The list of the 2 million-square-foot stadium’s unique features is long: Unlike the 25-year-old Georgia Dome it replaced, the new stadium has a retractable roof. The roof’s eight pinwheel “petals” open from the center.

It has what’s billed as the largest video board in the world running the circumference of the stadium, just below the roof line. It provides 63,000 square feet of high-definition images.

And it uses 4,000 solar panels, which helped it to become the first sports stadium certified a platinum-level facility under the U.S. Green Building Council’s Leadership in Energy and Environmental Design building rating program.

All those characteristics impacted the work of the 30 or so Knox employees on the $11 million contract, which included fabricating and installing spiral ductwork ranging from 66 inches to 96 inches in diameter. It totaled an estimated 800,000 pounds.

“It was some massive duct,” said McNamara, pointing out that the stadium had a number of characteristics that made it special — if not uncommon for a 104-year-old sheet metal contractor like R.F Knox. 

R.F. Knox field superintendent Dusty Paul inspects the outside-air spiral duct from the stadium’s 300-level section, which is near the 23-yard line on the field. Picture courtesy of R.F. Knox Co.

Not so big

“It was not one of the bigger projects we had going at that time,” he said, without a hint of boastfulness in his voice. There was only one other area sheet metal contractor in contention for the state-owned stadium project.

“I think after they weighed the options and when they came and saw our facility and saw what our capabilities were, I think it made their decision pretty easy,” McNamara said.

Knox officials point out the company has plenty of experience with large-scale projects: it did HVAC work on the Georgia Dome that was demolished to make room for the new stadium, as well as the still-standing George World Congress Center convention complex next door. Knox was even selected to take part in a 1958 restoration of the nearby state capitol’s golden dome, installing all of the metal on the 272-foot-tall structure, except for the gold leaf. 

A view of the 80-inch supply air round bowl duct and the 66-inch spiral duct near the stadium’s roof. Picture courtesy of R.F. Knox Co.

Hanging spiral ductwork inside Mercedes-Benz Stadium would require Knox employees to work even higher — the facility is 305 feet off the ground. Field superintendent Matt Marshall, a longtime Knox employee, said you couldn’t be scared of heights and work on the arena project.

The large spiral “bowl duct” was to be installed 240 feet above the football field, just underneath the retractable roof. Flexible connectors would allow the duct to move 10 to 12 inches when the roof was opening or closing.

“It was challenging,” said Marshall, who has 29 years of experience as a sheet metal worker. “We had to have 40-by-40 platforms to load the duct on, go on and install.”

Up to eight cranes covered the football field at the peak of the project.

Eighty-four-inch round outside air duct runs from the stadium’s bowl duct mechanical room to an outside air plenum box. Eighty-inch round supply duct serves the upper level. Picture courtesy of R.F. Knox Co.

Lined up

Ductwork was fabricated at R.F. Knox’s facility in Smyrna, Georgia, about 15 miles away, and transported to an 80,000-square-foot nearby warehouse for storage. Much of the duct was lined with Spiracoustic duct liner from Johns Manville before being hung. 

McNamara said Johns Manville officials told him it was the largest diameter spiral project the company had ever supplied liner for in the state.

Supply bowl duct 80 inches in diameter intertwines with 84-inch outside air duct. Picture courtesy of R.F. Knox Co.

A new stadium was first proposed for the Falcons in 2010, but the project did not get underway until May 2014. Originally slated to open in March 2017, delays at the site meant that R.F. Knox would only have five months to make and install the spiral duct. Coming on to a project that was already behind schedule meant that workers would have to pull some long days — and nights. Construction went on 24 hours a day, with nighttime lighting provided by the massive ribbon video board that circled the facility. Site work was supervised by Knox superintendent Dusty Paul.

With the light from the massive video screen, you wouldn’t have known it was dark outside, McNamara said.

Another look at the duct that is near the 23-yard line. Picture courtesy of R.F. Knox Co.

“It was like daytime in there,” he said. 

Because the project was in the heart of Atlanta’s busy downtown, access to the job site was limited, with only one entrance and exit.

The spiral duct for the stadium was fabricated by Knox workers at the company’s shop in Smyrna. Knox used a Mestek ISM gore locker and a 1987 Spiral Helix machine for fabrication.

“It’s a very old machine, but very durable,” said shop superintendent Chad Smith. “We do a tremendous amount of spiral in our shop.”

But using the equipment to make such large duct required ingenuity among the employees, Smith said.

“The challenge was running spiral pipe of this diameter, even at 18 gauge, as the pipe got longer, the weight of it would cause it to collapse, causing outward pressure to be exerted on the forming head, so we had to get creative with way to support the pipe as we were actually running it,” he said. 

Large cranes were used to move duct and workers into place to assemble the stadium’s HVAC system. Picture courtesy of R.F. Knox Co.

The stadium opened to the public Aug. 26, 2017. The Atlanta Falcons lost to the Arizona Cardinals 24-14 in the NFL preseason game that night.

In the past year, McNamara said he has been to several events at the stadium. He finds himself looking up often.

“Apart from the team on the field, the only other thing that draws your eye is that scoreboard and the bowl duct,” he said.

The 500-ton HVAC system that ties in to that large spiral duct uses 100 percent outside air. It’s easy on the ears, McNamara added. 

“You can’t even hear the units running,” he said. “It’s incredible, really.”

For reprints of this article, contact Jill DeVries at (248) 244-1726 or email devriesj@bnpmedia.com.