Summary:

Accessory Dwelling Units (ADUs) and Junior Accessory Dwelling Units (JADUs) have become a cornerstone of California’s housing strategy, providing homeowners with an opportunity to add affordable housing on existing properties.  Senate Bill 543 (SB‑543), signed into Law in October 2025, strengthens and clarifies state rules governing ADUs and JADUs to eliminate local inconsistencies, accelerate approvals, and expand housing supply.

Background: Why SB‑543 Was Needed

Since 2016, California has passed multiple laws to promote ADUs and JADUs, but local governments often misinterpret or resist these rules, creating delays and confusion.  According to the Department of Housing and Community Development (HCD), over 50 local agencies have incorrectly applied ADU/JADU laws, resulting in inconsistent fees, size limits, and permitting timelines.

SB 543 is a cleanup and modernization bill that codifies HCD guidance, standardizes definitions, and enforces compliance statewide.

Key Provisions of SB‑543

1.  Clear Size Standards

• ADUs: Homeowners retain the right to build at least one ADU up to 800 sq. ft. with 4-foot setbacks, regardless of local zoning.
• JADUs: Defined as ≤500 sq. ft. of interior livable space, contained within a single-family structure (e.g., converted bedroom or garage).

2.  Ministerial Approval and Timelines

• Local agencies must approve ADU/JADU permits ministerially (no discretionary hearings) within 60 days of a complete application.
• The initial review must occur within 15 business days, allowing applicants to correct any deficiencies promptly.

3.  State Oversight and Ordinance Compliance

• Local ADU and JADU ordinances must be submitted to HCD within 60 days of adoption.
• If an ordinance is noncompliant and the agency fails to respond within 30 days, the ordinance becomes null and void, and state standards apply by default.

4.  Fee Restrictions

• No school Impact fees for ADUs or JADUs under 500 sq. ft..
• Larger ADUs may only be charged fees proportional to their size relative to the primary dwelling.

5.  State Standards Supersede Local Rules

• Local ordinances cannot impose stricter requirements than state Law.
• Homeowners always retain the right to build at least one ADU under state minimum standards.

6.  Appeals and Post-Entitlement Permits

• SB‑543 clarifies that ADU/JADU approvals are subject to Permit Streamlining Act timelines, including appeals for denied or incomplete applications.

Impact on Housing Development

• Homeowners: Faster, predictable approvals and reduced fees make ADUs/JADUs more accessible.
• Local Governments: Must align ordinances with state Law and maintain transparency.
• Housing Supply: ADUs and JADUs are among the fastest-growing housing types, adding thousands of units annually in urban and suburban areas.

✅ Compliance Checklist for SB‑543

Before 1 January 2026:

• Submit the ADU/JADU ordinance to HCD within 60 days of adoption.
• Ensure ordinance complies with state size, fee, and timeline standards.
• Implement a ministerial approval process with a 60-day decision deadline.
• Train staff on initial review (15 business days) and appeal timelines.
• Remove any local rules that conflict with state minimum standards.

Bottom Line

SB‑543 is a significant step toward uniformity and speed in ADU/JADU permitting.  By reducing local red tape and enforcing state standards, California aims to quickly unlock thousands of new housing units—helping to address affordability and supply challenges statewide.  This urgency underscores the importance of SB 543 in the housing strategy.