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How To Construct and Prepare Buildings in Wildfire Zones

How To Construct and Prepare Buildings in Wildfire Zones

Wildfires have become an increasing threat over the past two decades, which means it’s more important than ever to prepare for the possibility of wildfires — especially if you live in a wildfire zone.

While the average number of fires has declined slightly over the past 30 years, the acreage affected has increased significantly. The average annual acreage burned in the 1990s was 3.3 million, but since 2000 the figure is more than double that at 7 million acres per year. Nationwide, 89,210 structures were destroyed by fire between 2005 and 2020.

When constructing buildings in a fire-prone area, it’s important to use fire-resistant materials and create defensible space.

Table of Contents

What Areas Are Most Impacted By Wildfires?

Fires can strike anywhere. But significant fires (those that burn at least 10 acres) are far more prevalent west of the Rockies than elsewhere in the United States. Hotspots include northwest Utah, northern Nevada, southern and western Arizona, and southern New Mexico. But the biggest fire danger in recent decades has been in California.

More than 40% of the acres burned in 2020 — as well as the majority of the 17,000-plus structures burned — were in the Golden State. The danger has been particularly acute in Southern California: The counties of Los Angeles, Kern, San Diego, Riverside, and San Bernardino all had between 21 and 52 state and federal disaster emergencies from 1950 to 2018, more than any other California counties.

How To Construct Fire-Resistant Buildings

Constructing a fire-resistant building all starts with using the right materials. You can also retrofit existing buildings with safer materials. Consider using some of the following.

Use Fire-Resistant Materials

Fire-resistant building materials

  • ICF Concrete — Insulated Concrete Forms (ICFs) are made of expanded polystyrene blocks that stack together. They help prevent fire by slowing the conduction of heat from one side of the wall to the other. ICF walls are known to withstand fire for four hours or more.
  • Fire-Resistant Bricks Bricks have a high fire-resistance rating since they are usually made in a fire kiln, and they are classified as non-combustible material because they are made with clay.
  • Steel or Metal — A steel or metal roof is extremely fire resistant and, as a Class A-rated material, is a good choice for a wildfire-resistant ICF home. It insulates against sparks, preventing a fire from spreading to your home.
  • Gypsum Drywall — Fire-rated gypsum drywall is more fire-resistant because it contains glass fiber. The gypsum is about 21% water, so when gypsum drywall is exposed to fire, the water is slowly released as steam, which helps it hold up longer to fire exposure.
  • Glass — Fire-resistant glass or dual-paned glass windows will double the time it takes a fire to enter your home. While the glass will still shatter, multiple panes offer an extra layer of protection. Tempered glass can help, too, but window framing is also important, and internal reinforcement bars can protect vinyl frames from sagging and giving way.
  • Wood — Fire-resistant wood contains chemicals that can remain stable under high temperatures. These types of wood significantly slow the spread of fire and can resist ignition.

Create Defensible Space

How to create a defensive space

Beyond using the right materials, creating a defensible space in the event of a wildfire is essential. Plan out safety zones around the building and select plants that grow low to the ground and are high in moisture, with low sap and resin content. Consider fire-resistant vegetation such as aloe, bush honeysuckle, cotoneaster, currant, ice plant, shrub apples, and sumac.

Zone 0

The area nearest to your home, from 0 to 5 feet, is the most important of all defensible spaces. It is known as the Immediate or Ember-Resistant Zone. In addition to removing combustible material such as vegetation and outdoor furniture from this area, clear roofs, rain gutters, and decks.

Zone 1

Referred to as the Lean, Clean, and Green Zone, this area extends 5 to 30 feet from where your home is: where your garden or yard might be. Some things to think about in this zone include trimming trees to keep branches at least 10 feet from other trees, removing dead branches and pine needles from your yard, and pruning flammable shrubs and other plants near windows.

Zone 2

This area, called the Reduce Fuel Zone, may extend to or even beyond your property line: 30 to 100 feet from your home. The goal here is not to eliminate vegetation but to reduce the size of flames and the chances of fire advancing. To this end, it’s helpful to keep grass to 4 inches high or lower and create both horizontal and vertical space between shrubs and trees. Keep all tree branches at least 6 feet off the ground.

Protect High-Risk Areas

Ways to fireproof your home

A tight building envelope is one that allows very few air leaks. This is an important element to keep in mind when constructing a fire-resistant home because air feeds fire, and openings to the exterior can allow heat and even fiery embers to enter the home. Pay special attention to the following areas.

Roofs

Wind-blown debris from fires can accumulate on roofs and in gutters and can be ignited by embers blown in from the fire source. To reduce the danger of your roof catching fire, make sure your home has a Class A-rated roof. Roof materials are rated as Class A, B, C, or unrated, with Class A providing the best fire-proof performance. Examples of Class A roofing materials are slate, metal, concrete, and clay.

Keep embers out by covering exterior attic vents and vents under the eaves with metal mesh with openings no larger than ⅛ of an inch.

Windows

Intense heat from a wildfire can cause windows to break, allowing burning embers to enter a home. Single-paned and large windows are vulnerable. Install multi-paned windows to provide more protection from breakage and fire intrusion. Consider using fireproof shutters or tempered safety glass.

Decks and Patios

Decks and patios can be a source of fuel for fires if ignited. Avoid storing logs, gasoline, timber, or other combustible materials under the deck. Use fire-resistant decking products such as composite boards or fire-resistant wood.

Walls

Wood is commonly used in the interiors of homes, and it is highly flammable. Use stucco, gypsum, brick, or ICF concrete walls to help add a layer of fire protection for your home.

Fire Protection Systems

Investing in a fire protection system can help you detect fires before they spread and help reduce the potential damage to your home. Installing smoke and fire alarms, sprinkler systems, or fire sensors can help you act quickly to minimize the damage.

How Wildfires Occur

A fire needs three things: fuel, oxygen, and heat. Dry conditions during the summer provide ideal conditions for fires to start and spread, which is why most wildfires start during the summer and early fall. In fact, all but one of California’s 20 largest wildfires started between June and October.

Factors That Can Cause Wildfires

Wildfires can be ignited by humans or natural causes including lit cigarettes, campfires, or lightning. Nearly 85% of fires stem from human activity. Some of the ways human actions spark wildfires include:

How Fires Spread

How wildfires can spread

Wildfire can spread and damage buildings in several ways:

  • Convection — Fire heats the air around it, causing it to rise and carry burning embers along with it to new locations.
  • Conduction — Wildfires that spread by conduction do so via direct contact between materials. Burning material can come into contact with combustible objects, and conductive material such as metal can spread heat to combustible items, causing them to catch fire.
  • Radiation — Heat released from fire travels by electromagnetic waves and can cause combustible material to ignite on contact.

Wildfire Home Preparedness Checklist

It’s essential to prepare for a disaster such as a wildfire to avoid or at least minimize damage to a building. Fire-resistant materials are important, but so is proper maintenance.

Wildfire home preparedness checklist

Wildfire home preparedness checklist button

Creating a fire-resistant building starts at the construction stage. From using land clearing equipment to create a defensible space to adding fire-resistant roofing and multi-paned windows, you can minimize the chances of significant damage from a wildfire in the future.

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