The firm was granted planning last month and is gearing up to start the project which will be delivered in three phases while the school remains open.
The first phase will start with the demolition of an existing 1930s block which has already been closed because of disrepair and asbestos.
This will be replaced by a new two-storey block containing the sports and main hall as well as kitchen, dining, art rooms and administration offices.
During this time a more modern second three-storey school block at the former Queensbury Academy school will be extensively refurbished.
Once completed a third final block will be demolished to make way for new sports facilities and landscaping.
The school has been designed by architect Bond Bryan with M&E consultancy from Watermans.
It comes forward as part of the second wave of the school rebuilding programme.