The Stucco Manufacturers Association has released a document called "Wildland-Urban Interface."

WUI is where human development and undeveloped land meet. Structures in the WUI zone face a higher potential to succumb to wildfires. The WUI zone is more widespread than most people know; almost 10 percent of the United States falls in a WUI zone, which grows yearly. According to the U.S. Fire Academy, 38 percent of all U.S. housing is in a WUI zone. While almost all states are impacted by WUI, the top five are California, Texas, Florida, North Carolina, and Pennsylvania.

PROTECTION: Cement plaster (stucco) is noncombustible according to Building Code Section R202 (passing ASTM E136) and meets California Building Code Chapter 707A (Exterior Covering). Cement plaster (stucco) is a preferred exterior siding material by CALFIRE and Building Departments in WUI zones. At 7/8 inch thickness, cement plaster provides a one-hour fire-rated exterior cladding on framed walls spaced 16 inches on-center (2021 IBC Table 721.1(2) Item 15-1.3 & 15-1.4) and ceilings applied at 5/8 of an inch thickness for joists spaced 16"on-center (2021 IBC Table 721.1(3) Item 13-1.2). The OSFM (Office of State Fire Marshall) also publishes a WUI-approved products/systems manual. Category 8140 covers exterior sidings.

Fire protection requires attention to several elements, including windows, roofs, and vegetation control around the house. Simply putting noncombustible stucco on the structure may not be adequate protection against a wildfire. A continuous, seamless, noncombustible cladding should extend from the foundation to an approved roof edge. Cement plaster (stucco) can provide significant wall and ceiling protection with proper detailing at the foundation, eaves, parapets, and areas such as exposed framing on the underside of balconies or decks.

The Stucco Manufacturers Association provides this brochure as a WUI guide for stucco details to protect framed structures from exposure to wildfire events. Foam plastic may be used under the cement plaster with an approved UL, ASTM, or NFPA fire testing report or as the building department allows. One-coat stucco is noncombustible and offers fire protection when installed per the ESR (Evaluation Report) and manufacturer's recommendations. The SMA recommends applying the one-coat stucco basecoat at a 1/2-inch thickness for enhanced performance. The finish coat for one and three-coat stucco may be cement-based or acrylic-based. Coated foam decorative shapes such as quoins, cornices, or window surrounds can be adhesively applied over the cement basecoat of stucco without compromising fire protection.