How Much Does an ADU Cost in San Francisco, CA?
Data version: Q2 2026 · Last updated 2026-04-21
Buildability City Score™: C (Bottom 25%) · Median permit time: 186 days
An 800 sqft detached ADU in San Francisco typically costs $280,000–$400,000 total, or $350–$500 per square foot. This range indexes published industry benchmarks to the San Francisco market tier (Tier 1, median home price $1,350,000). Actual bids vary with lot conditions, finish quality, contractor availability, and permit-specific requirements.
San Francisco ADU cost breakdown (800 sqft baseline)
Design & plans: $22,400–$48,000 (8–12% of total). Permits & impact fees: $8,400–$32,000 (3–8% of total). Site prep & excavation: $14,000–$40,000 (5–10% of total). Foundation: $28,000–$60,000 (10–15% of total). Framing & construction: $112,000–$200,000 (40–50% of total). Finishes, MEP, fixtures: $42,000–$100,000 (15–25% of total).
What drives the price in San Francisco
Three factors explain most of the variance in San Francisco ADU costs. First, finish quality: contractor-grade vs custom finishes can swing the total by 30–40%. Second, lot conditions: slope, soil, and utility extensions add $15,000–$75,000 on top of the base range. Third, design path: a pre-approved plan (if San Francisco offers one) typically saves 10–15% versus a custom architect design.
Impact fees and permit costs in San Francisco
Impact fees waived for ADUs under 750 sqft.
Permit timeline in San Francisco
Median permit timeline in San Francisco is 186 days (Buildability City Score grade C). Faster timelines indicate streamlined ministerial review. Slower timelines usually mean discretionary review, additional hearings, or design committees that add months to the schedule. Financing costs during a long review window meaningfully affect total project cost.
Methodology
The $280,000–$400,000 range is derived from NAHB ADU cost surveys, California HCD ADU cost reports (for West Coast markets), and RSMeans regional construction cost indices. We index the per-sqft range to the city's median home price because construction labor, material sourcing, and subcontractor availability all track local housing market pressure. Estimates are planning guidance only — verify with 2–3 licensed San Francisco contractors before budgeting.
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