Straight answers
What changes for ADUs in California in 2027?
Two things change on 1 January 2027, both from bills the Governor signed on 29 September 2026. AB 956 raises the number of detached, new-construction accessory dwelling units a local agency must approve ministerially on a lot with a single-family home from one to two, each with four-foot side and rear setbacks, and each of which the agency may limit to 800 square feet of livable space. SB 1117 changes the impact fee on a larger unit: where a lot has up to two accessory dwelling units, a unit over 750 square feet of interior livable space is charged only on the area above 750 square feet, and still in proportion to the size of the main house. Units of 750 square feet or less stay exempt from impact fees, as they are today.
Figures verified against the sources below · September 30, 2026
01 — The longer answer
The two California ADU bills that take effect in 2027
AB 956: two detached ADUs instead of one
Government Code 66323 lists the units a local agency has to approve without a discretionary hearing. Today paragraph (a)(2) reads one detached, new-construction accessory dwelling unit. From 1 January 2027 it reads two, on a lot with a proposed or existing single-family dwelling, with side and rear yard setbacks of no more than four feet. The conditions an agency may attach are the same as now and apply to each detached unit: a floor area limit of not more than 800 square feet of livable space, and the height limits in Government Code 66321. The paragraphs covering units inside a home and units on multifamily lots are not changed by this bill.
The junior ADU trade-off
The second detached unit comes with one limit, in a new subdivision (b). A local agency is not required to ministerially approve a junior accessory dwelling unit on the same lot where two detached, new-construction units have been constructed under paragraph (a)(2). The opening of the section is amended to match, so the right to any combination of the listed units now applies except as that subdivision provides. The carve-out names the junior unit only. In practice an owner planning for the maximum should decide early whether the lot's extra homes are two detached units or one detached unit and a junior unit inside the house, and confirm the sequence with the local planning department before applying.
SB 1117: impact fees only on the area above 750 square feet
Government Code 66311.5 already bars a local agency, special district or water corporation from charging any impact fee on an accessory dwelling unit of 750 square feet of interior livable space or less, or on a junior unit of 500 square feet or less. That does not change. What changes is the larger unit. Today an accessory dwelling unit over 750 square feet is charged proportionately in relation to the square footage of the primary dwelling. From 1 January 2027, for up to two accessory dwelling units on a lot, that proportionate fee applies only to the area in excess of 750 square feet. A lot with more than two accessory dwelling units keeps the current calculation. Impact fee has a defined meaning here: it does not include a utility connection fee or capacity charge, which the same section handles separately.
HOA and deed restrictions on lots that allow single-family use
AB 956 also edits two Civil Code sections. Section 714.3 voids a deed or contract term that effectively prohibits or unreasonably restricts an accessory dwelling unit, and section 4751 does the same for the governing documents of a planned development. Both currently apply to a lot zoned for single-family residential use. From 2027 both apply to a lot zoned to allow single-family residential use. Reasonable restrictions that do not unreasonably raise the cost of the unit or effectively prohibit it remain allowed under both sections.
What stays the same for a prefab ADU
Neither bill touches the height floors in Government Code 66321, the rule that an agency cannot prohibit a unit of at least 800 square feet with four-foot side and rear setbacks, or the 1,200 square foot ceiling where a local ordinance applies. Neither changes how a factory-built unit is approved: it still needs an HCD insignia of approval, placed at the plant before shipment. Both bills are ordinary statutes without an urgency clause, so the current text stays in force until 31 December 2026. If a second detached unit is the plan, ask the building department how it will treat an application filed before that date.
03 — Sources
Each figure above links to the authority it came from.
AB 956 (Quirk-Silva), Statutes of 2026, Chapter 791, approved and filed 29 September 2026: amends Government Code 66323(a)(2) to read two detached, new construction, accessory dwelling units that do not exceed four-foot side and rear yard setbacks for a lot with a proposed or existing single-family dwelling, each of which a local agency may limit to 800 square feet of livable space and to the height limits of Section 66321; adds subdivision (b), under which a local agency is not required to ministerially approve a junior accessory dwelling unit on the same lot where two such detached units have been constructed; and amends Civil Code 714.3 and 4751 to apply to a lot zoned to allow single-family residential use
leginfo.legislature.ca.govOffice of the Governor, 29 September 2026: AB 956 and SB 1117, both titled Accessory dwelling units and junior accessory dwelling units, are listed among the housing bills signed
gov.ca.govSB 1117 (Cervantes), Statutes of 2026, Chapter 809, approved and filed 29 September 2026: amends Government Code 66311.5(c)(1) so that, for up to two accessory dwelling units on a lot, impact fees for a unit over 750 square feet of interior livable space are charged proportionately in relation to the square footage of the primary dwelling unit and only on the area in excess of 750 square feet; properties with more than two accessory dwelling units keep the proportionate charge without that limit
leginfo.legislature.ca.govCalifornia Government Code 66323 as in force until 31 December 2026 (amended by Stats. 2025, Ch. 520): paragraph (a)(2) reads one detached, new construction, accessory dwelling unit
leginfo.legislature.ca.govCalifornia Government Code 66311.5 as in force until 31 December 2026: no impact fee on an accessory dwelling unit of 750 square feet of interior livable space or less or a junior accessory dwelling unit of 500 square feet or less; a larger accessory dwelling unit is charged proportionately in relation to the square footage of the primary dwelling unit; impact fee does not include a connection fee or capacity charge
leginfo.legislature.ca.govCalifornia Constitution, Article IV, Section 8(c)(1): a statute enacted at a regular session goes into effect on January 1 next following a 90-day period from the date of enactment. Both bills are recorded as non-urgency measures
leginfo.legislature.ca.gov
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