California’s accessory dwelling unit rules have evolved quickly in the last few years. The latest statewide updates make it easier to add multiple small homes on a single property, provided you follow objective standards and apply through a ministerial process. This guide explains how many ADUs you can build today, where multiple units are allowed, and how to plan a compliant, profitable project.
Understanding ADUs: What Are Accessory Dwelling Units?
An accessory dwelling unit is a self-contained home with a kitchen, bathroom, and sleeping area located on the same lot as a primary residence. You will also see junior accessory dwelling units, which are up to 500 square feet and carved from existing space within a single-family home. ADUs can be detached backyard cottages, attached additions, garage conversions, basement apartments, or converted portions of multifamily buildings. Because they use existing lots and infrastructure, ADUs offer a lower-cost path to new housing, flexible space for family, and potential rental income.
Recent Changes to California’s ADU Laws: What Homeowners Need to Know
State law now sets clear, objective rules that cities must use when reviewing ADU applications. Local ordinances still matter, but they cannot undermine state protections that require ministerial review, allow at least one parking space per unit or bedroom (whichever is less) with several exemptions, prohibit minimum lot size limits for ADUs, and guarantee approval of an ADU of at least 800 square feet with four-foot side and rear setbacks even if other local standards like lot coverage or floor area ratio would otherwise block it.
Two recent updates are especially important:
- Owner-occupancy. Cities cannot require an owner to live on a lot with an ADU. Junior ADUs still require owner-occupancy tied to the primary or the JADU itself.
- Separate sale of ADUs. Cities may choose to allow ADUs to be sold as condominiums under a local ordinance that meets state conditions. Some jurisdictions have already moved forward, while others are evaluating whether to opt in.
The state also reorganized ADU statutes into a new Government Code chapter, so if you see older section numbers in older articles, look for the updated cross-references in current guidance.
How Many ADUs Can You Build on Your Property?
The answer depends on whether your lot is single-family or multifamily and whether the multifamily building already exists.
Single-family lots. If your property has, or will have, a single-family home, the state requires local agencies to allow these combinations on one lot when site conditions permit:
- One ADU created from existing space in the primary dwelling or an accessory structure, and
- One new detached ADU, and
- One junior ADU within the home.
In practice, that can mean up to three added units on a single-family lot, for a total of four homes including the primary residence. The detached ADU must meet the standard four-foot side and rear setbacks and is guaranteed at least 800 square feet (with height limits described below). The converted-space ADU and the JADU follow their own carve-outs.
Multifamily lots with an existing building. If there is already a multifamily building on the lot, you may add:
- Interior conversion ADUs within non-livable areas like storage rooms, attics, or garages, up to 25 percent of the existing unit count, and at least one, and
- Detached ADUs in the yard or parking areas, up to eight, not to exceed the number of existing primary units on the lot.
Multifamily lots with a proposed building. If you are developing a new multifamily building, the state requires at least one interior conversion ADU and allows up to two detached ADUs, with the same setback and height rules.
Duplexes. A duplex counts as a multifamily structure. On an existing duplex lot, the detached ADU cap is subject to the “not to exceed existing unit count” rule. That typically limits detached ADUs to two, and conversion ADUs are capped by the 25 percent rule, with at least one allowed.
SB 9 projects. State lot-split and duplex rules can layer with ADU rules, but they do not require cities to allow more than four homes per lot in any combination of primary units, ADUs, or JADUs. Plan unit counts accordingly if you are pursuing both pathways.
Zoning and Lot Requirements: Are You Eligible to Build Multiple ADUs?
ADUs are permitted in residential and some mixed-use zones statewide, and cities must process them ministerially without discretionary review or a hearing. Key development standards to confirm on every site:
- Setbacks and size. A detached ADU is permitted with four-foot side and rear yard setbacks. Local standards cannot be applied to block an ADU of at least 800 square feet that meets those setbacks. Cities may set larger maximums, and attached ADUs often can match a percentage of the primary home’s floor area subject to minimums.
- Height. Detached ADUs have a base minimum allowable height of 16 feet, with higher limits of 18 or 20 feet in certain conditions like proximity to transit or where the primary building is taller. Check your jurisdiction’s ordinance for the applicable tier.
- Minimum lot size. Cities cannot impose minimum lot sizes that prohibit ADUs. Small lots can qualify if the ADU meets setbacks and objective standards.
- Parking. No more than one space per unit or bedroom, whichever is less. Parking is not required in several common situations, including within one-half mile of transit and when converting a garage or carport. If you convert covered parking to an ADU, replacement parking for the primary home is not required. Tandem spaces are allowed.
- Front setbacks and objective siting. Cities may apply a front setback, but they cannot use it to preclude an 800-square-foot ADU or require discretionary relocations.
- Utilities and impact fees. ADUs under 750 square feet are exempt from local impact fees. Water and sewer connection charges depend on whether you are converting existing space or building new, and on local agency policies. New detached units may trigger Energy Code solar requirements.
The Permitting Process: Steps to Get Approval for Your California ADU(s)
ADUs and JADUs are reviewed and decided ministerially. After you submit a complete application, the city has 30 days to determine completeness and 60 days to approve or deny based on objective standards. To keep your project moving:
- Confirm eligibility early. Verify your zoning, check for recorded easements, utilities, slope, and any coastal or wildfire area overlays. If you are in a common interest development, review the CC&Rs; associations must allow ADUs but may apply reasonable, non-conflicting rules.
- Choose your unit mix. On single-family lots, decide whether you will combine a detached ADU with a conversion ADU and a JADU. On multifamily lots, determine how many interior conversion ADUs fit within the 25 percent rule and where detached units can be sited.
- Prepare a code-ready set. Include a site plan with setbacks and parking, floor plans, elevations with height callouts, Title 24 energy forms, structural details, and utility notes. Using pre-approved plans offered by some cities can reduce review time.
- Address fire and life safety. Sprinklers are not required in an ADU solely because the primary home has them, but they may be required if the primary structure is being substantially altered or if local building code triggers apply. Provide fire-rated assemblies where required for conversions.
- Submit and track. Respond promptly to completeness checks limited to objective checklist items. If the city requests changes beyond objective standards, ask for the code citation and keep the review on the ministerial track.
Note that many jurisdictions restrict short-term rentals in ADUs to terms longer than 30 days. If your plan relies on short-term rentals, confirm local rules first.
Maximizing Rental Income: Financial Benefits of Building Multiple ADUs
Multiple small homes on one lot can create durable, diversified rent streams. To improve returns:
- Right-size the design. Studios and one-bedrooms near transit often lease quickly and benefit from the one-space parking cap. Two-bedroom units can support families and command higher rent where demand exists.
- Stack your mix. On single-family lots, pairing a detached ADU with a garage conversion and a JADU maximizes legal capacity while spreading costs across three rentals. On multifamily lots, interior conversions are often the lowest-cost units to build.
- Control operating costs. Plan for separate metering or submeters where feasible, durable finishes, and low-maintenance landscapes. If parking is tight, highlight transit proximity to leverage parking exemptions.
- Leverage financing tools. Some lenders now allow ADU rental income to help borrowers qualify, and local programs may offer loans or technical assistance. State grants fluctuate; check availability before budgeting them into your pro forma.
Pitfalls to Avoid and Common Questions About Building More Than One ADU in California
- Counting incorrectly. On single-family lots, you can often build a detached ADU, a conversion ADU, and a JADU. On an existing multifamily lot, detached ADUs are capped at eight and cannot exceed the number of existing primary units, and interior conversions are capped at 25 percent of existing units, with at least one allowed.
- Assuming SB 9 lifts the cap. Even with an urban lot split or SB 9 duplex, cities are not required to allow more than four homes on a lot in any combination.
- Overlooking owner-occupancy rules. ADUs cannot be subject to owner-occupancy requirements, but JADUs still require the owner to live in the primary home or the JADU.
- Short-term rental plans. Many cities require ADUs to be rented for longer than 30 days. Design for long-term rental demand unless your city explicitly allows short-term use.
- Selling an ADU separately without local authorization. A city must adopt an ordinance that meets state criteria before an ADU can be separately conveyed as a condominium. Do not assume you can sell a unit unless your jurisdiction has opted in.
- Parking and front-yard siting missteps. Use the four-foot side and rear setbacks for detached units, apply the one-space cap correctly, and know that front setbacks cannot be used to block an 800-square-foot unit.
Take Advantage of New California Laws—Plan Your Ideal Property with Multiple ADUs Today!
California’s current framework makes multi-unit ADU strategies far more achievable than even a few years ago. Begin with a clear unit-count plan based on your lot type, confirm the applicable objective standards, and use the streamlined ministerial path to move from concept to permits. Suppose you want help mapping a compliant mix of detached, conversion, and junior units that fits your budget and rental goals. In that case, FTR Renovation can translate these rules into a buildable, profitable plan.