A detached ADU is a stand-alone dwelling on the same lot as an existing home or apartment building. It is the ADU type that adds the most rent and the most value, and the type California law protects most aggressively. This guide covers the rules that apply statewide and the numbers you should expect.
The 800 square foot state exemption
Every California lot with a residential use is entitled to an 800 square foot detached ADU that a city cannot deny on lot coverage, floor area ratio, open space, or minimum lot size grounds. The unit must sit four feet from side and rear property lines and meet the state height limit. As of 2026, the 800 square feet is measured as interior livable space under SB 543.
Height
- 16 feet baseline for a detached ADU.
- 18 feet if the lot is within a half mile walking distance of major transit, or if the lot has an existing or proposed multifamily building. Cities must allow another two feet to match the main house's roof pitch.
- 25 feet or the zone's height limit, whichever is lower, for an attached ADU.
Larger units under local ordinances
The state exemption is a floor. Most cities allow bigger units: state law requires that cities permit at least 850 square feet for a studio or one-bedroom and 1,000 square feet for two or more bedrooms, and many jurisdictions, including Los Angeles, allow 1,200 square feet. Parcy's "Maximize value" toggle checks the local maximum and sizes units to it.
Setbacks, lot coverage, and placement
Four feet side and rear. Front setbacks follow the zone, but a city cannot apply a front setback that would block the 800 square foot unit. No setback is required when converting an existing garage or accessory structure in place. Detached ADUs can be placed anywhere the setbacks allow, which is why the buildable area on a parcel, after the existing footprint and easements, is the first thing Parcy computes.
What a detached ADU costs in 2026
| Type | Typical cost (SoCal) | Cost per sq ft |
|---|---|---|
| Garage conversion | $90,000 to $180,000 | $200 to $350 |
| Detached, 600 sq ft, prefab or pre-approved plan | $180,000 to $260,000 | $300 to $430 |
| Detached, 800 to 1,200 sq ft, site built | $280,000 to $450,000 | $350 to $500 |
| Two-story detached with garage below | $400,000 to $600,000+ | $400 to $550 |
Utility connections, impact fees (ADUs under 750 square feet are exempt from impact fees statewide), and soft costs for design and permits sit on top of these ranges. See the full ADU cost breakdown.
Rent and value
A new two-bedroom detached ADU in Los Angeles or Orange County rents for roughly $2,800 to $3,800 a month in 2026, with one-bedrooms around $2,200 to $2,900. Whether that rent shows up in your appraised value depends on how many units the lot ends up with; see how appraisers value ADUs.
Run your lot
Parcy pulls the parcel, applies these rules, draws the buildable area, and places the largest detached ADU the lot and your city allow. Get the app and enter your address.
Frequently asked questions
How big can a detached ADU be in California?
Every lot is entitled to an 800 square foot detached ADU. Cities must allow at least 850 square feet for one bedroom and 1,000 for two or more, and many allow 1,200 square feet.
What are the setbacks for a detached ADU?
Four feet from side and rear property lines. No setback is required when converting an existing structure in place.
How tall can a detached ADU be?
16 feet, or 18 feet on a multifamily lot or within a half mile of major transit, plus two feet to match the main house roof pitch.
Informational only. Not legal, architectural, or investment advice. Confirm current rules with your local planning department.