Defensible Space Guidelines

Zone 1: 5 to 30 feet from structure

*On smaller lots, management of this zone may require working with neighboring properties. If this cannot be accomplished, then increased stringency on managing Zone 1A (Noncombustible Zone) is required.*

Conifer Spacing: 

  • Conifers shall have, on average, 18' of horizontal spacing between tree tops (crowns). 

    • This spacing ​should be increased with slope.

  • Conifer limbs shall not be within 10 feet of the structure or overhanging the roof. ​

  • The lowest hanging branch on conifer limbs shall at least 6' off the ground.

  • All vegetation beneath conifers and extending out to the drip edge of the tree shall be removed.

Brush and Shrub Spacing:

  • Clear shrubs and brush growing beneath conifer trees.

    • Low growing shrubs​, as long as they are 3x less than the overall tree height.

    • Ex) If you have a 15' tree, the maximum shrub height beneath the conifer shall be less than 3 feet tall.

  • Irrigate your lawn and grass should have a maximum height of 4 inches. ​

  • Do NOT store firewood within 30' of a structure.

    • Or store it in an ember-resistant structure.​

Zone 2: 30 to 100 feet from structure

Conifer Spacing: 

  • Conifers shall have, on average, 12' of horizontal spacing between tree tops (crowns). 

    • This spacing ​should be increased with slope.

  • The lowest hanging branch on conifer limbs shall be no less than 6' off the ground.

    • For smaller trees, lowest limb shall be 1/3 of overall tree height.​

  • All vegetation beneath conifers and extending out to the drip edge of the tree shall be removed.

Brush and Shrub Spacing:

  • Clear shrubs and brush growing beneath conifer trees.

    • Low growing shrubs​, as long as they are 3x less than the overall tree height.

    • Ex) If you have a 15' tree, the maximum shrub height beneath the tree shall be less than 3 feet tall.

  • Irrigate your lawn and grass should have a maximum height of 4 inches. ​

  • Do NOT store firewood within 30' of a structure.

    • Or store it in an ember-resistant structure.​

Zone 3: 100 to 200 feet from structure

In this zone, the goal is to not eliminate fire, but have the ecosystem be resilient towards wildfire with proper spacing, pruning and horizontal/vertical clearance of vegetation. 

Encourage a mix stand with different species and age classes with proper spacing and pruning. 

Conifers should be thinned and pruned appropriately based on forest type.

If you are unsure, please contact your local DNRC Service Forester.

Emergency Vehicle Access- Vegetation Management

The following minimum standards shall be required for emergency vehicle access on individual lots in Missoula County. Defensible space shall be created within 100 feet of all driveways. 

Minimum Width:

  • For driveways more than 150 feet, a minimum width of 16 feet shall be applied (NFPA 1141, 2017).

  • If the driveway contains straight segments with clear lines of sight, the width may be reduced to 12 feet.

  • Consider adding pull outs along the length of the driveway to allow fire apparatus to pass.

Vertical & Horizontal Vegetation Clearance:

  • 13.5 feet of vertical height and 20 feet of horizontal feet shall.

  • Minium crown spacing of 10 feet shall be applied between conifers. 

  • Reduce ground fuels and surface vegetation loading and high fire hazard species (e.g. junipers).

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Image Courtesy of Community Planning Assistance for Wildfire (CPAW)

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When creating defensible space, landowners should consider managing multiple ecological goals, including slope stabilization with deeply rooted vegetation, riparian and wetland systems, wildlife habitat and more.