The California State Fire Marshal
- California State Fire Marshal (PDF) — Information bulletin regarding sprinkler system requirements.
The California Energy Commission
- California Energy Commission updates for ADU - Blueprint Newsletter Issue 129 January 2020 – March (PDF) — ADUs and adoption of 2019 Energy Code: PV (solar panel) Requirements for ADUs
HCD’s Codes and Standards Division
- HCD Information Bulletin — Provides clarification and outlining provisions of various residential types, ranging from recreation vehicles and manufactured homes to site-constructed California
The California Coastal Commission
- Final SB 1077 Guidance from the California Coastal Commission (PDF) — July 1, 2026
- ADU guidance memo for planning directors in coastal cities and counties (PDF) — January 21, 2022
HCD's ABC's of ADUs Webinar Series
Guidance from ADU Handbook Contributors
You'll find additional resources at the following websites, which are hosted by partners who contributed to HCD's Technical Assistance Booklet.
- Casita Coalition — ADU Best Practices Guidebook
- Casita Coalition — The statewide cross-sector nonprofit offers free downloads of ADU guidance memos for practitioners and homeowners on their Guidebooks and Resources page [casitacoalition.org], including guidebooks on Legalizing an Unpermitted ADU, SB 9 Two-Unit Developments and Lot Splits, Multifamily ADUs, ADU Best Practices, ADU Financing, and Garage Conversions.
Materials from Cities and Counties
- Napa Sonoma ADU
- San Mateo ADU
- Clovis Old Town Cottage Home Program (PDF)
- Del Mar Sample ADU Floor Plans
- City of Fresno ADU Program and Pre-approved Plans
- ADU amnesty program - San Mateo County
- ADU possibilities on your lot
- ADU Resource Center the American Institute of Architects (AIA)
- The ABCs of ADUs (PDF)
- Clovis Cottage Home Program (PDF)
- Accessory Dwellings — One-stop resource about accessory dwelling units. (Portland, OR)
- Everything About Building ADU in Los Angeles
- Second Unit Resources Center
- Ideas, Stories, and Photos
- How to Build an ADU — A step-by-step guide from design to move-in
- Second Unit Calculator — Calculate typical costs, rents, and more
- Idea Book (PDF)
- Workbook (PDF)