Roofing Fire Ratings: Class A, B, and C Explained

Roofing fire ratings classify roof assemblies by their ability to resist fire spread and protect structural components beneath the roof deck. The classification system — Class A, B, and C — is established under standardized testing protocols administered by recognized safety organizations and adopted into model building codes enforced across the United States. These ratings directly affect permitting, material selection, and insurance underwriting for residential and commercial construction projects.

Definition and scope

Roofing fire ratings measure a roof covering's performance against external fire exposure — specifically, how well the assembly resists flame spread, heat transfer through the roof deck, and the generation of burning brands that could ignite adjacent structures. The system does not assess structural fire resistance or interior fire containment; those functions fall under separate code provisions.

The three classifications are defined by UL (Underwriters Laboratories) through test standard UL 790, which is also designated as ASTM E108 by ASTM International. Both standards subject roof assemblies to three test conditions: flame spread, burning brand, and intermittent flame exposure. Class A represents the highest fire resistance; Class C represents the lowest qualifying resistance. Materials that do not meet Class C thresholds are classified as non-rated.

These ratings are incorporated into the International Building Code (IBC) and the International Residential Code (IRC), both published by the International Code Council (ICC). Local jurisdictions adopt and amend these model codes; the enforced version varies by state and municipality. In California, for example, the California Building Code (Title 24) specifies Class A requirements across all State Responsibility Areas designated as Very High Fire Hazard Severity Zones (VHFHSZ) by CAL FIRE.

The scope of a fire rating applies to the complete roof assembly as tested — not to individual materials in isolation. A roofing product listed as Class A must be installed in the specific configuration for which it was tested to carry that rating.

How it works

UL 790 / ASTM E108 testing evaluates three distinct fire exposure scenarios. A roof assembly must pass all three applicable tests to qualify for a given class designation:

1. Intermittent flame test — An intermittent gas flame is applied to the roof surface at a specified wind speed. Class A requires 15 intermittent 2-minute flame applications at a simulated wind speed of 12 miles per hour without flame spread exceeding 6 feet. Class B requires the same number of applications at the same wind speed with a 8-foot limit. Class C requires fewer applications (3) at 12 mph with a 13-foot limit.
2. Spread of flame test — A continuous flame is applied at the specified wind speed. Class A must not spread beyond 6 feet; Class B must not exceed 8 feet; Class C must not exceed 13 feet.
3. Burning brand test — Standardized burning brands (wood cribs of specified mass) are placed on the roof surface under wind. Class A uses a 2,000-gram brand; Class B uses a 500-gram brand; Class C uses a 100-gram brand. The assembly must not allow flame penetration to the deck.

The test ratings apply to assemblies, not standalone products. A concrete tile roof system that includes a specific underlayment may achieve Class A as a system, while the same tile installed over a different underlayment may rate Class B or lower.

Common scenarios

Roofing fire rating requirements arise in several distinct permitting and construction contexts:

Wildland-Urban Interface (WUI) construction — Jurisdictions that adopt WUI provisions under the IRC or IBC Chapter 7A (California Building Code) require Class A roof assemblies on all new or re-roofed structures in designated fire hazard areas. CAL FIRE's VHFHSZ maps define these zones at the parcel level.

Commercial occupancy requirements — The IBC assigns fire rating requirements by occupancy type and construction type. Type I and Type II construction classifications — applied to high-rise and large assembly occupancies — generally require Class A roof coverings.

Re-roofing permits — When a building permit is pulled for a full or partial re-roofing project, the inspector verifies that the installed assembly matches the rating required by the adopted code for that occupancy and fire zone. Product approval documents, typically ICC Evaluation Service (ICC-ES) reports or UL listing cards, are the standard documentation method used during inspection.

Insurance underwriting — Property insurers in fire-prone states reference roof fire ratings when determining coverage eligibility and premium tiers. Class A roofs on structures in high-risk zones frequently qualify for lower premium rates relative to Class C or non-rated assemblies, though the specific differential is set by individual carrier underwriting guidelines.

For professionals navigating material selection across these scenarios, the roofing listings section of this reference covers contractors and suppliers organized by service category.

Decision boundaries

The distinction between Class A, B, and C is not arbitrary; it reflects measurable performance gaps that directly affect code compliance and risk exposure:

• Class A vs. Class B — Class A assemblies withstand a burning brand 4 times heavier (2,000 g vs. 500 g) and permit no more than 6 feet of flame spread versus 8 feet. In WUI-designated areas, Class A is the minimum code requirement; Class B does not satisfy these jurisdictions.
• Class B vs. Class C — Class B withstands a 500-gram brand; Class C withstands only a 100-gram brand. Class C is generally permitted in standard residential construction outside fire hazard zones under the IRC, subject to local amendments.
• Non-rated materials — Wood shakes and similar combustible coverings without a qualifying assembly rating are prohibited in WUI zones and restricted by construction type in the IBC. Jurisdictions that previously allowed wood shake roofs have progressively banned re-roofing with non-rated materials in fire-prone areas.

Inspectors verify fire rating compliance by cross-referencing the installed product's UL listing or ICC-ES evaluation report against the permit drawings. A product substitution made in the field — such as swapping underlayment brands without checking assembly listing compatibility — can void the rated assembly classification and trigger a failed inspection or a required teardown. The roofing directory purpose and scope page describes how licensed roofing professionals are categorized within this reference, and how to use this roofing resource outlines the structure of listings and reference material available for locating qualified contractors by specialty.

References

• UL 790 — Standard for Tests for Fire Resistance of Roof Covering Materials (Underwriters Laboratories)
• ASTM E108-21 — Standard Test Methods for Fire Tests of Roof Coverings (ASTM International)
• International Building Code (IBC) 2021 — International Code Council
• International Residential Code (IRC) 2021 — International Code Council
• ICC-ES — ICC Evaluation Service (product evaluation reports)
• CAL FIRE — Fire Hazard Severity Zone Maps and Building Regulations (Office of the State Fire Marshal)
• International Code Council — WUI Code Resources