What a new detached ADU costs in San Diego
How much does a detached ADU cost in San Diego?
New detached ADUs in the City of San Diego declared a median $154,300 of construction in 2026 (middle half $102,900–$198,800, 293 permits). That is about $64,700 more than a garage conversion. Budget extra for design, engineering, City fees and utility connections.
In 2026, 293 City of San Diego building permits added a new detached ADU. The median declared construction value was $154,300, with the middle half between $102,900 and $198,800.
| ADU type | Permits | Low (25%) | Median | High (75%) |
|---|---|---|---|---|
| New detached ADU | 293 | $102,900 | $154,300 | $198,800 |
| Permits adding 2+ ADUs | 333 | $151,300 | $247,200 | $330,300 |
| Conversion | 307 | $59,600 | $89,600 | $144,400 |
Source: City of San Diego permit data (building permits issued Jan 1–Oct 15, 2026 that add at least one ADU). Valuation is the construction value the applicant declared to the City, not a final invoice or a quote. Types are sorted by words in the permit description.
What pushes a detached ADU up
- New foundation, framing and roof, unlike a conversion.
- Site work and utility runs from the street or main house: sewer lateral, water, power and often a panel upgrade. In 2026 permits on the same parcels, a panel upgrade followed an ADU by a median of about 68 days (what comes next).
- Solar: California's energy code generally requires it on newly built detached ADUs. Your Title 24 report will say.
Building two?
Permits adding two or more ADUs declared a median of $247,200. The first two ADUs on a property are exempt from Development Impact Fees regardless of size.
Fees to expect
- Development Impact Fees are waived for ADUs under 750 sq ft and for the first two ADUs on a property (SDMC §142.0640).
- Water and sewer capacity fees are separate and depend on the design, such as a new connection or meter.
- School fees, the General Plan Maintenance Fee and plan check/permit fees still apply. See the full fee notes.
How long the permit takes
Across 1,037 standard-track ADU permits issued in 2026, the median was 293 days from application to issue (fastest quarter 170 days or less; slowest quarter 486 days or more). Correction rounds are usually the longest part. Full timeline.