Detached ADU Cost in San Diego | Cost Per Square Foot

The published range: $300,000 – $450,000+, about $375–$600 per sq ft

San Diego builder guides publish detached ADU costs at $300,000–$450,000 and up, or roughly $375–$600 per square foot. Educational ranges, not a quote — your lot, size, finishes, and utility work set the real number, and only a builder who has seen the property can price it.

Detached ADU size	At the published $375–$600 per sq ft
600 sq ft	$225,000 – $360,000
750 sq ft	$281,250 – $450,000
1,000 sq ft	$375,000 – $600,000
1,200 sq ft (the City of San Diego's published ADU size ceiling)	$450,000 – $720,000

Why small detached units often price above the per-foot band: the expensive fixed pieces — foundation, utility connections, a kitchen, a bathroom — barely shrink with the floor plan. That is why published totals for typical detached builds start around $300,000 even at modest sizes.

Where the money goes

Site work and a new foundation
Framing, roofing, and exterior shell
Utility trenches — water, sewer, and electric from the street or the main house; distance is destiny here
The kitchen and bathroom — the two most expensive rooms per square foot
Interior finishes, flooring, fixtures, and appliances
Design, engineering, permits, and applicable fees
California Energy Code items — the City of San Diego's rules summary notes new detached ADUs need solar, on the ADU or the main house

Ways owners hold the number down

A preapproved or standard plan: San Diego accepts the County of San Diego, City of Chula Vista, and City of Encinitas standard plan sets; Santee accepts the same sets; La Mesa publishes its own pre-approved plans
One story and a simple roofline
Siting the unit close to existing utility lines
Standard finishes in the kitchen and bath, upgraded later if desired
Sizing honestly — every extra 100 sq ft is real money at these per-foot rates

Keep reading

ADU cost in San Diego — the full guide

All three published ranges, the educational cost estimator, cost drivers, and permit and utility fee notes.

Read the guide →

Garage conversion ADU cost

The published $100k–$210k alternative — often half the detached price when the garage works.

Read the guide →

San Diego ADU rules

Size ceilings, setbacks, and preapproved plans from the City of San Diego's own ADU page.

Read the guide →

Want a licensed builder to look at your actual lot?

That feasibility conversation — your lot, your city's current rules, your utilities, your budget — is the real answer to every cost and rules question. It is exactly what a match request starts: one licensed local builder, matched to your project, and nobody else.

Start a match request

The intake form lives on our main page — that page states whether intake is currently open.

San Diego ADU Match is a matching service, not a contractor. We never quote or estimate a price for your property, and we do not give feasibility or legal opinions — those calls belong to licensed builders and your city. Guides on this site are general information, not advice about your property.