Ajo Accessory Structures: ADU Rules Rules (2026)

Pima County Zoning Code permits accessory dwelling units (also called guest houses or casitas) in residential zones, particularly on larger lots in CR-3, CR-5, SR, SH, and GR-1 districts. The ADU must be clearly subordinate to the primary dwelling in size (typically limited to 50% of the primary dwelling's floor area or a maximum square footage cap). The unit must meet all building code requirements including separate utility connections or sub-metered connections, fire-rated separation from the primary dwelling, and compliance with Pima County flood plain management regulations if located in a floodplain. Setbacks follow standard accessory structure rules: typically 5-foot side and rear setbacks. Height is generally limited to the primary dwelling height or the zone's maximum (usually 25-30 feet). A building permit from Pima County Development Services is required. Under the 2024 state STR legislation, ADUs receiving a certificate of occupancy after September 14, 2024 may only be used as short-term rentals while the property owner resides on the property. Parking requirements typically include one additional off-street space for the ADU.