Designing for Wildfire Resilience in the PNW

The devastating wildfires in Southern California serve as a stark reminder of the increasing risks posed by climate change. As wildfire threats grow, homeowners and architects must integrate fire-resistant strategies into residential design to mitigate structural loss. Mountain homes, particularly those nestled in the forested landscapes of the Pacific Northwest, require thoughtful planning to withstand these natural disasters.

Beyond personal safety, wildfire resilience has financial implications. Homeowners insurance and construction loans are becoming more difficult to secure for properties in high-risk areas unless fire mitigation strategies are incorporated. This makes fire-resistant design not just a safety measure but also a financial necessity in the future.

Many jurisdictions adopt the International Residential Code (IRC), which regulates the fire resistance of exterior materials, primarily addressing urban fire risks. However, some communities implement Wildland Urban Interface (WUI) codes, which enforce stricter fire safety measures tailored to forested environments. Many of fire-resilient strategies listed below are also good practice for improved thermal and indoor air quality building performance.

Our Lakeview Cabin Project is an Example of Wildfire Fire Resilient Design Practices. Exterior material is fiber cement, but has a wood like appearance.

6 Effective Wild Fire Resilient Building Design Strategies:

1. Roof Assembly Approach

There are 2 general common approaches to detailing a roof system with its relationship to thermal insulation and internal moisture control.

Vented Roofs:

• The most common and cost-effective roof design uses ventilation to manage moisture by drawing outside air from soffits to the ridge.

• However, during wildfires, embers can be sucked into these vents, igniting the roof structure.

• To mitigate this risk, specify roof vents designed to block embers. These products are often more expensive, and have less aesthetic choices than typical soffit vents.

Unvented Roofs:

• Unvented roofs offer superior thermal and moisture control performance by using nonpermeable insulation that do not rely on outside, and as an added benefit, reduces the risk of ember intrusion.

• Although there are several methods to achieve unvented roofs,  “Flash and Batt” insulation system is the most common. Which combines closed-cell spray foam tight against the roof sheathing with traditional batt insulation underneath.

Roof details illustrating the difference between roof venting strategies and their relations to wild fire resilience.

See Continuous Insulation for more benefits of unvented roof assemblies.

2. Fire-Resistant Exterior Cladding

Exterior siding material selection plays a significant role in wildfire resilience as traditional untreated wood siding, such as cedar, is highly combustible.

Some alternative solutions include:

• Intumescent paint can add fire resistance to natural wood siding but is costly, and some products can slightly change the appearance and texture.

• Pressure-Treated wood siding, process which involves removing moisture and air from the lumber and replaces with additives that are fire resistant. Often modifies the color of the wood, and is more expensive than untreated lumber. But can be a good option if real wood siding is the desired aesthetic.

• Non-combustible options like steel or fiber cement siding are naturally more fire-resistant than untreated wood and can meet IRC Class A rating for combustible materials. Many metal and fiber cement products mimic the appearance of wood, combining aesthetics with fire resilience and lower maintenance costs. Often the most cost effective option.

Example of lap and board and batten fiber cement siding used as a wildfire resilience strategy.

3. Fire-Resistant Deck Materials

Decks are highly vulnerable as embers can land on the surface and start a structural fire.

• Wood decks, like siding, can be treated with intumescent paint, though at a high cost.

• Non-combustible materials, such as Class A-rated wood composite or fiber cement decking, provide better protection.

4. Fire Sprinklers

• Fire sprinklers help contain both internally and externally ignited fires.

• Considerations include local water pressure as pumps maybe needed to increase pressure when in use, and fire water storage.

• Aesthetic preferences - a recessed ceiling sprinklers offer a minimal look opposed to standard visible sprinkler head.

• While effective at putting out fires, sprinklers may cause water damage to interior finishes. But that can be easily replaced if your structure is still standing.

5. Airtight Building Envelopes

• A well-detailed and comprehensive weather-resistant barrier (WRB) and airtight building envelope helps prevent outside embers from infiltrating the home. This is achieved by paying special attention to continuous WRB at risk areas at window and doors, wall to roof connections, and exterior penetrations such as mechanical venting.

• Heat Recovery Ventilators (HRVs) and Energy Recovery Ventilators (ERVs) filter incoming air, acting as an additional barrier against fire embers. These systems also improve indoor air quality by filtering out outside wild fire smoke and pollutants.

6. Defensible Space and Site Planning

• Creating a physical buffer zone free of combustible materials, such as brush and trees, around a structure’s edge can significantly reduce fire risk. This defensible space is essential for protecting homes in wildfire-prone areas.

• Local regulations may have suggestions for defensible space design. Refer to your local codes.

• During design and site planning, the buildings placement on the site should consider fire resilience alongside traditional factors like views, access, and solar orientation. By choosing a naturally less wooded site and maintaining a defensible perimeter can significantly reduce fire risk, while maintaining as many trees as possible.

Many high-performance, sustainable building practices also contribute to wildfire resilience. While these strategies often involve upfront costs, they enhance long-term safety, durability, and insurability in fire-prone areas. Investing in fire-resistant design is not just about protecting a home—it’s about securing peace of mind in an increasingly unpredictable climate.