San Francisco County Municipal Code § 12.1 California Residential Code (CRC)

…An approved alternative procedure shall not be used to establish the seismic forces and their distribution unless the

corresponding internal forces and deformations in the members are determined using a model consistent with the procedure adopted. San Francisco Building Code sections that discuss non-prescriptive or “alternative” seismic design procedures are reproduced below: 104A.2.8 Alternate materials, design and methods of construction. The provisions of this code are not intended to prevent the use of any material, alternate design or method of construction not specifically prescribed by this code, provided any alternate has been approved and its use authorized by the building official. The building official may approve any such alternate, provided the building official finds that the proposed design is satisfactory and complies with the provisions of this code and that the material, method or work offered is, for the purpose intended, at least the equivalent of that prescribed in this code in suitability, strength, effectiveness, fire resistance, durability, safety and sanitation. The building official shall require that sufficient evidence or proof be submitted to substantiate any claims that may be made regarding its use. The details of any action granting approval of an alternate shall be recorded and entered in the files of the code enforcement agency.