Wildfire risk planning and defense

Home Ignition Zone

The concept of the home ignition zone was developed by retired fire scientist Jack Cohen in the late 1990s, following some breakthrough experimental research into how homes ignite due to the effects of radiant heat. The HIZ is divided into three zones.

The below zoning has been adapted and internationalised from the United States NFPA wildfire defensible space guidelines.

Immediate Zone

The home and the area from 0 to ~1.5m (0 to 5 feet) from the furthest attached exterior point of the home is considered a non-combustible area. This is the most important zone to take immediate action on as it is the zone most vulnerable to embers. Begin with the house itself then move into the landscape section of the Immediate Zone.

• Clean roofs and gutters of dead leaves, debris and pine needles that could catch embers.
• Replace or repair any loose or missing shingles or roof tiles to prevent ember penetration.
• Reduce embers that could pass through vents in the eaves by installing 3cm (1/8 inch) metal mesh screening.
• Clean debris from exterior attic vents and install ~3cm (1/8 inch) metal mesh screening to reduce embers.
• Repair or replace damaged or loose window screens and any broken windows Screen or box-in areas below patios and decks with wire mesh to prevent debris and combustible materials from accumulating.
• Move any flammable material away from wall exteriors – mulch, flammable plants, leaves and needles, firewood piles – anything that can burn. Remove anything stored underneath decks or porches.

Intermediate Zone

This zone starts at ~1.5 and goes to 9m (5 to 30 feet). It begins at the furthest exterior point of the home. Employing careful landscaping or creating breaks that can help influence and decrease fire behavior

• Clear vegetation from under large stationary gas tanks.
• Create fuel breaks with driveways, walkways/paths, patios, and decks.
• Keep lawns and native grasses mowed to a height of 10cm (4 inches).
• Remove ladder fuels (vegetation under trees) so a surface fire cannot reach the crowns. Prune trees up to 2 to 3 meters (6 to 10 feet) from the ground; for shorter trees do not exceed 1/3 of the overall tree height.
• Space trees to have a minimum of 5.5m (18 feet) between crowns with the distance increasing with the percentage of slope.
• Tree placement should be planned to ensure the mature canopy is no closer than 3m (10 feet) to the edge of the structure.
• Tree and shrubs in this zone should be limited to small clusters of a few each to break up the continuity of the vegetation across the landscape.

Extended Zone

This zone begins at 9m - 30m (30- 100 feet) and extends out to 60m (200 feet). The goal here is not to eliminate fire but to interrupt fire’s path and keep flames smaller and on the ground.

• Dispose of heavy accumulations of ground litter/debris.
• Remove dead plant and tree material.
• Remove small conifers growing between mature trees.
• Remove vegetation adjacent to storage sheds or other outbuildings within this area.
• Trees 9m (30 feet) to 18m (60 feet) from the home should have at least 4m (12 feet) between canopy tops.
• Trees 18m (60m) to 30m (100 feet) from the home should have at least 2m (6 feet) between the canopy tops.

Note: some trees/foliage types are far more flammable than others. 'Gummy', high-resin species will burn hotter and so should be spaced further apart. The distances here are given as minimums.