Genuine Dricon® FRT Wood – Fire Performance

Flame Spread & Smoke Developed Values

Dricon® FRT wood has been tested for fire performance by several independent laboratories and meets model code requirements for a Class A/Class 1 fire retardant. As a result of tunnel testing (UL 723, ASTM E 84, and NFPA 255 are essentially identical) an FR-S surface burning characteristic classification has been assigned to all softwood species of Dricon FRT wood.

The 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 to untreated red oak flooring. Flamespread ratings of various species of untreated lumber range from 60 to 230. A rating of 25 qualifies for Class A/Class1 requirements.

During this test, smoke emissions are also measured and ratings are assigned on the same scale. These flame spread and smoke development ratings are established during the first 10 minutes. However, unlike for fire retardant coatings, building codes require 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.

flamespreadDricon FRT wood has a flame spread and smoke developed index of 25 or less when tested in the E 84 tunnel test and shows no evidence of progressive combustion in 30 minutes. Dricon treatment reduces the flame spread of most species to less than 15 which is essentially the same as gypsum wallboard.  Standard tests for surface burning characteristics of materials referenced in the model codes as a basis of acceptance of fire retardant treated wood are all essentially the same.

  • UL 723-Standard Test Method for Surface Burning Characteristics of Building Materials was developed by Underwriters Laboratories Inc. and subsequently adopted by ASTM as Standard E 84.
  • ASTM E 84-Standard Test Method for Surface Burning Characteristics of Building Materials is essentially the same as UL 723. It also has been adopted by ANSI.
  • NFPA 255-Method of Test for Surface Burning Characteristics of Building Materials is essentially the same as UL 723 and 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.

Factory Mutual Research has also evaluated Dricon FRT wood and found that it meets their requirements for a Class 1 treated wood roof deck per their FMRC colorimeter. The ASTM E 162 radiant panel test and NFPA 258 smoke density test have been conducted by the Hardwood Plywood Manufacturers Association and have demonstrated the acceptability of Dricon FRT wood under Department of Transportation regulations for use in mass transit vehicles.


Dricon FRT wood has been tested in accordance with the following procedures:

  • ASTM D 1413
  • ASTM E 72
  • NFPA 255
  • ASTM D 3201
  • ASTM E 84
  • NFPA 258
  • ASTM D 3345
  • ASTM E 162
  • NFPA 259
  • ASTM D 5516
  • Boeing BSS 7239
  • UL 723
  • ASTM D 5664
  • MIL-L-19140

Fire Resistance

Hourly Ratings

Fire retardant treated wood has a surface burning classification and, by itself, does not have a resistance rating in hours any greater than untreated wood. Fire ratings in hours are assigned to door, wall, or deck assemblies following testing in accordance with ASTM E 119 and E 136. The references such as the Underwriter Laboratories “Fire Resistance Directory” specifically points out that FRT wood may be substituted for untreated wood in any related assembly. Dricon FRT wood can be used as a component of such assemblies in structures where the code does not permit the use of untreated wood.

Descriptions of fire resistance rated assemblies incorporating structural lumber are listed in several publications, with the following being those generally referenced in model building codes:

  • Fire Resistance Directory, published by Underwriters Laboaratories
  • Fire Resistance Ratings, published by Engineering and Safety Service of the American Insurance Service Group
  • Fire Resistance Design Manual, published by the Gypsum Association
  • Uniform Building Code, including a listing of fire resistance rated assemblies

For example, the Gypsum Association’s “Fire Resistance Design Manual” shows a one hour wall or partition assembly (WP 3605) that has wood studs covered by 5/8″ Type X gypsum board with specified nailing and positioning of the panels. This assembly could be used for interior, non-bearing partitions, requiring a one hour rating in a noncombustible structure if the studs were Dricon FRT wood. In a similar manner, by substituting Dricon FRT wood for untreated wood, other one and two hour wall and ceiling assemblies can be used in noncombustible type buildings. The model codes also permit use of ceiling assemblies with the top membrane omitted where only unused attic space is above.

Some model codes and local building officials will accept the Component Additive Method (CAM) for calculating fire resistance in lieu of actual assembly testing. The CAM concept entails adding the resistance rating of individual components to qualify the resistance rating of the assembly. The lumber and plywood used in rated assemblies or CAM listings are usually not identified as being untreated or FRT wood, but the model codes generally do require that any wood used in noncombustible types of construction be fire retardant treated. Also, due to wood’s natural ability to insulate, wood may be more acceptable than unprotected steel in fire resistant assemblies. For more information on CAM, download a one-page summary (PDF) or a comprehensive brochure from the American Forest and Paper Association.

One Hour Wood Truss Assemblies

Recent testing has provided effective and competitive designs for one hour rated floor/ceiling and roof/ceiling metal plate connected wood trusses. Unlike earlier designs, the one hour rating can now be achieved with only one layer of 5/8″ Type X gypsum wallboard applied directly to the bottom chord of the truss.

Dricon FRT wood can be used in place of untreated wood in many of these designs and will enable the use of these assemblies in many building construction types that do not permit untreated wood. These new construction assemblies provide greater savings than ever before when Dricon wood construction is substituting for hourly rated steel or concrete construction.