Published: 17 Oct 2026 · Last verified: 14 Oct 2026 · Next review: Jan 2027 Legislative summary, not legal advice. Changes are logged in Corrections.
If you read ADU builder blogs this summer, you saw the careful phrasing: “AB 956 is not yet law.” That was true then. On September 29, 2026, Governor Newsom signed it — Chapter 791, Statutes of 2026 — and it takes effect January 1, 2027. The careful phrasing is now outdated, but several sites have not updated their pages. This post is the update, verified against the chaptered text on the official California Legislative Information site.
The change is simple and large: on a lot with a proposed or existing single-family dwelling, your city must ministerially approve up to two detached, new-construction ADUs — no discretionary review, no CEQA. The old number was one.
Key facts
| Item | Value |
|---|---|
| Bill | AB 956 (Quirk-Silva), Chapter 791, Statutes of 2026 |
| Signed | September 29, 2026 (Governor Newsom) |
| Effective | January 1, 2027 |
| What changes | Gov. Code §66323: up to two detached, new-construction ADUs per single-family lot, ministerially approved |
| Per-unit limits | 800 sq ft max floor area · 4-ft side/rear setbacks · 16-ft height (18 ft + 2-ft roof slope near major transit) |
| JADU tradeoff | No ministerial JADU approval required once two detached ADUs are built (§66323(b)) |
| HOA / deed restrictions | Ban on ADU-prohibiting restrictions widened to lots “zoned to allow single-family residential use” (Civ. Code §§714.3, 4751) |
The new rules, line by line
AB 956 amends Gov. Code §66323, the ADU ministerial-approval statute, plus Civil Code sections 714.3 and 4751:
- Two detached ADUs, not one. A local agency must approve building-permit applications for up to two detached, new-construction ADUs per qualifying lot. The units may not be set back more than 4 feet from side and rear lot lines — the same setback the old law allowed for the single unit.
- Size and height stay capped. Each detached ADU may not exceed 800 sq ft of total floor area, and height limits of 16 feet apply — or 18 feet, with an additional 2 feet for roof slope, within a half-mile walk of major transit. These come from the referenced §66321(b)(4) framework.
- No double-dipping with a JADU. New subdivision (b): a local agency is not required to ministerially approve a JADU on the same lot where two detached, new-construction ADUs have been built. Two backyard cottages means the in-home JADU slot is gone.
- HOA rules get broader. The existing state ban on deed restrictions and HOA governing documents that prohibit or unreasonably restrict ADUs now reaches any lot “zoned to allow single-family residential use” — the reworded phrase captures single-family homes sitting on land zoned for multifamily use, which the old wording left in a gray zone.
The 2027 playbook: AB 956 × SB 1117
AB 956 arrives the same day as SB 1117 (Chapter 809), and the two bills multiply. SB 1117 makes impact fees on the first two ADUs per lot marginal — charged only on livable square footage above 750 sq ft.
Put them together: two detached 800 sq ft ADUs, each owing impact fees on 50 sq ft instead of 800. The illustrative math from our SB 1117 breakdown — Palo Alto’s roughly $8,000–$20,000 dropping to roughly $500–$1,250 per unit — applies per ADU, so the two-unit fee picture is roughly double the single-unit number, not some new cliff. These are our arithmetic from published city fee schedules, not city-published figures; cities must publish their own marginal implementations.
Three caveats that survive both bills:
- School fees don’t move. Both bills leave Ed. Code §17620 alone — districts, not cities, levy school developer fees, and an 800 sq ft ADU’s school fee is the same in 2027 as in 2026.
- A third unit loses the fee break. SB 1117’s marginal math covers the first two ADUs. Add another unit and it is assessed under the old proportionality rule — unless it stays at or under 750 sq ft.
- The lot has to fit two cottages. Two 800 sq ft units need roughly 2,700–3,100 sq ft of clear backyard (our arithmetic, not a code figure). On a standard 50×120 lot that means tight gaps and likely fire sprinklers; on a hillside, geotechnical reality still governs. Building codes, fire access, utilities, and local objective standards all still apply — AB 956 removes discretionary review, not physics.
What to do before January
- Design now, permit in January. AB 956 is not effective until Jan 1, 2027 — permits pulled in 2026 are assessed under 2026 rules, for both the unit count and the fees.
- Feasibility first. Zoning, coastal status, septic vs. sewer, slope, trees, fire jurisdiction, easements. “Two-ADU lot” is a diligence conclusion, not a listing claim.
- Model the JADU tradeoff. If your plan was one detached ADU plus a JADU, re-run the numbers against two detached ADUs — the rental math and the fee math differ.
Sources
- AB 956, Chapter 791, Statutes of 2026 — official chaptered text, California Legislative Information (leginfo.legislature.ca.gov), reviewed Oct 14, 2026. All statutory figures in this post (two detached ADUs, §66323(a)(2) and (b), 800 sq ft, 4-ft setbacks, 16/18-ft height framework, Civil Code §§714.3 and 4751 “zoned to allow” rewording, Sep 29, 2026 approval, Jan 1, 2027 effective date) are drawn from the chaptered text.
- Governor’s office announcement of the Sep 29, 2026 bill signings (signature confirmation).
- AB 956 enrolled-bill summaries: OpenScope Studio · Brownstein Hyatt Farber Schreck · Mondaq · California YIMBY, The Homework — October 7, 2026.
- Our related coverage: SB 1117 kills the 750 sq ft cliff · 3 ADU laws taking effect Jan 1, 2027 (publishes Oct 29).