USA: Building a wildfire-resistant home: Codes and costs-special on doors

- Dec 02, 2018-

  • Wildfire disasters will be more common if unmitigated home development continues in the wildland-urban interface.

  • A new home built to wildfire-resistant codes can be constructed for roughly the same cost as a typical home.

  • Costs vary for retrofitting an existing home to be wildfire-resistant, with some components such as the roof and walls having significant expense. Some of these costs can be divided and prioritized into smaller projects.

  • Technology and standards exist today that will make communities safer. Cities, counties, and other jurisdictions can implement wildfire-resistant building codes to reduce their vulnerability to wildfire.

Introduction

This study finds negligible cost differences between a typical home and a home constructed using wildfire-resistant materials and design features. Decades of research and post-fire assessments have provided clear evidence that building materials and design, coupled with landscaping on the property, are the most important factors influencing home survivability during a wildfire.

Today, one-third of all U.S. homes are in the wildland-urban interface, the area where flammable vegetation and homes meet or intermingle. And with more than 35,000 structures lost to wildfire in the last decade, more communities should consider adopting building codes that require new home construction to meet wildfire-resistant standards.

Exterior walls

Exterior walls are especially vulnerable from exposure to flames or prolonged exposure to radiant heat, such as from burning vegetation or a neighboring home. These exposures can potentially ignite combustible siding products. Some plastic siding products (e.g., vinyl) can also melt, exposing underlying sheathing. Wind-blown embers can accumulate in gaps or pass through openings around windows and doors. Glass in a window or door can break from radiant heat or flame contact, exposing the interior of the home. Wildfire-resistant siding and installation design features, tempered glass in windows, wildfire-resistant doors, and weather-stripping can reduce home vulnerability. The relative importance of each of these items varies depending on home-to-home spacing and location of vegetation on the property. Siting on the property relative to topography and typical wind directions can also be important factors in determining necessary external wall mitigations.

Wildfire-resistant construction for exterior walls was $12,190 (25%) less expensive than the typical home, with the cost savings resulting from the difference in using wildfire-resistant fiber-cement siding as compared to cedar plank siding. Fiber cement siding is already a common siding option in many regions and several styles options mimic the look of wood siding. While the change in siding reduced the cost of the wildfire-resistant home, cost increases for other exterior wall features are $5,370 (29%) more than typical exterior wall features. Retrofitting the exterior walls (including windows and doors) on the model home totaled $40,750. Depending on neighboring home spacing, not all retrofitting activities may be necessary, but several of these activities will have added benefits such as improved energy efficiency (e.g., multi-pane windows) and reduced maintenance.

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