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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.

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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.

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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. 

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

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

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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. 

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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.

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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.

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