SB 543 Just Put LA on a 15-Day Clock for ADU Permits
Chris Koss, AIA|Published October 12, 2025|Last updated June 10, 2026
SB 543, signed October 10, 2025, forces LADBS to determine ADU permit completeness in 15 business days. Miss the deadline and the application is deemed complete by operation of law.
Coverage and infographic via LA Construction Compliance. Bill text: SB 543 on leginfo.
Governor Newsom signed SB 543 on October 10, 2025, as one of four ADU bills in the 2025 package. Most of the headlines focused on the JADU size cap, but the provision that will actually change how LA homeowners experience permitting is buried further down: from January 1, 2026, LADBS has 15 business days to tell you whether your ADU application is complete, and if they miss the deadline, your application is deemed complete by operation of law. That single sentence rewrites the ADU permit timeline more decisively than anything since AB 68 in 2019.
The 15-business-day completeness clock
What changed. Before SB 543, the 60-day ministerial decision window did not start until LADBS confirmed your application was complete. Completeness review could drift for weeks while your construction loan accrued interest. The new statute fixes the gap. Local agencies have 15 business days to confirm completeness from the day you submit. If they fail to act, the application is deemed complete and the 60-day decision clock starts on its own. Combined, the worst-case path from clean submission to ministerial decision is about 12 calendar weeks. That is a hard ceiling where there used to be no ceiling at all.
The appeal track. SB 543 also requires every local agency to provide a written appeal process and reach a determination within 60 days of receiving an appeal. For owners and architects who have spent months arguing with plan check over interpretations of the LA ADU ordinance, this is a structural shift. Disputes that used to die in plan check limbo now have a calendar.
The combination rule
One lot, three units of ADU types. The headline-grabbing provision of SB 543 for property owners is the combination rule: on a single-family lot, you can now combine a converted-space ADU plus a junior ADU plus a detached ADU. Previously the rules around stacking types were murky and most jurisdictions disallowed combinations. SB 543 makes the combination ministerial. For a Mar Vista or Atwater Village lot with a single-family home, an existing garage suitable for conversion, and rear-yard space for a detached unit, the path to three legal dwelling units on one lot is now clear. That is a meaningful unlock for the LA accessory-housing math, and one that will quietly reshape how architects and property owners scope a project from day one.
The fee thresholds
DIFs. Development impact fees may not be imposed on an ADU with 750 or fewer square feet of interior livable space, or a JADU with 500 or fewer square feet of interior livable space. This codifies what California ADU law has been moving toward since 2019, but SB 543 also clarifies the measurement standard: interior livable space, not gross floor area. The difference matters for borderline projects where wall thickness or built-in storage pushes a unit from compliant to non-compliant. For a 760 square foot design that crosses the threshold, the avoidable cost can run $15,000 to $25,000 in soft fees alone.
School impact fees. ADUs or JADUs with 500 or fewer square feet of interior livable space are exempt from school impact fees. School fees in LA Unified School District territory typically run $4 to $5 per square foot, so the 500 sf exemption can save a few thousand dollars at the bottom-floor scale.
The JADU size cap
500 square feet of interior livable space. SB 543 redefines a junior accessory dwelling unit as no more than 500 square feet of interior livable space. This is a tightening from the prior 500 sf gross calculation, which let designers count wall assemblies and mechanical spaces into the cap. With the new interior-only definition, the buildable area of a compliant JADU is meaningfully smaller. For owners considering a JADU conversion of an existing bedroom or attached space, the design exercise gets sharper. Compliant JADUs will increasingly need built-in storage, fold-down furniture, and the kind of millwork that competent architects bring to small-space residential work.
What changes for LA permit-pullers on January 1
Submit clean or absorb the cost. The 15-business-day clock favors owners who submit a complete, well-documented package on day one. A partial submission triggers a corrections list, the clock resets, and you lose the benefit of the deemed-complete backstop. Get your architect, structural engineer, and Title 24 consultant aligned before the portal upload, not after.
Save the bulletin. LADBS will need to publish updated information bulletins to implement SB 543. Save the PDF version of the bulletin in effect on the day you submit; completeness disputes are easier to win when you can point to the rule as written when you filed. Track the City's information bulletins index for the SB 543 implementation update.
If you are starting an ADU project in LA, A-du's marketplace connects you to verified architects and permit expediters who are already operating under the new SB 543 timeline.