Work on a nearly $15 million addition at Thomas Middle School will likely begin next month after the Arlington Heights village board on Monday voted to approve the project.

Arlington Heights Elementary District 25 officials said they received construction bids last week for the expansion, which comes as several of the district's schools are accommodating increasing enrollment. The project is expected to cost $14.85 million, according to district documents.

Thomas Middle School has about 950 students, about 230 more than 25 years ago, but by next year enrollment will likely be over 1,000 students, said Stacey Mallek, assistant superintendent for business. But Thomas has roughly 20,000 square feet less than South Middle School on the other side of town.

"We continue to see enrollment increases on the north end of town," Mallek said.

The district recently completed expansions at Ivy Hill and Olive-Mary Stitt elementary schools, both of which feed into Thomas.

The expansion will include a building new, larger gymnasium and converting the old gymnasium into a band room, music room and five classrooms. There will also be a new entrance to the gymnasium area and a vestibule to seal it off from the rest of the school so it can be used by outside groups such as the Arlington Heights Park District or the Arlington Heights Youth Athletic Association.

The school will also add 39 parking spots, but it still has a parking agreement with nearby Orchard Evangelical Free Church for overflow parking during large events.

"This is a great-looking project and another exciting expansion of a very important facility in Arlington Heights," Village President Tom Hayes said.

Although exterior work will begin next month, interior work will not happen until the end of the school year, so it will not interrupt classes. Plans call for the expansion to be completed by the opening of the 2017-2018 school year.

"I think it's a great project," Trustee Robin LaBedz said. "The students will really benefit."