The downtown Denver skyline is getting a 40-story addition. Hines

broke ground Tuesday on 1144 Fifteenth, a $141.3 million skyscraper project that will be the first office building of its size built in the city in 30 years.

At 603 feet, the modern glass-and-aluminum tower will be the fourth-tallest building in Denver — if you ignore the 75-foot spire atop the Four Seasons Hotel and Residences next door, said Jay Despard, Hines’ managing director for Colorado. The city’s tallest is Republic Plaza, 370 17th St., at 714 feet.

“This is a very big deal for everyone who has been involved, and it’s also a big deal for Denver,” Despard said. “The average age of an office building in downtown Denver is 32 years old.”

Hines is no stranger to big Denver projects. The firm also built what’s probably the city’s most iconic building, the Wells Fargo Center — better known as the Cash Register Building — on East 17th Avenue.

Paul Washington, executive director of the Denver Office of Economic Development, said Hines’ new project also will take an important place on Denver’s skyline.

“This will be the most iconic structure in Denver,” Washington said.

Construction was expected to begin immediately, with completion set for January 2018. Hines is building the tower 100 percent on spec, the company said, with Jones Lang LaSalle handling the leasing.

Designed by architect Pickard Chilton, the 662,000-square-foot Class A office tower will take the place of a parking lot on 15th Street between Arapahoe and Lawrence streets. Across the street is the all-black MarkWest Tower, and a block down sits the residential Brooks Tower.

Amenities include 27 stories of office space with floor-to-ceiling windows, 858 parking spaces, a 5,000-square-foot fitness center and outdoor terraces, according to the project website. Retail and restaurants are planned.

Hines has wanted to build 1144 Fifteenth for years, Despard said. Previous attempts, in the late 1990s and again in 2007, fell apart because of economic factors.

“There’s a host of large tenants, bigger tenants, who haven’t been able to entertain being in new space — all the office development in the last 20 years hasn’t been big enough to accommodate them,” Despard said.

Other Hines projects in Denver include 1515 Wyn koop and 1601 Wewatta, two mixed-use office and retail buildings in LoDo; and 4600 South Syracuse, a 13-story office building in the Denver Tech Center and also designed by Pickard Chilton.

Emilie Rusch: 303-954-2457, erusch@denverpost.com or twitter.com/emilierusch