Fire Resistant Homes

Home Builder’s Guide to Construction in Wildfire Zones

Technical Fact Sheet Series No.4
FEMA 
Federal Emergency Management Agency
U.S. Department of Homeland Security
This document was prepared by: 
click to view entire report
URS Group, Inc
200 Orchard Ridge Drive, Suite 101
Gaithersburg, MD 20878

Exterior Walls

Purpose

To provide guidance on the design and construction of exterior walls in wildfire zones. Guidance pertains to both new and existing buildings.

Key Issues

Exterior walls are susceptible to wildfire flames, conductive heat, and radiant heat. Flames and heat can ignite combustible wall coverings. When exterior walls ignite, the fire can spread to other components of the building such as the roof, soffit, windows, and doors, resulting in substantial damage to or total loss of the building.

Wind-borne embers and firebrands are also sources of ignition. Embers can become trapped in cracks in walls, window openings, and door trim boards and ignite combustible materials. Wind-borne firebrands can ignite wall coverings.

Guidance for New Buildings

For the best protection, ensure that exterior wall coverings are noncombustible or fire-resistant and not susceptible to melting. Concrete, fiber-cement panels or siding, exterior fire-retardant- treated wood siding or panels, stucco, masonry, and metal are recommended materials. With these coverings, the covering itself should not ignite and fuel the fire. Examples of the types of coverings that are not recommended are wood siding that is not fire-retardant-treated, vinyl siding, metal siding susceptible to warping, and an exterior insulation finish system.

Ensure that the entire wall assembly has a fire-resistance rating tested in accordance with American Society for Testing and Materials (ASTM) E119. Although the above recommended types of coverings provide an initial barrier to flames, heat may pass through the covering and ignite underlying wall components. A fire-resistance rating indicates how long under test conditions a wall assembly can prevent flames and heat from passing through the wall. A minimum fire-resistance rating of 1 hour is recommended, but higher ratings provide greater protection. (concrete wall panel building system has a 4 hour fire rating)

Comply with the requirements of the fire-rated assembly, including using the exact type of materials, configuration, and attachment used during the testing that established the rating.