ADUs Explained: What State Law Actually Means for Your Backyard (or Basement)

Thanks to the reform of state Accessory Dwelling Unit (ADU) legislation in 2016, we have seen a massive and steady increase in homeowners wanting to add these units to their properties.

The state law establishes excellent baseline guidelines for both standard and Junior ADUs, standardizing rules around size, height, setbacks, and approval timelines. While this has undeniably made building an ADU more accessible, it is not a free-for-all.

The Layers of Regulation

Even with state protections, local municipalities can still enforce their own design and development standards. Furthermore, ADUs are subject to overlapping jurisdictions. Depending on your location, you may still have to navigate requirements from the California Coastal Commission, Wildland-Urban Interface (WUI) fire standards, and FEMA flood guidelines.

GSA’s Teaching Moment

The 60-Day Clock State law mandates that municipalities must review complete ADU permit applications within 60 days. However, the reality of this timeline is much more nuanced. When a city issues "plan check comments" requesting revisions, which happens on almost every project, that 60-day clock pauses until the revisions are submitted.

The Real Timeline

While ADU approvals are faster than standard permits, even a simple project like a basement conversion usually takes three to four months to achieve full permit approval.

Looking Ahead

State ADU legislation evolves every year. In the future, we hope to see more incentives for ADU development, such as limiting property tax reassessments or allowing ADUs to be sold separately from the main house. Notably, San Francisco has already begun approving separate sales on a limited basis.

Curious about the specifics? You can dive into the details in the state’s official ADU Handbook.