How to get an ADU permit in Marin County

Marin County has some of the most desirable real estate in the Bay Area, and some of the most complex permitting environments.

Here's what makes ADU permitting in Marin different from the rest of the Bay Area.

Each city operates independently

Marin County is not one jurisdiction. San Rafael, Mill Valley, Novato, Tiburon, Corte Madera, and unincorporated Marin County each have their own building department, their own plan check process, and their own interpretation of state ADU law.

What works in San Rafael won't necessarily work in Mill Valley. Application requirements, fees, and timelines vary significantly between cities.

What slows Marin ADU permits down

Septic systems. A large portion of Marin properties are on septic rather than sewer. Adding an ADU triggers a septic capacity evaluation, and in some cases a system upgrade, before a permit can be issued. This is one of the most common surprises for Marin homeowners who didn't see it coming.

Environmental review. Properties near sensitive habitats, hillsides, or flood zones may trigger additional review layers that extend the timeline.

HOA restrictions. Many Marin communities have HOAs with their own approval processes that run parallel to city permitting.

What to do before you start

Get a feasibility report specific to your city and property. State ADU law gives you significant rights, but Marin jurisdictions have nuances that can affect your project scope, timeline, and cost before you spend money on plans.

At PermitBox we cover all Marin jurisdictions. Book a consulting call or order a feasibility report at permit-box.co.