ADU Regulations in Marin County, California (2026)

Regulations at a glance

Local rules & notes

Front Setback Encroachment: The county cannot enforce a 25-foot front yard setback if it precludes the construction of an ADU of at least 800 square feet. Unpermitted Structure Conversion: The county attempted to limit ADUs to 'legal building area,' but state law requires allowing conversions of unpermitted structures and nonconforming spaces. Illegal Fire Zone Access Requirements: The county tried to mandate 20-foot wide paved road access for ADUs in Very High Fire Hazard Severity Zones, which HCD flagged as an illegal overlay.

For the official ordinance and latest updates, check your city or county planning department.

Frequently asked questions about ADU regulations in Marin County

• What is the maximum ADU size in Marin County, California?

  In Marin County, the maximum ADU size is typically 1200 square feet, depending on whether the unit is attached or detached. California state law allows up to 1,200 sq ft for detached ADUs and 800 sq ft for attached in many jurisdictions; Marin County may follow state defaults or have local limits. Verify with Marin County planning for your specific lot.

• What are the setback requirements for ADUs in Marin County?

  In Marin County, typical setback requirements are 4 feet from the side property line and 4 feet from the rear. These may be reduced to 4 feet under California Government Code § 65852.2 where applicable. Check with Marin County planning for overlay zones or design standards that could affect your site.

• What is the maximum height for an ADU in Marin County?

  In Marin County, the maximum height for an ADU is generally 16 feet. State law often allows up to 16 feet for detached ADUs and up to 25 feet when within 4 feet of the property line in some cases. Confirm with Marin County or county planning for your zone.

• Is ADU approval ministerial in Marin County?

  In Marin County, ADU approval is typically Ministerial (by-right) per Gov Code §65852.2. Ministerial (by-right) review means the city must approve qualifying applications without discretionary review, per California Gov Code § 65852.2. Your project must still meet objective standards; Marin County planning can confirm the exact process.

• Are there parking requirements for ADUs in Marin County?

  In Marin County, parking for ADUs is generally Often waived per state law; check local ordinance. California law often waives parking for ADUs within a half-mile of transit or in certain historic districts. Check with Marin County planning for your address.