In a meeting with the NAHB Construction Liability, Risk Management, and Building Materials Committee at the 2020 International Builders' Show, Lance MacNevin, director of engineering for the Plastic Pipe Institute’s Building and Construction Division, informed members of potential risks with certain types of plastic tubing used in home building. Specifically, he discussed the need to prevent accidental overexposure of crosslinked polyethylene (PEX) tubing and pipe to sunlight (UV light) to avoid damaging the long-term performance of the pipe.
MacNevin prepared the following information on the issue specifically for home builders.
Plastic piping materials are ideal for plumbing, fire protection and hydronic applications, with inherent advantages such as resistance to corrosion, ease of installation, light weight and lower material cost, not to mention environmental advantages.
But some types of plastic materials have sensitivities to the ultraviolet (UV) waves in natural sunlight. UV damage is not visible to the naked eye, but excessive UV exposure of certain plastic materials can lead to long-term degradation and a potentially reduced service life unless they are properly protected.
PEX tubing is one such material, especially when it is used in hot-water plumbing systems with disinfectants such as chlorine.
All distributors and users should know that PEX is not intended to be stored outdoors, and that even when stored indoors, PEX should be kept in the original packaging prior to installation for protection against UV/sunlight and other potential hazards.
Creating a UV-resistant PEX tubing material that is protected from incidental exposure to sunlight during installation is achieved through special formulations. Manufacturers add UV stabilizers or carbon black into the HDPE compound that is the building block of PEX before it is extruded, or manufacturers can extrude UV-blocking and absorbing barrier layers to exterior of the PEX tubing wall during manufacturing.
But how can end-users know how UV-resistant one brand or type of PEX tubing is?
To evaluate the UV resistance of a particular PEX tubing, manufacturers have their tubing tested and certified according to ASTM Standard Test Method F2657 Standard Test Method for Outdoor Weathering Exposure of Crosslinked Polyethylene (PEX) Tubing. ASTM F2657 provides manufacturers with a recognized test method for establishing claims of UV resistance, and is based on natural exposure in the worst-case North American location near Phoenix.
Keep in mind that a month near Phoenix may be equivalent to two to three months in other locations.
The evaluation procedure is described in ASTM F876 Standard Specification for Crosslinked Polyethylene (PEX) Tubing. ASTM F876 includes four categories for minimum UV resistance performance:
- 0 = Not tested or not rated
- 1 = one month
- 2 = three months
- 3 = six months
The verified UV resistance is marked on PEX tubing as the second digit in the PEX Tubing Material Designation Code (e.g., 5106), and should also be clearly described in a label on the PEX labeling, with wording as described in PPI Technical Note TN-32 “UV Labeling Guidelines for PEX Tubing and Pipe.”
Home builders should look for this rating when determining how to handle PEX tubing and piping.
Lance MacNevin, P.Eng., is director of engineering for PPI’s Building & Construction Division, focusing on pressure piping materials for plumbing and mechanical systems. He serves on committees within ASPE, ASTM, AWWA, CSA, IAPMO, IGSHPA, NSF, RPA and other industry organizations.