Can I build an ADU in San Francisco?

Yes — San Francisco allows Accessory Dwelling Units (ADUs) in every residential and most mixed-use zones, governed by the overlap of California state ADU law (Government Code §65852.2 and §65852.22) and SF's local ADU program in Planning Code §207(c)(4) and §207.1.

State ADU law preempts most local restrictions. Under §65852.2, jurisdictions must permit at least one ADU and one Junior ADU (JADU) per single-family lot, and allow ADUs in multifamily buildings (one detached ADU plus interior conversions of up to 25% of existing units, capped at 50% of converted ADU types). The state imposes 60-day permit-issuance timelines for ADU applications that comply with ministerial standards.

Common SF configurations:

• Garage conversion — converting an existing legal ground-floor garage into a habitable ADU. Often the fastest track because the envelope already exists.
• Basement/ground-floor addition — excavating or finishing existing under-house space; structural and waterproofing complexity drives cost.
• Detached backyard cottage — limited by SF rear-yard setback, height, and lot-coverage rules in Planning Code §134, §261.
• Vertical addition / addition atop existing structure — may trigger §311 neighborhood notification depending on size and façade impact.
• Internal subdivision of an existing oversized unit — interior-only conversions get the most favorable streamlined review.

Key SF-specific overlays:

• Article 10/11 historic properties require Historic Preservation Commission Certificate of Appropriateness for visible exterior changes.
• Coastal Zone parcels (small portion of westernmost SF) require SF Planning Coastal Permit coordination.
• Ellis Act and SF Rent Ordinance: ADUs added to multifamily buildings can be added without triggering rent control if classified as new construction post-1979, but tenant displacement during construction is governed by SFAC §37.9.
• SB 9 lot splits (Government Code §65852.21) are largely inapplicable in SF because SF rezoned to remove most single-family-only zoning, and SB 9 only triggers in single-family zones.

Fees and timeline: SF waives most school-district impact fees on ADUs under 750 sq ft per state law. DBI permit cost for a typical ADU runs $5K–$15K in fees plus utility connection charges. Total permit timeline is typically 4–10 months — faster for ministerial conversions, slower if §311 notice or HPC review is triggered.

Verify zoning, prior permits, and any deed restrictions on the SF Property Information Map and the Planning Department's ADU Handbook before scoping.