Ada County, ID Building Setbacks & Zoning: Lot Coverage Limits (2026)

Ada County's zoning ordinance, adopted by Ordinance 1002 on October 28, 2025 and current through Ordinance 1018, defines coverage at Section 8-10-2 as the area of a property occupied by the footprint of all structures, and separately defines lot coverage as the maximum percentage of the lot covered by all improvements where a lot coverage standard applies. Table 8-2-6-1, the dimensional standards table for the Rural Residential (RR) district in Section 8-2-6, sets the base lot coverage maximum at 10 percent for a standard 10-acre-minimum lot.

5 acres maximum, may cover up to 20 percent of the lot. The same table caps building height at 35 feet and requires 100 feet of minimum street frontage under either option. A separate allowance in the adjoining Rural Preservation (RP) district, Section 8-2-5(B)(2)-(3), lets institutional uses such as churches, schools and group day cares, and commercial stables or riding arenas, raise the maximum coverage on rural base district land from 10 percent to 25 percent. Table 8-2-6-1's notes limit the property to one dwelling unit, aside from an approved second unit such as a duplex, secondary dwelling, additional farm dwelling, caretaker dwelling or temporary living quarters, and cap the property at two dwelling units total.

An owner who cannot meet the coverage cap because of site constraints may apply to the Board of County Commissioners for a variance under Section 8-6-31, which implements Idaho Code Section 67-6516 and requires proof of unnecessary hardship without granting a special privilege or causing detriment to public health, safety or welfare. Variance applications are filed with the Director of Development Services, and decisions may be appealed under Section 8-6-13.