Consider PEX for buried, gray-water uses

The durability and flexibility of PEX piping makes it an excellent choice for buried/in-slab applications.

The durability and flexibility of PEX piping makes it an excellent choice for buried/in-slab applications.

In the past 15 years, PEX (cross-linked polyethylene) piping has become an increasingly popular product in the commercial building sector due to its flexibility; superior resistance to freeze damage, scaling, and corrosion; and stable material costs.
   Though PEX is a great product to replace metallic piping in the typical overhead applications, its real benefit comes with in-slab and below-grade installations where the product’s flexibility and continuous lengths can be utilized.

Below-grade Applications
For below-grade applications, certain PEX products can be directly buried in soil environments free of solvents (check with local code for burial approvals). For installations requiring a watertight piping system, look to a pre-insulated product that offers nominal diameters of 3/4 to 4 in., with a corrugated HDPE outer jacket and inner closed-cell PEX-foam insulation.
   Ideal building types for below-grade installations are single-level, retail-type layouts with large footprints and grouped fixtures. The PEX piping is typically routed from the building’s mechanical room through a trench to the various wet walls throughout the building. Installers can cut considerable amounts of time from projects by eliminating the need for lifts to install overhead hangers and supports.

In-slab Applications
Some PEX piping can also be installed directly in concrete. It’s best to take advantage of the flexibility of PEX piping to arrange the piping scheme so that fittings are out of the slab. However, if fittings must be buried in the slab, they must be approved for concrete burial. Another option is to use PEX products with an HDPE corrugated outer jacket. This jacket protects the piping from being damaged during the construction process.
   In-slab PEX piping is ideal for many applications, ranging from single-level churches and schools to high-rise multifamily buildings where pipe can be placed in the concrete slab, reducing the amount of overhead work required.

Gray-Water Applications
PEX products also are an excellent option for reclaimed water (or gray water) applications. In a gray-water system, water from sinks and showers is diverted to a holding tank where it goes through a filtering process. PEX reclaimed-water pipe distributes the filtered, reclaimed water from the holding tank to laundry, toilets and irrigation systems. For gray-water applications, reclaimed-water pipe is available in 1/2-, 3/4-, and 1-in. nominal sizes. Pipe for use with reclaimed water should be listed to NSF 14 (noted by cNSFus marking on the pipe) and NSF-rw for non-potable applications.
   For more assistance with using PEX for these types of applications, use the Uponor Plumbing Design Assistance Manual (PDAM), which is available at no cost at

Daniel Worm is associate product manager for plumbing at Uponor Inc., Apple Valley, MN. He can be reached at