ASTM E108 / UL 790 (Roof Fire Ratings)

ASTM E108, Standard Test Methods for Fire Tests of Roof Coverings, and UL 790, Standard Test Methods for Fire Tests of Roof Coverings, are the two closely aligned North American standards used to give roofs their familiar Class A, B or C fire ratings. ASTM E108 is maintained by ASTM Committee E05 on fire standards; UL 790 is maintained by UL Standards & Engagement. US building codes generally accept either standard.

The tests measure how a roof covering behaves when fire comes from outside the building: wind-blown embers, burning debris landing on the roof, or flames spreading across the surface. They do not measure fire resistance from inside the building, which is covered by separate assembly fire-resistance tests.

Test procedures

The standards include several exposures, run on decks of wood or noncombustible material as specified by the manufacturer:

• Intermittent flame test – a gas flame is applied to the roof surface in cycles while air blows across it, checking whether fire penetrates to the deck.
• Spread of flame test – a flame and wind are applied at the eave to see how far flame travels up the roof.
• Burning brand test – a burning block of wood (a "brand") is placed on the roof, and the deck underside is watched for flaming or penetration. UL 790 descriptions note brand exposure periods of up to 90 minutes.
• Flying brand test – checks whether the covering itself breaks off and sends burning pieces into the air.
• Rain test – used for treated materials such as fire-retardant wood shakes, to check that treatment does not wash out.

Classes

• Class A – effective against severe fire exposure, giving a high degree of protection to the deck.
• Class B – effective against moderate fire exposure.
• Class C – effective against light fire exposure.

In all three classes the covering must stay in place and not produce flying brands.

Stand-alone and assembly ratings

Some materials, such as clay and concrete tile, slate and many metal roofs, can achieve Class A on their own. Others reach Class A only as part of a tested assembly that includes a specific underlayment, cap sheet or fire barrier board. Product literature usually states whether a rating is "stand-alone" or "by assembly."

Code use

US codes require Class A or B roofs in many situations, and wildland-urban interface codes in fire-prone areas such as California often call for Class A. In Canada, the equivalent test is CAN/ULC-S107. In Europe, external fire performance is classified under EN 13501-5 using the CEN/TS 1187 test methods.