plays out on an existing home, see California fire class rules for re-roofs.
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, in category TGFU for roofing systems or TFWZ for prepared roof coverings) 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, and UL’s shingle guidance assumes 3/4-inch sheathing unless the instructions allow 15/32-inch plywood with a certified underlayment.
- Match the slope. Ratings can be slope-limited, and the ASTM E108 default test slope is 5 inches per foot. 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. A substituted component means the field roof no longer matches any tested assembly in UL category TGFU.
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, using shakes not pressure-treated under AWPA C1 as IRC R902.2 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.
- Adding rooftop solar that is not listed to UL 2703 with a fire classification matching the roof, which IRC R902.4 requires within 3 feet of a lot line or in designated areas.
Which path to Class A fits your roof
| If your roof is… | Path to Class A | Code or listing to check |
|---|---|---|
| Slate over a wood (combustible) deck | Deemed Class A when installed over underlayment | IRC R902.1 Exception 4 |
| Copper sheet over a wood deck | Deemed Class A at 16 ounces per square foot or heavier | IRC R902.1 Exception 3 |
| Steel or aluminum panels, or clay or concrete tile, over plywood or OSB | Listed product or listed assembly (often with a specified underlayment) | UL TGFU or TFWZ listing; deemed status in R902.1 Exception 2 covers noncombustible decks only |
| Any of the above over a noncombustible deck | Deemed Class A | IRC R902.1 Exceptions 1 and 2 |
| Fiberglass-mat asphalt shingles | Listed Class A product | UL TFWZ listing; 3/4-inch deck unless instructions allow 15/32-inch plywood with certified underlayment |
| Fire-retardant-treated cedar shakes | Listed assembly with the specified cap sheet | UL TFXX listing; AWPA C1 pressure treatment (IRC R902.2) |
| Low-slope membrane or coating | Listed roofing system: membrane, insulation, cover board and deck as tested | UL TGFU listing; for coatings, the maker’s data sheet (for example, GacoFlex U91 lists ASTM E108 Class A at 1 in 12 over metal and 2 in 12 over BUR) |
| Solar shingles or rack-mounted PV | Listed fire classification for the PV product or system | UL 7103 (BIPV) or UL 2703 (racked PV), IRC R902.3 and R902.4 |
| Untreated wood shakes | No practical path | Replace with a listed covering in any Class A area |
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, with the IRC requiring at least a Class C listing wherever the roof edge is less than 3 feet from a lot line. When in doubt, get the UL or ICC-ES 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; its burning brand is a single 12 x 12 x 2 1/4 inch Douglas fir crib.
What is ASTM E108?
ASTM E108 is the ASTM International standard “Standard Test Methods for Fire Tests of Roof Coverings.” It rates a roof covering Class A, B or C using spread-of-flame, intermittent-flame, burning-brand and flying-brand tests with a 12 mph wind across the deck, plus rain and weathering conditioning for coverings whose fire performance can change with exposure.
What is UL 790?
ANSI/UL 790 is UL’s version of the same roof fire test, with the same title and aligned methods, so listings and codes cite it as “ASTM E108 / UL 790.” UL certifies products that pass it in categories such as TGFU (roofing systems) and TFWZ (prepared roof coverings), and the IRC accepts either standard for Class A, B and C roofing.
Are asphalt shingles Class A?
Most modern fiberglass-mat asphalt shingles are Class A by material, listed by UL in category TFWZ and tested over 3/4-inch sheathing unless the instructions allow thinner decks with a certified underlayment. 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 deemed Class A under IRC R902.1, and copper sheets of at least 16 ounces per square foot are deemed Class A even over a wood deck. 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. Under IRC R902.1, slate over underlayment and 16-ounce copper are the only coverings deemed Class A by material over a combustible deck.
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 (which requires a rated roof wherever the roof edge is less than 3 feet from a lot line), and the International Wildland-Urban Interface Code set roof-classification requirements, and wildfire codes such as the 2025 California Wildland-Urban Interface Code (Title 24, Part 7), which replaced California’s Chapter 7A and R337 rules for permits from January 1, 2026, 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).
- UL, “Class A, B, and C Roof Ratings: Helpful hints for achieving code compliance,” The Code Authority newsletter, Issue 1, 2014 (code-authorities.ul.com).
- City of Seattle, 2021 Seattle Residential Code Chapter 9, adopting IRC Sections R902.1 to R902.4 (seattle.gov).
- International Code Council, International Building Code Section 1505 and International Residential Code Section R902 (roof classification); International Wildland-Urban Interface Code.
- California Building Standards Commission, 2025 California Wildland-Urban Interface Code, California Code of Regulations Title 24, Part 7 (effective January 1, 2026), and the State Fire Marshal’s Initial Statement of Reasons SFM 08/24 (dgs.ca.gov), which relocated the former California Residential Code R337 and California Building Code Chapter 7A provisions.
Cite this article: The Roofing Brief, “Class A Fire-Rated Roofs: What Qualifies Under ASTM E108 / UL 790, by Material,” theroofingbrief.com.