Ada County, ID Environmental Rules: Defensible Space (2026)

Section 8-2-25(C)(1), the WUI Overlay's Vegetation Control Standards, requires a minimum 50-foot defensible space around the perimeter of any habitable structure whenever a property owner undertakes a "modification," defined as new construction or the alteration, movement or change of use of a habitable structure. Inside that 50-foot ring, only single specimens of trees, ornamental vegetation, cultivated ground cover such as green grass or ivy, and native grasses and weeds trimmed to a maximum height of four inches are allowed, and the Director may approve heights up to six inches only where needed to control erosion on steep slopes.

All deadwood must be removed from trees in the defensible space, clustered trees must be thinned so crowns no longer overlap, and crowns must keep a 10-foot horizontal clearance from any structure or chimney outlet; trees six to ten feet tall may only be pruned up to one-third of their height. Firewood and combustible material cannot be stored under decks, eaves or unenclosed spaces beneath structures, and any firewood stored within the defensible space must sit at least 20 feet from structures and 15 feet from tree crowns.

Agricultural structures are barred entirely from the defensible space, and accessory structures allowed there must meet the fire-resistive construction standards of the Ada County Building Code, Title 7, Chapter 2. Driveways and private roads get their own five-foot vegetation clearance on each side, and if the property abuts a qualifying public street or private road, the width of that roadway counts toward the 50-foot defensible space requirement. Property owners remain responsible for maintaining the defensible space unless that duty is transferred to another party by binding contract.