ADUs in Marin County: Rules by Town

Marin is prime ADU territory — big lots, strong rents, and multigenerational families who want everyone close. Just remember that Marin is a patchwork of jurisdictions: the unincorporated county sets one set of rules, and each incorporated town has its own. Here’s how the ADU rules in Marin County work. (For the statewide baseline, see our Bay Area ADU guide.)

Unincorporated Marin County

These rules (Marin County Development Code §22.32.120) apply to areas not inside a city’s limits:

  • Size: Attached ADUs are capped at 50% of the main home’s floor area or 1,200 sq ft, whichever is smaller; JADUs at 500 sq ft.
  • Height & setbacks: Up to 25 ft (per underlying zoning), with at least 4 ft side and rear setbacks.
  • How many: A single-family lot can add one ADU over 800 sq ft plus a JADU, or two ADUs under 800 sq ft. Multi-family lots can add up to eight detached ADUs (not exceeding the number of existing units).
  • Parking: One space for a studio or 1-bedroom ADU, none for a JADU — waived within a half-mile of transit or in a historic district.
  • Special areas: Extra review in sensitive-habitat and high-fire-severity zones; coastal-zone ADUs need a Coastal Development Permit.
  • Timeline: Reviewed within 60 days; full permitting typically runs about three to four months.

Marin’s incorporated towns

San Rafael, Novato, Mill Valley, San Anselmo, Larkspur, Corte Madera, Fairfax, Tiburon, Sausalito, Ross, and Belvedere each have their own ADU ordinances. They must meet the state minimums (ministerial approval, 60-day review, 4-ft setbacks, parking waivers near transit), but details like maximum size, height, and design standards can vary town to town. If your property is inside a town’s limits, check that town’s planning department — and we’re glad to help you find the right contact.

This page is general information, not legal or construction advice, and rules change. Confirm specifics with your town or the county before you build. We’re always happy to refer trusted ADU architects and contractors who work in Marin — just ask.

San Rafael, neighborhood by neighborhood

San Rafael is where most of our Marin ADU conversations begin, and the answer changes street by street — lot depth, slope, and how much usable rear yard is left once the original house is accounted for. The older pockets around downtown often have deep lots and detached garages worth converting: Gerstle Park, just south of downtown around the historic park, and Bret Harte in the small pocket southwest of it. East toward the Bay the parcels get larger in Dominican and out at Peacock Gap, while Montecito and Happy Valley sit closer in near the 101/580 interchange. Sun Valley climbs northwest of downtown below the open-space hills, and the Canal district runs southeast along the water. Each of those pages has what we know about the housing stock, and we are glad to walk a specific lot with you before you spend anything on drawings.

Thinking about an ADU in Marin?

We’ll help you weigh the rules in your specific town, the cost, and the value it adds. Start with a free home valuation or call (415) 407-5324. See also: ADUs in San Francisco, San Mateo County, and the East Bay. — Beatrice Kopilenko, REALTOR® · DRE #01970797 · Primavera Realty