Detached ADUs in San Diego
Updated
A detached ADU in San Diego is a separate small home built in your backyard, apart from the main house. Because it stands apart from the house, it needs its own foundation and its own runs for power, plumbing, and HVAC [3]. Here are the City of San Diego's rules and what published guides say about cost and timing.
City rules for detached ADUs
- Size. A new detached ADU can be 150 to 1,200 square feet [1].
- Height. On lots that allow single-dwelling homes but not multiple dwellings, a detached ADU can be no more than two stories, and it must meet the zone's height limit [1].
- Front setback. It must meet the zone's front setback, but one ADU of 800 square feet or less may extend into it [1].
- Side and rear setbacks. A unit taller than 16 feet next to a residential property needs at least 4 feet on the interior side [1]. In a Very High Fire Hazard Severity Zone, it needs at least 4 feet on the interior side and rear, whatever its height [1].
- Parking. None required outside the Coastal Overlay Zone [1].
- Selling. Most ADUs can now be sold separately as condominiums [2].
What a detached ADU costs
We did not find a published survey of installed prices in San Diego, so here are the national and California figures we found:
| Source | Figure |
|---|---|
| HomeGuide, national, 2023 [3] | $150 to $250 per sq ft; $90,000 to $150,000 for 600 sq ft |
| Block Renovation, 2026 [4] | Site-built ADUs at $300 to $500+ per sq ft |
| Block Renovation, 2026 [4] | Site work and other extras for prefab: $65,000 to $160,000 |
HomeGuide notes that detached units need extra labor and materials to run electricity, plumbing, and HVAC to the building [3]. Newer sources run higher than the 2023 national average, so treat it as a floor.
In the City's August 2026 fee schedule, a detached ADU over 500 square feet starts at $8,085.26 for plan check and $8,401.90 for inspection, and one up to 500 square feet starts at $3,512.92 and $2,228.29 [5]. Impact and school fees can be added [5]. Try the ADU cost calculator for a rough range.
How long it takes
One San Diego builder reports that detached ADUs often take 12 to 24 months from first idea to completion [6]. Using a pre-approved plan can shorten City review to 30 days [1]. See our pre-approved ADU plans guide, and our prefab ADU guide if you are considering a factory-built unit.
FAQ
How big can a detached ADU be in San Diego?
In the City of San Diego, a new detached ADU can be 150 to 1,200 square feet [1]. On lots that allow only single-dwelling homes, it can be no more than two stories [1]. Other cities differ. Escondido, for example, has its own limits, covered on our Escondido page.
Can I rent out a detached ADU?
Yes, for long-term rentals. The City does not require the owner to live on site, but an ADU may not be rented for less than 31 days in a row [1]. If you plan to rent, ask lenders whether projected rent can help you qualify. Our ADU financing guide covers that.
Request a quote for a detached ADU from an independent local contractor.
A referral is not an endorsement, so check any contractor yourself before you sign.
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Sources
- City of San Diego Development Services, "Information Bulletin 400: Accessory Dwelling Unit/Junior Accessory Dwelling Unit," January 2026. Fetched 2026-11-11. https://www.sandiego.gov/development-services/forms-publications/information-bulletins/400
- City of San Diego Development Services, "Public Notice: Information Bulletin 400 Updates," August 27, 2025. Fetched 2026-11-11. https://www.sandiego.gov/sites/default/files/2025-08/dsd_ib400_adu.pdf
- HomeGuide, "How Much Does It Cost to Build an ADU?," November 13, 2023. Fetched 2026-11-11. https://homeguide.com/costs/adu-cost
- Block Renovation, "Prefab ADUs: What is the True Cost Savings," February 4, 2026 (updated June 17, 2026). Fetched 2026-11-11. https://www.blockrenovation.com/guides/prefab-adus-what-is-the-true-cost-savings
- City of San Diego Development Services, "Information Bulletin 501: Fee Schedule for Construction Permits," August 2026. Fetched 2026-11-11. https://www.sandiego.gov/development-services/forms-publications/information-bulletins/501
- SnapADU, "The State of Detached ADUs in San Diego (2026)," no date shown. Fetched 2026-11-11. https://snapadu.com/lessons-from-100-adu-builds-detached-adu-report-san-diego/