Fire Retardant Treated Wood Exterior


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.


FRX® exterior fire retardant treated wood combines 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.

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. 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