Post Grenfell, Do You Know the Code and Your Cladding Options?

By Kevin Kutschenreuter, Larry Wainight and Kirk Grundahl, P.E.

Given recent concern over combinations of foam plastic insulated sheathing (FPIS) with different types of cladding since the Grenfell Tower fire, it is worth taking a specific look at both the extent of cladding options available with FPIS and the important restrictions. Strictly keeping to the IBC can help keep builders and designers from both overreacting to a tragedy like the Grenfell Tower fire and from perpetuating unsafe practices.

The IBC directs builders and designers to a series of basic questions when it comes to cladding exterior non-load bearing walls. These questions include:

  1. What is the building occupancy? IBC Chapter 3.
  2. What type of building is it? IBC Chapter 6.
  3. What is the building’s height and area? IBC Chapter 5.
  4. How close is the building to other buildings? IBC Chapter 6.
  5. Will it have a sprinkler system? IBC Chapter 9, Chapter 14.
  6. Does it need to meet the NFPA 285 test standard? IBC Chapter 14, Chapter 15, and Chapter 26.

Question 6 is especially important when it comes to wall assemblies containing FPIS, and it is one of the more complex in this series to answer. Therefore, this article considers the IBC requirements surrounding the NFPA 285 test standard and its effects on allowable cladding, particularly in reference to FPIS assemblies.

NFPA 285: Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-Load-Bearing Wall Assemblies Containing Combustible Components

The NFPA 285 standard fire test mimics a fire that starts on the interior of the building in a room that reaches flashover, exits a window opening and impinges on the exterior of the building. A successful test is one where both the vertical and horizontal spread of the fire is limited.  The goal is to prevent the spread of fire horizontally to rooms on either side of the room of origin or vertically to the floor above the room of origin as well as along the face of the exterior wall, and inside the wall assembly. The test is generally required when there are combustible products in the wall assembly that is otherwise required to be of non-combustible construction. Walls containing Insulation products and cladding products such as aluminum composite panel (ACM) or metal composite panels (MCM) are required to be tested and pass the NPFA 285 fire test. 

NFPA 285 is typically required for wall assemblies that are over 40 feet tall and contain a flammable water-resistive barrier. The test, however, is waived in instances where the water-resistive barrier is the only combustible element and it is surrounded by substantially non-combustible materials, or when the water-resistive barrier has a demonstrably low heat release rate, heat of combustion, flame spread and smoke developed properties.

The IBC specifies, in a number of sections, exterior wall assemblies that must meet NFPA 285. These include when:

  1. There is a combustible water resistive barrier (Section 1403, note the exceptions).
  2. MCM is used (Section 1407.10),
  3. Exterior insulation and finish systems (EIFS) are used (Section 1408.2),
  4. Exterior high pressure laminate (HPL) systems are used (Section 1409.10.4),
  5. The wall assembly is used to screen mechanical equipment mounted on roofs (Section 1510.6.2), and
  6. FPIS is used (Sections 1404.8, 1404.13, and 1406.2).

In the sections of Chapter 14 that address FPIS specifically, Chapter 26 is referenced, and, of particular relevance, Section 2603.5.5 states that FPIS must meet NFPA 285.

However, 2306.5.5 lists some exceptions:

1. One-story buildings complying with Section 2603.4.1.4 as defined below. 

2. Wall assemblies where the foam plastic insulation is covered on each face by not less than 1-inch (25 mm) thickness of masonry or concrete and meeting one of the following: 

2.1. There is no airspace between the insulation and the concrete or masonry. 

2.2. The insulation has a flame spread index of not more than 25 as determined in accordance with ASTM E84 or UL 723 and the maximum airspace between the insulation and the concrete or masonry is not more than 1 inch (25 mm).

Exception 1 refers to 2603.4.1.4, which specifies a wall assembly in which the FPIS:

  1. Has a flame spread index of 25 or less
  2. Has a smoke-developed index of 450 or less,
  3. Is not more than 4" thick,
  4. Is covered with .032" thick aluminum or .0160" corrosion resistant steel, and
  5. Is in an application where an automatic sprinkler system is installed.

Exception 2 specifies a wall assembly where the FPIS is:

  1. Covered by a thermal barrier of at least 1" masonry or concrete and either
    1. No airspace between the FPIS and masonry/concrete,
    2. A flame spread index less than 25 and a maximum airspace of 1".

When these exceptions are met, NFPA 285 is not required.

Alternative Materials

Of note, not every possible wall configuration that needs to meet the NFPA 285 test standard is required to actually be tested. A certain degree of engineering analysis is allowable according to IBC 104.11, which states,

The provisions of this code are not intended to prevent the installation of any material or to prohibit any design or method of construction not specifically prescribed by this code, provided that any such alternative has been approved. An alternative material, design or method of construction shall be approved where the building official finds that the proposed design is satisfactory and complies with the intent of the provisions of this code, and that the material, method or work offered is, for the purpose intended, at least the equivalent of that prescribed in this code. … Where the alternative material, design or method of construction is not approved, the building official shall respond in writing, stating the reasons the alternative was not approved.

For example, where it can be demonstrated that a material tested in an NFPA 285 test can safely be replaced with no loss of fire resistance (or any other code-specified quality), that material is considered acceptable for that assembly without the need to conduct another NFPA 285 test. For example, an assembly may have passed an NFPA 285 test with an aluminum composite panel (ACM). Substituting ACM with MCM would likely be acceptable, as MCM is generally more fire-resistant and would serve to increase the fire-resistance of the assembly as a whole. Similarly, if the assembly has passed with the ACM, any non-combustible cladding would generally be accepted. These assessments are best left to fire protection engineers, professionally engineered and sealed design and/or an ANSI ISO/IEC 17065 product certification agency technical evaluation report where generally accepted engineering processes are in place to evaluate such assemblies.

In the end, as IBC 104.11 states, the building official must determine that “the proposed design is satisfactory and complies with the intent of the provisions of this code”… and if the building official decide it does not then “the building official shall respond in writing, stating the reasons the alternative was not approved.” Additionally, generally accepted engineering and a professional engineer’s seal is good way for a building official to know that an engineer is in under the authority of all engineering laws and the engineer has taken responsibility for the analysis generated.  

For more information, please see the following website locations:

NFPA 285 Testing and the Use of Engineering Extensions in Wall Assemblies Using Foam Sheathing

Foam plastics used in buildings of Types I-IV construction require an assessment of their ability to resist vertical and lateral flame spread.

For additional articles on this issue, please see: