Boulder, CO Environmental Rules: Defensible Space (2026)

5-2(n), defines defensible space as an area that has been modified and is maintained to reduce fire risk, intensity, and spreading by disconnecting fuel loads both vertically and horizontally, where natural and manmade fuels are treated, removed, or reduced to slow wildfire spread and alter fire behavior. 5-2(ff), applies that concept to landscaping in the band between 5 feet from the building and the property lot line, capped at 30 feet in width. For new buildings and new structures, new plants must come from the Boulder Approved Tree and Plant List, new trees must be spaced so mature canopies stay at least 10 feet apart, every existing juniper species must be removed, and non-approved existing trees other than junipers must be trimmed so branches within 6 feet of the ground or the lowest third of the tree's height are gone.

Understory plantings must keep at least 3 feet of vertical and horizontal clearance from tree branches and 5 feet from structures. The same planting rules apply to additions of 200 square feet or more and to new or expanded decks. 6 bans planting any Juniperus species in these mapped areas. The Division of Building Safety reviews landscape plans against these standards as part of building permit approval for work in the mapped wildland-urban interface.