Originally Published: June 16, 2017 5:59 a.m.
In this final part, we will look at how one can develop a defensible space around a home in or close to a forest environment in Prescott and Yavapai County. A wildfire can be devastating to a homeowner or community and a small amount of prevention can save large amount of heart ache. There are two components involved; developing a vegetative defensible space around the home and taking fire safe precautions when building or remodeling a home in a fire sensitive area.
First, we will look at creating a defensible space around a home, which is usually expressed as a distance extending outward from the structure and all attachments. This distance varies by the type of wildland vegetation growing near the home and ruggedness of the terrain. Firewise safety zones need to be considered when creating defensible space: Zone 1 is the area nearest the home and requires maximum hazard reduction for structural survivability. Zone 2 is a transitional area of fuels reduction designed to slow fire movement, and Zone 3 is the area farthest from the home, where traditional forest management techniques are used.
Zone 1 is a non-combustible defense space of 30 feet from the structure. Man-made elements such as masonry walls, patios, footpaths and driveways create convenient fire barriers and buffer zones. Landscape plants should be carefully spaced, low growing and free of oils, and nothing within the first 5 feet of the structure and deck unless the building has non-flammable siding. Do not plant directly under windows or next to foundation vents as these are weak spots that can let fire into the homes interior. Prune and maintain plants and remove all dead material. Do not store firewood or other combustible materials in this zone. Ideally, remove trees to reduce fire hazards; however, if you do retain trees close to the home, consider them part of the structure and extend the distance of the entire defensible space accordingly. Remove any branches that overhang or touch the roof and prune trunk limbs 6 to 10 feet above ground. Remove native brush and grass within 10 feet of structures and native ladder fuels under trees. Remove all needles and other debris from the roof, deck and all gutters; irrigate plants and trees regularly and remove slash, chips and other woody debris.
Zone 2 is a non-sustainable fire area designed to reduce continuous fuels and the intensity of any fire approaching structures. Typically, it should extend to at least 100 feet from all structures. It also provides a safer environment for firefighters to protect homes. Remove stressed, diseased, dead or dying trees and shrubs. Remove all ladder fuels and prune tree branches to a height of 6 to 10 feet from the ground. Small groups of two to three trees may be left in some areas, but leave a minimum of 30 feet between the crowns. Keep shrubs at least 10 feet away from the edge of tree branches. This will prevent the shrubs from becoming ladder fuels. Reduce the continuity of fuels by removing dead material, thinning and spacing brush 2 1/2 times the mature height of the vegetation. The maximum diameter of the clumps themselves should be twice the mature height of the vegetation. Cut grasses to a maximum of 4 inches above ground.
Zone 3 is a reduced fuel area that extends to a least 200 feet, and which should provide a gradual transition from Zone 2 to areas farther from the home that have forest management objectives. By removing ladder fuels under trees, thinning and separating chaparral and removing all dead material, it is possible to proactively manage forest land to reduce wildfire intensity.
The second part of our approach is ignition-resistant structures. Simple building forms have less surface area are less expensive to build, more energy efficient and easier to protect from wildfires. One of the most susceptible features to wildfire are decks. All the components of a deck are generally made of wood, or wood composites. Ignition can easily occur when the radiant energy from the fire gets hot enough or burning embers land on it. Heat from the deck, may cause glass windows to break, permitting flames to enter the interior of the structure. Or, combustible siding can ignite; the end result is the same.
Roofing is one of the most important ways to protect a structure from wildfire. When wildfires become intense, the lofted embers become a significant cause of the fire spread. Concrete, slate and clay tiles are products that are noncombustible and are recommended in forest environments, although sealing is important for fire suppression.
The exterior walls of a structure are most affected by radiant heat, wood panels and boards are the most common and economical forms of siding, but they are readily combustible. Stucco is non-combustible, which makes it a very good material for high-hazard areas. Brick, stone and block are also materials inherently noncombustible and can have a high fire resistance rating.
Windows are one of the weakest parts of a structure with regard to fire. They provide only a partial barrier to fire and only for a short time. Today’s energy codes require glass to be double-glazed or Thermopane; double-glazed windows last approximately 10 minutes before cracking; tempered glass used in patio doors is more resistant.
The actions we take by building appropriate structures and properly caring for the surrounding environment can significantly reduce wildfire risk. An awareness of how each building component is affected by fire will allow the owner, architect or builder to reduce those weak spots.
These safety recommendations are made by professional fire fighters experienced in protecting homes from wildfire. They are not requirements nor do they take precedence over local ordinances. However, these pre-fire precautions can save a lot of post-fire heart ache. In a development with many homes, and a lot of densely populated empty lots a fire can devastate the homeowners, but hardly effect the unoccupied lot owners. If your home catches fire you lose your home, your belongings, maybe your life, but either way it is a traumatic experience that may take years to recover. The lot owner loses a few trees and bushes; creating very little incentive or concern in maintaining a fire safe condition. The bottom line is that Wildland Urban Interface homeowners are responsible for their own wildfire safety.
Paul Scrivens is a member of the Firewise Committee in the Ranch at Prescott.