Section 304 — STRUCTURAL DESIGN LOADS AND EVALUATION AND DESIGN
304.4 Minimum Lateral Force for Existing Buildings.
San Francisco Building Inspection Commission Codes · edición 2022 · actualizado 2026-07-08 · San Francisco
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304.4 Minimum Lateral Force for Existing Buildings.
304.4.1 General. This section is applicable to existing buildings when invoked by SFEBC Section 503. This section may be used as a standard for voluntary upgrades.
An existing building or structure which has been brought into compliance with the lateral force resistance requirements of the San Francisco Building Code in effect on or after the dates shown in Table 304.4.1 shall be deemed to comply with this section except when a vertical extension or other alterations are to be made which would increase the mass or reduce the seismic resistance capacity of the building or structure. Where multiple building types apply, the later applicable date shall be used. Where none of the building types apply, compliance shall be at the discretion of the Director. Building type definitions are given in ASCE 41, Table 3-1.
TABLE 304.4.1 – DATES REQUIRED TO DEMONSTRATE BUILDING COMPLIANCE
| Building Type | Date of Compliance |
Model Code (for reference) |
|---|---|---|
| Wood Frame, wood shear panels (Types W1 & W2) | 1/1/1984 | UBC 1976 |
| Wood Frame, wood shear panels (Type W1A) | 7/1/1999 | UBC 1997 |
| Floor areas greater than 3,000 ft2 per level | ||
| Steel moment-resisting frame (Types S1 & S1a) | 12/28/1995 | UBC 1994 |
| Steel concentrically braced frame (Types S2 & S2a) | 7/1/1999 | UBC 1997 |
| Steel eccentrically braced frame (Types S2 & S2a) | 1/1/1990 | UBC 1988 |
| Buckling-restrained braced frame (Types S2 & S2a) | 1/1/2008 | IBC 2006 |
| Light metal frame (Type S3) | 1/1/2008 | IBC 2006 |
| Steel frame w/ concrete shear walls (Type S4) | 12/28/1995 | UBC 1994 |
| --- | --- | --- |
| Steel plate shear wall (Type S6) | 1/1/2008 | IBC 2006 |
| Reinforced concrete moment-resisting frame (Type C1) | 7/1/1999 | UBC 1997 |
| Reinforced concrete shear walls (Types C2 & C2a) | 7/1/1999 | UBC 1997 |
| Tilt-up concrete (Types PC1 & PC1a) | 7/1/1999 | UBC 1997 |
| Precast concrete frame (Types PC2 & PC2a) | 1/1/2008 | IBC 2006 |
| Reinforced masonry (Type RM1) | 7/1/1999 | UBC 1997 |
| Flexible diaphragms | ||
| Reinforced masonry (Type RM2) | 12/28/1995 | UBC 1994 |
| Stiff diaphragms | ||
| Seismic isolation or passive dissipation | 7/1/1992 | UBC 1991 |
304.4.2 Wind forces. Buildings and structures shall be capable of resisting wind forces as prescribed in San Francisco Building Code Section 1609.
304.4.3 Seismic forces. Buildings and structures shall comply with the reduced seismic forces, as defined in Section 304.3.2. The building separation limitations of Section ASCE 7-16 Section 12.12.3 need not be considered.
When upper floors are exempted from compliance by Section 503.11.1, the lateral forces generated by their masses shall be included in the analysis and design of the lateral force resisting systems for the strengthened floor. Such forces may be applied to the floor level immediately above the topmost strengthened floor and distributed in that floor in a manner consistent with the construction and layout of the exempted floor.
(Amended by Ord. 70-25, File No. 250211, App. 5/9/2025, Eff. 6/9/2025)