Updated fire-resistance-rated wood assembly guide available

Leesburg, Va. — With the International Code Council’s 2018 International Building Code (IBC) available for enforcement, the American Wood Council (AWC) released an update to Design for Code Acceptance (DCA) 3 – Fire-Resistance-Rated Wood Floor and Wall Assemblies.

The publication describes how interior and exterior wood-frame walls and wood I-joist floors can be used to meet building code requirements for fire-resistance-rated assemblies. Wood-frame assemblies are common for many reasons, including ease of use, affordability, low environmental impact, and energy-saving performance. The DCA 3 guide further increases the ease of use by laying out the fire-resistance ratings of a variety of wood-frame wall, floor, and ceiling assemblies.

The primary update to the guide is the addition of exterior wall-floor intersection detail solutions in Type III construction. Example details for code-compliant exterior wall-floor intersections in Type III-A platform construction are provided in Figures 1A through 1C. The addition of these figures clarifies that rim boards are part of the floor assembly and do not need to be fire-retardant treated in Type III platform construction. An example detail for an exterior wall-floor intersection in Type III-B construction is also provided.

For occupancies such as retail stores, offices, multifamily residential buildings, as well as other commercial and industrial uses, building codes require wall and floor/ceiling assemblies to be fire-resistance rated in accordance with standard fire tests. Depending on the application, wall assemblies may need to be rated for exposure from either one side or both sides. Exterior walls are required to be rated both for interior and exterior fire exposure where the wall has a separation distance of 10 feet or less. For exterior walls with a fire separation distance greater than 10 feet, the required fire-resistance rating applies only to exposure from the interior.

The solutions and example details outlined in DCA 3 are based on compliance with national model building codes. That said, some state and local building code amendments may require rating for exposure from both sides of exterior walls, regardless of fire separation distance. Code recognition of one- and two-hour rated wood-frame wall systems is also predicated on successful fire and hose steam testing in accordance with ASTM E119 – Standard Test Methods for Fire Tests of Building Construction Materials.

Today, wood-frame assemblies are used in architectural designs for many reasons. To fully realize the advantages of wood in buildings that require fire-resistance-rated assemblies, a variety of wood-frame wall and floor/ceiling assemblies have been successfully tested and shown to meet either a one-hour or two-hour fire resistance rating. Ultimately, the DCA 3 guide helps designers achieve fire-resistance requirements by providing details of tested assemblies, along with corresponding STC and IIC sound ratings for floor/ceiling assemblies.

Download Design for Code Acceptance (DCA) 3 – Fire-Resistance-Rated Wood Floor and Wall Assemblies at https://awc.org/codes-standards/publications/dca3.

By: Bradford Douglas, P.E., Vice President of Engineering; and Jason Smart, P.E., Manager of Engineering Technology, American Wood Council