Compliance Methods for Vertical and Lateral Flame Propagation (NFPA 285)

A particularly important revision to the 2024 IBC is the inclusion of a new Section 1402.8 that prescribes three methods for establishing compliance of exterior wall assemblies when the code requires the exterior wall assembly is tested in accordance with, and comply with the acceptance criteria of, NFPA 285. The three compliance methods are:

1. An exterior wall assembly tested in accordance with and meeting the acceptance criteria of NFPA 285.

Method 1 establishes compliance using specific NFPA 285 tests, conducted on test specimens of the specific exterior wall assembly configuration as it is to be constructed. This approach provides the most direct evidence of compliance for a specific set of building materials configured in a specific way.

2. An exterior wall assembly design listed by an approved agency for compliance with NFPA 285.

Method 2 establishes compliance through reference to a wall design that is listed by a third-party agency for compliance with NFPA 285. The wall assembly intended to be built must conform to the design as it is presented, or otherwise recognized, by the listing.

Wall assembly designs listed by a third-party agency are, at a minimum, based on at least one successful NFPA 285 test. Depending on the agency’s certification scheme and the scope of assembly designs recognized by the listing, a listed design might be further supported by additional information and data (up to, and including, multiple NFPA 285 tests). Finally, listing and certification typically requires initial product verification and some amount of ongoing manufacturing quality control and periodic review to maintain the listing.

3. An approved analysis based on an assembly or condition tested in accordance with and meeting the acceptance criteria of NFPA 285.

Method 3 explicitly prescribes the use of analysis to establish compliance. Within this provision, though, are two (2) crucial elements. The first being that the analysis must be based on an assembly or a condition that has been tested and complies with NFPA 285. Such a requirement ensures the starting point of the analysis is an assembly known to comply with NFPA 285 or a condition (e.g., a window head detail) in an assembly known to comply with NFPA 285. The second element requires approval of the analysis by the building official. This approach is often used to evaluate reasonable modifications to an assembly that has already been tested; examples include more robust base walls or different window/fenestration closures.

Commonly referred to as engineering judgements, EJs, or extensions of results, these analyses are the most practical, and commonly used, method used to establish code compliance of wall assemblies required to be tested to, and meet the acceptance criteria, of NFPA 285. The 2023 Edition of NFPA 285 includes a new Annex B Guide for Extensions of Results from Assemblies that Meet NFPA 285. Although the 2024 IBC references an earlier edition of NFPA 285 (the 2019 Edition), the information and guidance provided by Annex B may prove insightful for any party reviewing one of these analyses. NFPA provides free digital access for viewing NFPA standards. Go to nfpa.org for more information on free access to view NFPA 285 and other NFPA standards referenced in the I-Codes.

Each of the compliance methods has its benefits and challenges. For example, while the first method offers the most specific evidence of compliance, one or more NFPA 285 tests for the size of a project or the scope of assemblies in a given project may not be feasible due to the cost and logistics involved in testing. On the other hand, the third method offers flexibility but requires a high level of expertise to help ensure the analysis is accurate and reliable.

Clarification of Height Limitations in Section 1405.1.1

The 2024 IBC revises a code conflict regarding height limitations for combustible exterior wall coverings on buildings of Type I, II, III, and IV construction. A prescribed general height limitation of 40 feet has been clarified for materials and systems such as Metal Composite Materials (MCM) systems and Exterior Insulation and Finish Systems (EIFS) that are on exterior walls subject to provisions requiring those wall assemblies are tested to and comply with NFPA 285.

Section 1405 provides general requirements and limitations for the use of combustible materials on the exterior side of exterior walls. Section 1405.1.1 establishes four limitations to the use of combustible exterior wall coverings on buildings of Type I, II, III, and IV construction. One of these limitations (Item 2) prevents combustible exterior wall coverings on walls greater than 40 feet in height above grade plane. Experienced code users know there are several sections within Chapters 14 and 26 that permit uses over 40 feet based on NFPA 285 testing and compliance. Section 1405.1.1 was revised (revisions in bold text) to correct that conflict:

1. 1405.1.1 Types I, II, III, and IV-HT construction. On buildings of Types I, II, III and IV-HT construction, exterior wall coverings shall be permitted to be constructed of combustible materials, complying with the following limitations:
2. Combustible exterior wall coverings shall be limited to 40 feet (12 192 mm) in height above grade plane.

Exceptions:

1. Metal composite material (MCM) systems complying with Section 1406.
2. Exterior insulation and finish systems (EIFS) complying with Section 1407.
3. High-pressure decorative exterior-grade compact laminate (HPL) systems complying with Section 1408.
4. Exterior wall coverings containing foam plastic insulation complying with Section 2603.[…]

Section 1403 for Materials

Section 1403.8 (2021 IBC) for plastic panels, aprons and spandrel walls was removed from the 2024 IBC. This section, dating back over 20+ years, had become outdated and ineffectual as Chapters 14, 16, 17, and 26 have evolved to contain additional and more specific requirements for uses of plastic materials in exterior walls and wall assemblies.

New Section 1403.14 for insulated vinyl siding was added to the IBC along with the new defined term. Section 1403.14 requires the insulated vinyl siding cladding products are labeled by an approved agency for compliance with the requirements of ASTM D7793.⁴

Section 1407 for Exterior Insulation and Finish Systems (EIFS)

A new Section 1407.5 requires exterior wall assemblies containing EIFS to comply with Section 2603.5. The effect of this new provision is to help ensure the EIFS containing foam plastic insulation complies with the applicable requirements for the use of foam plastic insulation in exterior walls of buildings of all types of construction. Section 2603.5 contains fire safety provisions that include verification of fire-resistance ratings, testing for resistance to radiant ignition, testing for vertical and lateral flame spread, and other requirements.

New Section 1409 for Insulated Metal Panel (IMP) Systems

Recent decades have shown an increase in the understanding and use of Insulated Metal Panel (IMP) systems in building envelope applications. These versatile building products and systems have historically relied on Research Reports and ICC Evaluation Service (ICC-ES) Acceptance Criteria for establishing code compliance because the IBD did not recognize or contain requirements for IMPs as a building product. The new Insulated Metal Panel (IMP) defined term and Section 1409 help ensure differentiation of IMPs from other building products and establishes the minimum requirements for the different types and different uses of IMP products and systems in exterior wall assemblies today, for example:

• Differing requirements applicable to IMP panels with noncombustible core insulation vs. combustible core insulation.
• Differing requirements applicable to IMP systems used as the exterior wall or as an exterior wall covering.
• Differing structural and wind load design requirements based on use.
• Various fire safety provisions, including:
  • Use in exterior walls of Types I, II, III, IV, and V construction.
  • Use in exterior walls required to have a fire-resistance rating.
  • Surface burning characteristics of combustible core insulation.
  • Resistance to ignition and flaming from radiant exposure.
• Labeling