Cal. Pub. Cont. Code § 3002

(a) For purposes of subdivision (b) of Section 3400 and subdivision (a) of Section 10129, for any roof project, a material, product, thing, or service shall be considered equal if it meets all of the following requirements:
1. (1) The item is at least equal in quality, durability, design, and appearance but not necessarily of an identical color.
2. (2) The item will perform the intended function at least equally well.
3. (3) The item conforms substantially, even with deviations, to the detailed requirements contained in the specifications.
(b) A substitute may be unequal if the resulting roof system would be substantially different than other equal or better systems in terms of performance and durability, but not merely different by virtue of the inclusion of proprietary products or a proprietary warranty.