Skip to content

Material Fire Performance – Comparative Testing

One of the most energy-efficient applications of foam plastic insulation is its use to insulate and air-seal exterior walls of buildings. Under the International Building Code® (IBC), certain types of construction are required to have exterior walls that are made of noncombustible materials; however, certain combustible materials are permitted in these walls subject to certain conditions and requirements. Foam plastic is one of these permitted materials and one of the requirements is to test the wall assembly containing the foam plastic to ensure that limited flame propagation occurs. That test is NFPA 285.

NFPA 285

NFPA 285, “Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components,” is a standard test method published by the National Fire Protection Association. The test method evaluates fire propagation characteristics of exterior wall assemblies with combustible components. The test method was established recognizing that walls containing combustible components may contribute to fire spread vertically or horizontally. NFPA 285 is an assembly test, not a component test, meaning that the entire exterior wall assembly is evaluated by the test as opposed to individual materials or components of an assembly.

NFPA 285 is the standard recognized in the International Building Code® (IBC) for fire testing of exterior walls containing combustible materials such as foam plastic, continuous insulation, water-resistant barriers and combustible exterior wall coverings. For buildings of Type I – IV containing these combustible materials, the IBC requires testing to comply with the acceptance criteria of NFPA 285 when, depending on the configuration and materials, the wall is of any height or is greater than 40 feet in height. The NFPA 285 test is 30 minutes in duration and follows a specific fire exposure regimen.

Members of NAMBA provide products that meet the IBC requirements, including testing wall assemblies according to NFPA 285. Our products and assemblies that contain them are tested by accredited laboratories and certified by accredited certification agencies for compliance with NFPA 285 requirements. For example, Underwriters Laboratories, DrJ Engineering and Intertek Testing Services provide listing and evaluation reports for wall assemblies tested to NFPA 285. NAMBA supports NFPA 285 requirements and testing reports are readily available to designers, specifiers, building officials and the public.

NFPA 285 Background

History of NFPA 285 Standard Method of Test for the Evaluation of Flammability Characteristics of Exterior Nonload-bearing Wall Assemblies Containing Combustible Components in U.S. Building Codes

Driven by more stringent energy codes in the late 1970s, foam insulation was proposed for use as exterior insulation on noncombustible construction, described in the building codes as Types I, II, III and IV; however, the building codes existing at the time did not allow foam plastic insulation in this location on the building due to its combustibility. Potential flame spread on the exterior wall was a major concern.

In the early 1980s, the Society of the Plastics Industry (SPI) convened an Exterior Wall Task Group with a stated goal of developing a large-scale fire test that would qualify the use of foam plastic insulation on buildings of Types I, II, III and IV. Based on the input of building code and fire code officials, along with fire science and fire test experts, the program was designed to address a typical fire scenario where a fire occurs inside a room, achieves flashover, then breaks through a window to expose the exterior of the wall, resulting in fire traveling vertically and/or laterally on the exterior wall surface, leading to potential fire propagation from room to room or floor to floor. The result of numerous exterior wall assembly fire tests and extensive detailed discussion and debate was the development of the UBC 26-4 test, followed by the UBC-26-9 test, then ultimately the NFPA 285 test standard.

The NFPA 285 fire test, replicating a post-flashover interior room fire breaching the exterior wall assembly through a window, was therefore designed to evaluate:

  • Vertical and lateral flame spread over the exterior face of the wall assembly.
  • Vertical and lateral flame spread within the wall’s core, cavities or within the combustible components.
  • Vertical and lateral flame spread over the interior surface of the wall assembly.
  • Vertical and lateral flame spread from the compartment of fire origin to adjacent compartments or spaces.

NFPA 285 is a multi-story exterior wall assembly test conducted on a test specimen that is approximately 18 feet high and 14 feet wide, with a 78-inch wide window opening into the first floor room. The fire sources are two gas burners, one located inside the first floor room and the other on the exterior side and in the area of the window header. This set-up simulates a flashover where the fire suppression system has failed and all interior materials are burning. The burn (and test) lasts for 30 minutes.

The test assembly is mounted on the face of the apparatus, also called the test facility. Thermocouples are fitted in or on the various assembly layers, such as on the exterior wall surface, in the wall cavity air space, in stud cavity and in the insulation. The number and specific placement of the thermocouples depends on the specific configuration of the test specimen.

An exterior wall assembly will pass the test if all of the acceptance criteria stipulated in the test method have been met. These include limiting vertical and lateral flame progression (visual) in certain locations and avoiding temperatures exceeding 1000°F, exceeding 750°F, and exceeding 500°F in certain locations. Flame spread cannot exceed 10 feet above the top of the window, or more than 5 feet laterally from the centerline of the window.

This full-scale wall assembly test has proven to be a reliable measure of accept­able fire performance since 1988 when it was first adopted into building codes. As evidenced by exterior fire events reported internationally, there is a comparative absence of significant exterior fires for buildings properly designed and constructed in compliance with the building code requirements including (1) sprinklers and (2) either NFPA 285 and IBC Chapter 14 and 26 compliant exteriors or non-combustible exteri­ors.[i],[ii],[iii]

NAMBA supports a focus on ensuring NFPA 285 compliant designs are specified, fabricated, installed and inspected properly along with other fire protection measures as required by code. The NFPA 285 fire exposure is based on standard data for interior compartment fires and, therefore, provides a solid and comparable fire science basis to assess acceptable performance. NFPA 285 has been providing a reliable assessment of exterior fire flame spread risks for more than 30 years without any evidence of inadequacy in meeting the intended purpose.

[i] Wieczorek, C.J., Grenfell: The Perfect Formula for Tragedy, FM Global, 2017,

[ii] BRANZ, Fire Performance of Exterior Claddings, Fire Code Research Reform Program, April 2000.

[iii] White, N. and Delichatsios, M. (2014). Fire Hazards of Exterior Wall Assemblies Containing Combustible Components, Fire Protection Research Foundation,


Engineering Judgment and Analysis

Another code compliance route is through the use of an engineering judgment (EJ) analysis conducted by a competent fire test expert. The IBC permits these assessments under the duties and powers of the Building Official for approving the use of alternative materials, design and methods of construction and equipment. The Building Official has the authority to consider these types of evaluations in the approval of assemblies that are alternative to those actually tested.

For these analyses, NFPA 285 tested assemblies are used as the basis for evaluating how proposed changes in materials or installation details will influence the observed performance. At the end of the process, the Building Official determines whether the submitted EJ(s) is sufficient for approval of the assembly. Any EJ must answer the question of whether the variation, change or substitution will produce equivalent or satisfactory fire performance of the as-tested baseline assembly. Generally, EJ reports should:

  • Provide a means to connect designed and tested assemblies and address different construction configurations.
  • Be based on an NFPA 285 test and sound fire protection engineering.
  • Assess fire safety of variations in installation and/or change or substitution of components in a proposed design.