Defensible Space Zones (1,2,3,4)

4 The four zones of defensible space.

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Zone 1 | Zone 2 | Zone 3 | Zone 4

Defensible Space Zones.
Image courtesy of and
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Zone 1:  A Structure Ignition Zone is an area that must be made non-combustible within approximately 0 - 10 feet from the structure. This area around the perimeter of the structure is crucial for wildland fire survival.

In this area, only low volume, well-irrigated vegetation should be planted, and extreme care should be taken to keep this area free of all materials that could ignite during or after a flame front (advancing wall of flame). 

There should be no fire fuels under decks or windows. This is especially important during the high wind conditions of late summer and fall. It is imperative to patrol for and remove all fuels, such as leaves and pine needles, which tend to build up and become traps for burning embers.
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Dangerous leaf litter.
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Zone 2:  A Firebreak Zone is a radius of approximately 10 – 30 feet from the structure and requires reduction in the volume of the fire fuels (plants, shrubs, trees), and elimination of ladder fuels, in order to create an environment that will not sustain a wildland fire. In doing so, the fire is denied fuel and the effect of heat and flame on a structure will be substantially reduced. 

Grasses should be kept low during fire season, and dead vegetation accumulations removed. Mowing and thinning are normally needed annually. If mowing during fire season, work before 10 AM when there are high humidity conditions, low temperatures and no wind.

Many non-pyrophytic (low flammability) shrubs can be in the next zone out (Firebreak Zone), with only occasional non-pyrophytic trees in this area. Open walks, lawns, non-flammable ground covers will help to keep this area usable, lovely and free of wildfire.
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Green lawns are excellent fire breaks.
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Zone 3:  A Reduced Fuel Zone is a radius of approximately 30 – 100 feet (or more) from the structure. In this zone large non-pyrophytic trees can be maintained and grown with other non-pyrophytic species. Shrubs must not constitute continuous fuel beds. The separation distance charts are helpful in determining wise plant spacing.

Depending on the factors influencing fire intensity, behavior, and flame spread, this distance may be expanded much further from the structure. If your structure is above a 20% slope, this zone should extend 200 feet downhill. If above a 40% slope, you may need 400 feet of managed space.

Excellent example of Reduced Fuel Zone.
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This zone is an area of overall fuel reduction designed to create an environment that calms a wildfire by separating the available fuels and reducing the heat and flame generated by the fire. If done correctly, fire “offense” can be most effective here.

The required distance usually radiates out in all directions but often expands downslope from the structure, further as the slope increases. Steeper slopes will also require greater protection from erosion if fuel management measures are undertaken.
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Dangerous buildup of vegetation
in the Access Zone.
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Zone 4:  An Access Zone is 10 feet on either side of roads and driveways. The ingress and egress route(s) from road or highway should not be flammable for at least 10 feet on either side of the traveled way. To allow for emergency access, there should also be at least 14 foot clearance over the road. Addresses should be clearly marked. Remember that emergency vehicles may be entering as others are leaving.

Two access routes at minimum are recommended. As you plan your defensible space, also plan your escape routes.

Example of ladder fuels.
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As your landscape matures, it will need annual maintenance, and it will also require removal of some plants as they grow large and start to close in. The separation guidelines are useful for planning; you should also be wary of the development of ladder fuels. Ladder fuels are fuels that allow a fire to move from the ground or lower-levels of vegetation such as grasses and small shrubs into taller shrubs and low trees and into the upper portions or crown of the vegetation.
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Napa Firewise

  To empower the citizens of Napa County with the information, knowledge, and support they need to survive a wildfire.