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  • Defensible Space Frequently Asked Questions (FAQ)

    defensible space guidelines
    In light of climate change and associated drought conditions, there may be a need to create defensible spaces around structures. These are some of the most frequently asked questions about defensible space and how it relates to property development and fire prevention. 

    Print / Download printable version of the Frequently Asked Questions (FAQ)
      

    What is defensible space?

    Defensible space is a concept of maintaining an area around structures free and clear of flammable materials to mitigate the potential damage from wild and accidental fires. Creating a defensible space can also decrease the chance of fires spreading from private property to nearby wilderness areas.

    In short, a defensible space provides a buffer around a structure from fire and a place for firefighters to maximize structure protection when a structure is in harm from a fire. 

    For more detailed information, consult the International Wildland-Urban Interface Code (IWUIC). Currently, this code is only adopted and enforced on Mt. Lemmon but may be used as guidance to property owners elsewhere, subject to other adopted restrictions related to grading and protection of certain flora.

    Why is defensible space important for development on Mt. Lemmon?

    Mt. Lemmon is subject to the 2018 International Wildland-Urban Interface Code (IWUIC). As a result, greater scrutiny is placed on development for fire-resistant driveway design, ample water pressure, fire-resistant building materials, and a requirement that property owners maintain a defensible space of at least 30’ surrounding structures. Trees are allowed to remain in defensible space provided the crowns are at least 10’ apart.

    In Pima County, why is only Mt. Lemmon subject to the International Wildland-Urban Interface Code?

    Appendix F of the IWUIC classifies most of our native, protected plants growing in the Sonoran Desert as naturally fire-resistant. Drought-tolerant, deeply rooted trees (native palo verde, mesquite, ironwood, acacia) and plants containing large volumes of moisture in proportion to their overall volume (our saguaro, barrel, prickly pear and cholla cactus) will burn at a lower intensity, and generally grow with canopy already at least 10 feet apart. However, dead vegetation of any type can become fuel and may be removed per below guidelines.

    What healthy vegetation can be removed?

    All non-native plants may be removed without limitations on your property. These include commonly occurring grasses like buffelgrass, fountain grass, and other plant species like tamarisk and onionweed. In fact, all buffelgrass SHOULD be removed from your property.

    Can dead vegetation be removed and trees be trimmed?

    Careful and selective removal of dead vegetation is allowed. Fallen or dead limbs, dead plants, and pack rat nests composed of dead material may be removed within 30 feet of any structures.  
     
    Trees can be trimmed to maximize 10 foot separation from each tree canopy to each other within 30 feet of a structure. Trimming should be minimal and not harm or impact the survivability of the tree. It is recommended to use maintained mechanical equipment to promote clean cuts to the branches. If possible, chippers can be used to mulch the trimmed branches to provide mulch to the remaining vegetation. This can keep the vegetation cool during the summer high temperature months and provides nutrients to promote vegetative survivability. 
     
    Every effort should be made not to change the natural grade or unnecessarily disturb healthy vegetation when accessing or removing dead plant material.

    Can I remove vegetation beyond the 30 feet discussed above?

    Non-native plants (such as buffelgrass) are allowed to be removed beyond 30 feet of a structure. Further trimming, or complete vegetation removal requires consultation with the County Codes and may require permits prior to removal. The County Codes provide flexibility to property owners on how they may remove vegetation due to fire concern. However, each property needs to be evaluated by the appropriate County Department(s).  
     
    The applicable County Codes to consider are:
    • Title 16 Flood Plain Management (Chapters 16. 12 through 16.30) administered by the Pima County Regional Flood Control District (RFCD) (724-4600), and 
    • Title 18 Zoning (Chapters 18.61, 18.72 and 18.81) administered by Development Services (724-9000).
     
    Some questions to ask are:
    • Is my property in a Floodplain?
    • Does Regulated Riparian Habitat impact my property?
    • Are there protected Plant Species I should be concerned about removing?
    • Do I need a permit?
    • Can I use mechanical equipment to remove understory by grading?
     
    Generally speaking, most flat properties may be graded up to 70% of the site provided that:
    • 30% of the site is dedicated and protected as natural open space,
    • Saguaros, ironwood trees and safeguarded species are preserved, and
    • Mapped Regulated Riparian Habitat and other wash areas are undisturbed.
     
    Properties containing steep slopes (having an elevation rise of 7.5 feet over a horizontal run of 50 feet) have further limits of overall grading, but may allow up to 50% grading provided a permit is obtained in advance of any work.

    What else can be done to create defensible space and keep structures safer from fire?

    To assist with achieving defensible space around structures, the following flammable items should be removed from the 30-foot perimeter of a structure: 
    • Leaf piles
    • Dry grass
    • Wood piles
    • Lawnmowers
    • Gas grills
    • Propane or gas tanks
    • Lawn furniture
     
    Property owners should inspect the structure’s rain gutters for leaves and needles and clean out the debris on an as-needed basis. It is recommended to remove trees too close to structures and replace the removed tree in a location that would not endanger the structure in a fire. 
     
    Consider building with fire-resistant materials. Resilient structures are less susceptible to ignition from embers – the primary cause of structure loss. A resilient structure, for instance, is constructed of less flammable materials, has a class “A” roof (not a cedar shake roof or siding), and has metal screens over eave vents and under decks.
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