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ADU Cost In California
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A UC Berkeley Terner Center survey of California ADU owners found a median construction cost of $150,000, or $250 per square foot, with 37 percent of new ADUs costing less than $100,000 and 71 percent less than $200,000. The survey was published in 2021, so a project started today may cost more.
What A Statewide Owner Survey Found
The UC Berkeley Terner Center surveyed California ADU owners, and its write up of the Terner Center statewide ADU owner survey reports a median construction cost of $150,000, or $250 per square foot. In that survey, 37 percent of new ADUs cost less than $100,000 to build, and 71 percent cost less than $200,000. The survey was published in 2021, so costs for a project started today may differ.
Regional Medians From The Same Survey
| Region | Median Construction Cost | Per Square Foot |
|---|---|---|
| San Francisco Bay Area | $177,500 | $329 |
| Central Coast | $140,000 | $223 |
| Orange And San Diego Counties | $130,000 | $200 |
| Los Angeles County | $100,000 | $197 |
Source: Table 2 of the Terner Center report Implementing The Backyard Revolution, the full report behind the Terner Center statewide ADU owner survey.
Ranges By Type
The Angi ADU cost guide lists national ranges of $60,000 to $150,000 for a garage conversion and $110,000 to $285,000 for a new detached unit. These are not California specific figures. Angi is a home services marketplace, so treat its numbers as a rough guide, not a quote. We have not found a reliable published range for junior ADUs, so ask builders for written estimates.
- Garage conversions reuse a slab, walls, and roof, so they tend to cost less. See Garage Conversion To ADU.
- Detached units need a foundation, framing, a roof, and utility lines. See Detached ADU.
- Junior ADUs are carved out of the existing home. See Junior ADUs.
What Changes The Number
- Size. A larger unit costs more in total, and the per square foot figure also varies by region, as the table shows.
- Site work. Slope, trees, old sewer lines, and a long run to the electric panel all add cost.
- Utility connections. Units converted from existing space generally cannot be required to get a new utility connection. Other ADUs may be, according to the HCD ADU Handbook (March 2026).
- Fees. A unit of 750 square feet or less cannot be charged impact fees by local agencies. Larger units are charged in proportion to the size of the main home (Government Code section 66311.5).
- Design and permits. Plans, engineering, energy reports, and permit fees come on top of construction. Some cities publish ready-made plans that cut design cost. See Permits And Timeline.
Build A Budget Line By Line
Ask each builder to price design, permits and fees, site work, construction, utility connections, landscaping, and a contingency as separate lines. A quote with one lump sum is hard to compare. See Questions To Ask An ADU Builder.
Related guides: ADU Financing, Prefab Versus Site-Built.
Common Questions
What does an ADU cost in California?
The Terner Center owner survey found a statewide median construction cost of $150,000, or $250 per square foot. By region the medians were $177,500 in the San Francisco Bay Area, $140,000 on the Central Coast, $130,000 in Orange and San Diego Counties, and $100,000 in Los Angeles County.
Which part of California has the highest ADU costs?
In the same survey the San Francisco Bay Area had the highest median, $177,500, or $329 per square foot. Los Angeles County had the lowest, $100,000, or $197 per square foot.
Are these ADU costs current?
No. The survey was published in 2021, so treat the figures as a starting point and get written estimates from licensed builders for your own lot.
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