Published 2026 data for a custom detached ADU in San Diego is roughly $300–$500 per square foot for construction, plus design and permit fees. The all-in number homeowners actually write checks against — site work, utilities, fees, and design — lands closer to $375–$600 per square foot. Ads at $150–$200 per square foot usually describe a prefab product on a flat lot with no site work.
What does an ADU cost in San Diego in 2026?
| Project type | 2026 all-in cost | Notes |
|---|---|---|
| Junior ADU (JADU) | $55,000 – $110,000 | Up to 500 sf, inside existing walls |
| Garage conversion | $85,000 – $175,000 | Existing structure, new plumbing / electrical |
| Detached ADU — 400 sf studio | $150,000 – $220,000 | New foundation, roof, MEP |
| Detached ADU — 600 sf 1BR | $210,000 – $300,000 | Most common size |
| Detached ADU — 800 sf 2BR | $275,000 – $400,000 | Family-scale unit |
| Detached ADU — 1,200 sf max | $400,000 – $600,000+ | State maximum; coastal / hillside high end |
Line items nobody quotes upfront
- Utility connections and capacity fees — water meter, sewer, SDG&E, separate panels — often $5,000–$20,000.
- Impact fees are waived for ADUs under 750 square feet, often $10,000-plus in savings.
- Title 24, structural calculations, and soils reports. Soils alone run $2,500–$5,000, more on hillside or expansive-soil lots.
- City fees beyond plan check, including General Plan Maintenance and other DSD line items.
The real timeline, not the marketing timeline
SB 543 gives the city 15 business days to say whether an application is complete, then 60 days to approve or deny a complete application. That path works with pre-approved plans under AB 1332. Custom plans go through multiple cycles. Each cycle is typically 3–6 weeks. Coastal ADUs add 4–12 weeks for a Coastal Development Permit even with AB 462's 60-day coastal clock. Construction for a 400–1,200 sf unit is commonly 16–30 weeks after permit issuance.
We do not permit on the first submittal. Nobody does. What we do is a road map for permitting so correction cycles are short. Nalu Architecture Inc. is the architect, not the builder.
Related: coastal permit summary and residential services.
Questions we hear
How long does it take to permit an ADU in San Diego?
Custom ADUs typically take three to five months from submittal to permit because they run three or four plan-check cycles. The 60-day statutory clock applies to a complete application and is more realistic for pre-approved plans under AB 1332. Construction after permit is commonly 16–30 weeks.
Who designs ADUs in Encinitas, Oceanside, Carlsbad, and North County San Diego?
Nalu Architecture Inc. is a San Diego practice that designs custom ADUs and garage conversions across North County and the City of San Diego, including coastal lots that also need a Coastal Development Permit. Principal architect Chris Schumm, AIA, License C-36569.
NALU® is a registered trademark of Nalu Architecture, Inc. Architectural services are provided through Chris Schumm, AIA, California Registered Architect, License No. C-36569. This page is general planning information for 2026, not an opinion on a specific site. Every engagement is scoped and contracted individually.