NEWBURYPORT — The third phase of restoration at Newburyport High School is underway and expected to be completed by the start of the school year.

The project began as soon as school let out in June, said Steve Bergholm, director of facilities, who noted this phase focuses on the restoration of the cupola — a small dome adorning the roof.

“There’s a lot of rotted wood up there,” Bergholm said, adding that it led to leaks in the attic below.

The copper on the cupola is also being replaced. Everything will then be repainted, Bergholm said.

“This is all being done in a historically sensitive nature,” Bergholm said. “The architects draw up the plans for the work, they follow a strict set of guidelines for a restoration. We’re working with the Community Preservation Committee.”

The project will cost $375,000 and includes funding from the City Council and School Committee. The Community Preservation Committee donated $265,000 toward restoring and maintaining the building, Bergholm said.

“It’s phenomenal, the job they’ve done,” said Principal Andrew Wulf. “Talk about just a centerpiece for the city.”

There were some minor repairs to exterior woodwork when the high school was renovated in 2001-02, but Bergholm said the work wasn’t as extensive as the current project. The school was built in 1937.

The restoration began in 2014 with the first phase, in which the four main columns at the center entryway were refurbished. The second phase, completed in 2015, included restoring the front of the building near the auditorium and entrance, Bergholm said.

All of the work includes rehabilitation, replacing rotting wood, fixing up flashing and repainting, he added.

The fourth phase will take place next summer, which Bergholm said is fairly minor in comparison to the third phase and will include a lot of miscellaneous work. The cost for the fourth phase will be $85,000.

“There’s been a lot of support from the community for this project,” Bergholm said. “We actually started this project back in 2012 doing the existing conditions survey then. It’s really been a slow process of getting the funding lined up to do each phase as we go along. Hopefully, by next summer, we’ll actually be finishing the project.”

Staff writer Amanda Getchell covers Newburyport and Seabrook. Follow her on Twitter @ajgetch.