Cladding Safety with Metal Composite Material (MCM) and the NFPA 285-19

Faced with an updated test protocol for fire propagation, metal composite material cladding is passing the test
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Sponsored by Metal Construction Association's Metal Composite Material (MCM) Alliance
By Barbara Horwitz-Bennett

Insulation

On the topic of exterior insulation, Nelson explains that hygrothermal and thermal performance push increased insulation values to the exterior of the wall assembly as “ci,” or continuous exterior insulation.

At the same time, it’s important to be aware that all insulation is not created equal. In rating product types from worst to best, based on performance when exposed to fire, exterior insulation types rate as follows: spray polyurethane foam (SPF) open-cell, expanded polystyrene (EPS), extruded polystyrene (XPS), SPF closed-cell, polyisocyanurate (ISO), and mineral fiber.

Mineral wool insulations are a good choice, but if this is the only product specified, in order to confirm that a particular product is up to par, specifiers should request ASTM E136 test results from the mineral wall manufacturer.

In general, from a fire-protection perspective, XPS and EPS will not meet the requirements of NFPA 285 when used with aluminum composite materials. As is the case with WRBs, fire performance varies by chemistry type and by manufacturer, so specifiers should refer to individual manufacturers for specific fire performance information, in addition to test reports, certification reports, and/or engineering judgments.

With regards to how NFPA 285 and weather barriers currently tie into the IBC, testing is required for wall assemblies that exceed 40 feet in height, with some exceptions. One exception can be made if:

  1. Walls in which the WRB is the only combustible component and the exterior wall has a covering of brick, concrete, stone, terracotta, stucco, or steel, with minimum thicknesses in accordance with Table 1405.2 in the IBC
  2. WRB is the only combustible component in the wall and meets combustibility thresholds.

In addition, windows and doors, and flashing for windows and doors, are considered to be part of a water-resistive barrier for purposes of this section in the code. Consequently, WRBs trigger a review for NFPA 285 compliance, per chapter 14, when used with another combustible material in the wall assembly. At the same time, certain WRBs do not require NFPA 285 on buildings over 40 feet tall if they are the only combustible product in the wall assembly.

If the WRB is the only combustible component in the wall, it must meet the following performance criteria, per ASTM E1354, “Standard Test Method for Heat and Visible Smoke Release Rates for Materials and Products Using an Oxygen Consumption Calorimeter,” to qualify for an NFPA 285 testing exception:

  • When tested at 50 kW/m2, the peak heat release rate must be less than 150 kW/m2
  • The total heat release must be less than 20 MJ/m2
  • The effective heat of combustion must be less than 18 MJ/kg

Per ASTM E84, the flame-spread index must be ≤ 25 and the smoke developed index must be ≤ 450. NFPA 285 testing is required of wall assemblies containing plastic insulation (EPS, XPS, ISO) at any height with the exception of single-story buildings complying with Section 2603.4.1.4 of the IBC. This exception is intended for cold storage buildings. Also, insulated metal panels (IMPs) containing foam plastic insulation are governed by chapter 26 of the IBC.

Section 2603.5 of the 2018 IBC references “Exterior Walls of Buildings of any Height.” Because foam plastic insulation is combustible, compliance with NFPA 285 needs to be demonstrated in accordance with 2603.5.5. Furthermore, the exception requires that the insulation not exceed 4 inches in thickness and it must be covered by aluminum or steel. The minimum base metal thickness for the aluminum is 0.016 inches. An MCM facing of 0.019 inches meets this criterion. Authorities Having Jurisdiction (AHJ) have at times, however, negated MCM because its core does not fit the definition of a “foam plastic” core in 2603.

To summarize, the following conditions will create an NFPA 285 trigger, and therefore require that the wall assembly pass the test for flame propagation allowance before the assembly is recognized as meeting the performance requirements of the code.

  • Combustible claddings taller than 40 feet
  • Noncombustible and combustible claddings with plastic insulation for buildings of any height (with the single-story exception discussed above)
  • Noncombustible claddings, measuring more than 40 feet in height, if used with certain combustible WRBs

In addition to NFPA 285 requirements, as previously noted, MCM cladding is also subject to meeting a number of other standards. This includes a Class A Rating, which can be achieved by showing a flame-spread index of less than, or equal to, 25, and a smoke-developed index less than, or equal to, 450, per ASTM E84. The MCM must also be separated from the interior by a thermal barrier, typically gypsum.

IBC Product Labeling

Per the IBC 1406.14, MCM panels must be tested, inspected, and labeled. Per the IBC 1703.5, an approved testing agency must be utilized to test a representative sample of the MCM to relevant IBC code test standards, to maintain a record of the testing performed, provide sufficient detail to verify compliance with the test standard, and periodically perform an inspection of the in-plant manufacturing.

These third-party inspections maintain a level of quality by ensuring that what architects are specifying has been verified by an independent third party. This third party will evaluate the performance of the MCM. There are several labs that test the MCM and MCM systems. While the IBC does not require such an evaluation, it is highly recommended for quality assurance.

As an example, the International Code Council Evaluation Services Evaluation Services (ICC-ES) Report program provides a level of confidence to end-users by ensuring that the right tests in the IBC have been performed. In addition, ICC-ES has developed an Acceptance Criteria for MCM manufacturers. ICC-ES also ascertains that a third-party inspection program exists, ensuring that the MCM manufacturer continues to make a product of the same production quality. This is accomplished by monitoring the production of that material and the quality standards of the facility producing it.

An ICC-ES Evaluation Report includes the following:

  • Data on the product report holder and a description of the building product and its intended uses
  • The code(s) that were used to evaluate the product and a brief description of the product's properties
  • Installation instructions that identify requirements to help the inspector ensure the product is installed properly in compliance with the tested assemblies.
  • List of data (i.e., test reports, calculations, installation instructions) that were used in evaluating the product
  • Information to help identify the product in the field

 

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Originally published in Architectural Record
Originally published in January 2022

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