Construction on the new $35 million East Baton Rouge Parish main library is on track to be mostly finished by early September and the building could be open to the public by late fall, officials said Monday.

The 129,000-square-foot building will nearly double the size of the current main library, which is to be torn down and turned into a parking lot for the new facility.

“This is going to be a great building,” said Mary Stein, one of the library system’s assistant directors.

The library is designed to be technologically advanced, with 138 public computers and room for the building’s power and data capacity to be upgraded to meet future demands, Stein said. In addition, a large meeting room near the front of the building will have a 16-foot-wide LED screen on which movies could be shown, she said.

“Tech is the last thing we are ordering, so we can get the most advanced stuff,” Stein said.

The building is being designed to have as little impact on the environment as possible, said Benjamin Bradford, one of the project’s architects.

A rooftop terrace on the third floor, open to the public, will have plants that will be watered using storm water that collects on the roof, he said, and items discarded during construction are being recycled where feasible.

The library is one of the first public buildings in the city to be built with such environmental concerns in mind, said Kenneth W. Tipton Jr., another of the architects.

Most of the north wall of the building will be made of glass to take advantage of natural light, he said.

The lights in the library’s 9,000-square-foot main reading room will have light sensors that will turn the lights off when there is plenty of natural light, Tipton said.

“The building will respond to the natural environment,” he said.

Designers also made the building flexible to allow it to respond to evolving needs, Stein said.

“Many of these walls are not load-bearing,” she said, indicating several walls that marked off rooms in the building. If circumstances warrant, she said, some walls could be moved to allow for the expansion or contraction of certain departments or collections, she said.

Tipton said the building is designed to respond to changes.

“This is a people building with a library service connected to it,” he said. “It’s a place you want to be.”

Of the current main library, he said, “That’s a book building that people can get to.”

A third architect, Stephen P. Jackson, said the design reflected an intense study of the library services.

“We spent a lot of time on the programs,” he said. “We looked at numerous floor plans.”

Library staff were “intimately involved” in the design of the building, he said.

The current main library was built in 1968, and renovated in the 1970s and 1990s, Stein said.

The new main is designed to last at least 50 years, she said.

Planning for the project began in 2005, the design process began in 2007 and construction began in 2011.

The project is funded, without debt, through funds generated by the library system’s dedicated property tax.