What changes for ADUs in California on January 1, 2027

Two state laws signed on September 29, 2026 take effect on January 1, 2027. SB 1117 cuts the impact fees cities can charge on larger ADUs. AB 956 lets homeowners on a single-family lot build two detached ADUs through the state's approval path instead of one. Here is what each law does, who it covers, and what it leaves alone.

SB 1117: lower impact fees on ADUs over 750 sq ft

Impact fees are one-time charges a city or district puts on new construction to pay for parks, fire protection and other public facilities. State law already bars them on small ADUs. Above 750 sq ft, cities can charge them, in proportion to the size of the main house.

Today that proportion is figured on the whole ADU. Starting January 1, for up to two ADUs on a lot, it is figured only on the area above 750 sq ft. Every size in the law is interior living space.

What SB 1117 does not change

• ADUs of 750 sq ft or less, and junior ADUs of 500 sq ft or less, still pay no impact fee.
• With three or more ADUs on one lot, the fee is still figured the old way.
• Utility connection fees and capacity charges don't count as impact fees under this law, and school fees are not changed.
• It applies in charter cities too, such as Los Angeles and San Diego.

If your permit is already in process

If your ADU is over 750 sq ft and your city hasn't set your fees yet, ask the city which rule it will apply to you. The new law doesn't take effect until January 1.

AB 956: two detached ADUs on a single-family lot

California has a state approval path for ADUs: if the plans meet a short list of objective standards, the city has to approve them, with no hearing. Until now that path covered one new detached ADU on a lot with a single-family home. From January 1, it covers two.

To qualify, the lot has to be in a residential or mixed-use zone and have an existing or proposed single-family home. Each detached ADU needs 4 ft side and rear setbacks.

The limits that come with it

• Size. On this path a city can cap each detached ADU at 800 sq ft and apply the state's height limits. In many cities that means two units of 800 sq ft or less. A bigger ADU goes through the city's own ADU rules instead.
• Junior ADU. A lot that already has two new detached ADUs can't add a junior ADU through the state path.
• Rentals. If a unit built this way is rented, the rental has to be for longer than 30 days.
• Septic. If the lot is on septic, the city can ask for a percolation test done in the last 5 years, or 10 if the test was recertified.
• Multifamily lots fall under separate rules and aren't covered by this change.

HOA rules

State law already bars HOA rules from prohibiting ADUs on lots zoned for single-family homes. AB 956 extends that to lots zoned to allow single-family homes, which brings more lots under the protection.

How the two laws work together

A detached ADU built at AB 956's 800 sq ft cap is 50 sq ft over the 750 sq ft line. With two of them and no other ADU on the lot, SB 1117 means each one pays impact fees on just 50 sq ft.

What this means if you're planning an ADU

• Under 750 sq ft, nothing changes on impact fees. Our Model S (325 sq ft), Model 1 (497 sq ft) and Model 2 (749 sq ft) are all under the line.
• Over 750 sq ft, the fee drops. Our Model 3 is 996 sq ft, so from January 1 only 246 sq ft of it counts toward impact fees, as long as it is one of no more than two ADUs on the lot.
• Thinking about two detached ADUs? Check that your lot qualifies and whether your city uses the 800 sq ft cap. Model S, Model 1 and Model 2 are all under 800 sq ft.
• Every city still has its own ADU rules on top of state law. See the rules for your city, or see what our price includes.