ADU Tips, Costs & Regulations in Los Angeles

Four new California ADU laws take effect in 2027. Here’s what the 2027 ADU regulations mean for homeowners and investors: two detached ADUs under AB 956, lower impact fees on larger ADUs under SB 1117, tighter plan checks under AB 1621, and smoother SB 9 projects under AB 2601. Plus two honorable mentions.

Most investors look at a single-family lot and see one house. We saw four rentals. In this Encino project, we used SB9 to convert the primary home into a duplex, which unlocked two detached 1,400 sq ft, 3-bedroom ADUs in the back. Here's why we built bigger instead of building more, how stacked floor plans cut costs, and why we walked away from a fifth unit.

It’s a new year, which means a new round of ADU laws hitting California. By now, this pattern should feel familiar. Since 2017, California has passed new ADU legislation nearly every year to make it easier, faster, and more affordable for homeowners to build. And there’s a reason for that: ADUs work. After designing and building over 100 ADUs, I’ve seen firsthand how life‑changing these units can be for homeowners, renters, and families trying to stay in place while creating