West Sussex County Council officers say the school has grown in recent years to meet the demand for places which has led to the requirement for more teaching and administrative space,as well as washroom facilities.
The school is proposing to deliver a new teaching block incorporating eight classrooms, office space, toilets and a lift for disabled access.
It is proposed to situate it next to the south block, on a piece of land that is laid to grass, but only used as a walkway and does not form part of the team games playing field.
As a voluntary aided academy, the county council have no ownership of the buildings although the playing field, upon which the new teaching block is to be built, is owned by WSCC and leased to the academy trust under a 125 year lease.
Council officers have approved the passporting of £970,000 of developer contributions to the school to help fund the works.
A report says the school is contributing £400,000 from its reserves towards the project.
It goes on to say the current programme for delivery of the extra accommodation indicates it will be available for autumn 2022 with works starting on site in the spring.
The design and tendering exercise for the works would be managed by the academy trust and its appointed consultants.