Insulation and Vapor Retarders as Interior Finishes

by Marcy Marro | December 1, 2020 12:00 am

By David Tomchak

International Building Code (IBC) and Metal Building Insulation

Chapter 8 Interior Finishes, Section 803.1.1 of the IBC states interior wall and ceiling finish materials shall be classified in accordance with ASTM E84 (UL 723) and classified as the following:

Class A = Flame spread index 0-25; smoke developed index 0-450
Class B = Flame spread index 26-75; smoke developed index 0-450
Class C = Flame spread index 76-200; smoke developed index 0-450

Within a metal building, fiberglass insulation is most commonly specified and used in the walls and ceilings and left exposed to the interior of the building. Fiberglass insulation can also be specified in concealed spaces and in plenum applications. For example, insulation can be specified to be left exposed within an enclosed cavity of a metal building, which will serve as the return air plenum for the HVAC system.

Depending on the specified application, various building codes have Class requirements for the specified product being used.

Plenum applications. The following codes have specific requirements regarding this:

International Mechanical Code (IMC)
Uniform Mechanical Code (UMC)
National Fire Protection Agency (NFPA 90A)

All state that any insulation material exposed within a plenum must have:

Flame Spread < 25
Smoke-developed < 50

Insulating materials in concealed spaces. This is addressed by the IBC, Section 720.2, stating that the insulation must be Class A:

Flame Spread < 25
Smoke-developed < 450

As stated previously, the most common use of insulation in a metal building is for walls and ceilings, where it is left exposed. The IBC, Section 720.3 requires all exposed insulating materials be Class A:

Flame Spread < 25
Smoke-developed < 450

When it comes to insulating metal building ceilings and walls, there are several system options that can be specified. Per ASHRAE 90.1-2019, insulation systems can be single layer, double layer, liner system or filled cavity. In each of these systems, the insulation can be either faced (laminated) or unfaced.

In general, regarding fiberglass insulation systems within a metal building, there are three types of building materials that need to be Class A: unfaced metal building insulation, vapor retarders and faced metal building insulation.

Common Misconceptions Regarding Faced Metal Building Insulation

There is a significant difference between ASTM E84 (UL 723) testing on individual materials versus composite materials.

If the specified insulation system consists of faced metal building insulation that will be exposed to the interior of the structure, it must be Class A to meet code. Faced insulation is considered a composite material and therefore must be tested as such.

What does that mean? Faced metal building insulation is composed of fiberglass blanket, a vapor retarder facing and some type of adhesive. If the unfaced insulation has been tested and is Class A, and the vapor retarder facing has been tested and is Class A, and the adhesive has been tested and is Class A, it does not mean that the faced metal building insulation is Class A.

The true Class rating of faced metal building insulation can only be known by testing the material when all components are together, as a finished composite product.

Regarding fiberglass insulation systems within a metal building, there are three types of building materials that need to be Class A: unfaced metal building insulation, vapor retarders and faced metal building insulation.

How Do I Know if the Faced Metal Building Insulation I’m Specing is Class A?

The only way to know is if the surface burning characteristics index rating is on the product label. There are third-party certification companies that work with manufacturers to ensure that products comply with the ASTM E84 (UL 723) requirements.

As an example, many manufacturers use Underwriters Laboratories (UL) for certification. Certification with UL means that a product has been tested and is manufactured to consistently match the same parameters of the original product that was tested and complies. As an added assurance, the manufacturing facility keeps records of all production, and is routinely visited and evaluated by the third party. In this case, it would be UL. As a result, a UL Classification Mark would be printed on the label, as can be seen in Figure 1. The FHC 25/50 on this label refers to Fire Hazard Classification, with 25 being the flame spread index and 50 being the smoke developed in index. Therefore, the product would be Class A material.

In summary, the vast majority of fiberglass insulation systems in metal buildings should be specified as Class A material in order to comply with building codes. The only way to be certain that the materials specified to be used will meet building codes is if the surface burning characteristics index rating is on the product label (as in Figure 1).

David Tomchak is the director of marketing for Bay Insulation Systems, Green Bay, Wis. He currently serves on the board of directors for the Metal Building Manufacturers Association (MBMA), is an active participant in the Metal Building Task Group within the ASHRAE 90.1 envelope sub-committee, and serves on ASTM C16 and E05 committees. To learn more, visit www.bayinsulation.com[1].

Endnotes:

www.bayinsulation.com: http://www.bayinsulation.com

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