Two years after turning elsewhere for classroom space, the Math and Science Academy in Woodbury plans to construct a new addition just north of its Woodbury Crossing home.

The facility, to include 10 classrooms and a gymnasium, is expected to be open at the start of the 2013-14 school year, according to Cyndi Bluhm, a charter school board member.

Last month, the Woodbury City Council approved development and financing plans that call for the city to issue up to $11.5 million in tax-exempt bonds for the school. The resulting loan payments would be covered by the Math and Science Academy at no risk to the city, said Dwight Picha, the city's community development director.

School board members decided two years ago that with state funding nearly flat, the school's viability depended on increasing its population, Bluhm wrote recently on the school's website. The school, serving grades 6-12, began renting a five-classroom building nearby but anticipated needing additional classrooms, as well as a gymnasium.

Picha told the council at its Oct. 24 meeting that the school now had about 425 students and expected to have nearly 500 by the 2016-17 school year. "It's been a very successful school," he said.

"That's kind of what I've heard," replied Council Member Amy Scoggins. "Good for them."

The new facility is to be built on a one-acre site with an exterior that would match the current building's glass and stone, Picha said.

The school plans to have the gym double as a performance space with stage and bleachers. One classroom also would be used for band and performing arts classes, the website says.

Bluhm said financing is expected to be completed around Thanksgiving, with construction to begin soon after.