California’s 2026 ADU Law Changes: What This Means for Homeowners
If you looked into building an ADU a few years ago and put the idea on hold, it’s worth another look. California has passed more ADU legislation in the past two years than in the prior decade, and several of the changes that took effect in 2026 directly affect how long a Marin County or San Francisco project takes and who is allowed to build one.
This isn’t a comprehensive legal summary. It’s a practical look at what changed, what it means in the two markets we work in most, and what still depends on your specific property and jurisdiction.
You No Longer Have to Live on the Property (With One Exception)
For years, a common misconception was that homeowners had to occupy the primary residence to build and rent out an ADU. That requirement had already been loosened in stages, and as of 2026 it has been removed permanently for standard ADUs. You can build an ADU and rent out either the main house or the ADU, or both, without living on site yourself.
The one carve-out is junior ADUs, the smaller units created within the existing footprint of a home, which still carry an owner-occupancy requirement. If your plan is a detached backyard unit or a garage conversion rather than a JADU, this restriction no longer applies to you.
This matters most for property owners and long-term investors in Marin who were previously ruled out of ADU projects because they don’t live in the home full time. It’s worth revisiting the math on a project that didn’t pencil out under the old rules.
Faster Review on Paper, Still Property-Specific in Practice
A new state law requires local agencies to tell you within 15 business days whether your ADU application is complete. That’s a real improvement over the open-ended waiting that used to happen at the front end of a project, and it’s meant to stop applications from sitting untouched for weeks before anyone even confirms what’s missing.
In practice, this shortens the front end of the process, not necessarily the whole thing. In unincorporated Marin County, the Building and Safety office targets roughly 60 days for a complete review, and simple garage conversions in some Marin cities have moved through permitting in as little as 10 to 14 weeks when the application is clean the first time. Projects in jurisdictions with a Design Review Board, which includes several Marin towns, typically add another 8 to 12 weeks for public notice, even though state law limits how much discretionary review a city can apply to a qualifying ADU.
San Francisco’s process runs on a different track. Most standard-program ADUs go through the Planning Department and then the Department of Building Inspection, and the city’s own guidance sets expectations of several months to permit issuance, with the full project timeline (including design, plan preparation, and construction) commonly running well over a year from the initial decision to build. San Francisco also has specific pre-application steps, including posting a Notice of Addition at the property at least 15 days before filing, that don’t exist in the same form in Marin.
The honest takeaway: the paperwork moves faster than it used to, but “faster” in Marin and “faster” in San Francisco are still two different numbers, and a clean, complete first submission still matters more than almost anything else you control.
A Real Path to Legalize an Unpermitted Unit
If your property has a garage conversion, in-law unit, or second living space that was never permitted, and it was built before January 1, 2020, there is now a defined legalization pathway. Local agencies generally cannot deny the permit solely because the work was never authorized. Instead, the unit goes through an inspection focused on health and safety, with corrections required only for conditions that would make the structure substandard, not for every deviation from current code.
Marin County runs its own ADU Legalization Program under this law, and successfully completing it results in a Letter of Legalization, not a full certificate of occupancy, which is a distinction worth understanding before you start. San Francisco has a parallel legalization pathway through the Department of Building Inspection for similar pre-2020 unpermitted units.
If you’ve been living with a unit you’re not sure is fully legal, this is the first year in a while where getting it addressed is genuinely more accessible than it used to be, and it’s worth a conversation before you assume the fix is complicated or expensive.
Pre-Approved Plans Are Becoming a Real Shortcut, Where They Exist
Several Marin cities, including Mill Valley, now offer pre-approved ADU master plan programs. Because the structural design has already been reviewed and approved, the building permit process for a matching project is faster than a fully custom design, since the plan check is narrowed to site-specific items like setbacks, foundation conditions, and tree removal rather than the full structure. These programs come with real constraints. You generally can’t modify a pre-approved plan beyond flipping the floor layout, and plans are tied to the building code in effect when they’re approved, so it’s worth confirming a plan is still current before counting on it.
Marin County has also extended reduced or waived building permit fees for ADUs and JADUs through 2026, and county resources, including a dedicated ADU planning site, offer free consultations and vendor guidance. San Francisco does not currently have an equivalent pre-approved plan program at the same scale, so custom design remains the standard path there.
What This Means If You’re Planning a Project Now
None of this changes the fundamentals of a good ADU: your lot still needs to support the setbacks, your utilities still need capacity, and your design still needs to hold up structurally and aesthetically next to the main house. What’s changed is the administrative path around those fundamentals, and in several cases that path is now shorter or more forgiving than it was two years ago.
If you’re early in the process, the most useful thing you can do is find out which specific track applies to your address before you commission full architectural plans. Whether you’re in a Marin city with Design Review, unincorporated Marin, or San Francisco, the answer changes what you should expect for both timeline and cost of the permitting phase itself.
A Side Note
Building codes, permit requirements, and legalization pathways vary by city and by property, and the state legislature has shown no sign of slowing down on ADU-related bills. Treat this as a starting point for a conversation with your local planning or building department, or with a contractor who works in ADU permitting regularly, rather than a final word on your specific project.
Talk to Us Before You Commit to Plans
If you’re weighing whether a garage conversion, a detached ADU, or legalizing an existing unpermitted space makes sense for your Marin County or San Francisco property, our team at Home Team Services Remodeling is happy to walk through what applies to your specific address and jurisdiction before you spend money on design.