FM Articles

Rigid-Foam Insulation to Meet Fire Requirements


Some design professionals are responsible for a particularly important task: properly specifying rigid-foam insulation that meets fire requirements for safe school and hospital facilities. With these facilities at risk of slow evacuation, it is crucial that the proper fire and life safety measure are implemented to minimize the spread of flames, and to allow sufficient time for the fire service to arrive. To help achieve this, design professionals specify wall assemblies that meet National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-loadbearing Wall Assemblies Containing Combustible Components, which requires rigorous testing of foam-plastic insulation and other materials.

Unfortunately, a centralized database of NFPA 285-compliant wall assemblies does not exist. With new product developments and assembly tests occurring often, the lack of a database makes it increasingly difficult for design professionals to stay up-to-date with NFPA 285 compliant wall assemblies. Rather, properly specifying rigid foam insulation in wall assemblies is assisted by understanding the following points related to NFPA 285:

  • International Building Code (IBC) requirements vis-à-vis NFPA 285
  • The fire test procedures that insulation must pass
  • The types of insulation that meet the requirements of NFPA 285 for various wall types and exterior finishes

NFPA 285 Basics
In short, NFPA 285 is intended to evaluate the fire performance of materials in wall assemblies that are required to be non-combustible. The official scope explains, “This test provides a method of determining the flammability characteristics of exterior, non-load-bearing wall assemblies/panels. The test method described is intended to evaluate the inclusion of combustible components within wall assembled/panels of buildings that are required to be of non-combustible construction. It is intended to simulate the tested wall assemblies’ fire performance.”

It is important to note, NFPA 285 is not product-specific. Although a given component may pass the test in one assembly, this does not mean it will be compliant in another assembly. As a result, when designing NFPA 285-compliant wall assemblies, components cannot be mixed and matched without engineering evaluation conducted within limits imposed by the IBC.

Fire Test Procedures for Rigid-Foam Insulation
NFPA 285 testing involves construction of a two-story room, with the proposed wall assembly as the exterior wall. The lower room includes a window opening (non-glazed). To simulate a building fire, a gas burner is placed in the center of the lower room, and a second, portable gas burner is placed in the window opening. The two burners are ignited at specified intervals during the 30-minute test and must heat the first floor to defined temperatures by specified times. The test measures all components of the wall assembly on a “pass” or “fail” basis as evaluated by the horizontal and vertical spread of flames across the wall assembly.Rigid-FoamDue to the combustible nature of all rigid-foam insulations, they must pass as components within NFPA 285-tested assemblies to be used in any commercial building, including schools and hospitals. The most commonly used rigid foams in these settings are polyisocyanurate (polyiso), expanded polystyrene (EPS) and extruded polystyrene (XPS). Each of these rigid foam insulations have been used in NFPA 285-compliant wall assemblies, although some are better-suited for certain types of assemblies than others. Even if a specific manufacturer’s polyiso, EPS, or XPS product has passed the test, it does not mean other manufacturers’ products of the same type have also passed. For individual product compliance questions, consult the manufacturer as they are able to answer questions about the NFPA 285 compliance of their products.

Rigid foams behave differently from one another during a fire, as shown in testing under American Society for Testing and Materials (ASTM) E84, Standard Test Method for Surface Burning Characteristics of Building Materials. Polyiso insulations are available in both Class A (flame spread <25) and Class B (flame spread <75), while most EPS and XPS products are Class A. EPS and XPS have ASTM E84 values <25 largely because they melt and no longer remain in the test position. This is acknowledged in ASTM E84 Section 1.4, “Testing of materials that melt, drip, or delaminate to such a degree that the continuity of the flame front is destroyed, results in low flame spread indices that do not relate directly to indices obtained by testing materials that remain in place.”

Rigid-Foam Insulation Options for NFPA 285 Compliant Walls
There are a number of possible options to consider when specifying rigid foam insulation for schools and hospitals. To narrow the results, consider the following factors for each insulation type.

Insulation manufacturers offer multiple polyiso product options, including rigid boards with various facer types, along with composite panels. Many of these products have passed NFPA 285 testing within steel-frame, wood-stud, concrete masonry unit (CMU), and concrete wall assemblies, with numerous cladding options and weather barriers. In order to create thinner NFPA 285-compliant wall profiles than are possible with XPS, polyiso products offer a high R-value per inch. One option, Hunter Xci Ply, includes polyiso laminated to fire-treated plywood, which helps simplify exterior cladding installation by providing the full panel surface as an attachment point rather than using attachment systems such as Z-girts, clips or rails.

EPS and XPS are polystyrene rigid foam insulations available in a range of product compositions. Each of these products have been used in NFPA 285-compliant wall assemblies incorporating steel studs, CMU, and concrete although there are limitations on cladding. Notably, as window and door header details are vital to NFPA 285 compliance, XPS requires more complicated fire-protective details such as a steel angle and mineral wool to protect the insulation from flash-over during a fire, than polyiso does.

Although there is no perfect solution for every wall assembly, some polyiso brands are NFPA 285-compliant in a wide range of wall assemblies and provide high R-value per inch for thinner walls. As a designer, understanding IBC requirements, NFPA 285 testing methods, and the ability of insulation and assemblies to meet the requirements of NFPA 285 will help allow you to properly specify which rigid-foam insulation will meet the fire safety requirements of schools and hospitals.

MacGregor Pierce is Xci product and technical manager for Hunter Panels, a manufacturer of polyisocyanurate insulation products. His more than 30 years of experience in the construction industry include working as a general contractor for commercial buildings, and directing logistics and product development for Hunter Panels. Pierce is also active with insulation codes and compliances. He can be reached at