Structure and Site Hazard Assessment

Factor 2: Roof Cleanliness

Accumulation of combustible debris on a roof increases fire hazard. The fire resistance of most roofing materials is reduced when needles and debris burn on the roof surface.

Factor 3: Building Exterior

With the exception of the roof, siding material is the structural component most vulnerable to fire. An interface fire involving the forest and vegetation surrounding a building will produce flames that can start the exterior on fire.

The high winds that often accompany wildfires can carry airborne firebrands and embers. Lodging in and against the structural exterior, these firebrands can easily become fires. Untreated wooden shake or shingle siding provides no fire protection for the building. Vinyl siding is vulnerable to fire exposure. It quickly melts, exposing areas of the building exterior where sparks and embers might lodge.

Factor 4: Eaves, Vents, and Openings

While vents perform the important function of removing trapped moisture from attics, soffits and crawlspaces, they are ready-made openings that can allow heat and embers to enter a building and ignite it. Open eaves (exposed rafter ends unenclosed by fascia and soffits) increase structural fire hazard because more of the under-eave area is exposed to heat and embers. Under-eave soffit vents placed close to the exterior wall also increase structural fire hazard as heat and embers travel up exterior walls and directly into soffit vents.

All openings should be properly located and screened with corrosion-resistant, 3 mm wire mesh.

Factor 5: Balcony, Deck or Porch

Stilt construction allows fire to get under overhangs and ignite the building. The fire hazard is further increased if vegetation, debris, or stored combustibles accumulate under the overhang. Closing in balconies and decks and building them with flame-resistant materials affects the hazard rating.

Slotted deck surfaces can allow needle litter to accumulate below the deck, increasing the fire hazard. There should be access to these spaces so that needle litter can be easily removed.

Factor 6: Window and Door Glazing

Window glazing that fractures and collapses creates an opening in a building exterior that allows firebrands to enter the building so that it burns from the inside. Avoid having concentrations of fuels within 10 metres of windows and glass doors.

Large windows, often used in interface homes to maximize view, are more vulnerable to fracture and collapse than smaller windows or multiple-pane windows.

Triple or double (thermal) pane windows are more fracture- and collapse-resistant than are single pane windows. Tempered glass provides more safety than plate glass does, but it is unlikely that an interior will ignite from thermal radiation through intact plate glass.

Factor 7: Location of Woodpiles and Combustibles

Firewood, building material, or other combustible debris piles and wooden storage shacks are all serious fire hazards. These items will ignite and burn intensely. Homeowners often do not consider the potential fire hazard of these items and must be encouraged to clean up or relocate such accumulations of fuel farther away from the building. Where combustibles are located downslope from a building, the hazard to buildings is increased.

None or 10m from the building

Important note: Any combustible building (garage or carport) or assembly (fence or trellis) should be included in the assessment of Factor 7.

Factor 8: Setback from Edge of Slope

The slope of the ground affects fire behavior and the rate of spread. Fire will burn more rapidly uphill than on a flat or level surface. Consider the location of the building on flat or rising ground and its position on the slope. Convective heat and firebrands from burning fuels on the slope below the building can readily ignite buildings located on the mid to upper portion or crest of a hill.

Structures located on a slope must feature entirely non-combustible exteriors and sound design principles or they will be especially vulnerable to fire. Structures located at the crest of a hill can be protected somewhat by setback provisions. A single-storey building should be set back 10 metres from the crest of the slope. Taller buildings will need proportionally greater setback distances.

Special factor: Structures located on a slope that feature an entirely non-combustible exterior and that have been built using FireSmart design principles will get a zero point rating.

0
Adequate


6
Inadequate

Factor 9: Forest Vegetation (Overstory) within 10m of Structure

Crown fire in the forest vegetation presents a significant hazard to adjacent buildings. Buildings may ignite by radiant heat transfer when the fire is burning all around it, or when firebrands land on the building before the wildfire arrives.

Crown fire is most likely to occur and spread rapidly in dense coniferous forest. Mixedwood forests are less likely to sustain crown fire, although firebrand transport from pockets of coniferous trees can threaten buildings. Deciduous forests are unlikely to sustain crown fire, especially after leaf flush.

The photos here illustrate the various types of forest overstory. Using them as a guide, please select that which is best representative of the forest overstory within 10m of your structure.

Factor 9: Forest Vegetation (Overstory) 10-30m from Structure

Now select that which best represents the type of forest vegetation found 10-30m from your structure.

Factor 10: Surface Vegetation within 10m of Structure

Surface vegetation includes grasses, herbs, shrubs, dead and down debris (logs, branches, and twigs), and immature trees up to 2.5 metres in height. Concentrations of surface fuels will sustain high-intensity surface fires and can initiate crown fires.

A surface fire can ignite interface buildings by direct contact with the building exterior or nearby flammable materials. Untreated surface fuels can also support and spread small accidental ignitions from the site to the surrounding continuous forest.

Treatment of surface vegetation is most critical within 10 metres of buildings. Aggressive removal of all surface fuels and replacement with non-combustible or trimmed lawn is recommended.

The photos below illustrate various types of surface vegetation. Using these as a guide, please select that which best represents what lies within 10m of your structure.

Factor 10: Surface Vegetation 10-30m from Structure

Treatment of surface vegetation in the area between 10 and 30 metres from buildings is also important. Removing all or most understory vegetation or accumulated ground fuels is recommended.

Please select that which best represents what lies 10-30m from your structure.

Factor 11: Ladder Fuels 10m from Structure

Ladder fuels are shrubs, immature trees, and branches extending near the ground (e.g. within 2 metres) that give surface fires a pathway to the upper canopies of the trees. Trees with branches extending near the ground (within 2 metres) have ladder fuels. Removal of ladder fuels reduces the likelihood of crown fire development.

Absent: ladder fuels are considered absent if fewer than 25 percent of tress on site have ladder fuels closer than two metres to the ground.

Scattered: ladder fuels are scattered if 25-75 percent of trees on site have ladder fuels closer than 2 metres to the ground.

Abundant: ladder fuels are abundant if more than 75 percent of trees on site have ladder fuels closer than 2 metres to the ground.

Factor 11: Ladder Fuels 10-30m from Structure

Now select that which best represents the type of ladder fuels 10-30m from your structure.