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California&#;s wildfire season is just around the corner, and many building owners are wondering if their commercial roof will protect their building from fire.
Class A ratings are obtained when material survives a severe fire test. Class B ratings are awarded after successfully withstanding moderate fire exposure and Class C demonstrates survivability of only the lightest fire test.
The International Building Code (IBC), states that all roof coverings are required to be tested in accordance with ASTM E 108 or UL 790.
According to Carlisle Syntec:
The Standard Test Methods for Fire Tests of Roof Coverings, UL 790 (ASTM E108), includes three key tests to provide fire classification of roof covering materials and systems. These are the Spread of Flame Test, Intermittent Flame Test, and Burning Brand Test. During the Burning Brand Test, heat is transferred directly through the roof covering (single-ply, BUR, shingles, etc.) as well as the other roof components (insulation, underlayments, etc.), which protect the roof deck.
In most Burning Brand Tests conducted over a combustible deck (3/8- or 15/32- inch plywood), the roof components play a significant role in achieving the fire rating of the overall roofing system. Accordingly, many certifications of roof covering materials describe the specific types of roof components to be used based on the testing conducted.
That means the roof material is tested, as is the underlying insulation and roof deck, whether combustible or not.
Class A roofing is the preferred choice for any commercial building, especially if it is in an area prone to wildfires. To achieve a Class A rating, the roof must be effective against severe fire exposure. This is proven if it can:
Common stand-alone Class A roof coverings include clay tiles, slate, asphalt glass fiber composition shingles, and concrete tiles.
PVC and TPO products are both available with a Class A rating, although TPO is the most common commercial roof.
Acrylic and silicone roof coating may have a UL Class A fire rating. However, they are part of a commercial roofing system and that entire system must be considered when determining the roof&#;s fire rating.
Assembly-rated Class A roof coverings are those that meet Class A standards when combined with other elements. For example, metal roofs are non-combustible, but it still requires the underlying material to meet specification in order to receive a Class A fire rating. For example, a plywood deck under a commercial roof may ignite due to heat transfer through the metal unless there is additional protection to prevent this.
When using assembly-rated roofing material, it&#;s crucial the customer read the manufacturer&#;s specifications carefully. These will detail exactly which materials to combine for your roof to achieve a Class A rating.
Class B roofing is effective against moderate fire exposures. This is proven when the roofing can:
Pressure-treated shakes and shingles are the most common roofing materials to fall under the Class B rating although these are rarely used in commercial roofing.
Class C roofing provides only light fire protection. Roofing with a Class C rating is able to:
Examples of common Class C building materials include untreated wood shakes and shingles, plywood, and particleboard. None of these materials is recommended on a commercial or residential roof.
This type of roof provides little, if any, fire resistance and should be avoided. Most commercial roof building codes will not accommodate any type of unrated roofing material.
Understanding the fire rating for your roofing materials will help you determine how safe your commercial building is in the event of a fire, and whether it is up to code.
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If you&#;re concerned about the threat of fire to your commercial building, feel free to call us at 925-724-.
Additional reference provided by Build Direct »
The fire rating of roof coverings is determined for all materials used in code-compliant housing, and is classified as Class A, B, C, or unrated. Class A provides the best fire resistance, and therefore the best protection for your home. We recommend having a Class A fire-rated roof covering, but you should understand its limitations, particularly those related to edge-of-roof issues, since standard roof tests do not evaluate potential vulnerabilities at these locations.
At 12 in. by 12-in, the Class A brand is the largest one shown in this photo. The Class B brand is 6 in by 6 in. A and B brands consist of a three layer sandwich construction of 3/4 in. square sticks nailed together, with sticks in the middle later running perpendicular to the outside layers. The Class C brand is about the size of an ice cube.
Burning A brand on a roof deck
Flame-through to the underside of a roof deck. This roof covering failed, so as constructed, this is not a Class A roof.
Roof coverings can obtain a Class A rating based on the covering alone (called a stand-alone Class A) or based on the covering and underlying materials that provide additional fire protection (called an assembly-rated Class A). If you are unsure of the fire rating of your roof covering, the manufacturer of the roof covering can tell you. Often this information will be on the manufacturer&#;s website. If you are unsure about the type of roof covering you have, you should check with a licensed roofing contractor. Your local building department may also be able to help.
Common stand-alone Class A roof coverings include:
This asphalt composition roof covering is a stand-alone Class A.
Common assembly-rated Class A coverings include:
This aluminum roof covering is an assembly-rated Class A. The underlying Type 72 capsheet (roll roofing) material provides additional protections, and is required for the Class A rating.
This fire retardant treated wood shake roof covering is an assembly-rated Class A roof. The underlying gypsum-glass fiber panel (DensDeck) material provides additional protection, and is required for the Class A rating. In this case, the fire retardant treated shake is a stand-alone Class B covering.
It can be difficult to determine if the fire rating of a given product has a stand-alone or assembly-rated rating, since a published Class A rating could refer to either. If you aren&#;t sure, obtain a copy of the installation instructions for the roofing materials. If the installation instructions call for Dens-Deck, a Type 72 capsheet material, or other materials in addition to Type 15 or 30 roofing felt and structural sheathing (plywood or oriented strand board), you have an assembly-rated Class A covering.
For more information: link to &#;What is a Fire Safe Roof?&#;
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