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Meeting the Codes: Polymer Pipes in Plenums

May 19, 2024
Prioritizing fire safety, one insulation expert discusses substrate, thickness, and installation options.

By BILL TOLLIVER, Product Technical Manager, Pipe & Insulation, Owens Corning

A recent webinar question really opened my eyes to the importance of understanding several factors regarding polymer pipes in plenums and meeting the codes. An attendee asked, “Why don’t you use aluminum foil to wrap polymer pipes to meet the code in plenum spaces since it passes the surface burning results of 25/50 according to ASTM E84?” 

Because of this question, I felt it important to explain factors that come into play with polymer pipes in plenum and meeting the code. In this article, we will explore the factors that should be evaluated when covering pipes and components in plenum areas as well as trends in the market regarding pipes installed in these spaces.

Supporting fire safety from the top

Let’s begin by describing the plenum area, the purpose it serves in a commercial building and the potential fire risks this area presents. Typically located above a suspended ceiling in commercial buildings, the plenum is an open-air space that passively carries supply or return airflow through it.

Plenums often house a complex network of mechanical pipes along with connections that support fire protection, electric conduits, water supply pipes and drains. The continuous airflow in plenum areas means that an abundance of oxygen is available to facilitate the spread of smoke and flames in the event of a fire.

To help address this concern, both the International Building Code (IBC) and the International Mechanical Code (IMC) require that materials such as cables, wires, piping and insulation meet special requirements regarding their flammability. The International Building Code (IBC) Section 720.7 Insulation and covering on pipe tubing states that insulation and covering on pipe and tubing shall have a flame spread index of not more than 25 and smoke-developed index of not more than 450 according to the test method ASTM E84. An exception to this requirement is that insulation and coverings on pipe and tubing installed in plenums must comply with the International Mechanical Code (IMC).

The International Mechanical Code (IMC) sets forth the following requirements in Section 602.2.2 Materials with plenums. Except as required by sections 602.2.1.1 through 602.2.1.8, materials within plenums shall be noncombustible or shall be listed and labeled as having a flame spread index of not more than 25 and a smoke-developed index of not more than 50 when tested in accordance with ASTM E84 or UL 723. A list of exceptions is provided. Exception 5.3 states “Combustible materials fully enclosed within materials listed and labeled for installation within a plenum and listed for the application."

Thus, combustible materials, such as polymer pipes that do not meet surface burning characteristics of ASTM E84 or UL723 with a flame spread index of not more than 25 and smoke developed index of not more than 50, often called FHC 25/50, can be used in the plenum space if fully enclosed within materials which are listed and labeled for installation within a plenum and listed for the application.

Look beyond the FHC ratings

As the webinar atendee’s question acknowledged, aluminum foil tested alone meets ASTM E84 with a surface burning characteristic of FHC 25/50. However, this rating, as tested, does not make it an appropriate material for covering polymer pipes to meet the code in plenum spaces. To meet the code, the material, in this case aluminum foil, would have to have been tested as an assembly with the polymer and “listed and labeled” for use in the plenum.

As an example, the Owens Corning ASJ Max jacketed Fiberglass pipe insulation is listed and labeled with the third-party Underwriters Laboratories (UL). The certification to “Insulated plastic pipe assemblies” (BSMP) signifies that the pipe insulation has been tested to be in compliance with IMC, section 602.21, exception 5.3”. Included in the test report and part of the requirement to claim compliance, are details that include the insulation manufacturer, product description, minimum insulation thickness, and the type and thickness of polymer piping being covered.

Factor in different polymer pipe materials

An essential factor to consider when looking at a manufacturer’s compliance statement is the type of polymer listed in it. There is an ongoing trend toward the use of more types of polymer pipes in the plenum. These polymer pipes tend to be lighter weight and more economical than steel or steel alternatives, as well as quicker to install. Polymer pipes can easily be cut to the desired length, and they don’t corrode.

However, testing and listing has not kept up with the growth of the many types of polymers and not all insulation manufacturers offer products tested and listed for this market. Ensuring that an insulating material is tested and listed for installation on a particular polymer pipe is an essential step in selecting a pipe insulation.

Beyond PVC/CPVC and polypropylene (PP-R) pipes, listed and labeled pipe insulation material may not be available for some polymer pipes such as ABS, polyethylene (PE) and polyurethane (PU) pipes to be used in plenums. In instances where a listed and labeled pipe insulation material is not available, plenum wrap may be used to wrap pipes. Plenum wrap typically has mineral wool inside it to help support fire safety and has a heavy foil facing on both sides.

A higher price point compared to other insulating options and handling on the jobsite are challenges with plenum wrap. Several steps are involved, and the wrap must be cut and wrapped/fitted around various components. Plenum wrap can be particularly challenging to use on small pipes.

While the code calls out some fire sprinkler piping, pneumatic tubing and other components that do not need to be tested and listed, the tubing or piping must meet specific requirements as detailed in IMC Section 602.2.1.2 and 6-2/2.1.3, respectively.

Consider the thickness of the polymer pipe

Insulation materials which are listed and labeled for covering polymer pipes in plenum spaces indicate in the certification the minimum thickness of the insulation as well as the maximum thickness that the insulating material can cover. The minimum insulation thickness must be met to assure the FHC rating can be met. Keep in mind that while insulation may meet the sufficient thickness required to deliver fire protection on polymer pipes per the manufacturer’s literature, it may not be sufficient to meet other requirements such as condensation control, freeze protection or process control needs.

The thickness of the polymer refers to the wall thickness of the polymer pipe and these values can be found online in tables according to their size and schedule.

Protecting product integrity in the install

Selecting the correct thickness of insulation must be followed up with proper installation on plenum pipes to maintain the integrity of the fiberglass.

The type of hanger used to support the pipe and insulation is important. Choose oversize hangers with saddles, as inline hangers may require removal of fiberglass. Removing fiberglass insulation will mean reducing the amount of fire protection.

The proper thickness of the insulation is essential to supporting life safety in the plenum. And when installing, Owens Corning recommends oversizing the insulation over valves and fittings to avoid any cuts that could decrease fire protection. For these scenarios, Owens Corning’s pipe insulation offers FlexCore technology that allows the pipe to be installed over smaller size pipes without the need to filet at fittings. Not only does this reduce the need to filet out material but it can also help save time and effort during the installation.

Safety will always be the top priority in the plenum area. Giving careful consideration to the materials that wrap polymer pipes can help protect an area that is typically out of sight but should never be overlooked.

About the Author

Bill Tolliver

Based in Granville OH, Bill Tolliver is a product technical manager for Pipe & Mechanical Insulation at Owens Corning. He first joined the company in 1992.