California overhauled its ADU rules again for 2026. Most of the coverage compressed the changes into headlines that are close to right but wrong in the details that cost you money. Here is what the statutes actually say.
SB 543: the 15-business-day clock
This is the headline change, and it's the one most often misdescribed. The bill text reads that a permitting agency "shall determine whether an application to create or serve an accessory dwelling unit is complete and provide written notice of this determination to the applicant not later than 15 business days after the permitting agency received the application."
So why does it matter? Because of the loophole it closes. Before 2026, a city could bounce an application back as "incomplete" over and over, and the 60-day approval clock never started. SB 543 forces the completeness decision onto a deadline, which means the 60-day clock now actually has to begin. It also requires the city to list exactly what's missing and how to fix it — and once you resubmit, the agency cannot add new requirements it didn't raise the first time.
Square footage is now measured as interior livable space
SB 543 ties the size thresholds to interior livable space rather than overall footprint, so wall thickness no longer counts against you. It sounds like a technicality. It isn't — it can be the difference between landing under a fee threshold and paying to cross it.
The two fee thresholds people mix up
There are two separate exemptions with two different numbers, and conflating them is a common and expensive mistake:
| Threshold | What it exempts you from |
|---|---|
| ADU 750 sq ft or less (interior livable space) | Development impact fees |
| JADU 500 sq ft or less | Development impact fees |
| Under 500 sq ft | School facilities fees — new for 2026 under SB 543, via Education Code section 17620 |
In plain terms: staying under 750 square feet keeps you clear of impact fees, and staying under 500 additionally clears school fees. This is a large part of why so many San Diego ADUs are designed to land just under 750.
AB 1154: junior ADUs no longer require owner-occupancy
Also effective January 1, 2026. If a junior ADU has its own bathroom and doesn't share sanitation facilities with the main house, the owner no longer has to live on the property. That opens JADUs to owners who don't occupy the home. One limit stays in place: JADUs cannot be rented short-term — under 30 days is still prohibited.
AB 462: the coastal exemption that skips San Diego
AB 462 exempts ADUs from Coastal Development Permit requirements — but only in Los Angeles County, and in counties placed under a Governor-declared state of emergency after February 1, 2025. San Diego County is not covered. If you own in Pacific Beach, La Jolla, Ocean Beach, Point Loma or Mission Beach, your coastal ADU still follows the normal Coastal Zone process, and this law changes nothing for you.
The Coastal Zone is also where San Diego's local rules diverge from the rest of the city — we covered that separately in San Diego's Bonus ADU rollback and what the unit caps mean.
What this adds up to in San Diego
State law got faster and cheaper for small ADUs in 2026, while the City of San Diego separately tightened how many bonus units you can put on one lot. Those two moved in opposite directions, which is why the coverage has felt contradictory. For a homeowner planning one backyard unit, 2026 is a better year than 2025: a real deadline on the city, fees tied to livable space, and school fees off the table under 500 square feet.
Permits and fees for a San Diego ADU still typically run $14,000–$22,000 all-in — plan check, permit, school fees and utility connections combined — with construction on top.
Laws change and local implementation varies. This page reflects what we could verify from the bill text as of August 2026. Confirm current requirements for your parcel with the City of San Diego Development Services Department before committing money to a design.
Sources: California Legislative Information — SB 543 bill text · Dannis Woliver Kelley — SB 543 school impact fee exemption · City of San Diego — ADU/JADU Information Bulletin 400