From IBC to Install: How to Specify Fire-Retardant-Treated Wood with Confidence
A Practical Guide from the Experts at Biewer Lumber
Fire-retardant-treated wood (FRTW) is a critical material in modern commercial
construction — yet it remains one of the most misunderstood and inconsistently specified
products in the building industry. When fire-retardant-treated wood is not clearly defined in
the construction documents, the result is often plan review comments, delayed approvals,
material substitutions, and unexpected costs.
At Biewer Lumber, we specialize in pressure-impregnated fire-retardant-treated wood and
work closely with architects, engineers, and building officials to ensure FRTW is specified
correctly from design through installation.
This guide explains how fire-retardant-treated wood fits into the International Building
Code (IBC), what differentiates high-performance FRTW from surface-applied alternatives,
and how to specify the right product with confidence.
Where Fire-Retardant-Treated Wood Fits in the IBC
The International Building Code (IBC) permits fire-retardant-treated wood in specific
applications where untreated combustible materials would otherwise be prohibited. These
allowances enable designers to maintain wood framing solutions while meeting fire
performance requirements.
Common IBC-approved applications for FRTW include:
- Roof assemblies
- Exterior wall framing in certain construction types
- Areas where combustible materials are otherwise restricted
The purpose of these code provisions is not simply to reduce flame spread, but to ensure
predictable and verifiable fire performance over the life of the building. That is why the
IBC places importance on:
- Treatment method
- Performance testing
- Documentation and evaluation reports
- Exposure and environmental conditions
Not all fire-retardant-treated wood meets these expectations equally.
Pressure-Impregnated vs. Surface-Applied Fire-Retardant Treatments
One of the most important distinctions when specifying FRTW is the treatment process
itself.
Pressure-Impregnated Fire-Retardant-Treated Wood
Pressure-impregnated FRTW is manufactured by forcing fire-retardant chemicals deep into
the wood fiber under controlled pressure conditions. This results in:
- Uniform treatment throughout the entire cross-section
- Consistent, predictable fire performance
- Reliability after cutting, drilling, or notching
- Long-term performance aligned with code intent
Because the fire-retardant chemistry penetrates the wood rather than sitting on the
surface, pressure-impregnated FRTW maintains its performance characteristics even as
the material is fabricated and installed.
Surface-Applied Fire-Retardant Treatments
Surface-applied treatments rely on coatings or shallow penetration to achieve flame-
spread performance. These systems can be more susceptible to:
- Uneven coverage
- Physical damage during handling and installation
- Reduced effectiveness in demanding commercial environments
For this reason, most commercial and institutional projects benefit from specifying
pressure-impregnated fire-retardant-treated wood to meet both code requirements and
long-term performance expectations.
Key Specification Elements That Prevent Delays
Clear, precise specification language is essential to avoid confusion, substitutions, and
approval issues. Fire-retardant-treated wood should never be specified generically.
A well-written FRTW specification should clearly define:
- “Fire-retardant-treated wood” (not just “fire treated wood”)
- Treatment method: pressure-impregnated
- Intended exposure conditions (interior vs. exterior)
- Applicable ICC-ES or third-party evaluation reports
- Compliance with IBC and ASTM testing standards
This level of clarity ensures that the material delivered to the jobsite is the material the
design team intended — and the material the code official expects.
Installation and Field Considerations
Even the highest-quality fire-retardant-treated wood must be handled and installed
correctly to maintain its performance.
Best practices include:
- Following manufacturer guidelines for cutting, drilling, and fastening
- Understanding any requirements for field treatment or sealing of cut ends
- Avoiding improper storage or exposure prior to installation
Pressure-impregnated FRTW simplifies field handling because treatment consistency
reduces performance risk after normal construction activities.
Why Design Teams Rely on Biewer FRTW
At Biewer Lumber, fire-retardant-treated wood is not an add-on — it is a core product
category supported by deep technical expertise, testing, and documentation.
Our pressure-impregnated FRTW is:
- Manufactured under controlled conditions
- Supported by code-compliant testing and evaluation reports
- Designed for predictable, repeatable performance
- Backed by a team that understands both the material and the code
That combination allows architects, specifiers, and contractors to move through design,
approval, and construction with confidence.
Specifying Fire-Retardant-Treated Wood with Confidence
Fire-retardant-treated wood does not need to introduce risk into a project. When pressure-
impregnated FRTW is clearly specified, properly documented, and supported by a
knowledgeable supplier, it becomes a reliable, code-compliant solution that supports both
fire safety and design flexibility.
By understanding the code, selecting the right treatment method, and working with a
trusted manufacturer like Biewer Lumber, design teams can ensure fire-retardant-treated
wood performs exactly as intended — from IBC reference to final installation.