NEW ADU LAWS FOR 2027
In 2027, you can build two backyard ADUs under state law.
Two new California laws give you more room to build and change how impact fees are calculated. Governor Newsom signed AB 956 and SB 1117 on September 29, 2026. Both take effect January 1, 2027.
THE SHORT ANSWER
You can build two detached ADUs of up to 800 square feet each.
On a lot with an existing or proposed single-family home, state law will require approval of two new detached ADUs. On a lot with no more than two ADUs, impact fees for a unit over 750 square feet will apply only to the extra space. An 800-square-foot ADU will pay on 50 square feet.
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What changes on January 1, 2027
State law will protect a second detached ADU.
AB 956 increases the state allowance from one new detached ADU to two on a lot with an existing or proposed single-family home. Each can have up to 800 square feet of living space, with 4-foot side and rear setbacks. The local agency can apply the size and height limits allowed by this law, but cannot impose other objective zoning or design standards on these units.
The second ADU can exceed your lot’s floor area limit.
In the City of San Diego, ADUs count toward the floor area limit: the total amount of floor space allowed on your lot. Today, one ADU of up to 800 square feet can exceed that limit. AB 956 extends the state protection to two detached ADUs, so using up your lot’s floor area allowance will no longer rule out the second one.
You can also convert your garage.
An ADU converted from a garage or other existing space can be combined with the two new detached ADUs. A junior ADU is different: if you build both detached units under this law, the local agency does not have to approve a junior ADU as well.
An 800-square-foot ADU will pay impact fees on just 50 square feet.
An ADU of 750 square feet or less already pays no impact fees. Today, going above 750 means those fees are calculated on the whole unit, in proportion to the main house. SB 1117 changes the calculation for lots with up to two ADUs: only the area above 750 counts. For an 800-square-foot unit, that is 50 square feet. On lots with more than two ADUs, the whole-unit calculation remains. JADUs of 500 square feet or less remain exempt. Water and sewer connection and capacity charges, and school fees, are unchanged.
See what the City charges todayHOA protections will cover more lots.
AB 956 extends the protection against HOA and deed restrictions from lots zoned for single-family use to lots zoned to allow it. Reasonable restrictions can still apply, but restrictions that effectively prohibit or unreasonably restrict an ADU are unenforceable.
COMMON QUESTIONS
What homeowners ask next.
When do the new laws take effect?
Both take effect on January 1, 2027.
Do I still need a permit?
Yes. Each ADU still needs a building permit. The difference is that the City has to approve a qualifying ADU, with no hearing.
Can each ADU be larger than 800 square feet?
The two-unit allowance described here protects detached ADUs of up to 800 square feet each. Larger units fall outside that allowance.
Should I wait until 2027 to apply?
If your plan needs the second ADU or the lower fee, ask the City how it will handle an application filed before January 1, 2027.
Does this apply in unincorporated San Diego County?
Yes. State ADU law applies to the County as well as to the City of San Diego.
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