Aftermarket Treatment or Coating of Trus Joist Products for Fire Resistance

We are often asked if Weyerhaeuser engineered lumber products can be treated with a fire retardant. Our position, below, on aftermarket treatment can also be found in Fire-Rated Assemblies and Sprinkler Systems Guide, TJ-1500 on page 15.

Can Weyerhaeuser engineered lumber products be treated with a fire retardant?

Weyerhaeuser does not recommend the application of fire retardants to engineered lumber products using pressure treatment or dipping. Reductions to the structural properties and impacts on dimensional stability may occur and those reductions have not been evaluated. The application of any fire retardant treatment by pressure treatment or dipping voids Weyerhaeuser’s product warranty. Topical, non-pressure treatments suitable for wood products can be applied subject to limitations stated in Weyerhaeuser's Technical Bulletin TB-310. However, Weyerhaeuser does not evaluate their compatibility or durability or make any claims as to their effectiveness. Consult with the manufacturer of the fire-retardant treatment for data on the compatibility, durability and effectiveness of topical treatments.


Topical Coatings that do not void Weyerhaeuser warranty for use with ELP products per the limitations of TB-310 are not prohibited.  However, Weyerhaeuser does not provide any guarantee of compatibility or effectiveness and will not issue a letter approving these coatings.  It is up to the coating manufacturer and applicator to verify compliance with TB-310.

In addition, when considering any coated products for use as an alternative to Fire-retardant-treated (FRT) wood, it is important to understand that while many coatings may provide a Class A flame spread rating, that alone is not equivalent to FRT and these products may not be permitted for exterior walls in Type III construction.  To be approved as an alternative to FRT material, the coating should be evaluated by an accredited agency such as the International Code Council Evaluation Service (ICC-ES) for use on engineered wood products.

 The requirements for a coated product to be considered an alternative to FRT wood include:

  •  Meets the performance requirements in IBC Section 2303.2 (extended ASTM E84 -30 min. test)
  • Demonstrates effectiveness after accelerated aging conditions – including exposure to water, freezing, and UV light to ensure the coating will remain intact and effective throughout the construction cycle and the life of the structure.
  • Demonstrates potential corrosiveness similar to untreated wood or requires corrosion-resistant metal hardware/connectors.
  • Demonstrates no reduction in mechanical properties of the wood product due to the coating both before and after exposure to conditions of elevated moisture and temperature.
  • Is applied through a process with established quality control and oversight by an accredited agency.

ICC-ES has developed acceptance criteria to evaluate and ensure that FRT alternatives meet these requirements. AC47 pertains to structural composite lumber.  The coating manufacturer should be able to supply this documentation as well as assurance of compatibility with engineered wood in compliance with TB-310.

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