skip navigation
Share this:

Firefighting in the Wildland Inter-Urban Interface

Firefighting in the Wildland Inter-Urban Interface

With the height of the state’s fire season months away, some experts are warning that current conditions are signaling an active fire season for 2019: precipitation is lower than normal while temperatures are higher, the soil has a low-moisture content, and, most concerning of all, 51 fires have already taken place this year—the majority in Western Washington. In fact, the National Interagency Coordination Center has rated most areas west of the Cascades at above normal for significant wildfire risk for the months of April-July.

Throughout the West, fire has been part of the forest life cycle for centuries with regular, low-intensity fires removing dry and dead underbrush and trees but leaving healthy plants relatively unscathed. Humans, however, have severely disrupted this cycle, both through fire management strategies and increased development in lands that were formerly wild, creating what is known as the wildland-urban interface (WUI). 

The Wildland-Urban Interface

The US Forest Service (USFS) defines the wildland-urban interface (WUI) as “an area close to or intermingled with forests and grasslands, with at least one home per 40 acres.”

According to a 2018  study led by reasearchers with USFS and the University of Wisconsin-Madison, one-third of all homes in the US are located in the WUI, and the footprint of the WUI itself has grown by 33% from 1990 to 2010 primarily due to new housing development. In Washington State 2.2 million homes are exposed to the threat of wildfire according to the 10-year strategic plan for wildland fire protection from the state’s Department of Natural Resources (DNR).

Over the past century, federal and state agencies have aggressively suppressed fires that would have otherwise burned at lower intensity and cleared out the built-up underbrush. This has resulted in forested lands crowded with dead, sick, or weakened plants—a dense mass of vegetation that is extremely vulnerable to fire. It is under these conditions that the high-intensity, massive, and particularly devastating wildfires occur, such as the one that leveled the town of Paradise, CA. Complicating this factor even further is the WUI zone. The Washington State Society of American Foresters (WSAF) listed some reasons why in its position statement Addressing the Threat of Wildfire in the Wildland-Urban Interface:

Firefighting tactics on wildland fires differ considerably from those in structure firefighting, as access to homes and availability of water are often limited in WUI zones, fuels are not confined, and weather is a larger factor. Combining wildland fire fighting and structure protection during extreme wildfire conditions is costly and dangerous.


Properly prepared, a WUI can provide firefighters a defensible area from which to suppress wildland fires. The same 2009 memo from the WSAF identified three broad areas that can boost fire prevention.

1. Increase responsibility on part of the homeowner to ensure properties are prepared: This can be accomplished through use of fire-resistant materials in new construction or retrofits, by maintaining a perimeter of defensible space around the home (free of dead vegetation), and by reducing fuel ladders (low-lying vegetation like grasses or branches) that help fires jump into tree tops.

2. Increased investment in firefighting at a statewide level: This includes building a statewide corps of reliable (i.e., paid) structural and wildland firefighters and directing more state resources to training and equipment specific to wildland firefighting. Recently, the Washington State Legislature approved $45.5 million in wildfire prevention funding, a small decrease in the $55 million wildfire and forest health request the Commissioner of Public Lands Hilary Franz submitted to the legislature in late 2018.

3. Local governments invest in developing Community Wildfire Protection Plans (CWPP): These plans identify WUIs and target resources towards wildfire response, community preparedness, and specific risk-reduction activities. Over 60 CWPPs and supporting material are available for download at DNR’s Community Wildfire Protection webpage.

Land Use

There are benefits to coordinating land use and fire planning, such as when codes:

  • establish landscaping regulations that promote defensible fire perimeters,
  • encourage use of fire-resistant construction materials,
  • require adequate access to emergency vehicle through minimum road width, and
  • incentivize risk-reduction features in new developments.

Wildfire-resistant construction is guided by the International Code Council’s International Wildland Urban Interface Code (IWUIC), the National Fire Protection Association’s Standard for Reducing Structure Ignition Hazards from Wildland Fire (NFPA 1144), and the California Building Code Chapter 7A, though the IWUIC is the most frequently referenced. Sample IWUIC recommendations are as follows:

  • Ignition-resistant building materials and building techniques.
  • Driveway access for emergency vehicles.
  • Landscape plans for new residences and subdivisions that provide defensible space.
  • Sprinkler systems on structures over 5,000 sq. ft.
  • Restrictions on outdoor burning, outside storage, etc.

Some Washington local governments have adopted the IWUIC through ordinances (adjusted via local amendments), including:

  • Chelan Municipal Code 15.06—Appoints the Planning and Building Department as the enforcement agency and requires building code officials to consult with the appropriate fire marshal or fire districts.
  • Kittitas County Code Ch. 20.10—Identifies all county land as within the WUI and creates three zones based on risk, applying varying levels of regulation to each, from requiring sprinkler systems to requiring structures be constructed from non-combustible materials and surrounded by a defensible space.
  • Yakima County Code Ch. 13.12—Allows both the Building Official and the Fire Marshal to enforce the code throughout the county and categorizes areas within the WUI by risk factor, then regulates these accordingly.
  • Wenatchee Municipal Code Ch. 3.36—Creates a primary and secondary WUI zone with the primary zone being immediately adjacent to the vulnerable undeveloped areas and the secondary zone extending 1,500 feet from that boundary. Requirements for development in each zone is based on anticipated fire risk.

Other Risk-Mitigation Activities

Local governments can also promote risk mitigation activities in WUIs and throughout the jurisdiction through a variety of activities:

Additionally, the complexity and scale of wildland firefighting, including how to service WUIs, requires considerable cross-jurisdictional cooperation. Chelan County’s draft CWPP (2018) involved input and cooperation from seven county fire districts, five cities, three unincorporated communities, countless county agencies, the DNR, USFS, the National Park Service, the Bureau of Land Management, and county residents. The plan combines and incorporates existing CWPP plans from jurisdictions in the county into a single, countywide wildfire risk assessment with mitigation recommendations.

What fire prevention activities does your jurisdiction offer? Please email me.

MRSC is a private nonprofit organization serving local governments in Washington State. Eligible government agencies in Washington State may use our free, one-on-one Ask MRSC service to get answers to legal, policy, or financial questions.

Photo of Leah LaCivita

About Leah LaCivita

Leah joined MRSC as a Communications Coordinator in the fall of 2016 and manages MRSC’s blog and webinar training program, in addition to developing website content.