by Nick Gromicko, CMI®
Wildfire mitigation is the implementation of a variety of precautionary measures to protect a building from a wildfire. Homes in heavily forested, dry areas should be
inspected periodically and modified appropriately, especially during dry spells, to ensure their fire resistance. Grasslands and chaparral also experience serious fires.
While the following information is not exhaustive, and strategies and laws vary by region, homeowners and inspectors can use it as a rough guide.
Systems and components to check include the following:
- Unscreened vents are problematic because they can allow the entry of stray, airborne embers into the home even if the wildfire itself is some distance away. Flames can also enter through vents if embers ignite nearby vegetation or debris, especially accumulated pine needles. Vents are typically located at the attic, crawlspace, and the lower portion of the roof. Homeowners may install a metal insect screen to protect their houses against this danger. Chapter 7A of the California Building Code, for instance, recommends the use of non-combustible wire mesh screen with ¼-inch or 1/8-inch openings. Openings as small as 1/8-inch do a better job of preventing embers from entering the vent, but holes this small can also restrict air flow through the vent. Specialty vent screens are available that prevent the passage of embers without restricting air flow, such as one design that incorporates intumescent paint that swells when exposed to heat. Vent designs that incorporate plastic components do not comply with these requirements.
- Combined with surrounding combustible debris, fencesare an excellent fuel source for a wildfire. Practice the following:
- Use metal instead of wood. Climbing vines growing on a chain link fence are attractive, protect the homeowner’s privacy, and pose a minimum fire hazard.
- If you must use wood, use fire-resistant lumber. Heavy, thick wood is also better than thin wood, which will ignite more quickly.
- Do not attach the fence to the building if it’s made of a combustible material.
- Clean flammable debris, such as leaves, pine needles, trash and dead plants, from the base of the fence. If the fence posts catch fire, they can serve as a wick that will eventually ignite debris at the post’s base. When the fence is no longer standing, this wind-driven, flaming debris can be more easily carried toward the building.
- Do not store firewood near the fence.
- Decks are a significant source of fuel, and an ignited deck threatens a large portion of the attached structure. Consider the following:
- The thicker the wood, the better. While thick wood will ultimately release a great amount of heat, it will take longer for it to ignite, giving fire crews a better chance at putting the fire out before it spreads.
- Combustible materials, especially firewood, should not be stored under raised decks. Any flammable vegetation should be cleared from beneath the deck. Stones may be used to prevent the growth of vegetation.
- Deck boards should not be loosely placed, as flames may move from the lower to the upper surface through these cracks. Embers can also become trapped there. Homeowners should be careful not to install the boards too tightly, however, as this will limit water drainage and encourage decay.
- Limit the number of glass doors and windows that separate the deck from the structure. Heat from a deck fire can cause the glass to fail and permit flames to enter the house.
- If windows break, the fire will easily enter the house. This can happen under the barrage of flying embers and debris, which typically rain down on the area surrounding a fire. Glass may also break when it’s subjected to extreme heat as the wildfire nears; the visible glass heats and expands faster than the portion protected by the window pane, which will cause small, growing cracks to form at the edges of the window. Also, if the window frame ignites, the fire can quickly spread to the interior of the building. Prevent this outcome in the following ways:
- Install dual-pane windows. The outer pane will protect the inner pane, allowing it to adjust more gradually and uniformly to the heat, minimizing the chance that it will crack.
- Install tempered glass. While more expensive than standard, annealed glass, tempered glass resists extreme heat better than its alternatives. Tempered glass can be identified by a small etching in a corner of the pane.
- Install insect screens. Under exposure to radiant heat, insect screens act as heat shields. Bronze screens are more effective than aluminum screens. However, none will significantly protect against flame impingement.
- Create a custom cover for the window that may be installed quickly prior to evacuation. Windows may also be equipped with roll-down shutters.
- Clean vegetation and flammable debris from the windowsill.
- Replace decayed wood around the window, as it will ignite at a lower temperature than sound wood.
- If siding ignites, it will provide the fire with a rapid vertical path to other vulnerable parts of the building’s exterior. Siding should be non-combustible and sheathed. Fill in any gaps will caulk.
- Roofs and gutters are vulnerable components because they can collect falling embers for hours before and after the wildfire passes through the area. Practice the following strategies:
- Use a Class A fire-rated roof covering.
- Remove flammable debris from all areas of the roof, especially nooks and crannies that serve as collection points.
- Skylights are a weak point, and the same precautions should be followed for them as for ordinary windows.
- Clean out birds’ nests. Birdstops may be installed to prevent future nest-building.
- Install metal flashing where two sloped roof surfaces meet, as this is a natural weak point.
- Clean the gutters. Ignited debris in the gutters can allow the flames to bypass the fire-resistant roof and enter the roof’s underside, or even the attic. Pay close attention to second-story gutters, as their inaccessibility allows them to be overlooked. Gutter guards should be installed and periodically inspected to ensure that they are still in place.
- Trees and vegetationshould be cut back from the home's perimeter. Many forested residential jurisdictions enforce strict codes for this type of mandatory property maintenance. Also:
- Plants should be clustered so they don’t allow the fire to follow a continuous path to the house.
- The smaller the plant, the better, especially those near the house. Larger trees are generally not as much of an issue as small brush, but trees can radiate a tremendous amount of heat toward the house if they catch fire.
- Construct slash piles.
- Do not let plants touch the siding, as their flames will allow the vertical spread of flames.
- Regularly water live plants.
- Remove dead plant matter.
- Avoid the use of flammable mulch or bark as plant bedding.
- No part of a tree should be within 6 feet of the house.
- Trees can be placed at the edge of the property to steer winds and flaming debris away from the house.
In summary, numerous aspects of buildings and their surrounding property can be modified in order to mitigate the risk of damage by a wildfire.