How Much Does an ADU Cost in San Diego, CA?
Data version: Q2 2026 · Last updated 2026-04-21
Buildability City Score™: B (Middle 45%) · Median permit time: 90 days
An 800 sqft detached ADU in San Diego typically costs $220,000–$320,000 total, or $275–$400 per square foot. This range indexes published industry benchmarks to the San Diego market tier (Tier 2, median home price $900,000). Actual bids vary with lot conditions, finish quality, contractor availability, and permit-specific requirements.
San Diego ADU cost breakdown (800 sqft baseline)
Design & plans: $17,600–$38,400 (8–12% of total). Permits & impact fees: $6,600–$25,600 (3–8% of total). Site prep & excavation: $11,000–$32,000 (5–10% of total). Foundation: $22,000–$48,000 (10–15% of total). Framing & construction: $88,000–$160,000 (40–50% of total). Finishes, MEP, fixtures: $33,000–$80,000 (15–25% of total).
What drives the price in San Diego
Three factors explain most of the variance in San Diego 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 Diego offers one) typically saves 10–15% versus a custom architect design.
Impact fees and permit costs in San Diego
Impact fees in San Diego depend on the ADU size and whether your lot sits inside a transit priority area. Many California cities waive fees for ADUs under 750 sqft. Permit fees alone typically run $2,500–$8,500 on an 800 sqft ADU in the Tier 2 market tier.
Permit timeline in San Diego
Median permit timeline in San Diego is 90 days (Buildability City Score grade B). 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 $220,000–$320,000 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 Diego contractors before budgeting.
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