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ADU construction cost in California: price per square foot by size

ADU construction cost in California runs roughly $150,000 to $500,000+ for a detached unit in 2026, depending on size, region and your lot. Here's what builders publish, what's in their numbers and what isn't.

Fact-checked against 17 sourcesUpdated Oct 26, 2026

A worker framing a wall

ADU construction cost by size

The clearest public price list by size comes from Snap ADU, a San Diego builder. Its March 2026 prices for a turnkey detached unit include design, permit management, about $35,000 of sitework on a level lot and standard finishes. They leave out city fees, demolition, retaining walls and a separate electric meter.

500 sq ft, 1,000 sq ft and 2 bedroom ADU cost, San Diego (Snap ADU, March 2026)
SizeLayoutBuilding onlyTypical all-inAll-in per sq ft
500 sq ft1 bed, 1 bath$220,000about $300,000$600
750 sq ft2 bed, 1 bath$275,000about $350,000$465
1,000 sq ft2 bed, 2 bath$335,000about $425,000$425
1,200 sq ft3 bed, 2 bath$360,000about $450,000$375

How much does a 2 bedroom ADU cost?

In Snap ADU's pricing, a two-bedroom unit runs about $350,000 at 750 square feet with one bath, or about $425,000 at 1,000 square feet with two. The second bathroom and extra space add about $75,000. The same builder estimates a second detached unit built at the same time costs about 85% of the first.

ADU building cost by region in California

Builders in each region publish their own ranges. They don't all count the same things, so compare what's included before comparing totals.

Cost to build an ADU in California by region (builder-published, 2026)
RegionDetached ADUPer sq ftGarage conversionSource
San Diego$250,000–$450,000+$375–$600 all-in$150,000–$225,000+Snap ADU (Mar 2026); Lars Remodel (Oct 2026)
Los Angeles$200,000–$400,000+ for one-story 800–1,200 sq ft$250–$400 new construction$100,000–$225,000Acton ADU (Apr 2026)
Bay Area$250,000–$500,000+; most $300,000–$450,000Not published$120,000–$150,000Maxable (2026)
Sacramento$150,000–$300,000+; 600 sq ft about $180,000–$260,000$300–$500$80,000–$150,000Block Renovation (Jun 2026)

Sources: Snap ADU, Lars Remodel, Acton ADU, Maxable and Block Renovation. Acton ADU puts Westside Los Angeles at the top of its range and says hillside lots can exceed $500 per square foot. Maxable's typical Bay Area range includes design, permits and site work. For a full San Diego breakdown, see what an ADU costs in San Diego.

What goes into the cost to build an ADU

Every ADU bid splits into soft costs (design, engineering and permits) and hard costs (the site, the building and the utility hookups). Block Renovation's June 2026 Sacramento guide breaks out a 600-square-foot detached unit with mid-range finishes:

ADU build cost breakdown, 600 sq ft detached (Block Renovation, Sacramento, June 2026)
CategoryTypical range
Design, engineering and Title 24 energy work$14,000–$20,000
Permits and fees (under 750 sq ft)$2,000–$8,000
Site prepAbout $30,000 flat lot; about $55,000 sloped
Foundation and framing$50,000–$80,000
Mechanical, electrical and plumbing$15,000–$30,000
Kitchen and bath$13,000–$28,000
Solar (required by the energy code)$8,000–$12,000
Utility connections$5,000–$15,000
Contingency (10–20%)$20,000–$45,000

New detached ADUs generally must have new solar panels under California's energy code. Attached ADUs are treated as additions and don't trigger that requirement.

Site work and utilities

This is where budgets slip. Snap ADU lists a separate SDG&E meter at $10,500 to $15,000, 2 to 4 feet of slope at $10,000 to $20,000, retaining walls from $20,000 to $30,000+, a sewer pump around $5,000 and fire sprinklers at $5,000 to $10,000. In the Bay Area, Maxable says utility connections for a detached unit typically add $15,000 to $30,000 and recommends a 10% to 15% contingency.

What ADU builder cost quotes include

Ask each builder for a line-item bid and check it against the table above. The Contractors State License Board warns that trenching for water, sewer and power is easy to leave out of a bid, and suggests getting at least three bids on the same plans. Our guide on how to hire an ADU contractor explains the contract and payment rules.

ADU cost per square foot, and why small units cost more

A kitchen, a bathroom, a foundation edge, a utility trench and a permit cost about the same whether the unit is 500 or 1,000 square feet. Spread over fewer feet, they push the price per foot up. Acton ADU says the same: fixed costs like kitchens, bathrooms and utility connections don't shrink with size.

In Snap ADU's pricing, going from 500 to 1,000 square feet doubles the space but adds only about $125,000, so the all-in price falls from $600 to $425 per square foot. A smaller unit is still cheaper in total. It's just less space per dollar.

Permits, impact fees and school fees

These are builder estimates, not official fee schedules. Ask your city's permit office for a fee estimate on your plans. Our guide to California ADU laws covers the fee rules in more detail.

How ADU construction costs have risen since 2021

The state's California Construction Cost Index, built from Engineering News-Record building cost data for San Francisco and Los Angeles, stood at 7,090 in January 2021 and 10,717 in September 2026, a rise of about 51%. Over the 12 months to September 2026 it rose about 4.7%, from 10,238.

Old ADU cost figures are out of date. A widely quoted UC Berkeley survey found a median statewide ADU construction cost of $150,000, or $250 per square foot. That survey was published in April 2021, before the run-up in building costs. Don't budget from it.

Ways to lower your ADU construction cost

For loans and grants, read our ADU financing guide and ADU grants in California.

ADU cost calculator

Pick your size, type and site conditions and estimate your cost with our ADU cost calculator. Treat the result as a starting budget, then get written bids. When you're ready, compare verified ADU builders in San Diego and check a contractor's license before you sign.

Common questions

How much does it cost to build an ADU in California?
Builder prices published in 2026 put a detached ADU at about $150,000 to $300,000+ in Sacramento, $200,000 to $400,000+ in Los Angeles, $250,000 to $450,000+ in San Diego and $250,000 to $500,000+ in the Bay Area. Garage conversions cost less.
What is the ADU construction cost per square foot?
Most 2026 builder ranges fall between about $250 and $600 per square foot for a detached ADU. Small units sit at the high end because the kitchen, bath and hookups cost about the same at any size.
How much does a 500 sq ft ADU cost?
About $300,000 all-in in San Diego, or $600 per square foot, based on Snap ADU's March 2026 prices. In Sacramento, Block Renovation puts a 600 square foot unit at about $180,000 to $260,000.
How much does a 1,000 sq ft ADU cost?
About $425,000 all-in in San Diego for a two-bedroom, two-bath unit, based on Snap ADU's March 2026 prices. In Los Angeles, Acton ADU puts a mid-range 1,000 to 1,200 square foot detached unit at $300,000 to $380,000.
How much does a 2 bedroom ADU cost?
In San Diego, about $350,000 for a 750 square foot two-bedroom with one bath, or about $425,000 for 1,000 square feet with two baths, according to Snap ADU's March 2026 prices.
Is it cheaper to convert a garage than build a new ADU?
Usually. 2026 builder ranges for garage conversions run about $80,000 to $150,000 in Sacramento and $150,000 to $225,000+ in San Diego, well below detached units in the same areas.

Sources

General information, not legal or financial advice. Rules and fees change; confirm with your city's permit office before you rely on them.

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