Originally Published as: Fire-Rated Products in Post-Frame Construction: Why Not All Protection Is Equal
With increasing wildfire risk and stricter codes, post-frame builders face more inquiries about fire-rated materials. Examining fire-retardant-treated wood, recent testing data, and new ember-protection products highlights the importance of these details.
Fire performance is now a central topic in post-frame construction. Builders in wildland-urban interface areas are receiving more questions from clients and code officials about fire-retardant-treated wood (FRTW), while homeowners in fire-prone regions are seeking information on supplemental products for ember intrusion. Both issues require careful attention, as important details can be easily overlooked.
Fire-Retardant-Treated Wood: What the Code Actually Requires
The International Building Code (IBC) addresses structural fire-retardant-treated wood in Section 2303.2, which defines FRTW as wood “impregnated with chemicals by a pressure process or other means.” The code is explicit that surface treatments don’t qualify: “The use of paints, coatings, stains or other surface treatments are not an approved method of protection as required in this section.”
The distinction between pressure-impregnated and surface-applied treatments is central to a testing program commissioned by the Western Wood Preservers Institute (WWPI), with support from the Southern Forest Products Association (SFPA), and released in December 2025. WWPI represents preserved-wood treaters and preservative manufacturers in western North America and has provided technical support to the industry for over 75 years.
The Testing: Not All Fire-Retardant Treatments Are Equal
The WWPI/SFPA program tested lumber and plywood treated with six fire-retardant formulations: three pressure-applied and three non-pressure-applied. Testing was conducted at an independent laboratory using ASTM E2768-11 (reapproved 2018), the protocol specified in Section 2303.2 for structural FRTW. In this test, a Steiner Tunnel exposes samples to direct flame for 30 minutes. To pass, the flame front must not progress beyond the 10.5-foot mark at any time.
The results were clear. All 10 pressure-treated FRTW samples met the standard. Of the 21 non-pressure-applied samples, 19 failed to reach 30 minutes without the flame front passing 10.5 feet. Two non-pressure-applied samples lasted the full duration. However, WWPI notes that the substrate, Select Structural Douglas fir, may have influenced results. An untreated sample of this substrate lasted 27.3 minutes, over 90 percent of the test window, before failing.
Because fire-retardant-treated wood is used in high-occupancy structures such as multi-story apartments, it is critical to avoid potentially ineffective products based on questionable marketing claims.
WWPI’s findings highlight a marketing trend: non-pressure-applied fire-retardant products are sometimes promoted as “code-compliant,” “Class A rated,” or “ASTM E84 tested.” However, these claims alone do not qualify a product as FRTW under IBC Chapter 23. ASTM E84 is a 10-minute flame-exposure test for interior finishes under Chapter 8 of the IBC, which is a shorter and different test than the 30-minute ASTM E2768 protocol required for structural FRTW. A product may have an E84 or Class A rating and still not meet the structural fire-retardant requirements.
For post-frame builders, the key takeaway is clear: when a project requires FRTW, whether by code, insurance, or owner request, confirm that the product was pressure-treated and tested to ASTM E2768, not just labeled as fire-rated. WWPI’s FireResistantWood.org provides a list of pressure-treated FRTW sources and a summary distinguishing code-compliant FRTW from other products.
A Different Layer: Ember Protection at the Vent
Fire-retardant-treated wood protects structural members from direct flame contact. However, it does not address another common ignition source in wildfire-prone areas: wind-borne embers entering through attic, gable, soffit, or foundation vents. The Insurance Institute for Business & Home Safety has identified ember intrusion through vents as a leading cause of structure ignition during wildfires, regardless of whether the building’s framing is fire-retardant-treated.
The Universal Ember Guard Carbon Filter from safe soss® addresses this vulnerability as part of a three-step “Block, Seal, Defend” system developed by Nicholai Allen, a Southern California wildland firefighter. This self-extinguishing, phosphate-infused activated-carbon filter installs behind existing code-approved vents and metal mesh screening without requiring vent replacement. It is designed to reduce ember intrusion and smoke infiltration while maintaining normal ventilation. The product is sold with a heat-resistant ember guard tape for temporarily sealing small gaps and a hose-applied wildfire risk-reduction spray, and is available through Lowe’s.
Help block wind-borne embers and smoke from getting into your vents. Embers are the leading cause of home loss during wildfire.
— safe soss® product messaging
It is important to clarify the product’s intended use. The Ember Guard Carbon Filter is marketed as a supplemental, retrofit defense for existing structures, not as a code-compliant material or a substitute for pressure-treated FRTW where required by code, insurers, or jurisdictions. Its installation guidance specifies placement behind existing vents, not as a replacement building material. For post-frame builders working on agricultural, commercial, or residential structures in fire-prone areas, this product is a useful option when clients seek additional protection beyond framing and cladding. However, it should be considered as an ember defense layer, alongside defensible space and vegetation management, not as a replacement for a structural fire rating.
What This Means on the Jobsite
Confirm pressure treatment, not just a fire-related claim. Ask suppliers if FRTW was pressure-impregnated and tested to ASTM E2768, as required by Section 2303.2, rather than relying on “Class A” or “ASTM E84 tested” language for structural applications.
Understand the difference between interior and structural requirements. ASTM E84’s 10-minute test applies to interior finish materials under IBC Chapter 8. It is not equivalent to the 30-minute ASTM E2768 test required for structural FRTW.
Use ember-entry products as supplements, not substitutes. Vent-mounted ember filters and similar retrofit products provide additional protection against ignition pathways that FRTW does not address, but they do not meet structural fire-retardant requirements.
When in doubt, go to the source. WWPI’s FireResistantWood.org publishes a source list. When uncertain, consult the source. WWPI’s FireResistantWood.org provides a list of pressure-treated FRTW suppliers and technical documentation for direct reference by builders and clients. Builders who can speak to all three, with the testing data to back it up, are in a stronger position with code officials, insurers, and clients alike.
Sources & Resources
Western Wood Preservers Institute (WWPI), “Fire tests confirm not all fire-retardant treatments are equal,” December 16, 2025. https://fireretardantwood.org/blog/fire-tests-confirm-not-all-fire-retardant-formulas-are-equal/
FireResistantWood.org — WWPI’s fire-retardant-treated wood resource site, including a sources list and technical library.
PreservedWood.org — WWPI’s overview of fire-retardant-treated wood uses and specifications.
International Building Code, Section 2303.2 (Fire-retardant-treated wood).
ASTM E2768-11 (reapproved 2018), Standard Test Method for Extended Duration Surface Burning Characteristics of Building Materials (30-Minute Tunnel Test).
safe soss® — manufacturer site for the Universal Ember Guard Carbon Filter and related wildfire defense products. https://safesoss.com/
Firestable Insulation Company – https://firestable.com
Dynamic Fire Protection – https://dynamicfireprotection.net
Global Fireproof Solutions, Inc. – https://globalfire.us
