When Rice Building Systems of Sauk Rapids, Minn., set out to construct a new concept store for St. Cloud, Minn.-based Coborn’s Inc., they had strict orders to capitalize on innovative materials and efficient design, while maintaining the 90-year-old Midwest grocery chain’s high standards for quality and customer service.

When plumbing bids went out, the copper systems that were typical for other Coborn’s stores came back way too high. So, Rice sent out rebids, opening the doors to alternative plumbing materials including crosslinked polyethylene (PEX) and CPVC.

“The owners wanted value engineering,” said Chris Rice, president of Rice Building Systems. “We knew any bid that came back had to incorporate suitable cost savings in addition to intelligent design and efficient installation methods to effectively meet our budget and tight construction schedule.”

Scott and Ben Kiffmeyer, owners of Kiffmeyer Plumbing, Inc. in Sauk Rapids and 19-year veterans in the plumbing industry, had used PEX tubing in several previous installs and offered up a unique idea that would provide the value engineering that Coborn’s was looking for while also conforming to the stringent construction schedule.

“Rice came back asking for ideas, and we went to them with the concept of running PEX underground,” said Scott Kiffmeyer. “That’s how we got the job.” The underground PEX concept came from a presentation Kiffmeyer Plumbing received from Dean Corrigan of FourMation Sales and Casey Swanson, commercial sales representative from Uponor, a PEX manufacturer located in Apple Valley, Minn., that also offers design and technical support for plumbing, fire sprinkler and radiant floor heating and cooling systems.

“They needed to get the plumbing system in quickly, so this was a great application to speed up their construction schedule,” said Swanson. “It was also much more cost-effective than doing copper overhead.” The plumbing system, which used ½" through 2" Uponor AquaPEX® tubing for the 36,330-square-foot store, ran the PEX tubing underground instead of overhead like a typical copper plumbing system application. The underground PEX system also incorporated Uponor’s unique engineered plastic (EP) fittings, which are approved for direct burial in soil. The fittings use a cold-expansion ProPEX® connection method, which uses a simple expander tool to make fittings, without the need for torches, glues, solvents or gauges.

According to Mike Rivers, technical support supervisor at Uponor and lead designer for the project, the Coborn’s design incorporated a few firsts in PEX commercial plumbing. “The flush bank was all PEX, which is one of the first that we are aware of in the Midwest,” said Rivers. “Typically these are installed with copper, but with PEX, you have to increase the height of the header to allow for more play with the 1" lines that come down.”

Rivers stated the designers performed residual pressure calculations at both the farthest fixture and flush bank locations to verify the system met minimum pressure requirements. “We had them hang the 2" header line four feet, six inches off the floor with 1" pulls to the flush valves located two feet, six inches below,” he said. “This allowed for less stress on the fixture connections.”

For the entire plumbing system, the install started in mid-August 2009 and the system was turned over in mid-November. Both Rice and Kiffmeyer estimate installing PEX underground saved at least a week of installation time compared to installing an overhead copper pipe system. “PEX provided great time and labor savings, which, in turn, offered great cost savings for the owner,” said Scott Kiffmeyer. “It was only 14 weeks from the day we started the underground installation to the day the store opened.”