Three CA bills signed last week change ADU rules on Jan 1 (AB 956, SB 1117, AB 1621)
Newsom signed AB 956, SB 1117 and AB 1621 on Sept 29, and all three take effect January 1, 2027. AB 956 lets you build two detached ADUs on a single-family lot instead of one, but the city no longer has to approve a JADU once both are built, so you still top out at four homes total. SB 1117 means an ADU over 750 sq ft only pays impact fees on the square footage above 750, which matters a lot if you're building a 1,000 to 1,200 sq ft unit. The catch is that the fee break only applies to lots with two ADUs or fewer, so a garage conversion plus two backyard units puts you back on the old formula unless each one stays at 750 or under. AB 1621 isn't an ADU bill, but it caps building permit plan check at two rounds and cuts appeal deadlines to 30 business days, which should help anyone stuck in endless correction cycles. I wrote up the details, including what's still unclear, here: https://www.adupilot.com/blog/ab-956-sb-1117-ab-1621-california-2027