California Further Expands State Accessory Dwelling Unit Law
New Laws Require Approval of Two Detached ADUs on Single-Family Lots and Limit Impact Fees
In nearly every legislative session for the last several years, the California Legislature has amended changes to laws governing accessory dwelling units (ADUs) and junior accessory dwelling units (JADUs). 2026 is no exception, as Governor Gavin Newsom signed Assembly Bill 956 and Senate Bill 1117 on September 29, 2026, effective January 1, 2027.
State law already required local agencies to ministerially approve a detached ADU on a lot with a single-family dwelling, without applying any local standards. AB 956 doubles that by-right allowance to two detached ADUs. AB 956 also broadens state limits on HOA rules and private covenants that restrict ADUs.
State law already required a local agency to pro-rate impact fees for ADUs larger than 750 square feet based on the size of the ADU compared to the size of the primary dwelling. SB 1117 changes the impact-fee calculation on a lot with up to two ADUs by excluding the first 750 square feet of each unit from the fee calculation. This may require changes to local impact-fee schedules.
The principal changes are summarized below.
AB 956 Requires Approval of Two Detached ADUs
Two Detached ADUs on a Single-Family Lot
Government Code section 66323 requires a local agency to ministerially approve building permit applications for specified ADUs and JADUs or qualifying combinations of those units. Before AB 956, section 66323(a)(2) required ministerial approval of one (but only one) detached, new-construction ADU of up to 800 square feet on a lot with a proposed or existing single-family dwelling. AB 956 doubles that number to two.
A local agency may continue to impose side and rear setbacks of up to four feet, an 800 square foot size limit and the applicable statutory height limit on each detached ADU. This now allows for an owner to get two detached ADUs.
AB 956 does not change the separate rules governing detached ADUs on lots with existing or proposed multifamily dwellings.
Maximum Single-Family Lot Combinations
Read together with the combination language added to section 66323 in 2025, AB 956 establishes two principal maximum configurations for a qualifying single-family lot:
- One converted ADU; one JADU; and one detached, new-construction ADU (for a total of three), or
- One converted ADU; two detached, new-construction ADUs (also totaling three).
Note that a local agency is not required to ministerially approve a JADU on the same lot where two detached, new-construction ADUs have been constructed. AB 956 eliminates the requirement to approve a JADU in that configuration but it does not affect the separate requirement to approve a qualifying converted ADU under section 66323(a)(1).
Broader Limits on HOA Rules and Private Covenants
AB 956 also amends Civil Code sections 714.3 and 4751. Those statutes make provisions in deeds, HOA governing documents and other private real estate documents unenforceable if they “effectively prohibit” or “unreasonably restrict” the construction of an ADU or JADU. Those protections previously applied only to lots zoned for single-family residential use. AB 956 extends them to all zoning districts that permit a single-family residence as a primary residential use, even if the district is not exclusively a single-family residential zone (think multifamily and mixed-use zones that still allow a single primary dwelling). The statutes continue to allow reasonable restrictions within specified limits.
Note: These are issues for private HOAs and private property owners to sort out. Public agencies are rarely in a position to enforce a private property restriction, such as CC&Rs.
SB 1117 Revises Impact Fees for ADUs
New Calculation for Lots with Up to Two ADUs
An ADU with 750 or fewer square feet of interior livable space is already exempt from impact fees under Government Code section 66311.5. Before SB 1117, once an ADU exceeded 750 square feet, an agency could calculate a proportionate impact fee using the unit's entire floor area.
Now, with SB 1117, for up to two ADUs on a lot, the “proportionate” impact fee for an ADU larger than 750 square feet is calculated using only the excess above 750 square feet.
For example, if the applicable impact fee for a 2,000-square-foot primary dwelling is $20,000, for a 1,000-square-foot ADU, the proportionate fee under the old rule would be $10,000 ($20,000 x (1,000 sf / 2,000 sf)). But now under SB 1117, the proportionate fee would be just $2,500 ($20,000 x ((1,000 sf – 750 sf) / 2,000 sf)). In other words, it drops from 50% of the normal fee to 12.5%.
Rules for Third and Additional ADUs and Utility Charges
For a lot with more than two ADUs, SB 1117 retains the old rule for proportional calculation using the ADU's full square footage. The bill also preserves the existing exemption for an ADU of 750 square feet or less and the separate exemption for a JADU of 500 square feet or less.
The revised calculation applies only to “impact fees” imposed by local agencies, special districts and water corporations. This includes fees governed by the Mitigation Fee Act and the Quimby Act but this does not include utility connection fees or capacity charges. They remain governed by the separate standards in section 66311.5.
Next Steps for Local Agencies
Every local ADU ordinance must comply with the changes made by these two bills before the end of the year or the local ordinance becomes null and void as a matter of law on January 1, 2027.
Every city and other local agency should review its ADU ordinance, application materials and permitting procedures before January 1, 2027, to ensure compliance. A local agency that adopts an amended ADU ordinance must submit it to the California Department of Housing and Community Development within 60 days after adoption.
Contact your BBK attorney for assistance updating local ordinances to comply with AB 956 and SB 1117.
