Fire-Retardant-Treated Wood (FRTW) is a vital safety tool for contractors, code officials, architects and other building professionals. Getting the most out of the materials requires understanding how to cut, drill, and fasten the material correctly to maintain performance and meet code requirements.
So what are some of the common questions builders, architects, and contractors ask about cutting and handling FRTW? And how would our team at Hoover Treated Wood Products answer these to provide greater, more actionable clarity for building professionals looking to put FRTW to use?
Key Takeaways
- FRTW can be cut, drilled and joined on the jobsite using standard woodworking tools — cross-cuts, holes, joints and plywood cuts are all permitted without affecting fire performance.
- Ripping and milling of lumber are not allowed after treatment. These operations change the wood’s surface and profile, which can alter the fire-resistance characteristics UL certifies. That work must happen before treatment.
- Field cuts don’t require retreatment. Because the fire retardant is pressure-impregnated through the wood (not coated on the surface), a fresh cut performs the same as the rest of the board.
- Fastener choice should match the application. Use hot-dipped galvanized for most interior work and stainless steel for exterior, coastal or high-moisture conditions, since fire-retardant chemistry can be more corrosive to metal than untreated wood.
You can also learn more about FRTW in our Specifier’s Guide to Fire-Retardant-Treated Wood.
Can You Cut Fire-Retardant-Treated Wood?
Yes — within limits. FRTW can be cut and drilled on the jobsite with standard woodworking tools, and most common operations won’t affect its fire performance. The key difference from untreated lumber: you can’t rip or mill FRTW lumber after treatment, because that exposes untreated wood and changes the surface burning characteristics UL certifies.
What UL allows after treatment for Hoover’s PyroGuard™ and Exterior FireX™ products:
- Cross-cuts and end cuts to length
- Holes and joints (tongue-and-groove, bevel, scarf and lap)
- Corbels on rafter tails
- Cutting plywood in any direction, without restriction
- Light sanding to remove raised grain or prep for finishing
What UL does not allow after treatment:
- Ripping lumber along its length (for example, a 2×4 down to 2x2s)
- Cutting stair stringers, which has the same effect as ripping
- Milling or resurfacing
If your project needs custom shapes, thicknesses or ripped dimensions, have that work done before treatment. Hoover can also custom-cut to length before the pressure-treatment process begins, which ensures accuracy, saves time on the jobsite and reduces waste. One more field note: end coating is not required after cutting.
For construction professionals using Hoover FRTW products, we offer tech notes for our PyroGuard™ and ExteriorFireX™ products with specific instructions for cutting, ripping, or milling. These documents are the best reference for ensuring your work meets engineering expectations and code compliance requirements.
Do Field Cuts Require Retreatment When Working with FRTW?
No. This is one of the most common questions on the jobsite, and it usually comes from having to end-treat preservative-treated wood after it is cut in the field. The code requires end-treating of PTW. FRTW is different. The retardant is pressure-impregnated through the wood, so a fresh cross-cut, drilled hole or notch is just as protected as the rest of the board. There’s no brushing, dipping or re-coating to do in the field. That’s why the code does not require end-treating of FRTW. Install it as directed and it performs as rated.
For more about cutting fire-retardant-treated wood, review the PyroGuard and ExteriorFireX™ technical notes for material-specific details. This will ensure that your FRTW installation meets code and performs as intended.
What Are the Best Fasteners for FRTW?
Corrosion resistance is the priority. Treatment with PyroGuard™ does not cause fasteners to corrode. Corrosion is caused by wetting from rainfall or other sources. PyroGuard™ treatment is not significantly more hygroscopic than untreated wood. Fire-retardant chemistry can be more corrosive to metal than untreated wood. And more so as moisture, humidity and other environmental factors can hasten corrosion, standard fasteners can degrade faster than the application calls for. Match the fastener to the environment:
- Hot-dipped galvanized nails or screws for most interior applications
- Stainless steel in coastal, exterior or high-moisture conditions
- Coated structural screws that meet the relevant ASTM standards
Requirements differ because of environments. PyroGuard™ is used in interior dry environments. ExteriorFireX™ is used in exterior wet environments. Neither is more corrosive than untreated wood. Check the fastener recommendations in each product’s technical notes before you specify.
What Safety Practices Should You Follow When Cutting FRTW?
Treat it like any fine-woodworking job, with extra attention to capturing and cleaning up excess dust. FRTW sawdust carries the treatment chemistry, so capturing and cleaning it up matters more than with untreated lumber:
- Use dust collection whenever possible
- Wear appropriate PPE (eye protection, gloves and a dust mask or respirator)
- Work in a well-ventilated area
- Clean up sawdust after cutting to keep the workspace safe
Does Drilling or Cutting Fire-Retardant-Treated Wood Affect Its Performance In a Fire?
No, not when the work is done correctly. Hoover’s FRTW is pressure-impregnated, so the fire-retardant chemistry penetrates deeply into the wood rather than sitting on the surface as a coating. That’s why cross-cuts, end cuts, drilled holes, joints and standard plywood cuts don’t reduce protection, and why field cuts don’t require retreatment.
The exceptions are ripping and milling. Because these operations change the surface and profile of the lumber, they can affect the surface burning characteristics UL certifies, so they aren’t permitted after treatment. If your project calls for ripped dimensions or milled profiles, that work needs to happen before treatment, not on the jobsite.
Stick to the allowed operations in the PyroGuard™ and Exterior FireX™ technical notes and your FRTW will deliver the same fire performance for which it was tested and rated.
What Is the Best Way to Handle FRTW on Your Next Project?
Just follow the guidelines for cutting, drilling, and fastening fire-retardant-treated wood. Doing so ensures that you’ll get the fire performance and code-compliant results you’ve come to expect from Hoover Treated Wood Products. If you have questions about cutting FRTW or selecting fasteners for your next project, just reach out. Our team is here to help.
Contact us for more information or to speak with a Hoover Treated Wood Products representative about our FRTW solutions.
