There are several considerations a designer must take into account when using fire retardant treated (FRT) wood in a building design. A building’s construction type will dictate whether certain materials, including FRT wood products, are permissible in the the building. Additionally, depending on the type of FRT used, wood used in trusses may require a change in design values and reduction in connector capacity in the truss design. This guide provides an overview of the provisions a designer should make when using FRT wood in building designs. 

For additional information regarding FRT wood products applicable to the following, please see:

Step-by-Step: 

Intro

Introduction

  • Fire retardant treatments (FRT) were developed to be applied to building materials, such as dimension lumber (FRTW) and plywood, to reduce the ability of the wood to fuel a fire.
  • This treatment can allow FRT materials to be used as an acceptable alternative for building code requirements that specify noncombustible material in specific applications.
  • While reducing flammability, FRT may also degrade the structural properties of the wood.
  • Trusses designed with FRT lumber may require:
    • A reduction in the design values of the wood materials, and/or
    • A reduction in the capacity of connectors used
  • The following steps describe how to properly design trusses using FRT lumber.

Step 1

Accredited Product Certification Report

  • Obtain the Accredited Product Certification Report for the FRT lumber product
  • Make sure the report is from an accredited ISO/IEC 17065 Product Certification Body

Step 2

Reduction Values

  • The evaluation report should contain reduction values for lumber and connectors for the FRT product

Step 3

Apply to Truss Design

  • Most truss design software applies FRT lumber and plate reductions to the truss design via a reduction of the lumber and plate DOL values.
  • Example:
    • Typical roof DOL * Reduction value = Reduced DOL
    • 1.15 * 0.8 = 0.92
  • Verify that the reduced DOL has been used for the truss design.