the beauty and versatility of wood with the fire safety and insurance
advantages of non-combustible materials.

The people who developed FRX® wood for interior applications and the people who developed FRX® shakes and shingles now offer FRX® wood, fire retardant treated wood that retains its fire retardancy in outdoor use.

FRX® wood is pressure treated lumber and plywood that is chemically treated to reduce the spread of flames and provide tested fire protection for applications directly exposed to weather.

FRX® wood may be substituted for materials classified as non-combustible in certain building types designated by the model building codes and requiring ASTM D-2898 conformance.

FRX® wood combines that beauty and versatility of wood with the fire safety and
insurance advantages of non-combustible materials.


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The ASTM E-84 tunnel test compares surface burning characteristics of tested materials to those of asbestos cement board and untreated red oak lumber. A rating of 0 is assigned to asbestos cement board and a rating of 100 is assigned to untreated red oak flooring. Flame spread ratings of various species of untreated lumber range from 60 to 230. During this test, smoke emissions are also measured and ratings are assigned on the same scale. The ratings are established during the first 10 minutes. Unlike for fire retardant coatings, however, building codes required that the test be extended from 10 minutes to 30 minutes and the flame spread not progress more than 10 1⁄2 feet beyond the burners and show no evidence of progressive combustion.

Further ASTM E-84 testing is then conducted on material that has undergone the ASTM D-2898 accelerated weathering test, also referred to as the "800-inch rain test." FRX® lumber and plywood maintain flame spread indexes of less than 25, indicating compliance with building code requirements for exterior FRTW.

Standard tests for surface burning characteristics of materials referenced in the model codes as a basis of acceptance are all essentially the same:

  ASTM E-84 Standard Test Method for Surface Burning Characteristics of Building Materials.
  NFPA 255 - Method of Test Surface Burning Characteristics of Building Materials is essentially the same as ASTM E-84.
  UBC Standard 8-1 Test Method for Surface-Burning Characteristics of Building Materials is based on Standard Test Method ASTM E-84.

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FRX® wood is appropriate for use in a wide array of
applications, including:

  Exterior decks
  Covered walkways
  Trim & molding
  Open-air roof systems
  Soffet & fascia
  Construction staging


FRX® wood has been tested via ASTM D-143 and MIL-L-19140E. Following are the design value adjustments for FRX® wood.

Strength Design Factors
FRX® Fire Retardant Treated Lumber Compared to Untreated Lumber
Applicable at Ambient Temperatures Up to 80°F

* Arch Wood Protection does not recommend the use of FRX® wood in high temperature interior applications. Dricon® FRTW should be used in these situations. Contact Arch Wood Protection or visit us online at for more information.


1. Does it meet building codes?
Yes. FRX® wood meets the performance requirements of the model building codes.

2. Can it be painted or stained?
Yes, though not all paints and stains are compatible with exterior fire retardant treated wood, due to the nature of the polymer. For an up-to-date listing of acceptable coatings, click here. Follow the manufacturers' recommendations for best results. As with untreated lumber, the surface should be clean and dry. It is also recommended to apply coating to a sample piece before overall application to determine compatibility and desired appearance. Flammability of the finish should be considered before any application.

3. What species can be treated?
At the present time, Douglas fir, hem-fir, southern yellow pine and western red cedar.

4. Can FRX wood be used in ground contact?
FRX® wood can be used outdoors, but is intended only for above ground uses.

5. Is there a reduction in strength compared to untreated wood?
Yes. The treating and drying processes cause a reduction in strength that varies with treatment, species of wood, applications and specific properties. Adjustment factors for FRX® wood are shown previously in the Strength Properties section of this site.

6. What types of fasteners should be used with FRX wood?
Galvanized steel hardware is recommended. Although the FRX® wood treatment does not increase the corrosion of bare steel, the galvanizing process provides an extra margin of safety in wet environments.

7. Can I cut FRX wood?
Yes. Cutting lengths, drilling holes, and light sanding are permissible. It is not necessary to field-treat cut ends to maintain the flame spread rating. FRX® lumber should not be ripped or milled. FRX® plywood can be ripped or cross-cut.

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Arch Wood Protection and Arch Treatment Technologies produce wood preservatives and
additives that enhance the qualities of wood by pressure treatment processing.
Visit for more information.

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