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

Mono County's ADU standards are codified in the General Plan Land Use Element, Development Standards Chapter 16 (the County combines its General Plan and Zoning Code). Section 16.030 permits ADUs and junior ADUs in any land use designation that allows single-family residences, or in Specific Plan areas. Under Section 16.040.A, ADUs are approved ministerially by building permit when they are: built within an existing single-family or accessory structure (with up to a 150 sq ft expansion for ingress/egress); detached one-bedroom units up to 850 sq ft; or detached two-bedroom units up to 1,000 sq ft, all subject to a maximum four-foot side and rear setback that must prevent snow shedding onto adjacent properties. Larger units (one-bedroom 850-1,400 sq ft; two-bedroom 1,000-1,400 sq ft) require Director Review under 16.040.B, and units over 1,400 sq ft require a Use Permit (16.040.C). Section 16.050.A exempts ADUs under 750 sq ft from development impact fees and exempts all ADUs from Housing Mitigation Ordinance (HMO) fees. Per Section 16.040.F, ministerial review must occur within 60 days, consistent with Government Code 65852.2 (now recodified at Gov. Code 66310 et seq.). A junior ADU is defined as no more than 500 sq ft within an existing single-family structure.