Monterey, CA Accessory Structures: ADU Rules (2026)

Monterey allows one ADU on any parcel zoned for single-family or multifamily use, and a single-family lot can add both an ADU and a junior ADU at the same time if the ADU is either built within 800 square feet as new detached construction or converted from existing living area or an existing accessory structure such as a detached garage. A multifamily parcel can add one attached ADU, up to two detached ADUs, or convert non-livable space into ADUs equal to 25 percent of the existing legal units, whichever is greater.

Floor area for an attached or detached ADU is capped at 850 square feet for a studio or one-bedroom unit and 1,000 square feet for a unit with more than one bedroom. Setbacks are four feet from the side and rear property lines for new ADUs, though converted space or an ADU rebuilt in an existing structure's footprint needs no setback beyond what fire safety requires. Height is capped at 16 feet for a detached ADU on a lot with a single-family or multifamily dwelling, rising to 18 feet within a half-mile of a major transit stop or high-quality transit corridor (with an extra 2 feet allowed to match roof pitch), and an attached ADU cannot exceed 25 feet or the height that applies to the primary dwelling, whichever is lower, and cannot exceed two stories.

Design standards require the ADU's materials, colors, roofing and roof pitch to match the primary dwelling, subject to a discretionary exception through architectural review. ADUs are prohibited entirely in Airport Safety Zones 1 and 6 under the 2019 Airport Land Use Compatibility Plan, and cannot be built where water or sewer service is inadequate, a standard the Monterey Peninsula Water Management District verifies.