{"id":203385,"date":"2023-02-10T10:00:47","date_gmt":"2023-02-10T15:00:47","guid":{"rendered":"https:\/\/www.constructionspecifier.com\/?p=203385"},"modified":"2023-01-26T14:57:03","modified_gmt":"2023-01-26T19:57:03","slug":"building-for-better-fire-resilience-in-wui-zones","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/building-for-better-fire-resilience-in-wui-zones\/","title":{"rendered":"Building for better fire resilience in WUI zones"},"content":{"rendered":"
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Photo courtesy ROCKWOOL North America Photo courtesy <\/em><\/span><\/figcaption><\/figure>\n

By Rick Roos<\/strong><\/p>\n

Wildfires continue to make headlines and the long-term prognosis is concerning, as experts forecast more of the same in coming years. Yet, building in wildland urban interface (WUI) zones continues at a fast pace. WUI zones are areas of transition between unoccupied land and human development, where structures and other human development meet or intermingle with undeveloped wildland or vegetative fuels. Communities adjacent to and surrounded by wildland are at varying degrees of risk from wildfires. WUI zones are not limited to densely forested areas; they can just as easily be inhabited areas close to brush or grassland. Dry, hot, and windy conditions\u2014together with an ignition source\u2014increase the risk of fire quickly spreading in any WUI zone.1<\/sup><\/p>\n

Why are people still building, and rebuilding in WUI zones? Primarily for affordability. These zones continue to expand because of ongoing population growth and urban sprawl, driving significant housing development into environments in which fire can move readily from forests and grasslands into neighborhoods. It is important to note new builds in WUI zones are primarily residential, but commercial builds in these regions are not uncommon. The principles for building for optimal fire resilience are the same in both scenarios.<\/p>\n

The Good Haus<\/strong><\/p>\n

The Good Haus, a zero net energy (ZNE), near passive, high-performance house in California\u2019s Sierra Nevada foothills (see the section on page 4 titled \u201cCould This Be the Perfect House for Rural California?\u201d) exemplifies good design inclusive of consideration to fire resilience. Atmosphere Design Build principals Mela Breen and David Good (the home\u2019s designer and builder) were drawn to rural northern California for different reasons: the natural beauty of the area and a desire for an active outdoor lifestyle that made the region ideal for their business and home. Their goal was to build a high-performance NZE home, which meant designing an exceptionally high performing building envelope. Central to its objective and in keeping with Passive House ideals, the plans called for a super-insulated home to ensure efficiency, occupant comfort, and building durability. An airtight and efficient thermal envelope would also dramatically reduce heating and cooling demands and permit a modest photovoltaic (PV) solar array to meet those demands. In keeping with the values of their practice, Breen and Good sought to incorporate sustainable, environmentally conscious building materials to support a healthy home with a smaller impact on the planet.<\/p>\n

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Wildland urban interface (WUI) zones continue to expand due to population growth and urban sprawl, driving significant housing development into environments where fire is more prone to move readily from forests and grasslands into neighborhoods. <\/span>Photo courtesy <\/em><\/span><\/figcaption><\/figure>\n

However, construction of homes in WUI areas must subscribe to a higher standard of fire resilience to increase the odds of preserving structures and providing occupants additional time to find safety. Breen and Good understood this and made certain their material selection and the assembly design supported their needs for optimal fire resilience, as well as thermal performance. They chose to go beyond state\/local code requirements to ensure their investment in their forever home would have greater protection in the event of fire.<\/p>\n

The decision to look beyond state\/local code requirements was a smart one, as the focus is often placed on materials alone, with the thought that if noncombustible siding materials are selected, the rest of the home is safe. However, fire protection is much more complicated than that.<\/p>\n

What does the code say?<\/strong><\/p>\n

Building codes set minimum requirements for many construction features, such as fire protection. They outline the basic requirements a home must meet to be up to code, such as the performance expectations for allowable materials and assemblies, and the required technical standards for construction, such as those which have been adopted into the code and published by ASTM and the National Fire Protection Association (NFPA).<\/p>\n

The bottom line: codes are not enough; building or rebuilding a home with the greatest possible fire resilience is voluntary. One\u2019s approach to this is predicated on a concerted effort to learn and understand best practices to address fire resilience.<\/p>\n

Take a holistic approach<\/strong><\/p>\n

Specifying fire-resistant materials for the building envelope is a good place to start. However, best practices today demand more. This includes considering fire safety at the start of the design process\u2014it cannot be an afterthought\u2014and taking a holistic approach to building in WUI zones. What does a holistic approach look like? Architects and builders need to think differently about the house design, especially if they are rebuilding after a fire. How can one design a better building to provide a greater opportunity to stop fire from penetrating the structure and, in the worst-case scenario, buy additional time for occupants to get to safety? It requires, in part, understanding how homes catch fire. Then, it is important to look at materials to determine whether they are combustible or noncombustible, if they are ignition or fire-resistant, and whether they have low or high flame-propagation rates. The next step is a challenging one: taking this information into account while designing fire-resistant assemblies.<\/p>\n

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Figure 1 A fire-resistant roof assembly includes not just the surface product, but also the underlayment, sheathing, insulation, joists, and other components that go into a roof system. <\/span> Illustrations courtesy ROCKWOOL North America <\/em><\/span><\/figcaption><\/figure>\n

Canada\u2019s National Research Council (NRC) published a new WUI guide, National Guide for Wildland-Urban Interface Fires<\/em>, in July 2021, which provides detailed insight about WUI fire characteristics and associated hazards. For example, \u201cthe descent and landing of burning embers downwind, ahead of a burning fire, is referred to as spotting or, in the case of the WUI, ember rain.\u201d2<\/sup> Since embers from wildfires fall, start by looking at the roof assembly, then walls, any exterior structures, and then to the outside landscaping around the home.<\/p>\n

Roofs<\/strong><\/p>\n

A fire-resistant roof assembly includes not just the surface product, but also the underlayment, sheathing, insulation, joists, and other components that comprise a roof assembly. ASTM E108, Standard Test Methods for Fire Tests of Roof Coverings<\/em>, Class A-rated surfaces such as clay, concrete, slate, and many types of asphalt or metal are good surface selections, but builders also need to consider components beneath the surface material. For example, noncombustible roof boards can improve the roof assembly\u2019s fire resilience. There are noncombustible options, including several stone wool products. Builders should look for products with a flame-spread index of zero and a smoke-developed index of zero, which can improve a roof assembly\u2019s ability to withstand conditions during a wildfire.<\/p>\n

Other measures for creating a fire-resistant roof assembly include:<\/p>\n