San Diego County Municipal Code § 1505.1 General

The roof covering for every new structure and addition to an existing structure shall be fire-retardant, that is at least Class A rated in accordance with ASTM E 108 or UL 790. A construction project for an addition to an existing structure, or the alteration, repair, recover, or partial replacement of an existing roof, that involves more than 50 percent of the roof area of the existing structure or 2,500 square feet, whichever is less, within any one year period, shall require that the entire structure's roof covering complies with this section. For the purposes of this section, gambrel roofs, mansard roofs and other similar roof configurations shall be considered roofs regardless of the steepness of the roof pitch.

Exceptions:

1. The roof covering of a building not classified as an R-3 or U occupancy may have a minimum Class B rating when not located in a wildland-urban interface fire area.

2. On a qualified historical building a wood roof covering may be repaired or reconstructed as allowed by the State Historical Building Code.

A roof for a structure located in a wildland-urban interface fire area shall also comply with the California Wildland-Urban Interface Code.