A minimum defensible space of 100 feet is recommended for homes and outbuildings on flat ground—up to 200 feet or more on sloped sites. Defensible space is commonly divided into three zones.
Defensible space is divided into three zones. Thank you Idaho Firewise for this information.
Zone 1 – Immediate Zone, Your Buildings and the First 5-feet
The Immediate Zone includes both the home and the area 0 to 5 feet out from the furthest attached exterior point of the home.
In Zone 1, take steps to eliminate ignition potential. Use gravel mulch in this zone and use only the most fire resistant plant material – e.g. short, high moisture content plants such as flowering annuals or perennial succulents hardy to your USDA zone. The home itself should be constructed using ignition resistant building materials. Screen any openings with 1/8″ metal mesh to block embers from collecting inside the home or under decks. Be aware of anything that could be flammable in this zone such as leaf litter, dead vegetation, pine needles, even items such as a possibly flammable doormat or hanging baskets made from fibrous material.
Zone 2 – Intermediate Zone, From 5- to 30-feet (Clean and Green)
Zone 2 should consist of a well-maintained greenbelt. Surround islands of fire resistant plant material with rock or brick retaining walls and/or well-watered turf. Keep lawns mowed to a height of four inches and clear vegetation regularly to keep the landscape ‘lean, clean, and green’. Water plants and lawns appropriately to keep them from becoming dry. Trees and shrubs in this zone should be limited to small clusters to break up the continuity of the vegetation across the landscape. Consider using hardscapes, dry river beds, or water features as a means of beautifying the landscape as well as making it more fire resistant. Tree placement should be planned to ensure the mature canopy is no closer than ten feet to the edge of the structure.
Zone 3 – Extended Zone, From 30- to 100-feet and Beyond (Pruned and Groomed leading to Natural Vegetation)
Keep in mind that your property line may end prior to 100 feet. In these instances working collaboratively with your neighbor is important in helping to protect multiple properties.
In Zone 3, remove highly flammable vegetation and replace it with fire resistant species. Maintain Zone 3 by thinning and pruning, removing dead and dying plants, and periodic fertilization and irrigation, as needed. Place firewood and propane tanks on gravel or concrete pads at least 30-feet away from structures and surround them with non-flammable fencing. Trees 30-60 feet from the home should have at least 12 feet between canopy tops. Trees 60 to 100 feet from the home should have at least 6 feet between canopy tops.
For more information on hardening your home, refer to the NFPA publication Reducing Wildfire Risks in the Home Ignition Zone.