Merced County, CA Accessory Structures: ADU Rules (2026)

Merced County adopted Chapter 18.62 (Accessory Dwelling Units) as part of its 2019 Zoning Code update (Ordinance 1976). It applies to R-1, R-1-5000, R-2, and R-3 parcels occupied by a single-family dwelling. Only one ADU is allowed per parcel. A detached ADU's total floor area may not exceed 1,200 square feet; an attached ADU may not exceed 50 percent of the existing dwelling's living area, with a maximum increase of 1,200 sf. ADU height may not exceed the height of the primary structure or the maximum allowed by the zone, whichever is less. When an existing garage is converted to an ADU, no setback is required; an ADU built above a garage needs five-foot side and rear setbacks. ADUs are only allowed where public water and sewer are available and connected, and an ADU is not treated as a new residential use for utility connection fees. Rentals must be 30 continuous days or longer (no short-term rental), and an ADU cannot be sold separately from the primary residence. Section 18.62.050 requires a recorded affidavit stating one unit will be owner-occupied before building permits issue. Because the county code predates the 2024 state recodification, it still cites Gov. Code §§65852.2/65852.22; those statutes are now Gov. Code §§66310-66342.