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State law

SB 543: what changed for ADU permits in 2026

SB 543 didn't change what you can build so much as how your application has to be handled. It also renumbered parts of the code, which is why older guides now point to sections that have moved.

At a glance

1 Jan 2026
the date the new procedure took effect1
15 business days
for a written completeness decision1
60 business days
for a final decision on an appeal1

Key points

  • In force since January 1, 2026.1
  • Section 66317 now requires a written completeness decision within 15 business days.1
  • It provides a written appeal with a 60-business-day limit.1
  • Fee rules now sit in § 66311.5 and unpermitted-unit rules in § 66311.7.2

The procedure it put in place

The bill amended Government Code Section 66317, the section that governs how an ADU application is processed.1 As the section now reads, an application moves through defined steps:

  1. Completeness. Within 15 business days of receiving the application, the permitting agency decides whether it is complete and says so in writing.1
  2. A usable list. If it is incomplete, the notice lists the missing items and how to supply them.1
  3. A closed list. The agency can't add new completeness items when you resubmit.1
  4. A default. No timely answer means the application is deemed complete.1
  5. An appeal. Incomplete determinations and denials can be appealed in writing1, with a final determination due in 60 business days.1

How ADU size is measured

The size limits in the ADU chapter are now written in terms of interior livable space. Los Angeles County's planning director, in a memo to staff, reads SB 543 as specifying exactly that, and has told staff to measure ADU floor area as interior space intended for human habitation.3 The same memo records that SB 543 was signed on October 10, 2025.3

Who is bound by it

The duties fall on the "permitting agency", and the code defines that term broadly: any entity involved in reviewing the permit for which there is no substitute, expressly including utilities and special districts.2 A homeowner whose plans are waiting on an outside district has the same timetable to point to.

Junior ADUs

The same bill touched the junior ADU article. Junior ADU applications now have a matching 15-business-day completeness review.4

Sections that moved

Subject Old section Current section
Fees, impact fees and utility connections § 66324 § 66311.52
Unpermitted units built before 2020 § 66332 § 66311.72

The bill also amended Section 66321, which limits how far local size and height rules can go.1

What it left alone

The 60-day decision period for a lot with an existing dwelling is still there1, and so is the sentence providing that a completed application not decided in 60 days is deemed approved.1 Review remains ministerial.1

What this page doesn't cover

This summary is drawn from the code as it reads today. It doesn't reproduce the bill's legislative history or compare the wording line by line with the 2025 text, and cities are still updating their handouts to match. Where a city's published process and the statute appear to differ, our city pages set the two side by side.

Common questions

When did SB 543 take effect?

On January 1, 2026.1 A Los Angeles County planning memo records that the Governor signed it on October 10, 2025.3

Does SB 543 apply to junior ADUs?

Yes. Junior ADU applications get the same 15-business-day completeness review.4 The decision period is covered under junior ADUs run on similar clocks.

Did SB 543 change ADU impact fees?

It moved the fee rules from Section 66324 to Section 66311.5.2 The 750 square foot rule itself is explained on our impact fees page.

Keep reading

About this page

Written by
The Lotline Editorial Team. Editorial policy
Where it comes from
We wrote this from material published by California Legislative Information and Los Angeles County Department of Regional Planning. You'll find each document, and the part we used, under References below.
How it was checked
Before publishing, we checked each statement against the original wording of its source. How we work
Last reviewed
. Rules and city procedures change, so confirm current requirements with your permitting agency.
Corrections
Email support@lotlinepermits.com. We check every report against the document and fix what is wrong.

References

  1. 1California Government Code, Title 7, Division 1, Chapter 13, Article 2 (Sections 66314 to 66331)California Legislative Information. Read on November 10, 2026.Cited: § 66317, amendment note; § 66317(a)(2)(A); § 66317(d)(2); § 66317(a)(2)(B); § 66317(a)(2)(D); § 66317(a)(2)(F); § 66317(d)(1); § 66321, amendment note; § 66317(a)(3); § 66317(a)(1).
  2. 2California Government Code, Title 7, Division 1, Chapter 13, Article 1 (Sections 66310 to 66313.5)California Legislative Information. Read on November 10, 2026.Cited: § 66311.5, amendment note; § 66311.7, amendment note; § 66313(k).
  3. 3Accessory Dwelling Units: Senate Bill 543 and Assembly Bill 1154 (memo to staff)Los Angeles County Department of Regional Planning. Dated December 30, 2025. Read on November 10, 2026.Cited: page 2, Measuring Floor Area; page 1.
  4. 4California Government Code, Title 7, Division 1, Chapter 13, Article 3 (Sections 66333 to 66339.5)California Legislative Information. Read on November 10, 2026.Cited: § 66335(a)(2)(A).

General information, not legal advice. Read the disclaimer.