Continuous insulation performance

by sadia_badhon | December 2, 2020 9:59 am

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by Marcin Pazera, PhD

The goals of building fire safety and energy efficiency are compatible when industry stakeholders work together to make sure proper assemblies are designed, the correct materials are specified, and installers have the experience to combine the building design and materials properly in the field.

Building occupant safety is always a top priority. Incorporating redundant fire protection measures and strategies during a building’s design and construction can minimize fire risks and limit the potential harm to people and loss of property when fires occur. While the cause and intensity of every fire is different, the fire-safety measures required by today’s building codes (e.g. fire suppression systems, building egress requirements, fire-resistive assemblies, and construction material fire test standards) are tools professionals can use for a balanced approach to fire safety in built structures.

Key attributes of any building enclosure’s design is the long-term performance of materials and assemblies. The way in which the materials are integrated into a building’s envelope is critical to its overall performance including fire safety. Within a fire-resistive assembly, standards do not rely on individual component fire tests because materials can behave differently when combined and exposed to fire.

Building code overview

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The International Code Council (ICC) describes building codes as “a jurisdiction’s official statement on building safety. They are a set of minimum standards to ensure the health, safety, and welfare of the people. Codes address all aspects of building construction—fire, life safety, structural, plumbing, electrical, and mechanical. The regulation of building construction can be traced through history for more than 4000 years. Through time, people have become increasingly aware of ways to make buildings safer for occupants and avoid catastrophic consequences of building-construction failures.”

The construction codes and standards used today were built on the experiences and lessons learned from large fires and other failures that resulted in significant losses of life and property. With over a 100 years of diligent work and thousands of contributing members, more than 300 codes and standards have been developed through the research, training, outreach, education, and advocacy efforts of groups, including the National Fire Protection Association (NFPA) and other global bodies like the Underwriter’s Laboratories (UL) and Factory Mutual (FM).

In the United States, the International Building Code (IBC) is the most widely adopted model code. Developed by ICC, IBC is reviewed through a consensus development process every three years. IBC, together with the International Energy Conservation Code (IECC), outline the minimum requirements for various building systems, including exterior wall systems incorporating energy-efficient materials like polyisocyanurate (ISO) insulation. The International Existing Building Code (IEBC) is often adopted by jurisdictions to further regulate alterations or other modifications made to existing buildings.

These standards evolve over time to reflect new information that becomes available and as new products, research, and practices are developed and tested. In recent years, efforts to improve energy efficiency and reduce thermal bridging in exterior wall assemblies through the use of continuous insulation (ci) have increased the installation of ISO insulation or other products. To ensure fire safety is maintained in our pursuit of greater energy efficiency, the industry tests these exterior wall assemblies to rigorous fire performance standards.

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IBC Chapters 14 and 26

IBC 2018 requires exterior walls on buildings of Construction Types I-IV to comprise tested and evaluated assemblies. The specific requirements for assemblies or materials will be determined by Chapters 14 and 26. Within both sections of the code, fire testing of assemblies in accordance with NFPA 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components, is required under certain conditions.

As a general rule, according to 2018 IBC, exterior walls of any height on buildings of Construction Types I-IV containing foam plastic insulation “shall be tested in accordance with and comply with the acceptance criteria of NFPA 285” (Section 2603.5.5). It should be noted NFPA 285 is an assembly and not a material test. Therefore, approval is dependent on all components of the exterior wall assembly.

Under Chapter 26 of 2018 IBC, other performance requirements for foam plastic insulation apply when products are used in certain exterior walls. For example, foam plastic insulation products must have a flame spread index of 25 or less, and a smoke-developed index of 450 or less (Class A as tested per ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials, or UL 723, Standard for Test for Surface Burning Characteristics of Building Materials). Industry professionals should be familiar with the complete requirements of Section 2603.5 of 2018 IBC when specifying and installing foam plastic insulation in exterior walls of commercial buildings.

Additionally, Chapter 14 includes requirements for exterior walls that are constructed with other combustible components such as metal composite materials (MCMs) and exterior insulation finish systems (EIFS). The general rule for the use of foam plastic insulation still applies when used with various exterior wall coverings—exterior walls of any height for Construction Types I-IV that contain foam plastic insulation must be tested and comply with NFPA 285.

Details on NFPA 285

NFPA 285 provides a method for determining the flammability characteristics of exterior wall assemblies that are constructed with combustible components ranging from insulation and wall coverings to water-resistive barriers (WRBs). Developed from research initiated in the late 1970s and originally adopted as part of the Uniform Building Code (UBC) in 1988, NFPA 285 has been a keystone of building fire safety for many decades. The 2000 version of IBC was the first ICC-published code to incorporate NFPA 285, and the requirements have been expanded over subsequent versions to include additional assembly configurations.

POLYISOCYANURATE INSULATION PERFORMANCE

Polyisocyanurate (ISO) insulation is a closed-cell, rigid foam board consisting of a foam core sandwiched between two facers. When used as a continuous insulation (ci) on exterior walls, ISO can function both as a high-R, energy-efficient insulation solution—creating a thermal barrier that reduces thermal bridges—and as an environmental barrier to protect the building from air and water intrusion. ISO is widely known for its high R-value per inch compared to other insulation options, and is installed on the exterior side of the building’s structure or frame and covered by an exterior finish. Many building professionals may be familiar with ISO’s reputation as an insulation material for commercial roofing that delivers excellent thermal and fire performance. All construction materials, including ISO insulation, must provide a suitable margin of fire safety. ISO insulation possesses a high level of inherent fire resistance when compared to other foam plastic insulations due to its unique structure of strong isocyanurate chemical bonds. These bonds result in improved resistance to high temperature exposure as well as enhanced fire resistance. Additionally, ISO does not melt or drip when exposed to flame because it is a thermoset material. ISO forms a protective surface char when exposed to a sufficient flame, which resists the propagation of fire across the material (flame spread). This physical property is exhibited in the ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials, or “Steiner Tunnel” test where ISO insulation test specimens remain intact during the test’s fire exposure. Additionally, ISO can pass the National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components, without exterior gypsum or added fire-stopping around the windows. ISO’s fire performance may offer other advantages and flexibility desired by design professionals. Building professionals should verify with the manufacturer the installation guidelines applicable to the specific material and assembly.

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NFPA 285 provides a method for evaluating fire propagation of exterior wall assemblies for post-flashover fires of interior origin. The specific characteristics evaluated include the ability of the wall assembly to resist vertical and lateral flame propagation over the interior and the exterior surfaces and the cavity of the assembly and resistance to vertical flame propagation within the combustible components (NFPA 285, 2019). To achieve this, the method uses a full-scale, two-story (two room) test facility with a movable frame (Figure 1). The two-story wall assembly that will undergo testing is constructed on the test frame and moved and mounted onto the test apparatus. As required by the standard, the test assembly includes a specifically sized window opening. Two gas burners are used to sustain fire. One is placed inside the first-story test room (test room burner), and the window gas burner is fixed outboard of the wall opening.

The primary performance characteristics evaluated by NFPA 285 are the capability of the entire test wall assembly to resist the following:

• flame propagation over the exterior face of the wall assembly;
• vertical flame propagation within the combustible core components from one story to the next;
• vertical flame propagation over the interior (room side surface of the panels from one story to the next); and
• lateral flame propagation from the compartment of fire origin to adjacent spaces.

The test’s performance requirements are assessed both through visual observations and temperature data obtained during the 30-minute burn (plus an observation period) via thermocouples located throughout the wall assembly.

Compliance with NFPA 285

The most straightforward way to demonstrate a wall assembly complies with NFPA 285 is an existing or new test report. In this scenario (where a test report is used), the components of the specified wall assembly and configuration must be the same as the materials and configuration tested at the accredited laboratory. Product manufacturers, including ISO insulation manufacturers, have conducted thousands of fire tests under NFPA 285 requirements. However, given the number of materials that are used in modern construction and the variability in configurations, it would be impossible to test every possible exterior wall configuration.

Therefore, similar to many other applications (e.g. structural) under the code, IBC recognizes the ability to use engineering practices to evaluate substitute materials or different assembly configurations. An engineering judgment is a professional analysis letter issued by a competent expert with relevant training, licensing, and/or experience in the fire engineering field. Engineering judgments must be based on at least one baseline tested or approved assembly. The author of the engineering judgment will then use fire test data to compare the substitute material to the material tested in the baseline assembly and evaluate how the substitute material will perform when combined with the other components of the evaluated assembly. Like the test itself, the engineering judgment is concerned with how the overall assembly will perform as compared to the baseline assembly. In instances when other aspect of the assembly differ (e.g. air gap within the assembly), the evaluator may take other considerations, data, and past experience into account. Ultimately, the engineering judgment is intended to answer the question: “Does the variation, change, or substitution provide a wall assembly that exhibits the same or similar fire performance as the based NFPA 285 test(s)?”

In the case of ISO insulation, an engineering judgment may be used to qualify the use of a thinner insulation board as compared to a thicker one that was part of the baseline assembly. Engineering judgments may also allow for the substitution of other materials that comprise the wall assembly (e.g. exterior wall covering, WRB). It is important to note under IBC’s model code language, the authority having jurisdiction (AHJ) has the authority to accept (e.g. “acceptable to the code official”) the engineering judgment for a specific project.

Conclusion

Today’s fire safety codes and standards have evolved in response to failures and successes of the past. The codes and standards protecting buildings and occupants are continually reviewed and updated as necessary. It is important for design professionals and other key stakeholders in the construction industry to be familiar with the requirements for fire safety and performance and energy efficiency that apply to exterior wall assemblies using ISO ci or other products. Building professionals should always consult the local code requirements and/or verify said requirements with local officials. With this knowledge, a wide variety of materials can be used to construct safe and high-performing exterior wall systems.

[5]Marcin Pazera, PhD, is the technical director for Polyisocyanurate Insulation Manufacturers Association (PIMA). Pazera coordinates all technical-related activities at PIMA and serves as the primary technical liaison to organizations involved in the development of building standards. He holds a doctoral degree in mechanical engineering from Syracuse University. He has expertise in building enclosure and product manufacturing encompassed-research, testing, product conception and development, and computer modeling/analysis.

Source URL: https://www.constructionspecifier.com/continuous-insulation-performance/

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