ADU laws SF - SB-9 lot split rules California

Zoning reform is reshaping the Bay Area’s housing landscape. Streamlined ADU laws, density allowances, and relaxed permitting are opening up new opportunities for homeowners and developers, especially in Marin.

Has Zoning Reform Changed Anything?

California’s recent zoning reforms and ADU (Accessory Dwelling Unit) laws have had a real, if gradual, impact on housing potential in the Bay Area. In San Francisco, local implementation of state laws has made it easier to add ADUs to existing structures, legalize previously unpermitted units, and convert underused space. These changes aim to boost density without changing neighborhood character dramatically.

In Marin, the effect is even more notable. Cities that previously made ADU construction slow or restrictive have had to streamline their permitting processes to comply with state mandates. Homeowners can now add small detached cottages or convert garages into livable spaces more easily than before. For many, this means new options for multigenerational living, rental income, or property value growth.

Beyond ADUs, state density and lot-split reforms (SB-9) are gradually enabling two-unit developments and lot splits in some single-family zones. While adoption has been cautious in Marin and SF, the regulatory environment is more flexible than it was even five years ago. Homeowners exploring these paths should pay close attention to local design guidelines, setback rules, and utility requirements, which still shape what’s actually feasible on a parcel.

Zoning reform hasn’t transformed neighborhoods overnight, but it has expanded what thoughtful owners and developers can achieve with the right planning.