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Kevin Hanneman

Specifying and Using Fire Retardant & Preservative Treated Wood

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Our good friends at the Western Wood Preservers Institute have created some excellent resources to assist Industry professionals in gaining an increased understanding of how fire retardant & preservative treated wood products are made and used. In particular, there are two (2) courses which can be taken entirely online to help build upon your existing knowledge base. The 2 courses are available at (click link to visit site):

  1. Fire Retardant Treated Wood Specification & End-Use
  2. Preservative Treated Wood Specification & End-Use

The online courses includes sections on types of preservative & fire retardant treatments and required levels of retention as dictated by end-use application, desired service life, and exposure conditions; specifying with American Wood Protection Association Use Categories; preserved wood and building codes, including current issues concerning treated wood in residential and commercial construction; and an overview of Best Management Practices (BMPs).

Learn more about Western Wood Preservers Institute by visiting their website at

“It needs to be PT & FRTW.”

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One of the purposes of this blog is to help increase reader’s knowledge and understanding of what we do in the Wood Treatment Industry and how that impacts you and your customer(s) so you can make the best and most informed decisions as it pertains to fire retardant and preservative treated wood products.

What exactly are you looking for?

Lately I’ve been seeing a lot of quotes where customers tell me they’re looking for treated wood that must be “PT & FRTW”. The use of acronyms and deciphering people’s handwritten notes based of their limited understanding of my job is and always will be challenging, but that’s what we have Q&A for, right?

When this situation happens —

I ask something along the lines of, “Are you looking for a combo system or are you asking for code compliant fire retardant treated lumber or plywood?”

The customer usually responds saying, “I’m not sure, I just know the material needs to be PT & FRTW.”

My intent in sharing this with you is to help clarify what the acronyms PT and FRTW represent (where applicable), and to bring some common understanding to these two terms.

Code Speak & Definitions.

What does PT & FRTW mean? For starters, PT could mean a lot of things. Pressure-treatment, preservative treatment, or physical training. Considering my job and probably yours since you’re reading this, we’ll focus on pressure treatment and preservative treatment as possible correct choices.

As for FRTW, it’s crystal clear to me what is being asked for – Fire Retardant Treated Wood (FRTW). Let’s define FRTW per section 2303.2 of the International Building Code (IBC) so we’re all on the same page.

Fire-retardant-treated wood is any wood product that, when impregnated with chemicals by a pressure process or other means during manufacture, shall have, when tested in accordance with ASTM E84 or UL 723, a listed flame spread index of 25 or less and show no evidence of significant progressive combustion when the test is continued for an additional 20-minute period. Additionally, the flame front shall not progress more than 10-1/2 feet (3200 nm) beyond the centerline of the burners at any time during the test.”

With the customer asking for Fire Retardant Treated Wood, this singles out a specific product that has been treated via pressure process to perform in such a manner as detailed by the code. In the world of wood treatment, there are a variety of (a) processes and/or methods involved in wood treatment that deliver a set of (b) benefits enabling treated materials to be used in specified and/or code required application(s).

Briefly, it’s important to note that the AWPA C20 & C27 specification standards of yesteryear have been replaced by the AWPA UCS (Use Category System). Fire Retardants fall under Commodity Specification H. The precise Use Category for Interior Fire Retardant is UCFA and exterior FRTW is UCFB (exterior FRTW). The UCS further defines compliant fire retardant treatment process by “protectants” based off their ingredients providing the designations of: FR-1 (P-49) and FR-2 (P-50) respectively. So with a little knowledge of the product being evaluated for use, or in determining what solution(s) best work for your customer, a little knowledge of the code and applicable standards go a long way!

Arriving at a compliant solution.

After a few short questions with my beloved customer looking for “PT & FRTW”, it was determined that they simply wanted FRTW lumber & plywood. It is important to note that there are products available that are both preservative & fire retardant treated [the BENEFIT] which by code is done by pressure impregnation [the PROCESS].

We’ll dive into combination fire retardant & preservative systems in another post coming soon.

You want an ALTERNATIVE?

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 Alternative Materials & Methods and the Emergence of Spray-Applied Fire Retardants.

With the emergence of spray-applied fire retardants and other topically applied systems, I feel that it’s only pertinent to discuss how these products, which represent a viable alternative to traditional Fire Retardant Treated Wood, can be approved for use in specified and/or code required applications.

Alternative Materials, Design and Methods of Construction and Equipment is outlined in Section 104.11 of the IBC, and provides an alternative method for meeting building code requirements via an alternative material, in accordance with the alternative means and methods provision of the code, provided the product meets the same performance requirements as whatever you’re replacing. It’s also crucial that the alternative material/product is not lesser in quality, strength, effectiveness, fire resistance, durability and safety.

The Scenario.

For my example, I have a customer that wants to use fire treated plywood featuring a fire-retardant coating system instead of the traditional “pressure impregnated” FRTW or FRT plywood. In other words, this alternative product would not be FRTW (not pressure impregnated) but could serve as a code compliant alternative to FRTW if we can provide the required supporting documentation.

If you’re confused, don’t be. This process is simple once you understand: (a) what the code is asking for and (b) how to provide the answers/documentation to your local AHJ so they can make their determination.

At the end of the day, while this provision in the code exists, it’s up to the Code Official (AHJ) to approve or deny the alternative material/method for use based on the supporting data provided (e.g. Research Reports, Testing Data). If you want your materials to get approved for use, then you’d better do your homework and have your ducks in a row.

What the code says.

Let’s get into action and first understand what our requirements are by referencing Section 2303.2 of the IBC: Fire Retardant Treated Wood.

Fire-retardant-treated wood is any wood product, that when impregnated with chemicals by pressure process or other means during manufacture, shall have, when tested IAW ASTM E84 or UL 723, a listed flame spread index of 25 or less and show no evidence of significant combustion when the test is continued for an additional 20-minute period. Additionally, the flame front shall not progress more than 10-1/2” feet beyond the centerline of the burners at any time during the test.

The IBC defines FRTW as material that has been treated by a pressure process. The materials we want to use as an alternative to FRTW weren’t treated by a pressure process, therefore, we cannot label them “FRTW”. Fine, let’s call that product POTATOES. By the way, we have great POTATOES!!!

In order to meet the performance requirements of the 2303.2, our POTATOES must:

  • pass the 10-minute ASTM E84 Test, plus the additional 20-minute period, as defined.
  • In addition to demonstrating equivalence in performance, our alternative materials must also be evaluated for:
    • strength degradation
    • corrosion (fasteners)
    • hygroscopicity

*Since the FIRE testing component of this is the key to success here, we’ll focus on fire.

Teting Mumbo-Jumbo.

ASTM E84 is the Standard Test Method for Surface Burning Characteristics of Building Materials. This test lasts for a period of 10-minutes and provides two data points: Flame-Spread & Smoke Developed. The IBC requires an additional, or extended, 20-minutes of testing after the initial 10-minutes, making this test a “Modified E84 Test in accordance with IBC 2303.2”.

The Flame-spread Index, or FSI, details the tested material’s propensity to burn rapidly and how quickly flame spreads on the surface of the material. The Smoke-Developed Index is a measure of the concentration of smoke a material emits as it burns.

The most widely-accepted flame-spread classification system appears in NFPA Life Safety Code 101 – grouping flame-spread & smoke development by Class A, B or C, and this is where the IBC derives the baseline performance requirements for FRTW, and/or their alternatives from.

Class-A is what the IBC requires for FRTW materials (or their alternatives) and that is “Flame-Spread of 0-25, Smoked Developed 0-450”.

Summing it up.

Now that your product has been all tested and certified, the “presentation” portion of your facts for approval should be rather straight forward. First, provide your research report along with your “modified” ASTM E84 test results that demonstrate equivalence in performance to what was prescribed by the code, and make sure you have your strength, corrosion and hygroscopicity data are on point. This information is more often than not found within the research report IF that data point was in fact captured in the scope of the evaluation.

Gaining approval for an alternative product isn’t always a walk in the park. Some jurisdictions simply won’t allow certain products or methods for use, while other jurisdictions are much more open to outside-the-box thinkers and our creative solutions. As mentioned before, gaining acceptance begins with your product’s valid and supporting research reports from approved sources backed-up by test results from an approved agency. Last but certainly not least: know your product, know your audience, and prepare for your competition to try to shut you down. I say — bring it on!