Ada County, ID Accessory Structures: ADU Owner Occupancy (2026)

Section 8-4-23 governs any secondary attached or detached dwelling, the county's term for what most homeowners call an ADU, and subsection B sets the general standards every approved secondary dwelling must keep meeting after construction, not just at permit issuance. Subsection B(3), Occupancy, requires that either the principal dwelling or the secondary dwelling must be continuously occupied by at least one person having ownership interest in the subject property. That means an owner cannot rent out both the main house and the ADU to unrelated tenants and live elsewhere; someone with recorded ownership interest has to be living in one of the two units at all times.

The occupancy duty sits alongside the rest of subsection B's baseline standards: a principal permitted dwelling with a valid zoning certificate and certificate of occupancy, or one under active construction with a valid building permit, must already exist on the lot; no more than one additional permanent dwelling of any kind, including an additional farm dwelling, caretaker dwelling, or secondary dwelling, may sit on the property; the lot must measure at least 6,000 square feet; and the secondary dwelling itself must still meet the dimensional standards of its zoning district.

Because the occupancy condition runs with the property rather than expiring at final inspection, the county enforces it through the recorded deed restriction required under subsection F, which converts the secondary dwelling into non-habitable space automatically the moment ownership-based occupancy stops.