ADU Rules & Cost in California
A 700 sq ft detached ADU in California typically costs $192,500–$315,000 ($275–$450/sq ft). Here is what the rules allow.
Statewide ADU law: Cal. Gov. Code §66314 et seq. (former §65852.2)California ADU rules at a glance
California has the strongest statewide ADU law in the country. Cities must approve a detached ADU up to 800 sq ft (and generally up to 1,200 sq ft) ministerially within 60 days, with only a 4 ft side/rear setback. Owner-occupancy cannot be required, and impact fees are waived for ADUs under 750 sq ft. A junior ADU (JADU, up to 500 sq ft inside the home) is also allowed.
- Statewide law
- Yes
- Max detached size
- 1200 sq ft
- Guaranteed minimum
- 800 sq ft
- Setback
- 4 ft
- Owner-occupancy
- Not required
- Approval time
- 60 days (ministerial)
Parking: No parking required if within 1/2 mile of public transit, in a historic district, or part of the existing/proposed primary residence.
Estimate your California ADU
Pre-set to California. Adjust the type and size for your project.
Your property
ADU typeEstimated cost in California
$192,500 – $315,000
≈ $275–$450/sq ft turnkey · midpoint $254,000
- $172,700
- Construction
- $45,700
- Design & permits
- $35,600
- Site work
- ✓Size within the guaranteed minimum. Your 700 sq ft ADU is at or under the 800 sq ft your city must allow regardless of other rules.
- ✓4 ft setback. State law caps the side and rear setback at 4 ft, so even a tight lot usually works.
- ✓No extra parking likely required. No parking required if within 1/2 mile of public transit, in a historic district, or part of the existing/proposed primary residence.
- ✓No owner-occupancy requirement. You can rent out both the main home and the ADU — you do not have to live on the property.
- ✓Lot has room. A 700 sq ft ADU uses about 12% of your 6,000 sq ft lot — comfortably within typical coverage limits.
- ✓Ministerial approval in 60 days. By law your city must approve a complete ADU application within 60 days, without discretionary review or a public hearing.
- ✓Impact fees waived. ADUs under 750 sq ft are exempt from impact fees in this state — a saving of several thousand dollars.
Rule basis: Cal. Gov. Code §66314 et seq. (former §65852.2)
If you rent it out
$1,350–$2,175
est. rent/mo
8.4%
gross yield
12.8 yrs
payback
~$19,809/yr after a 7% vacancy allowance, before financing & maintenance.
Financed over 20 yrs at 7.5%, the build is about $2,046/mo — vs ~$1,775/mo in estimated rent.
Estimates are for planning only and are based on regional construction-cost indices and published statewide ADU statutes. Local ordinances, lot conditions and contractor pricing vary — always confirm with your city planning department and a licensed contractor.
Cost by ADU type in California
| ADU type | 600 sq ft | $/sq ft |
|---|---|---|
| Detached new build | $165,000–$270,000 | $275–$450 |
| Attached addition | $150,000–$247,500 | $250–$413 |
| Garage conversion | $90,000–$165,000 | $150–$275 |
| Junior ADU (JADU) | $75,000–$135,000 | $125–$225 |
| Prefab / modular | $135,000–$225,000 | $225–$375 |
Financing your ADU
A handful of loan and grant programmes are built specifically for ADUs. These are informational links we don't currently earn a commission on — not paid placements.
RenoFi
Compare RenoFi ADU loan options →Renovation-specific loans (home equity loan, HELOC or cash-out refinance) that lend against your home's value after the ADU is built, so you can often borrow more than a standard HELOC allows.
Fannie Mae HomeStyle Renovation
See HomeStyle Renovation →A conventional mortgage that rolls ADU construction costs into a single loan, with down payments as low as 3% for qualifying first-time buyers.
CalHFA ADU Grant Program
Check CalHFA grant status →Reimburses up to $40,000 of pre-development costs (design, permits, soil tests) for California homeowners building an ADU.
Current round of funding is fully allocated — the page covers what to check for reopening.
Want financing options matched to your project?
Tell us roughly what you need to borrow and we'll point you to lenders who work with ADU projects.
ADU rules by city in California
Estimates are for planning only and are based on regional construction-cost indices and published statewide ADU statutes. Local ordinances, lot conditions and contractor pricing vary — always confirm with your city planning department and a licensed contractor.