Protecting Your Business from Wildfire – Fire Hazard Severity Zone Areas

Moderate Fire Hazard Severity Zone Areas

Moderate Fire Hazard Severity Zones have the following conditions:

  • The area has been designated as a moderate (or lower) hazard area by local or state authorities
  • Flat terrain with no grades greater than 9%
  • Limited wildland or conservation area exposure
  • No known history of wildfires in the area

Exception to building recommendations required for all zones:

Exterior siding is not restricted in this fire hazard severity zone

High Fire Hazard Severity Zone Areas

High Fire Hazard Severity Zones have the following conditions:

  • The area has been designated as a High or Significant hazard area by local or state authorities
  • Hilly terrain with grades that average 10%–20%
  • Has a shared border with a wildland or conservation area consisting of forested, shrub or chaparral vegetation within 100 ft of the site
  • A history of wildfires in the area

Building recommendations beyond those required for all zones:

Exterior windows, window walls, glazed doors, and glazed openings within exterior doors:

Use insulating-glass units with a minimum of one tempered pane, or glass block units, or have a fire resistance rating of not less than 20 minutes when tested according to UL 9 or NFPA 252. Glazing frames made of vinyl materials should have welded corners, metal reinforcement in the interlock area (i.e., at the horizontal meeting rail in a hung window, vertical member in a casement windows), and be certified to ANSI/AAMA/NWWDA 101/I.S.2-97 structural requirements.

Gutters

Incorporate a noncombustible gutter cover device. If the roof slope allows, the gutter cover device should be installed so that it is parallel to the plane of the roof slope (with steeper sloped roofs this may not be possible).

Exterior wall coverings should meet one of the following:

Combustible siding with an integral horizontal lap joint (tongue and groove, ship-lap, rabbeted bevel) is acceptable. The chinking in chinked-style log wall constructions should be fire rated. Panelized siding with a vertical ship-lap joint is also acceptable.

Ignition-resistant materials as defined in this document.

Noncombustible material in accordance with ASTM E 136.

Exterior personnel doors

Should be of noncombustible construction, or solid core having stiles and rails not less than 13/8-in. thick with interior field panel thickness no less than 11⁄4-in. thick, or should have a fire resistance of no less than 20 minutes when tested in accordance with NFPA 252 or UL 10.

Additional Parcel/Surroundings Recommendations beyond those required for all zones and the Moderate Fire Hazard Severity Zone:

High-piled storage of combustible material should not exceed 10 ft in height and should be located a minimum of 50 ft from the building.

Outdoor storage of large quantities of combustible and flammable liquids should be located greater than 50 ft away from the building or stored in detached noncombustible buildings.

Liquefied propane (LP) tanks should be located at least 50 ft from the building and other structures on the property. Acceptable alternatives include the following: (1) create a 10 ft noncombustible (rock, gravel, mulch or irrigated lawn) zone around the tank, (2) enclose the tank using noncombustible materials, or (3) unless otherwise prevented by the local AHJ, bury the tank following requirement in NFPA 58 or FM Global Property Loss Prevention Datasheet 7-55.

Buildings and structures

Set back a minimum of 30 ft from any property line adjacent to a national forest, state park, open space preserve or other protected wildland.

Fire hydrants

Should be located within 250 ft of the building connected to a reliable public or private water supply.

Extreme (Very High) Fire Hazard Severity Zone Areas

Extreme Fire Hazard Severity Zones have the following conditions:

  • The area has been designated as an extreme, severe or very high hazard area by local or state authorities.
  • Steep-sloped terrain with grades that average more than 20%.
  • Has a shared border with a wildland or conservation area consisting of forested, shrub or chaparral vegetation within 100 ft of the site.
  • A history of wildfires in the area.

Recommendations and those specified for the Moderate and High Fire Hazard Severity Zones should also be incorporated with those specified for this hazard zone.

Additional Building Recommendations beyond those required for all zones and the Moderate and High Fire Hazard Severity Zones:

Exterior wall assemblies

Clad with a noncombustible material in accordance with ASTM E 136, or with the exception of exterior- rated, pressure-impregnated fire-retardant- treated shakes or shingles, rated as an ignition- resistant material.

Floor projections

Maintain the fire resistance of the exterior walls, or the projections should be enclosed to the grade.

Attached decks, such as a balcony or porch, should meet one of the following criteria:

Consist of a noncombustible solid surface decking (e.g., lightweight concrete with noncombustible top surface), and enclosed on the underside of the deck with the enclosure material being attached to the underside of the deck support structure.

Consist of a combustible decking product that complies with the requirements of Chapter 7A of the California Building Code.

For slopes greater than 20%, a 6 ft tall noncombustible wall (e.g., concrete block, or stone) should be located on the downslope side of each attached deck, located between 20 ft and 30 ft from the outer edge of the deck and extending along the side of the building to which the deck is attached.

Exterior windows, window walls, glazed doors, and glazed openings within exterior doors

Use insulating-glass units with tempered glass, have glass block units, or have a fire resistance rating of not less than 20 minutes, when tested according to UL 9 or NFPA 80.

Additional Parcel/Surroundings Recommendations beyond those required for all zones and the Moderate and High Fire Hazard Severity Zones:

For buildings built mid-slope and the slope is greater than 20%:

For slopes between 21% and 40%, the defensible space recommendations should be increased to 150 ft in the downslope direction, following the recommendations established for the 30- to 100-ft zone.

For slopes greater than 40%, the defensible space recommendations should be increased to 200 ft in the down slope direction, following the recommendations established for the 30- to 100-ft zone.