There is a flurry of activity at TD Garden, and it’s not just the Stanley Cup playoffs and Backstreet Boys concerts.

There are towers and buildings being erected alongside and above the sports and entertainment arena on the site of the old Boston Garden as well as an expansion of the venue itself. Collectively known as The Hub on Causeway, the almost 1.9 million-square-foot mixed-use project that Delaware North is building with Boston Properties will include two office towers, a residential tower, a hotel, and a podium that will feature a new entertainment performance space, a Star Market, a 15-screen movie theater, and a number of restaurant and retail locations. Valued at $1.2 billion, the aptly named Hub is transforming Causeway Street into one of the city’s foremost destinations.

“Hub is going to change the neighborhood and help fill some of its needs,” Amy Latimer, TD Garden president, told the Boston Globe in a video interview. “It’s changing the vibe.” It will also change what Latimer refers to as the “street-to-seat” experience for fans coming to the arena.

 “You could live in an apartment here, and almost never have to leave,” says Carl Wall, foreman for American Plumbing and Heating. Between the grocery store, the shops, the offices where residents could work, the eateries, and all of the activities, tenants wouldn’t even need to go outside, he adds. Of course, if they did want to leave, the MBTA’s subway and commuter rail stations would just be an elevator ride away.

American has been handling the plumbing for the first and second phases of the Hub project, which included the first office tower, the 440-unit residential tower known as Hub50House, and the podium that connects everything together. Wall is leading a crew of 30 Local 12 plumbers that is working on the third and final phase of the project, which includes a 31-story office tower totaling 525,000 square feet. Verizon will be leasing 440,000 square feet of the space. The building began going vertical in February, and plans call for it to be completed in 2021. American has two additional crews inside the Garden. Wall estimates that there are approximately 100 plumbers from the company on site.

According to Tim Fandel, business agent for Local 12, there are about another 30 plumbers representing other shops that have been working on other aspects of the Causeway Street project. Throughout the four-year construction span of the Hub development, many GBPCA contractors have been involved including: JC Cannistraro, which worked on the boutique, 272-room citizenM hotel; A. H. Burns, the plumbing contractor for the Star Market grocery store; Valante Mechnaical, which worked on the tenant fitout for Rapid7, the cybersecurity firm which moved its headquarters to one of the office towers; Douglas R. Howard, which did some of the remodeling work inside TD Garden; and E.H. Marchant, which is handling the plumbing for Big Night Live, the entertainment and nightlife space being operated by Big Night Entertainment and Live Nation.

Work on the 35,000-square-foot concert hall began in April and is scheduled to be turned over in October. “This project has a very aggressive schedule,” Fandel says. “These guys hit the ground running.” Big Night is advertising shows planned for early November at the venue.

The multi-level club will include five bars, two kitchens supporting two restaurants and private dining areas, and a total of 44 toilets among Big Night’s bathrooms. Local 12 plumbers installed an array of eight Navien tankless water heaters at the site. The units generate a tremendous amount of hot water virtually in an instant, according to Matt Wade, foreman for E.H. Marchant. The heaters, which are piped in tandem, function as one modular system.

“If there is a problem with one unit, we can trade it out without impacting the whole system,” Wade explains. “The Naviens work on demand. If there is light use, only one unit might kick on. As demand increases, others will turn on.”

Big Night will accommodate as many as 2,000 patrons, including 1,500 in its main showroom. There will also be VIP rooms, along with bathrooms and prep kitchens on the 2.5 level above the performance space. The mezzanine level is supported and suspended from a structure above, not down to the floor.

“That makes plumbing a challenge,” acknowledges David Story, superintendent for Trinity Building and Construction, the general contractor for the Big Night Live project. There was a very tight space for using building information modeling (BIM) to coordinate the time-consuming, critical work performed by the plumbers as well as the sprinkler and HVAC contractors.

Another challenge that the project posed was the sound acoustic work done on the high ceilings to mitigate the music and noise emanating from the concert hall. Kinetic hangers were used to frame the ceiling with four layers of drywall, which made it difficult to rough in the mechanical and plumbing systems.

“Having a subcontractor like E.H. Marchant is great,” Story says about the GBPCA shop. “They’ve done work like this before. I know we can count on them.”

In addition to the event space, Big Night will include two restaurants operated by celebrity chef Guy Fieri. One will be Tequila Cocina, a 200-seat Mexican eatery.

As with many Boston construction sites, the logistics of arranging deliveries and moving materials has proven to be difficult for the plumbing contractors at the Hub. In addition to having no staging area, the crews have had to contend with all of the activity at the TD Garden, which has remained open throughout the project. Commuters using the North Station subway and commuter rail trains compound the congestion.

“In 35 years, this is the tightest job I’ve worked on,” says American Plumbing’s Wall. All deliveries need to be scheduled in advance and carefully orchestrated. Unplanned events can throw a curve ball—or a puck—at the process. When the Bruins were in the playoffs, for example, the city closed down some of the streets around the site, and the project’s loading docks were inaccessible. “And we didn’t even win the Stanley Cup,” notes Wall with a laugh.

Prefabrication has been playing a big role in the job, the American Plumbing foreman notes, adding that nearly everything for the job is built at the contractor’s shop. “While the steel is going up, we’re already prefabbing all of our gang bathrooms.”

“The Hub is a four-year project,” says Fandel. “Without prefab and other efficiencies, it would be a six-year project.”

At 60,000 square feet, the new Star Market is Boston’s largest grocery store. Built above a garage, the entire plumbing system is embedded in the market’s ceiling. When coordinating installation, the A. H. Burns crew had to consider a second plumbing system in the ceiling, which services the new food court located directly above the Star market in the Garden.

One of the American Plumbing crews working on the TD Garden expansion is also on a tight schedule according to its foreman, Jack Whalen. The team of 22 plumbers began working in May and is scheduled to wrap in September. In order to handle the workload, Whalen says the crew is working seven days a week with extended shifts on weekdays. The expansion will add several women’s bathrooms to the arena as well as new bars and food concessions.

“Getting access to the floors, especially on days when concerts or other events are scheduled, is hard,” Whalen says. “But we will get it all done. We always do.”