SB 9 & Lot Splits
“Informal” Housing – It’s Not Just a Formality - California YIMBY
A new study analyzing satellite imagery of San Jose has revealed that approximately 78% of detached accessory dwelling units (ADUs) built between 2016 and 2020 were constructed without proper permits.
Researchers from Stanford used computer vision technology to identify 1,336 new detached ADUs across 15,000 parcels, then cross-referenced city permit data to determine that 1,045 of these units were unpermitted.
The findings are particularly striking given San Jose's reputation as ADU-friendly, with programs including same-day permitting processes.
The research found that unpermitted ADU construction was concentrated in lower-income neighborhoods with higher density, fewer white residents, and more household overcrowding.
About 20% of the identified ADUs were built on lots that did not meet minimum size requirements for legal ADU construction.
For California property owners and developers, the study highlights ongoing barriers in the formal permitting process despite statewide ADU reforms that have enabled tens of thousands of legal units across the state.
ADU laws allow homeowners to build secondary housing units on their properties, typically in backyards or converted garages.
The prevalence of informal construction suggests that streamlining permits and reducing regulatory barriers could help bring more housing development into compliance while addressing California's housing shortage in communities that need it most.
