The Ottawa-Carleton District School Board is expanding Longfields-Davidson Heights Secondary School.
The $12-million expansion is part of a bid to address the ongoing population growth in Barrhaven.
The school was built in 2009 to accommodate 1,350 students, but just five years later, its student population has swelled to more than 2,000.
Principal Patsy Agard says the three-storey expansion will include 32 new classrooms and an exercise space, which are sorely needed.
"Our population has increased beyond, I think, anyone's expectations with all of the housing that was added on after the planning of this school," she told CFRA. "It certainly is needed."
The school has been using 27 portable units.
The new extension is set to be completed in time for Fall 2015.