Siding and the Wildland Urban Interface

The United States has seen a shocking increase in wildfire in recent years. Along with the increase in wildfires is an increase in new homes within the Wildland Urban Interface (WUI). The WUI refers to the area between developed and undeveloped land. By building in these wildfire prone areas, humans are only furthering the threat of severe wildfire by adding additional fuel.

With that in mind, it is no surprise that new codes and regulations have been put in place. These codes ensure that any new development in these sensitive areas will follow protocols for fire safety.

We will look further at what the WUI is and why it is at risk. Additionally, we will discuss what you as a builder, architect, or homeowner need to know before building in a WUI zone.

What is the Wildland Urban Interface

The WUI is an area in which human development intermingles with undeveloped wildland or vegetative fuels that are both fire dependent and fire prone ( Many Americans have been led to believe that wildfire does only harm to forest land, when in fact most forests and natural areas rely on fire. Wildfire has been a natural  aspect of the landscape for far longer than human existence, making much of America’s landscape a fire-adapted ecosystem. Our landscapes depend on recurring fire to renew the forests and rangeland.

As a society, we have only very recently begun to understand the way in which our landscape needs fire. For the past hundred years, natural resource agencies have been suppressing wildfires using a 10:00 AM rule. This rule strives to extinguish every wildfire by the next morning. However, as a consequence of this suppression, fuels and underbrush that are meant to burn as part of a natural fire regime have instead been accumulating and creating a huge fuel load. This, combined with climate change and an increase in human-caused fires due to more people living in the WUI, has resulted in a fire season that lasts almost all year, with fires that cause more damage than ever before.

With these factors taken into consideration, authorities deem communities within the WUI as at-risk communities. An at-risk community is a community within the WUI, or a group of homes and other structures within, or adjacent to, federal land. These are areas where conditions are susceptible to a large-scale wildland fire, thereby posing a serious threat to human life or property.

Understanding WUI Codes

In attempt to protect lives and reduce costs associated with the losses from WUI zone wildfires, many areas are now adopting WUI Codes that are specifically for mitigating these risks. The standards of such a code will vary depending on the scope that a community is willing to adopt and enforce. Most WUI codes will include the following categories:

  • Structure Density and Location
  • Building Materials and Construction
  • Vegetation Management
  • Emergency Vehicle Access
  • Water Supply
  • Fire Protection

The California Building Code (CDC) requires that the exterior wall covering or wall assembly of new structures in a WUI zone comply with one of the following:

  1. Noncombustible material
  2. Ignition-resistant material
  3. Heavy timber exterior wall assembly
  4. Log wall construction assembly
  5. Wall assemblies that have been tested in accordance with the test procedures for a 10-minute direct flame contact exposure test set forth in ASTM E2707 with the conditions of acceptance shown in Section 707A.3.1
  6. Wall assemblies that meet the performance criteria in accordance with the test procedures for a 10-minute direct flame contact exposure test set forth in SFM Standard 12-7A-1

What this means is that if you are building a new structure in a WUI zone, you will need to familiarize yourself with local WUI building codes and ensure you are meeting the necessary requirements.

Why Nakamoto Forestry’s Shou Sugi Ban is a Good Option

At Nakamoto Forestry, our shou sugi ban (or yakisugi) wood siding has been charred, meaning it’s a naturally ignition-resistant material. Our products have been lab tested for flame spread and we have current certifications for many of our products. 

A flame spread rating measures how fast and how far a flame spreads over a material. Flame spread rating range from an index of 0-200 with zero representing no ignition. Class A is the best rating and corresponds to an index of 0-25 and is WUI compliant. Next is Class B, this has an index of 26-75 and is still a WUI compliant material. Class C is not WUI compliant with an index of 76- 200.

Our flame spread results on our unoiled wood are as follows:

MaterialClassFlame Spread Index
Suyaki™ Class A 25
Gendai™Class B30
Pika-Pika™Class B35
Sugi™ Class B30

Many of our products with an oil coating have also been tested and certified as Wildland Urban Interface compliant. Additionally, we offer two types of fire retardant that can be applied prior to the oil treatment to further increase fire resistance, making our siding an easy choice for both safety and beauty!

Please reach out to our sales team for further information on our products’ flame spread ratings and for assistance in finding the right option for your project.

Feature image source.

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