Building Codes

FRX® wood has been issued an evaluation report (ESR-1159) by International Code Council (ICC) Evaluation Services, providing evidence that it meets the requirements of the model building codes for exterior fire retardant treated wood. ICC creates model building codes adopted in many locations throughout the U.S.; its evaluation reports are accepted in nearly all cases by local building officials.

Model Specifications

ICC-ES Reports

SDSs for Treated Wood Products

Qualified Product Listing

FRX® Fire Retardant Treated (FRT) wood is also listed as a Qualified Product by the U.S. Navy (MIL-L-1914OE). Because it has a flame spread index of 25 or less, FRX® wood may be substituted for materials classified as non-combustible in certain building types designated by the model building codes and requiring ASTM D2898 conformance.

Fire Performance

Model building codes require a flame spread rating of 25 or less and a smoke developed rating of 450 or less, when the standard surface burning test is extended to 30 minutes and after weathering, to qualify as a Class A material.  FRX® fire retardant treated wood maintains ratings less than both those levels for all species listed.

The ASTM E84 tunnel test is used to determine the flame spread and smoke developed ratings. The 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. Furthermore, building codes required that the test be extended from 10 minutes to 30 minutes and the flame spread not progress more than 10 ½ feet beyond the burners and show no evidence of progressive combustion.

For exterior use, FRT® wood must undergo further ASTM E84 testing, which is conducted on material that has been through the ASTM D 2898 accelerated weathering test, also referred to as the “800-inch rain test.”

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 Material

NFPA 255 – Method of Test Surface Burning Characteristics of Building Materials

UBC Standard 8-1 Test Method for Surface-Burning Characteristics of Building Materials

Acceptable Species

Lumber:  Douglas fir, hem-fir, southern yellow pine, western red cedar, and spruce/pine/fir are currently available

Plywood:  Douglas fir, southern yellow pine, and spruce/pine/fir

Lumber & Plywood Sizes

All common sizes of most construction species of lumber and plywood can be pressure treated with FRX® fire retardant.  Size is generally limited only to the treating plant’s ability to treat, dry and handle large members.  All thicknesses of plywood can be treated.  The treatment is also effective for logs, siding, and laminated veneer lumber.


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



The treatment has little effect on the color of the lumber. Deposits of FRX® fire retardant solution may appear on the surface of wood (“efflorescence”) or exude from the edges of plywood during drying (“intumescence”). On most species, discoloration is barely noticeable. Marks made by stickers used to separate the layers of lumber during the kiln drying following treatment will be noticeable on lumber. If required, FRX® exterior treated wood can be special ordered with the good face free of sticker marks. The pressure treatment and subsequent drying may result in a slight waviness in plywood; however, typically the plywood can be straightened when nailing.