Fire Ratings for Roofing Materials
Fire ratings for roofing materials classify how well a roof assembly resists ignition, flame spread, and burning debris under standardized test conditions. These classifications directly affect code compliance, insurance underwriting, and permitting outcomes across all 50 states. Understanding the three-class rating system — and the test protocols behind it — is essential for anyone specifying, installing, or inspecting a roofing assembly.
Definition and scope
A roofing fire rating is a performance designation assigned to a roof covering or assembly after it has been tested against standardized fire exposure protocols. The two primary testing standards used in the United States are ASTM E108 and UL 790, which are functionally equivalent. Both evaluate roof coverings mounted on a representative deck under controlled flame exposure, burning brand exposure, and intermittent flame application. The International Building Code (IBC) and the International Residential Code (IRC), published by the International Code Council (ICC), adopt these test results as the basis for occupancy-based roofing requirements.
The rating applies to the roof assembly — meaning the specific combination of deck, underlayment, and covering — not to any single material in isolation. A Class A shingle installed over an incompatible deck or missing underlayment may not qualify for the rating printed on its packaging.
The broader regulatory context for roofing includes state fire marshal rules, local amendments to model codes, and insurer requirements that can be stricter than the base IBC or IRC text.
How it works
ASTM E108 / UL 790 define three performance classes through a set of four sequential tests:
- Flame spread test — Measures how far a flame travels across the roof surface under a sustained gas burner exposure.
- Burning brand test — Exposes the assembly to glowing wood brands of specified size and mass to simulate airborne ember contact, a primary wildfire ignition pathway.
- Flying brand test — Assesses whether the assembly itself generates burning brands that could ignite adjacent structures.
- Intermittent flame test — Cycles the gas burner on and off to simulate variable fire exposure.
The three resulting classes are:
| Class | Flame spread limit | Brand size (UL 790) | Typical materials |
|---|---|---|---|
| A | 6 feet or less | Large (12 in × 12 in) | Concrete tile, clay tile, metal, fiberglass-mat asphalt shingles, slate |
| B | 8 feet or less | Moderate (6 in × 6 in) | Some pressure-treated wood shingles, certain built-up systems |
| C | 13 feet or less | Small (1.5 in × 1.5 in) | Untreated organic-mat asphalt shingles (largely phased out) |
Class A represents the highest fire resistance. Class C is the minimum acceptable rating under most current model codes for occupied structures. Unrated materials — including untreated wood shakes in their natural state — are prohibited by the IBC for all occupancies except specific limited exemptions. Wood shake and shingle roofing systems can reach Class A or B only when installed with a fire-resistant underlayment or interlayer system that is tested as part of the assembly.
The National Fire Protection Association (NFPA) publishes NFPA 276, a complementary standard specifically addressing fire testing of roof-covering assemblies that incorporate photovoltaic modules — relevant as solar integration becomes more common on residential and commercial roofs.
Common scenarios
Wildland-urban interface (WUI) zones. California's Building Code Title 24, enforced by the California Office of the State Fire Marshal, requires Class A assemblies for all new construction in State Responsibility Areas and Very High Fire Hazard Severity Zones. This affects a large share of California's 58 counties and has been adopted by reference in Oregon and portions of Washington.
Insurance underwriting. Property insurers in fire-prone markets routinely require documentary proof of Class A certification as a condition of coverage. Roof replacement permits that specify a downgrade from Class A to Class B or C can trigger policy cancellation in some carrier guidelines.
Historic structures. Owners of buildings listed on the National Register of Historic Places sometimes face conflicts between preservation guidelines (which may require wood or slate materials) and local fire codes. Many jurisdictions allow the Authority Having Jurisdiction (AHJ) to approve tested assembly alternatives that preserve material appearance while meeting Class A performance.
Low-slope and flat roofing. Flat and low-slope roofing systems — including modified bitumen, TPO, and EPDM — are rated as assemblies. A Class A designation for a single-ply membrane depends on the insulation board and deck type tested alongside it, not the membrane alone.
Metal roofing. Bare steel and aluminum panels inherently achieve Class A performance. However, certain coated or composite metal products must be tested as assemblies, since foam-core panels can affect the rating. Metal roofing systems that carry a UL listing mark have passed the full assembly protocol.
Decision boundaries
Choosing the appropriate fire-rated assembly involves resolving three factors that can conflict with each other:
Jurisdiction-mandated minimum class. The IBC Section 1505 sets Class A as mandatory for all buildings in High Fire Hazard Severity Zones and for Groups A, B, E, F, H, I, M, R-1, R-2, and R-4 occupancies in most configurations. The IRC Section R902 requires Class A or B for most one- and two-family dwellings in identified hazard zones. Local amendments can raise but not lower these minimums.
Assembly vs. material certification. A roofing contractor replacing only the surface layer — not the deck or underlayment — must verify that the new covering is compatible with the existing assembly. Installing a labeled Class A shingle over a non-tested substrate can void the classification, creating a liability gap at inspection.
Permit documentation. Building departments typically require the product's UL or ICC Evaluation Service (ICC-ES) listing to be submitted with the permit application. The National Roof Authority's main reference hub provides background on how listing documents are structured. Permitting and inspection concepts for roofing explains how inspectors verify assembly compliance in the field, including underlayment checks that directly affect fire rating validity.
Synthetic roofing materials present a growing classification question — synthetic roofing materials that mimic slate or shake often carry Class A ratings, but the specific product and assembly must appear on the listing document submitted at permit.