San Francisco ADU Structural Engineering

The City and County of San Francisco Department of Building Inspection (DBI) is the building-permit authority, while San Francisco Planning reviews zoning and historic-resource issues when they apply. The City's ADU program can allow an attached or interior unit in an existing building, but the project still has to satisfy applicable Planning, Building, Fire, and other agency requirements. On a typical older rowhouse or apartment building, the question is not simply whether an ADU is allowed: it is whether the proposed opening, stair, foundation, or added story can be integrated into a building with unknown past alterations and limited staging.

The structural investigation starts with an as-built survey, permit history where available, framing direction, existing foundation type, and the relationship to party walls and neighboring structures. Bay Area seismic design can make new shear walls, collectors, hold-downs, diaphragm repairs, or foundation strengthening more important than the ADU's square footage suggests. Soft or liquefiable ground near the bay and filled areas is different from a hillside site; the engineer should use the geotechnical information available for the parcel instead of assigning one citywide foundation detail. Temporary shoring, underpinning, and vibration control belong in the conversation when new openings or excavation are close to a neighbor.

A practical submittal begins by confirming the Planning zoning or historic-review path, then preparing architectural, structural, and any required fire or utility documents for DBI's permit process. DBI's Permit Center and electronic services are the authoritative source for current intake instructions; a complete application may still receive corrections from several review disciplines. Structural drawings should clearly distinguish existing conditions, demolition, new work, seismic load path, and construction sequencing so a plan reviewer can evaluate the conversion rather than infer it from a floor plan.

California Government Code section 65852.2 establishes a statutory action window for a complete ADU application in the circumstances described by the statute. That is a review requirement, not a promise that a San Francisco project will receive a permit or be built within that period. DBI and Planning intake, historic or site-specific review, correction cycles, utility work, shoring, and inspection scheduling can all affect the overall duration; only the agencies and the project team can establish a current project schedule.