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AB 956, SB 1117 & AB 1621: What Changes for ADUs in 2027

Wang Jin

Founder, ADU Pilot

Bottom Line

Bill Chapter (2026) What it changes Code section Who it helps most
AB 956 (Quirk-Silva) Ch. 791 Two detached ADUs by right on a single-family lot instead of one; a JADU is no longer guaranteed once both are built Gov. Code §66323; Civ. Code §714.3, §4751 Owners with deep lots who want two backyard cottages [1]
SB 1117 (Cervantes) Ch. 809 Impact fees on an ADU over 750 sq ft charged only on the area above 750, if the lot has no more than two ADUs Gov. Code §66311.5 Owners building ADUs larger than 750 sq ft [2]
AB 1621 (Wilson) Ch. 780 Building permits capped at two plan check rounds; appeals decided in 30 business days for 25 units or fewer; inspectors cannot demand changes from approved plans without written findings Gov. Code §65913.3, §65589.5 Anyone stuck in plan check correction cycles [3]

All three were signed the same day and none is an urgency statute, so all three take effect January 1, 2027. [4][5]

The three most useful things to know:

  1. The bills interact. A garage conversion plus two detached ADUs, the layout AB 956 makes possible, is three ADUs, and SB 1117's fee break only applies to lots with up to two. Keep each unit at 750 square feet or less and neither bill's limit matters for fees. [1][2]
  2. AB 1621 is a permitting law, not an ADU law. It very likely reaches ADU building permits, but the ADU statute it did not amend still sets a 60-business-day appeal window, so expect a period of confusion. [3][9]
  3. We found no other ADU-specific bill signed this month. SB 1196 and AB 1738, both on many 2026 watch lists, were signed in versions that never mention ADUs, and AB 2601, signed September 30, speeds SB 9 lot splits rather than adding ADU rules. [13][14][15][20]

AB 956: Two Detached ADUs, Four Units Max

Before AB 956, Government Code §66323 guaranteed one detached, new-construction ADU on a single-family lot, which together with a conversion ADU and a JADU formed the "1+1+1" stack. AB 956 raises the detached count to two, each with 4-foot side and rear setbacks and a size cap of 800 square feet if the city imposes one. [1]

The Senate added a catch to avoid a five-unit lot: a city "is not required to ministerially approve" a JADU "on the same lot where two detached, new construction, accessory dwelling units have been constructed." The Senate Floor analysis described this as "maintaining consistency with SB 9's functional cap of four units per parcel." [1][12] So the guaranteed maximum stays at the main house plus three ADUs. What changes is that you can now swap the in-home JADU for a second backyard unit.

AB 956 also changes the HOA and deed-restriction statutes from lots "zoned for" single-family use to lots "zoned to allow" it, which protects single-family homes in multifamily and mixed-use zones. The HOA protection still covers only planned developments, not condominiums. [1]

The practical limits are fire separation and fire access, not ADU law. Our full AB 956 guide runs the lot-fit math, explains the unresolved JADU-first question, and covers SB 9 and AB 1033 interactions.

SB 1117: The 750-Square-Foot Fee Rule, Rewritten

Current law already bars impact fees on an ADU with "750 square feet of interior livable space or less." Above that line, a city can charge fees "proportionately in relation to the square footage of the primary dwelling unit." [6] The result is a cliff: a 751-square-foot ADU is charged on all 751 square feet.

SB 1117 splits that rule in two. [2]

  • "For up to two accessory dwelling units on a lot," the proportional fee applies "only on the area in excess of 750 square feet of interior livable space."
  • "For properties with more than two accessory dwelling units on a lot," the old whole-unit formula still applies.

The Assembly Local Government Committee analysis summarized the change as allowing builders of larger ADUs "to deduct 750 square feet from the chargeable size." [7] The bill also declares fee relief a matter of statewide concern, so it applies to charter cities such as Los Angeles, San Diego, and San Francisco. [2] It passed the Senate 37–0 and the Assembly 70–0. [18]

The two-ADU limit was not in the bill as introduced. The Assembly Local Government Committee added it in July 2026, citing SB 1211's expansion to as many as eight detached ADUs on multifamily lots. [7] It was aimed at apartment properties, but the same wording catches a single-family lot with three ADUs under AB 956.

Here is an illustration with a 2,000-square-foot main home and a hypothetical $20,000 impact fee for a new single-family home. Real fee schedules vary widely by city.

ADU size Fee through Dec 31, 2026 2027, lot with 1–2 ADUs 2027, lot with 3+ ADUs
750 sq ft $0 $0 $0
800 sq ft 800 ÷ 2,000 × $20,000 = $8,000 50 ÷ 2,000 × $20,000 = $500 $8,000
1,000 sq ft 1,000 ÷ 2,000 × $20,000 = $10,000 250 ÷ 2,000 × $20,000 = $2,500 $10,000
1,200 sq ft 1,200 ÷ 2,000 × $20,000 = $12,000 450 ÷ 2,000 × $20,000 = $4,500 $12,000

The 1,000- and 1,200-square-foot rows matter more than they look. State-exempt "66323" ADUs can be capped at 800 square feet, but many cities allow larger ADUs under their local ordinances, and that is where SB 1117 saves the most.

What SB 1117 does not change: school districts can still charge fees on ADUs of 500 square feet or more of interior livable space, and utility connection fees for detached ADUs are still charged in proportion to the unit's burden on the system. [6] For the full fee picture, see our California ADU impact fees guide.

Three questions are open. First, SB 1117 counts "accessory dwelling units," and state law defines ADUs and JADUs separately, so a JADU most likely does not count toward the two-ADU limit, but no agency has confirmed that. [8] Second, the text applies the old formula to "any impact fees charged for an accessory dwelling unit" on a property with more than two, which reads as all of the ADUs on that lot; California YIMBY, the sponsor, describes it as applying to the first two ADUs only. [2][19] Third, the bill does not say how to count units when a third ADU is added years after the first two.

AB 1621: Two Plan Check Rounds and Faster Appeals

AB 1621 amends the postentitlement permit statute, Government Code §65913.3, which governs building permits and other approvals after a project's land-use approval. It was sponsored by the California Building Industry Association and passed both houses without a no vote. [3][11][17] From January 1, 2027, it does four things. [3]

  1. Two plan check rounds. A local agency "shall not require or request more than two plan check and specification reviews in connection with an application for a building permit." After two rounds, the agency may deny a still-noncompliant application, and the applicant may ask for more rounds. The cap applies only to building permits, not grading or other permits.
  2. Faster appeals. A final written decision on an appeal is due within 30 business days for housing projects of 25 units or fewer (down from 60) and 45 business days for 26 units or more (down from 90). If the appeal is denied, decided late, or not offered, the applicant "may seek a writ of mandate to compel approval of the application."
  3. No mid-construction redesigns. An inspector cannot require a deviation from approved plans unless the agency makes written findings that a reasonable person could not read the approved plans as compliant, or that the change is needed to address a specific, adverse impact on public health or safety.
  4. Housing Accountability Act teeth. Violating any of those process rules, not just the existing time limits, is now a violation of the Housing Accountability Act. [3]

The Governor's office summarized it as "limiting repeated plan-check reviews and tightening appeal timelines so local jurisdictions approve permits for new housing in a timely manner." [4]

Does AB 1621 apply to ADUs?

Probably, but nothing official says so yet. Section 65913.3 borrows its definition of "housing development project" from §65905.5, which "includes a proposal to construct a single dwelling unit." [10] The same statute already requires agencies to post example applications for project types "including, but not limited to, accessory dwelling unit." [3] Read together, an ADU building permit looks like a postentitlement permit covered by the two-round cap and the inspection rule.

The complication is that AB 1621 did not touch the ADU statute. Government Code §66317 still gives ADU applicants an appeal process with a final decision due "not later than 60 business days" after a written appeal. [9] From January 1, 2027, an ADU owner may be able to point to either timeline, and cities may point to the slower one. Until HCD or a court sorts this out, cite both §66317 and §65913.3 in any appeal and ask the city in writing which it is applying.

AB 1621 does not change the ADU-specific clocks under §66317: a completeness decision within 15 business days and approval or denial within 60 days of a complete application. [9] Where those clocks are missed, our permit enforcement playbook explains the remedies.

Where the Three Bills Collide

Take an owner with a detached garage and a deep lot who files in early 2027 for a garage conversion plus two new detached ADUs.

AB 956 guarantees all three units through ministerial review, but the city does not have to approve a JADU on top. [1]

SB 1117 treats the lot as having three ADUs, so a detached unit above 750 square feet is charged on its full size, not just the excess. If the owner builds each cottage at 750 square feet or less, impact fees are zero under any reading. If the owner drops the garage conversion and builds only the two detached units, each can go past 750 square feet (up to 800 under the state rule, or larger where the local ordinance allows) and pay fees only on the excess. [2]

AB 1621 limits the building department to two plan check rounds for each building permit, and bars inspectors from demanding design changes from approved plans without written findings. [3] Whether a three-ADU application is one permit or three is a local practice question; ask before you file.

The decision that falls out of this: if you want three ADUs, design to 750 square feet each. If you want larger units, two ADUs is the fee-efficient layout.

Bills That Did Not Become ADU Law This Month

Several bills on 2026 ADU watch lists, including in our May build-now-or-wait framework, ended up somewhere else.

Bill Final status ADU impact
SB 1196 (McNerney) Signed September 27, 2026, Chapter 684 Sets CPUC timelines for small electrical energization projects. The chaptered text does not mention ADUs. [15]
AB 1738 (Carrillo) Signed September 18, 2026, Chapter 271 Remote inspection option for specified work on one- or two-family dwellings, phased in by January 1, 2028, or July 1, 2028. The chaptered text does not mention ADUs. [14]
AB 2601 (Lee) Signed September 30, 2026 Lets an SB 9 two-unit application be processed at the same time as the urban lot split parcel map, with similar concurrent processing for small-lot subdivisions. Its digest adds no new ADU rules. [13][20]
AB 2127 (Johnson) Passed the Assembly; Senate hearing canceled at the author's request in June 2026 ADUs on lots with private sewage systems. Not enacted. [16]

What to Do Before January 1, 2027

If you are permit-ready now for one detached ADU, build it, and site it to leave room for a second. None of the three bills has a transition rule for applications pending on January 1, so do not count on 2027 rules applying to a 2026 filing. [1][2][3]

If you are planning an ADU over 750 square feet, fees assessed under the 2027 formula are charged on the excess area only, as long as the lot will have no more than two ADUs. Ask your city when it assesses impact fees (often at permit issuance, not submittal), then compare the saving with a few months of construction cost inflation and lost rent.

If you want two detached ADUs, you need a 2027 application for the second unit to be state-guaranteed. Our AB 956 guide covers whether your lot fits.

If your current permit is stuck in correction cycles, AB 1621 does not help until January 1, but keep a dated record of every plan check round now. It will matter if you resubmit or appeal in 2027.

Frequently Asked Questions

Q: What is AB 1621 in California?

A: AB 1621 (Wilson, Chapter 780, Statutes of 2026) limits building permit reviews to two plan check rounds, shortens appeal deadlines to 30 or 45 business days, lets applicants seek a writ of mandate when an appeal is denied or late, and bars inspectors from requiring deviations from approved plans without written findings. It takes effect January 1, 2027. [3]

Q: What does SB 1117 do for ADUs?

A: From January 1, 2027, it charges impact fees on an ADU larger than 750 square feet only on the area above 750, as long as the lot has no more than two ADUs. ADUs of 750 square feet or less remain exempt. [2]

Q: What does AB 956 do?

A: It requires cities to approve two detached, new-construction ADUs on a single-family lot instead of one, but a city no longer has to approve a JADU once both detached units are built. [1]

Q: When do AB 956, SB 1117, and AB 1621 take effect?

A: All three take effect January 1, 2027. [5]

Disclaimer

This article reflects AB 956, SB 1117, and AB 1621 as chaptered and the law as of September 30, 2026. None takes effect until January 1, 2027, HCD has not issued guidance on any of them, and local fee schedules and permit practices vary. Fee figures are illustrations based on a hypothetical schedule, not quotes. Consult a licensed California land-use attorney, architect, or your local planning department before making design or timing decisions. Nothing in this article constitutes legal, financial, or construction advice.

References

  1. [1] California Assembly Bill 956 (Quirk-Silva), Chapter 791, Statutes of 2026, chaptered text. https://leginfo.legislature.ca.gov/faces/billTextClient.xhtml?bill_id=202520260AB956
  2. [2] California Senate Bill 1117 (Cervantes), Chapter 809, Statutes of 2026, chaptered text. https://leginfo.legislature.ca.gov/faces/billTextClient.xhtml?bill_id=202520260SB1117
  3. [3] California Assembly Bill 1621 (Wilson), Chapter 780, Statutes of 2026, chaptered text. https://leginfo.legislature.ca.gov/faces/billTextClient.xhtml?bill_id=202520260AB1621
  4. [4] Office of Governor Gavin Newsom. "Governor Newsom signs housing legislation, cementing California's record progress to reduce unsheltered homelessness and build more homes." September 29, 2026. https://www.gov.ca.gov/2026/09/29/governor-newsom-signs-housing-legislation-cementing-californias-record-progress-to-reduce-unsheltered-homelessness-and-build-more-homes/
  5. [5] California Constitution, Article IV, Section 8(c) (effective date of statutes). https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=CONS&sectionNum=SEC.%208.&article=IV
  6. [6] California Government Code §66311.5 (ADU impact fees, school fee threshold, utility connections; text in effect through December 31, 2026). https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=GOV&sectionNum=66311.5
  7. [7] Assembly Committee on Local Government. Analysis of SB 1117 (hearing July 1, 2026). https://alcl.assembly.ca.gov/system/files/2026-06/sb-1117-analysis_0.pdf
  8. [8] California Government Code §66313 (ADU and JADU definitions). https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=GOV&sectionNum=66313.
  9. [9] California Government Code §66317 (ADU permit completeness, 60-day approval, and appeals). https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=GOV&sectionNum=66317.
  10. [10] California Government Code §65905.5 (definition of "housing development project"). https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=GOV&sectionNum=65905.5.
  11. [11] AB 1621 committee and floor analyses, including Senate Floor Analysis (August 24, 2026) and Assembly concurrence analysis (August 25, 2026). https://leginfo.legislature.ca.gov/faces/billAnalysisClient.xhtml?bill_id=202520260AB1621
  12. [12] AB 956 committee and floor analyses, including Senate Floor Analysis (September 14, 2026). https://leginfo.legislature.ca.gov/faces/billAnalysisClient.xhtml?bill_id=202520260AB956
  13. [13] California Assembly Bill 2601 (Lee), enrolled text and status. https://leginfo.legislature.ca.gov/faces/billTextClient.xhtml?bill_id=202520260AB2601
  14. [14] California Assembly Bill 1738 (Carrillo), Chapter 271, Statutes of 2026, chaptered text. https://leginfo.legislature.ca.gov/faces/billTextClient.xhtml?bill_id=202520260AB1738
  15. [15] California Senate Bill 1196 (McNerney), Chapter 684, Statutes of 2026, chaptered text. https://leginfo.legislature.ca.gov/faces/billTextClient.xhtml?bill_id=202520260SB1196
  16. [16] California Assembly Bill 2127 (Johnson), bill status. https://leginfo.legislature.ca.gov/faces/billStatusClient.xhtml?bill_id=202520260AB2127
  17. [17] AB 1621 floor votes. https://leginfo.legislature.ca.gov/faces/billVotesClient.xhtml?bill_id=202520260AB1621
  18. [18] SB 1117 floor votes. https://leginfo.legislature.ca.gov/faces/billVotesClient.xhtml?bill_id=202520260SB1117
  19. [19] California YIMBY. "SB 1117." https://cayimby.org/legislation/sb-1117/
  20. [20] Office of Governor Gavin Newsom. "Governor Newsom issues legislative update 9.30.2026." September 30, 2026. https://www.gov.ca.gov/2026/09/30/governor-newsom-issues-legislative-update-9-30-2026/

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