Marin County ADUs

Single-family properties are allowed to add ADUs according to California Government Code Section 65852.2.

ADUs may be established on single-family properties through the conversion of existing spaces such as garages or through new construction that is attached to or detached from the primary home.

The property must have an existing or proposed primary home to be eligible to build an ADU.

ADUs that are permitted between January 1st, 2020 and December 31st, 2024 shall not be required to the owner-occupied.

Single-family homes are allowed 1 ADU per property. Additionally, if the property is owner occupied, the property may also be allowed a Junior ADU.

According to state standards, the maximum allowable floor area for an ADU on a single-family property is 800 sf and the minimum allowable floor area of an ADU is 150 sf. Local ordinances may allow larger sizes, but additional requirements may apply.

A height of up to 16 feet is allowed for a detached accessory dwelling unit on a lot with an existing or proposed single-family home. If the ADU is attached to the primary home, then a height of up to 25 feet is allowed. Height limits do not apply to conversions of existing spaces to ADUs.

Required parking for the ADU may not exceed one space per bedroom. The ADU shall be exempt from parking requirements if located within 1/2 mile walking distance of a public transit station. When a garage, carport, or covered parking structure is demolished in conjunction with the construction of an accessory dwelling unit or converted to an accessory dwelling unit, the local agency shall not require that those off-street parking spaces be replaced. (Gov. Code, §65852.2, subd. (a)(1)(D)(xi). (pg. 17 link)

The minimum required setback for a new construction ADU on a single-family property is 4 feet from the rear and interior side property lines. Front and street side setbacks may be greater than 4 feet. Conversions of legally established structures converted into an ADU are exempt from these setback requirements.

The installation of fire sprinklers shall not be required in an accessory dwelling unit if sprinklers are not required for the primary residence.

The maximum allowed timeline for a city or county review cycle for a valid permit application for an ADU is 60 days.

ADUs that have less than 750 sf of living area are exempt from impact fees.

A local agency shall require that a rental of the accessory dwelling unit created pursuant to this subdivision be for a term longer than 30 days.

A local agency shall not require, as a condition for ministerial approval of a permit application for the creation of an accessory dwelling unit, the correction of nonconforming zoning conditions.