Seddon has started work on a £1.8m extension to Bolton Sixth Form College in Deane Road designed by architect IBI Taylor Young.
The steel-framed extension will add a fifth floor to the existing building, finished in 2010. The new floor will contain a refectory, kitchen, classrooms and office space.
Seddon will create a temporary roof over the existing building during construction. The college will remain open throughout.
Building work is expected to complete in December 2013.