Hardening Exterior Walls & Siding with Wildfires in Mind

Exterior walls and siding are key components of your home’s defense against wildfires. Fire-resistant walls can block or slow the spread of flames, while non-combustible siding materials help reduce the risk of ignition from radiant heat or embers.

This article discusses effective ways to harden your home’s exterior walls and siding, ensuring they’re ready to resist the challenges posed by wildfires.

Choosing Fire-Resistant Siding Materials

The materials you choose for your exterior siding can make a significant difference in protecting your home from wildfires. Some siding materials are more resistant to heat and flames, making them better suited for homes in wildfire-prone areas.

Fiber Cement Siding: Fiber cement siding is made from a blend of cement, sand, and cellulose fibers. It is highly fire-resistant, non-combustible, and can withstand extreme temperatures without igniting. Additionally, fiber cement siding is durable and available in a variety of styles, including options that mimic wood.
Stucco: Stucco is another excellent choice for fire resistance. A three-coat stucco system over a metal Lath provides substantial fire protection, as it’s both non-combustible and resistant to heat. Stucco also offers an airtight seal, which helps prevent embers from entering cracks or gaps.
Brick or Stone Veneer: Brick and stone Veneer are fire-resistant materials that provide a robust barrier against flames. These materials are less likely to ignite from radiant heat and can withstand embers that land on the surface. However, brick and stone veneer should be installed with a proper fire-rated backing material for optimal protection.
Metal Siding: Steel and Aluminum Siding are non-combustible and very resistant to fire. Metal siding can also help deflect radiant heat away from the home. While metal can transfer heat, it doesn’t ignite, making it a good option for homes in high-risk fire areas.

Sealing Gaps and Openings

Embers can penetrate through small gaps, crevices, or cracks in exterior walls, increasing the risk of interior fires. Properly sealing these areas can prevent ember intrusion and protect your home from ignition.

Fire-Resistant Caulk: Use fire-resistant caulk to seal gaps around windows, doors, and any other openings in your siding. Look for caulk labeled for exterior use that can expand and contract with changing temperatures.
Metal Flashing: Install metal flashing around windows, doors, and other vulnerable areas to block embers and reduce the risk of fire spreading. Metal flashing is durable, non-combustible, and can help direct water and debris away from your walls.
Weatherstripping and Fire-Resistant Foam: Apply fire-resistant weatherstripping and foam around doors, vents, and other openings. These materials help seal the perimeter of doors and windows, reducing the risk of ember penetration and improving Energy Efficiency at the same time.

Fire-Rated Wall Assemblies

Fire-rated wall assemblies can provide added protection by creating barriers that resist flame spread and heat transfer. Consider these options to further harden your exterior walls:

Two-Hour Fire-Rated Walls: In wildfire-prone areas, a two-hour fire-rated wall assembly can provide increased fire resistance. This type of wall is often constructed with a combination of fire-resistant Sheathing, Insulation, and Fire-Rated Drywall to contain flames and prevent them from spreading quickly.
Sheathing with Fire-Resistant Insulation: Use fire-resistant sheathing materials, such as Gypsum board or cement board, for extra protection. Adding mineral wool insulation, which is naturally fire-resistant, further enhances the wall’s ability to withstand high temperatures and prevent flames from spreading.
Exterior Wall Cladding Systems: Fire-resistant exterior cladding systems can offer another layer of protection. Cladding systems often consist of a non-combustible material that is installed over a fire-rated sheathing. Some systems are specifically designed to prevent the spread of flames and minimize heat transfer to the underlying wall structure.

Using Fire-Resistant Paints and Coatings

Fire-resistant paints and coatings can provide an additional level of defense by reducing the flammability of siding materials.

Intumescent Paint: Intumescent paint expands when exposed to heat, creating a char layer that insulates and protects the underlying material. This type of paint can be applied to wooden siding to reduce its flammability, but it may need periodic reapplication.
Fire-Retardant Sprays: Fire-retardant sprays can be applied to a variety of siding materials to slow the ignition process. These sprays are especially useful for wood-based siding, which is more susceptible to fire. Check the product’s reapplication schedule, as fire-retardant treatments may lose effectiveness over time.
Heat-Reflective Coatings: Heat-reflective coatings can be applied to siding to reduce heat absorption and deflect radiant heat away from your home. This can be particularly beneficial for metal and stucco siding, helping to keep surface temperatures lower during a wildfire.

Managing Surrounding Vegetation and Defensible Space

Vegetation around your exterior walls can contribute to fire spread if it isn’t managed properly. Proper defensible space practices can reduce the likelihood of flames reaching your home’s walls. See our previous article for more detail as well.

Create Defensible Zones: Establish defensible space zones around your home, with Zone 1 (0-5 feet) being the most critical area. Keep this zone clear of any plants or combustible materials that could ignite and spread flames to the siding.
Remove Flammable Mulch: Avoid using flammable mulch like wood chips in areas immediately surrounding your home. Instead, use non-combustible options such as Gravel, rocks, or Concrete to create a firebreak along the base of your exterior walls.
Trim Vegetation Regularly: Regularly trim back any bushes, shrubs, or trees that grow close to your walls. Avoid having plants touching your home, as they can easily ignite and transfer flames to your siding. Trees should be trimmed so that branches are at least 10 feet away from your walls and roof.

Additional Resources

Hardening your exterior walls and siding is essential to reducing your home’s vulnerability to wildfires. For further information on fire-resistant materials and techniques, check out these resources:

Firewise USA Program: The Firewise USA program, sponsored by the National Fire Protection Association (NFPA), provides resources and guidelines for reducing wildfire risks to your property. Visit the Firewise USA Program for more information on hardening your home.
Ready for Wildfire: The California Department of Forestry and Fire Protection (CAL FIRE) offers extensive resources on wildfire preparedness, including guidelines for fire-resistant building materials. Visit Ready for Wildfire to learn more about protecting your home from wildfires.
CalFire: The California Department of Forestry and Fire Protection has live maps to track wildfires and advice on prevention measures. Highly recommended resource: https://www.fire.ca.gov/

Wrap-Up

By using fire-resistant materials, sealing gaps, and managing the surrounding vegetation, you can significantly reduce your exterior walls’ vulnerability to wildfires. A well-prepared home, reinforced with non-combustible siding and fire-resistant barriers, is more likely to withstand the intense heat and ember storms that accompany wildfires.

Combining these structural improvements with a defensible space around your property creates a comprehensive wildfire protection plan, ensuring that your home is as resilient as possible. With careful planning and regular maintenance, you’ll be better equipped to protect your property and loved ones from the dangers of wildfires.