Grand Junction, CO Accessory Structures: ADU Rules (2026)

Grand Junction's Municipal Code addresses accessory dwelling units, sometimes called garage apartments or carriage houses, at GJMC § 21.04.040(e)(1)(i), Accessory Use-Specific Standards. An ADU is allowed only alongside a single-unit attached dwelling, a single-unit detached dwelling, or a duplex; it cannot accompany a cottage court dwelling. The Code overrides more restrictive ADU limits in an Outline Development Plan (ODP) or Planned Development (PD) ordinance, so a property owner cannot be held to an older, stricter PD condition. ADUs are excluded from density calculations, meaning adding one doesn't count against a lot's allowed units per acre.

Every ADU needs a Planning Clearance from Community Development, and the applicant must show compliance with three groups of standards. On maximum number, a lot with one detached single-unit dwelling, or an attached single-unit dwelling containing two units, may add two ADUs if at least one is physically attached to the principal dwelling, such as in an attic, basement, or carriage house; a duplex lot is capped at one ADU. On site layout, the ADU must be clearly subordinate in design and location to the principal structure, cannot sit in front of it, but may share the principal structure's side setback, and on a corner lot may use the principal structure's setback along the street frontage; a detached or attached ADU may also use the minimum rear setback that applies to accessory structures generally. On structure requirements, the ADU must meet all building and fire code requirements and cannot exceed 900 square feet of habitable space.