B-07 2020-Current: Class "A" Roof Requirements

Sonoma County requires Class “A” roof assemblies on the following types of structures:

• Any new structure regulated by this code
• Any existing structure regulated by this code when more than fifty percent of the roof area is re-roofed.
• Any addition regulated by this code when the addition creates a new floor and the floor area of any single floor of the addition exceeds 640 square feet.

Class A roof assemblies are those that are effective against severe fire test exposure. Class “A” roof assemblies and roof coverings shall be listed and identified as meeting the Class “A” testing requirements of ASTM E 108 or UL 790 (CBC 1505.1 and 1505.2).

The County provides several exceptions to the rule. The purpose of this bulletin is to provide guidelines on how to apply Class “A” roofs to common construction situations.

Technical Details

1. Composition shingles and built-up roofs
   These types of roofs must be components of a Class “A” listed system. The manufacturer of the product obtains a listing for the product(s) and the installation method, and documents this information in the product literature. This information is also present on the product wrapping and should be made available to the field inspector upon request.
2. Roof decks
   A roof deck is a roof that is also designed as a walking surface. A roof deck requires a Class “A” roof. This roof may be covered with flammable material, such as redwood decking. (CBC Chapter 7A contains additional requirements in State Responsibility Fire Suppression Areas.)
3. Fire-retardant wood shakes
   Although the CBC allows this type of roof on single family dwellings, the County ordinance is more restrictive. In order to meet the County code, the product must be tested and listed as a Class “A” system.
4. Slate, tile, concrete or metal roofs
   The building code states that such roofs, when applied in accordance with the manufacturer’s instructions, are equivalent to a Class “A” listed assemblies. Such roofs therefore comply with the County ordinance.
5. Greenhouses
   Typical roofing on a greenhouse is sheet plastic, polycarbonate, or glass. A Class “A” roof is not required for this type of structure.
6. Patio covers
   Patio covers are structures attached to a single family dwelling, covered with glass or plastic. A Class “A” roof is not required for this type of structure.
7. Fabric membrane structures
   These structures may be temporary (permitted for not more than 6 months) and regulated by the Fire Marshall, or permanent and regulated by the Building Official. Typical uses may be crush pad canopies, riding arenas, yurts, or other miscellaneous structures. They must use a material that has been certified as “flame-retardant” by the State Fire Marshall. This product will have a “SFM” label for identification in the field.
8. Residential car covers
   These are typically a prefabricated pole and canvas structure that is assembled in the field. They may be used to house anything from a single passenger vehicle to an RV. When used as a vehicle or boat shelter, a Class “A” roof is not required for this type of structure.
9. Awnings
   Fabric shade devices projecting from the wall of the building do not fall under the roofing requirements. See CBC Section 3202.2.3 for construction requirements.
10. Sod roofs and other extremely unconventional roofs
    Sod roofs for underground homes or caves are considered Class “A” roofs. Sod roofs and other unconventional roofs not listed above shall be reviewed on a case-by-case basis.

References

• Sonoma County Code, Section 7-13
• 2019 California Building Code, Sections 1.1.3.2, 101.3.2, 1505.1, 2606.10, & 3202.2.3
• ASTM E 108
• UL 790
• ASTM D 2898