Spray Polyurethane Foam Insulation and Its Use in Attics and Crawl Spaces

By Jesse Beitel

The use of spray polyurethane foam (SPF) plastic insulation in buildings is regulated by building and fire codes. Most of the building codes used by jurisdictions in the United States are based on either the International Building Code (IBC) or the International Residential Code (IRC). The IRC regulates one- and two-family dwellings while the IBC regulates all other buildings.

SPF and all other foam plastic insulations are combustible materials, so their use is regulated. The primary regulations concerning SPF and foam plastics are found in Chapter 26 Plastics of the IBC and in Section R316 Foam Plastic of the IRC. Chapter 26 and Section R316 regulate all types of plastics, but of primary interest are the regulations for foam plastic insulation. The codes treat all foam plastic insulations the same, so there are no specific requirements based solely on the type of foam plastic insulation. However, there are specific requirements based on many of the applications for foam plastic insulations.

There has been a significant growth in the use of SPF in these applications over the past several years. At the same time, there has been confusion over the code requirements and the testing required for these applications. The primary focus of this article is the code requirements and testing required for the use of SPF in attics and in crawl spaces. In essence, the regulations pertaining to SPF in the IRC are a subset of regulations pertaining to SPF in the IBC. This article will address the requirements in the IBC since these have the greatest applicability.

IBC Code Requirements

There are three general code requirements for SPFs along with a very specific requirement for when SPF is used in an attic or crawl space:

1.    §2603.2 - SPF must be “labeled” by an independent third party agency;
2.    §2603.3 - SPF must be tested per ASTM E 84 “Standard Test Method for Surface Burning Characteristics of Building Materials.” The SPF must achieve a Flame-spread Index (FSI) of 75 or less and a Smoke-Developed Index (SDI) of 450 or less. Typically, the SPF is tested at a maximum 4-inch thickness since this is the maximum thickness that can be accommodated by the test apparatus; and
3.    §2603.4 – SPF must be separated from the interior of the building by a 15-minute thermal barrier. The code prescriptively specifies a 15-minute thermal barrier to be ½-inch thick gypsum wallboard or equivalent material.

When SPF is used in attics or crawl spaces, there is an exception to Item 3 above. This exception reads:
“2603.4.1.6 Attics and crawl spaces. Within an attic or crawl space where entry is made only for service of utilities, foam plastic insulation shall be protected against ignition by 1½-inch-thick (38 mm) mineral fiber insulation; ¼-inch-thick (6.4 mm) wood structural panel, particleboard or hardboard; 3/8-inch (9.5 mm) gypsum wallboard, corrosion-resistant steel having a base metal thickness of 0.016 inch (0.4 mm) or other approved material installed in such a manner that the foam plastic insulation is not exposed. The protective covering shall be consistent with the requirements for the type of construction.”

The purpose of the required thermal barrier is to protect SPF from ignition for some period of time in the event of a fire. This requirement has been in the code since the introduction of foam plastics into the code in the mid-1970s. This requirement recognizes the combustible nature of foam plastic and thus provides protection for some minimum time period.

The exception noted above allows SPF when used in an attic or crawl space to not be covered by a thermal barrier; instead, an ignition barrier can be used. This exception recognized that when attics and crawl spaces are limited in their use, the potential for ignition of the SPF is less likely than that in other areas of the building. While the code does prescriptively specify several types of ignition barriers that can be used, the code does not provide specific performance characteristics for a material to qualify as an ignition barrier, as it does for a material to qualify as a thermal barrier.    

Exemptions

Section 2603.9 of the code allows a foam plastic to be exempted from certain requirements, such as the thermal barrier or ignition barrier requirements. This exemption is allowed if the foam plastic can meet the acceptance criteria of one of several tests or if a full-scale “realistic” test is performed to show that the performance of the foam meets the intent of the code while not meeting the exact prescriptive requirements.

Figure 1

In the mid-1980s, an ad hoc, full-scale, simulated crawl space test was developed. The test used a three-sided, 8ft. x 8 ft. x 4 ft. high simulated crawl space with a wood floor system on top. The concept for the test was to compare the fire performance (time to flames exiting the crawl space and burn through the floor) of a code-approved assembly (foam plastic insulation plus ¼-inch-thick plywood) to an assembly that only contained the foam plastic insulation. If the fire performance of the assembly without the plywood was the same or better as the fire performance of the code-approved assembly, then the assembly without the plywood would meet the intent of the code and could be used if approved by the authority having jurisdiction. Figure 1 provides a photograph of SPF undergoing this test.                          

This ad hoc test was successfully used by various foam plastics to gain acceptance for the use of the foam insulation without the ignition barrier. These tests were also used to gain recognition for this application from the ICC Evaluation Service (ICC-ES). Over time, additional tests, such as variations of room/corner tests and/or variations of the crawl space test, were used to gain acceptance.  Additionally, SPF was tested either without an ignition barrier or more typically with an intumescent coating applied over the SPF. Thus, a foam plastic insulation could be used without a code-prescribed ignition barrier based on one of the following tests:
1)    Full-scale test to eliminate the thermal barrier; or
2)    Ad hoc testing, comparing a code-approved assembly to the tested assembly.

Figure 2

Testing Procedures

It was later recognized that some testing had been done in a different manner or that some tests were run in comparison to another baseline material. This raised concerns regarding the appropriateness of the testing.

To address these concerns, the Spray Polyurethane Foam Alliance (SPFA) created an industry-wide task group.  Beginning in January 2008, The SPFA task group addressed the concerns and developed a new test method to qualify SPF assemblies for use in attics and crawl spaces. This provided an alternative means to meet the codes for this application. This new test procedure was accepted by ICC-ES in June 2009 and is published in Appendix X of ICC-ES’ Acceptance Criteria AC377 “Acceptance Criteria For Spray-Applied Foam Plastic Insulation.”

The Appendix X test method is a variation of the NFPA 286 “Standard Methods of Fire Tests for Evaluating Contribution of Wall and Ceiling Interior Finish to Room Fire Growth.” The test uses the same test room, ignition source, and instrumentation as NFPA 286. The primary differences are in the acceptance criterion and mounting procedures of the SPF to the walls and the ceiling of the test room.

The test method requires that the SPF be installed at the maximum thickness and density that the manufacturer wishes to use. The test method provides two similar installation methods, and either one can be used by the manufacturer. It is important to note that the SPF must be applied to the three test walls and the ceiling. Figure 2 provides a photograph of SPF prior to Appendix X testing.

The most significant difference between the Appendix X test and the standard NFPA 286 test is in the acceptance criterion. The acceptance criterion in the Appendix X test is based on the “Average Time to Flashover” of the test assembly when compared to a baseline test using SPF and ¼-inch-thick plywood. A series of tests were conducted with various SPF materials covered with the code-prescribed plywood. Based on measurements of time to flashover of four parameters, the average time to flashover was determined to be 4 minutes, 18 seconds. If a test evaluating an SPF, with or without a coating, exhibits an average time to flashover equal to or greater than 4 minutes, 18 seconds, then the tested material passes. Figure 3 provides a photograph of a material undergoing the Appendix X test.

SPF in Attics and Crawl Spaces

At this point, AC377 allows SPF to be used in attics and crawl spaces when one of the following is accomplished:
•    A code-prescribed ignition barrier is installed over the SPF;
•    A code-prescribed or equivalent thermal barrier is applied over the SPF;
•    The SPF or the SPF with a protective coating  meets a standard full-scale room/corner fire test to demonstrate that a thermal barrier is not required;
•     The SPF or the SPF with a protective coating meets the acceptance criteria of Appendix X test in AC377; or
•    For crawl spaces only – The SPF or the SPF with a protective coating meets the crawl space test described in Appendix C of AC 377 using ¼-inch-thick plywood as the baseline.

The work by SPFA has resulted in a science-based approach to evaluating SPF for use in attics and crawl spaces. This approach and the new test method have provided a significant improvement in evaluating and controlling the flammability characteristics of SPF for use in attics and crawl spaces.

Since joining Hughes Associates, Inc., Jesse J. Beitel has provided consulting services on a wide range of flammability problems and issues to include technical studies, experimental programs, and code representation. This work has included product and materials research and design, development of new test methodologies, and recognition of new technologies in the codes. His clients include manufacturers, trade associations, private industries and the U.S military. Mr. Beitel is a recognized expert on the flammability of materials, especially foam plastics used in construction. Contact him at jbeitel@haifire.com or (410) 737-8677.

 

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