The short answer: Location moves ADU cost more than almost anything else in California. UC Berkeley’s 2021 owner survey found median costs of $100,000 in Los Angeles County, $130,000 in Orange and San Diego counties and $177,500 in the Bay Area. A 2026 builder guide puts a 600 sq ft detached ADU at $200,000 to $340,000 in Los Angeles, $180,000 to $300,000 in San Diego and $300,000 to $450,000 in the Bay Area. City fees add a different layer in each place.
Last verified: October 26, 2026 · Written by Marc
This guide compares neutral research with one builder’s 2026 estimates and the fee rules each city publishes. It is general information, not financial advice. The survey figures are from 2021 and the builder ranges are a vendor’s view, so use both to frame a budget and confirm it with local bids.
California’s three largest ADU markets behave differently. Bay Area labor costs push construction prices up, Los Angeles exempts ADUs from some city fees, and San Diego sits in between with its own fee rules. Owners who use a statewide number for a Bay Area project, or a Bay Area number for a project elsewhere, budget badly. This guide puts the regional figures side by side, explains why they differ and shows the city fees that change the final number.
What neutral research found
UC Berkeley’s Terner Center and Center for Community Innovation published two sets of figures. They are the most recent neutral regional data, but they are old.
| Region | 2021 survey: median cost | 2021 survey: per sq ft | 2020 report: estimate |
|---|---|---|---|
| Los Angeles County | $100,000 | $197 | $148,000 |
| Orange and San Diego counties | $130,000 | $200 | Not given |
| San Francisco Bay Area | $177,500 | $329 | $237,000 |
| Central Coast | $140,000 | $223 | Not given |
| California, statewide | $150,000 | About $250 | About $167,000 |
The 2020 report attributes the gap between Los Angeles and the Bay Area largely to labor costs, and notes that Bay Area costs “can exceed $800 per square foot” at the high end. The 2021 figures are medians of what owners reported spending, mostly on units built before the recent rise in construction costs, so they are a floor, not a current price.
What a 2026 builder guide estimates
ADU Scale, a California builder, gives all-in ranges for a 600 sq ft detached ADU by region in its June 2026 guide:
| Region | 600 sq ft detached ADU, all-in (ADU Scale, June 2026) |
|---|---|
| San Diego | $180,000 to $300,000 |
| Los Angeles | $200,000 to $340,000 |
| Orange County | $230,000 to $370,000 |
| San Francisco and the Bay Area | $300,000 to $450,000 |
Both sources put the Bay Area highest. They disagree on the order of the others: the survey had Los Angeles County lowest, while the builder has San Diego lowest. That disagreement is a reason to treat regional figures as orientation, not as a price for your lot.
Common mistake: multiplying a regional per-square-foot figure by the size you want. Small units cost more per square foot because the kitchen, bathroom, hookups, permits and design cost roughly the same at 400 or 800 sq ft. Ask bidders for prices at two sizes instead.
Los Angeles: fees the city publishes
Zoning Administrator Memo 143 (Revision 1) says Los Angeles ADUs are exempt from the city’s Park Fee and Affordable Housing Linkage Fee, and notes that the Los Angeles Unified School District charges a school fee on ADUs larger than 500 sq ft. Connection fees must be proportional to the load the unit adds. Plan check and permit fees are calculated per project with the city’s fee calculator.
San Diego: the General Plan Maintenance Fee
San Diego’s General Plan Maintenance Fee applies to all ADUs and JADUs, including small ones. It was $496 in fiscal year 2023 and is $737 per permit application on the city’s current schedule, and a June 2026 staff report proposes replacing it with an 11.25% surcharge on plan-check and permit fees. Check Information Bulletin 501 for the rule in force when you apply. Development impact fees are exempt for ADUs under 750 sq ft and JADUs, and school fees are collected separately.
The Bay Area: San Francisco and Oakland
- San Francisco calculates fees per project rather than publishing a flat figure. The city says its fees run roughly 6 to 9 percent of construction cost, paid in two installments at filing and issuance. For water and sewer, the SFPUC says that in most cases ADUs pay no additional capacity charges, but it requires a fixture count form.
- Oakland’s fiscal year 2026-27 zoning fee schedule lists $1,061.45 for secondary units and ADUs: an $878.58 base fee plus a general plan update charge and a technology and records charge. That covers zoning review only; building permit fees are separate.
A hypothetical example shows how much the fee approach matters. On a $300,000 Bay Area ADU in San Francisco, fees of 6 to 9 percent of construction cost would be $18,000 to $27,000. The same construction budget in a city with a flat zoning fee and a valuation-based building permit can produce a very different total, so get a written estimate from your city.
Practical tip: Ask each city for its ADU fee estimate in writing at two sizes, at or under 750 sq ft and at your preferred size. The state impact fee exemption at 750 sq ft is the same everywhere, but the other city fees are not, and the comparison shows what the extra space really costs.
State fee rules that apply everywhere
- Impact fees: none for an ADU of 750 sq ft or less of interior livable space; larger units pay in proportion to the main home.
- School fees: units under 500 sq ft are exempt; larger units may be charged.
- Utility connections: units built from existing space are not treated as new residential uses for connection fees unless built with a new home, and charges must be proportionate.
Our guides to ADU impact fees and ADU permit cost by city explain how the thresholds interact.
How to build a budget for your region
- Start with the regional range above for your unit type and size.
- Get the city’s fee estimate in writing.
- Add utility and site costs, which vary by lot more than by region.
- Collect three line-item bids with the same inclusions.
- Compare the bids with the regional ranges; a bid far below them usually leaves something out.
- Add a contingency for site surprises.
Frequently asked questions
How much does an ADU cost in Los Angeles?
UC Berkeley’s 2021 owner survey found a median of $100,000 in Los Angeles County, about $197 per sq ft, for units mostly built before recent cost increases. A June 2026 builder guide puts a 600 sq ft detached ADU in Los Angeles at $200,000 to $340,000 all-in. Los Angeles ADUs are exempt from the city’s Park Fee and Affordable Housing Linkage Fee.
Why is the Bay Area more expensive?
UC Berkeley’s 2020 report attributes the gap with Los Angeles largely to labor costs, and notes that Bay Area costs can exceed $800 per square foot at the high end. In the 2021 survey, the Bay Area median was $177,500, or $329 per sq ft, the highest of any region. A 2026 builder guide also puts the Bay Area highest, at $300,000 to $450,000 for a 600 sq ft detached unit.
How much does an ADU cost in San Diego?
The 2021 survey grouped Orange and San Diego counties, with a median of $130,000, or $200 per sq ft. A June 2026 builder guide puts a 600 sq ft detached ADU in San Diego at $180,000 to $300,000 all-in. San Diego also charges its General Plan Maintenance Fee on every ADU, $737 per application on its current schedule.
Are these figures still accurate?
The 2021 survey figures are a benchmark, not a current price: construction costs have risen since the surveyed units were built. The 2026 ranges are recent but come from one builder, not a study. Use both to frame a budget, then replace every line with written local bids and a city fee estimate for your lot.
Do ADUs pay impact fees in these cities?
Not at 750 sq ft or less of interior livable space, under state law, which applies in all three regions. Larger ADUs pay in proportion to the main home. Other fees differ by city: Los Angeles exempts ADUs from its Park Fee and Linkage Fee, San Diego charges its General Plan Maintenance Fee and San Francisco’s fees run about 6 to 9 percent of construction cost.
The bottom line
ADU cost in Los Angeles, the Bay Area and San Diego differs mainly because of labor and city fees. UC Berkeley’s 2021 survey found medians of $100,000 in Los Angeles County, $130,000 in Orange and San Diego counties and $177,500 in the Bay Area, while a 2026 builder guide puts a 600 sq ft detached unit at $180,000 to $450,000 depending on the region. Fees add a city-specific layer.
Your next step is to request a written fee estimate from your city and three line-item bids. Then build the full budget with our ADU budget breakdown and compare the statewide picture in what an ADU costs in California.
Sources
- Terner Center and CCI: First statewide ADU owner survey (2021)
- Terner Center and CCI: Reaching California’s ADU Potential (2020)
- ADU Scale: California ADU cost guide (builder, updated June 2026)
- Los Angeles City Planning: ZA Memo 143, Revision 1
- City of San Diego: Fee Schedule
- City of San Diego: GPMF staff report (June 2026)
- City of Oakland: zoning fees FY2026-27
- SF.gov: ADU permits
General information, not legal or financial advice. Rules and prices change; confirm with the agency or professional involved.
Cover photo: “Jefferson Park Bungalows” by Christopheraweed, CC BY-SA 4.0, cropped, via Wikimedia Commons.
Questions or a correction?
If something in this guide is unclear, out of date or does not match what your city told you, send me a message. Include the source if you have one.