What Is a Class A Fire Rated System?

What Does Class A Fire Rated Mean?

Class A is not "fireproof." It means flame spreads across the surface slowly enough, and smoke develops at a low enough rate, that the material qualifies for the most demanding code applications. Class B (FSI 26-75) is the next tier down and is acceptable for many residential decks where the deck is not also a roof over conditioned space.

Fire ratings apply to complete tested systems, not individual components. A Class A coating on the wrong substrate is no longer Class A. Always verify the rating against the manufacturer's tested assembly and the project's ICC-ES evaluation report.

What Are Fire Ratings?

Fire ratings classify how building materials react when exposed to fire. For deck waterproofing systems, the most common classifications are Class A and Class B, based on testing per ASTM E84. All walking roof decks must meet Class A requirements, like any compliant roofing products.

These ratings tell you two things: how quickly flame spreads across the surface and how much smoke the material produces when burning. Building codes use these ratings to determine which products can be used in different applications.

ASTM E84 Testing

ASTM E84 is the standard test method for measuring surface burning characteristics. The test exposes a material sample to controlled flame in a 25-foot tunnel and measures two values:

Flame Spread Index (FSI)

Measures how quickly fire spreads across the material surface. Lower numbers mean slower spread. The scale uses red oak flooring (FSI = 100) and cement board (FSI = 0) as reference points.

Smoke Developed Index (SDI)

Measures the amount of smoke produced during burning. Lower numbers mean less smoke, which is critical for safe evacuation during a fire.

Class A vs Class B

Class A Fire Rated Roof Systems

A Class A fire rated roof is a roof covering assembly tested per ASTM E108 (the roof-covering counterpart to E84) and classified for the most severe fire exposure: spread of flame, intermittent flame, and burning brand. Class A is the IBC default for roof coverings in Type I and II construction, and it's required in California Wildland-Urban Interface zones under CRC Chapter 7A.

Walking deck systems that double as roof coverings (decks over conditioned space) must meet roof-covering Class A under ASTM E108, not just surface burning Class A under ASTM E84. The two tests evaluate different fire exposures. A coating with an E84 Class A flame spread number is not automatically a Class A roof covering.

For balcony and walking deck projects in California, look for both classifications in the manufacturer's ICC-ES evaluation report and confirm the tested assembly matches what you're installing.

When Each Rating is Required

Class A Typically Required For:

• Multi-family residential buildings (condos, apartments)
• Commercial properties and public buildings
• Projects in wildfire-prone areas
• Building codes requiring roof covering Class A rating
• Fire-resistance-rated assemblies

Class B Acceptable For:

• Single-family residential projects
• Light commercial applications
• Projects where building codes don't specify Class A
• Interior applications with less stringent requirements

Always verify requirements with your local building department. Code requirements vary by jurisdiction, building type, and occupancy. For a side-by-side breakdown with worked examples, see Class A vs Class B fire rating for decks.

Common Misconceptions

Class A Doesn't Mean Fireproof

No surface material is fireproof. Class A means the material resists flame spread and limits smoke production better than Class B or C materials, but it will still burn under sufficient heat.

The Entire System Must Be Tested

Fire ratings apply to the complete system as tested, not individual components. Using different substrates, coatings, or installation methods than what was tested invalidates the rating.

Fire Rating vs Fire Resistance

Fire rating (Class A/B) measures surface burning characteristics. Fire resistance rating (1-hour, 2-hour) measures how long an assembly prevents fire spread through a floor or wall. These are different tests with different purposes.

Reading Fire Test Reports

When reviewing product documentation, look for:

• ASTM E84 test report showing actual FSI and SDI values
• Classification (Class A or Class B) based on those values
• Exact system configuration tested (substrate, coatings, thicknesses)
• ICC-ES evaluation report confirming the fire rating for code compliance
• Limitations on use (substrate types, application methods, slope restrictions)

Example Fire Rated Walking Deck Systems

Deck Flex has two complete Walking Deck and Roof Covering Systems that are ICC-ES listed (ESR-3672) with documented fire ratings:

Fire Ratings vs WUI Chapter 7A Requirements

ASTM E84 fire ratings (Class A/B) and ASTM E108 roof covering classifications address general building code fire performance. In California's Wildland-Urban Interface (WUI) zones, Chapter 7A of the California Residential Code adds additional fire requirements specific to wildfire exposure.

For deck walking surfaces in WUI zones, CRC Section R337.9.3 provides seven compliance options — including the use of classified roof covering systems tested per ASTM E108. This means a walking deck system with a Class A roof covering classification already meets one of the R337.9.3 compliance paths.