How far apart should trees be for defensible space?

Zone 1 and Zone 2 spacing

In the pine-dominated setting, Zone 1 (5 to 30 feet from the house) calls for separating individual trees or small groups of trees by 10 to 30 feet. The guide also says to trim branches within 10 feet of the house, chimney, deck or roof and within 10 feet of other trees.

In Zone 2 (30 to 100 feet or more) the guide says to maintain an average canopy spacing of 10 feet between the canopies of trees such as Jeffrey pine and white fir. For pinyon and juniper in sagebrush country it asks for a separation of 1.5 to 2 times the average tree height.

What slope changes

Fire runs faster uphill, so the guide recommends a larger Zone 2 when a house sits above a steep slope. Its table lists the distance to manage for trees as 100 feet on flat to gently sloping ground and on moderate slopes (21 to 40 percent), and 200 feet on very steep ground. If there is a thick shrub layer under the trees, use the shrub values instead.

The guide also warns that stripping too much from the bottom of a slope does little for fire and can cause erosion or a weed invasion.

Why a number on paper is not the plan

Spacing is measured crown to crown, not trunk to trunk, so a tall tree with a wide crown needs more room than its trunk suggests. Trees that touch each other or the roof matter more than any rule of thumb.

The arborist measures at the property and writes the plan; your fire district sets the standard that applies to your address. Our crews work with a masticating head on brush and hand-clear near structures. Read whether all your trees have to come out next.