Environmental Rules in Ada County, ID (2026)
5 county-level rules, plus city-specific rules for 1 city in Ada County, Idaho.
Verified from official government sources
Stormwater Management
New development in unincorporated Ada County must submit an engineer-prepared drainage study and drainage plan under Section 8-3-5(B) before the county issues a zoning certificate, showing where stormwater is routed, sized to the upstream drainage basin, and coordinated with any irrigation ditches or laterals crossing the site.
Stormwater Drainage Rules in Ada County
Some RestrictionsAda County Code 8-3-5(B)
All required drainage studies and drainage plans shall be based upon peak and total discharge estimates and shall be submitted by a professional engineer licensed in the state of Idaho... When drainage courses and irrigation facilities exist on site, documentary evidence of consent to re-routings by all interested landowners and drainage and irrigation entities affected and having rights to, an...
Erosion Control
Construction on Ada County Hillside Overlay sites, meaning any grading on a slope of 25 percent or more, must meet current EPA and Idaho Department of Environmental Quality erosion and sediment control rules, keep the site's drainage system operational throughout the build, and cannot alter major watercourses without an approved crossing or drainage structure.
Construction Erosion Control Rules in Ada County
Some RestrictionsAda County Code 8-2-30(E)(6)
6. Sediment: a. All construction must meet current EPA and IDEQ erosion and control rules. b. The overall drainage system shall be completed and made operational at the earliest possible time during construction. No certificate of occupancy shall be issued on the property until the drainage system is complete. c. Alterations of major watercourses shall be prohibited, except for approved roadway...
Flood Zones
Ada County requires a floodplain development permit for any construction, grading, filling or fencing within Special Flood Hazard Areas mapped on FEMA's Flood Insurance Rate Maps, and bans new construction outright inside the regulatory floodway. This reaches hillside and foothill drainageways over ten acres, not just the Boise River itself.
Floodplain Development Rules in Ada County
Significant RestrictionsAda County Code 8-2-28(D)
D. Applicability: These regulations shall apply to "development" as defined in this Section, excluding additions to existing buildings when the addition is not classified as a "substantial improvement" per this Section, within all Special Flood Hazard Areas identified by one or more of the following: 1. The federal insurance and mitigation administration in a scientific and engineering report e...
Defensible Space
Any new construction or alteration of a habitable structure inside Ada County's Wildland-Urban Interface Overlay District must maintain a 50-foot defensible space clear of flammable vegetation around the building, with specific pruning, spacing and tree-crown clearance standards enforced under Section 8-2-25.
Wildfire Defensible Space Rules in Ada County
Some RestrictionsAda County Code 8-2-25(C)(1)(b)-(c)
b. A modification requires a minimum fifty foot (50') defensible space around the perimeter of any habitable structure. Property owners shall maintain the defensible space unless that responsibility is transferred to another party through a binding contract. The defensible space shall meet the criteria in subsections c through j below. c. Only single specimens of trees, ornamental vegetation, c...
Flood Elevation Requirements
New and substantially improved buildings inside an Ada County Special Flood Hazard Area must set their lowest floor at least two feet above the Base Flood Elevation, the county's mandatory two-foot freeboard, verified on a FEMA Elevation Certificate before a floodplain permit is approved.
Base Flood Elevation Rules in Ada County
Some RestrictionsAda County Code 8-2-28(F); 8-2-28(G)(5)(b)
FREEBOARD: A factor of safety usually expressed in feet above a flood level for the purposes of floodplain management... The Base Flood Elevation (BFE) plus the freeboard establishes the Flood Protection Elevation (FPE). Freeboard shall be two feet (2')... b. For Residential Structures, the application shall include an Elevation Certificate on the most current FEMA Approved forms. The Elevation...
Environmental Rules by City in Ada County
1 cities in Ada County have their own environmental rules rules. Each link goes to that city's dedicated page with code citations.
All Ada County ordinances
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