There’s a reason why I’ve dragged my feet in converting my fixer garage into an ADU: Every year California improves statewide laws with regulations for building accessory dwelling units (ADUs).
In 2025 some of the most exciting laws squash rules that some local cities were hoping to impose. Maxable is a company that provides end-to-end guidance to homeowners hoping to build an ADU. From the Maxable blog:
- All properties quality – “If you are a homeowner in California, you are entitled to at least one 800 sq ft, 16 ft tall ADU on your property regardless of lot size, floor-area ratio, or front setbacks.” (In my experience if you have a 2-4 unit building, it’s important to learn the exact rules related to multifamily.)
- More flexibility – Your city cannot require the owner to live on the property to be able to build an ADU. Investors rejoice!
- Faster approvals – “If you live in a city with a population of at least 200,000, your local planning department is required to have a pre-approved ADU plans program in place.” I wish my city had plans like the beautiful ADU pre-approved plans Santa Cruz offers!
- Solar panels required except…“Prefab ADUs, which are typically factory-built, are exempt from this regulation.”
- More units, up to 8 – Woah: “Multi-family property owners can now build one detached ADU per living unit on their property, with a max of eight.”
- Check out the Maxable post for more…
Considerations when building ADUs in California in 2025
While 2025 laws have changed, it’s especially important in the face of potential labor shortages and increased building materials costs to accurately estimate the complete building and permitting costs, not to mention the time to complete the job.
Do you need to update your sewer line, add drainage, or do other work on the main house? It might be worth completing whatever updates you need to do at the same time. Especially in cities that have notoriously slow building departments.
If you are priced-out of custom ADU designs, there are several great pre-fab ADU companies who focus on efficiency to offer several ADU models. Large lots offer more flexibility to buy a pre-fab ADU which tend to be designed on the longer side, rather than taller or more square. (Yes, I’m frustrated!)
When searching for pre-fab ADUs be sure to use terms such as shed, cottage and backyard office, as you’ll find more results. For example, Studio Shed, Abodu, Nest ADU (which I hadn’t heard of till I started searching! Do you know of someone who has a Nest ADU? I’d love to hear how they chose it and how they like it.)
However before you commit to a pre-fab ADU, consider if you want to build 2 or more units. It might be more efficient to build those as a duplex. Or perhaps you can buy 2 pre-fab ADUs and arrange them for optimal utility and system configuration. After all it’s the sewer, plumbing, foundation, etc. work that really can add up.
If you plan to take advantage of the new 2025 California ADU laws, I’d love to hear your plans and questions. Message me here or @agentsusie on Intagram.
See the Maxable roundup of new California ADU laws in 2025. California FTW!
Architect Jason Kaldis stands by a compact ADU he architected as a garage conversion.
