ADU rules in Marin County, CA — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Marin County Code §22.32.120 regulates ADUs in unincorporated areas. Detached and conversion ADUs under 800 square feet receive ministerial by-right approval. ADUs are allowed in single-family, multifamily, and mixed-use zones. The county currently extends its ADU permit fee waiver through December 31, 2026.
Section 22.32.120 of the Marin County Development Code regulates Accessory Dwelling Units in unincorporated Marin. Following 2024 state-law alignment, ADUs under 800 square feet — both detached and conversion ADUs of non-livable spaces — are processed ministerially by right with no discretionary review. ADUs are permitted in single-family, multifamily, and mixed-use zoning districts. State-mandated objective standards apply for height, setbacks, and parking. Junior ADUs (JADUs) up to 500 sq ft within an existing single-family dwelling are also allowed. The county adopted an urgency ordinance on January 28 to bring local rules into compliance with state ADU law.
Building an ADU without a permit or violating §22.32.120 is a zoning violation. Code Compliance issues notices requiring permit application or removal. Unpermitted ADUs cannot legally be rented and may trigger civil penalties.
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See how Marin County's adu rules rules stack up against other locations.
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