Minneapolis Convention Center

The Minneapolis Convention Center knew it was time to replace three out of the four copper domes on its roof when black gooey asphalt from the roof dropped onto a car at the Twin Cities Auto Show in 2012. While the copper domes with their concentric diamond patterns were iconic symbols to the city, they had been causing headaches from the day they were installed 23 years ago

“The copper domes had an ice and water shield underneath them, and as the water shield became hot it would melt and drip, creating a void that allowed ice to back up and enter the system,” explained Terry Thone, senior consultant and president of Roof Spec, Inc. of St. Paul, the roofing consultants on the project.

Added Lane Carlson, facilities operation manager at the Minneapolis Convention Center, “One side of the dome would heat up from the sun while the other side remained cold. There was not a sufficient amount of flexing of the skin and copper panels in these freeze/thaw cycles.”

After spending several hundred thousand dollars a year making short-term repairs to the roof, it was finally decided to replace three of the domes. (The fourth dome, built in 2001, was not leaking.) The City of Minneapolis and its residents wanted the new domes to mimic the old domes, and also match the remaining fourth dome. However, replacing the three domes with copper was estimated to cost $12 million.

Roof Spec had another recommendation, however the Décor Roofing System, which combines Sika Sarnafil’s G410 thermoplastic single-ply roofing membrane with Décor profiles to give the appearance of a standing seam metal roof. It is one of the only roofing systems of this type that includes warranty coverage for the hot-air welded ribs that give roof the appearance of metal. Not only would Décor provide the look the City sought, but at an estimated cost of $4 million it would save the City $8 million dollars.

One of the first challenges was finding the roofing contractor to do the installation. “The contractor had to meet the City’s employment requirements that included a certain percentage of female and minority project workers,” Carlson said. “Most construction companies said they couldn’t meet that goal.” One company that met those criteria was Central Roofing Company of Minneapolis. That would turn out to be one of the easiest aspects of the project.

“We faced a deadline of 125 days to remove the old copper and install the Décor system,” remarked Warren Stock, senior vice president at Central Roofing Company.“ We had a crew of 60 people working six days a week, 10 to 12 hours a day.”

Keeping the crew safe was another concern. With a 12/12 pitch and the 70-foot center point height of the domes, tie-off protection was required 100 percent of the time, according to Stock.

Accessing the three, unconnected domes, which were in the middle of the roof and surrounded by flat roofs and solar panels, was not easy.“We had to use a Potane crane with multiple set-ups and a custom crafted conveyor system,” Stock explained.“During this time the convention center remained operational, and we often had to work around conventions and events and review which areas under the domes were being used. We had to take into account noise issues, trucking issues, and safety issues.”

The crew began work by tearing off the old copper, which was later recycled. Then two layers of ice and water shield were installed, followed by ¼ inch of gypsum board and the Décor membrane. “We had 24 panels of membrane for each row, ranging in size from 30 x 50 feet to 20 by 15 feet. The panels would narrow proportionally as we went up the dome,” Stock stated. “In the end we had 104 panels with 440 seams – all at an angle.”

To mirror the old copper roof in size, shape, color and batten configuration, 13 miles of Décor ribs were used. The longer ribs were installed on site, and the shorter ones were fabricated and welded together in a company warehouse, then brought to the site and welded in place.

Despite all the challenges, Central Roofing Company was able to complete the job on time and on budget. “They were awesome to work with and exceeded expectations,” Carlson remarked. It was this professionalism that earned Central Roofing Company Second Place in the Sika Sarnafil’s 2013 Contractor Project of the Year, Steep Slope Category.