While estimates of California’s housing shortage are all over the map, most studies exceed 1 Million homes. ADUs are one very important tool to help combat the state’s chronic lack of affordable housing. It may seem trivial to add one unit in a backyard or convert a basement into an apartment, but collectively ADUs now account for about 20% of the state’s new housing. In contrast to large apartment buildings or expanded suburbs, ADUs are relatively quick and provide a “surgical” path to new housing using existing land, sewers, water and other infrastructure. They are not a complete solution but may be the greenest and most sustainable housing strategy available.
ADUs can be stand alone (detached) structures, attached to an existing home or converted from existing basement, garage or other indoor space. Among the state’s leading providers of ADUs, Wellmade Design-Build offers an affordable and attractive panelized solution that can be constructed in almost any backyard. DNM Architecture is proud to be part of Wellmade’s design, permitting and documentation team.
A Brief History of California's ADU Rules
To understand the current state of California’s ADU rules, it’s helpful to understand how much things have changed in the last 10 years. Prior to 2016, while localities were encouraged to allow ADUs on single-family lots, local governments had wide-ranging authority to restrict development. Many did just that, creating a situation whereby residents were forced to navigate an extraordinarily difficult environment with vastly differing rules on a town-by-town (or even neighborhood) basis – not an ideal situation for a state facing a massive housing crisis.
2023-2025 – Current California ADU Regulations
Under a series of new state laws that took effect on January 1, 2025, ADUs became easier to build in California than ever before.
- AB 976 eliminated owner-occupancy requirements except for Junior Accessory Dwelling Units, or “JADUs”,
- SB 1211 expanded the number of detached ADUs for multifamily properties up to eight units at 1 ADU per multifamily unit,
- AB 2533 provided a path to legalization of previously unpermitted ADUs without significant penalties, and
- AB 1332 relaxed setback requirements, increased height limits up to 25 feet in some cases, required pre-approved ADU plans to speed up permitting, and created a 30-day timeframe for local governments to approve or deny permits on these units
2026 - Updates
Additional new regulations are set to go into effect on January 1, 2026, including:
- Provides that owner occupancy of a primary dwelling is not required if the JADU has separate sanitation facilities,
- Requires that a JADU be rented for a term longer than 30 days, meaning JADUs cannot be used for short term (Airbnb) rentals,
- Provides other clarifications on the unit entrance and kitchen.
- Clarifies that ADU floor area is measured as “interior livable space”, meaning that exterior wall thickness or attic areas with low ceilings are not included in the ADU area;
- Shortens the maximum to evaluate the completeness of an ADU application to 15 business days;
- Requires local agencies to ministerially approve ADU applications within 60 days (or they’re deemed approved) and provide clear reasons for denial;
- Generally prohibits construction, connection, and impact fees and capacity charges on ADUs under 750sf;
- Amends fire sprinkler requirements for JADUs to match ADUs.
The latest edition of the CA Accessory Dwelling Unit Handbook is a comprehensive guide to current state regulations regarding ADUs. While most cities and counties have local ADU regulations, all of them must comply with these state standards.
With this alphabet soup of legislation to navigate, working with an experienced and qualified architect on your ADU project may be more important than ever. DNM Architecture has completed dozens of panelized and fully custom ADUs in both northern and southern California. Email or call us to start your own ADU and take advantage of all the advantages offered by the full range of California housing legislation.