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Building Inspection Commission corrects code wording to restore reduced seismic-upgrade trigger
Summary
The Building Inspection Commission unanimously approved a revision to San Francisco Existing Building Code section 506.4.3 to restore the prior trigger that points increases of 10% and 100 occupants to the reduced IBC seismic forces (approximately 75%), reversing an inadvertent 2019 code-cycle change that pointed the provision to full IBC forces.
The San Francisco Building Inspection Commission on Oct. 21 approved a technical correction to the city’s existing building code to ensure an increase in a building’s occupant load of 10% and at least 100 people triggers the reduced International Building Code (IBC) seismic-force upgrade — not a full IBC upgrade.
Mr. Harris, speaking for the Code Advisory Committee, told commissioners the 2019 code-cycle renumbering inadvertently altered section 506.4.3 so the city’s code now refers to full IBC seismic forces when the intent was to reference the reduced (about 75%) IBC force level used for triggered upgrades. "The error is that in the current 2019 code, the way that it is currently written, we require full seismic code upgrades ... That was not intended," Mr. Harris said during the presentation.
The correction restores the 2016 San Francisco Existing Building Code language that points an occupant-load increase of 10% and 100 persons to the reduced seismic-force level. Mr. Harris explained that full upgrades remain required when a change raises a building’s risk category — for example, converting an office to an emergency facility — but not for the incremental occupant-load trigger.
Commissioner Clinch moved to approve the proposed revisions; the motion was seconded and carried unanimously in a roll-call vote. President McCarthy thanked Mr. Harris for clarifying the technical distinction and staff for drafting the fix. The commission’s action directs staff to publish the corrected code language so the intended reduced-force trigger is explicit in the San Francisco Existing Building Code.
What changed and why it matters: the city’s existing building code recognizes two upgrade levels — a full IBC seismic-force upgrade (the design forces used for new buildings) and a reduced IBC force level (roughly 75% of new‑building forces) used historically for triggered upgrades. Because the 10%/100-person test is a relatively high hurdle, the correction limits the instances when owners must perform a full seismic upgrade while preserving stronger requirements tied to changes in risk category.
Next steps: the approved correction will be incorporated into the San Francisco Existing Building Code and reflected in implementation guidance; staff said they will circulate the final text and update affected administrative documents.
