At a special council meeting of the Liberal Democrat cabinet, councillors agreed the secondaryschool would be on a temporary site in a building previously used by the Environment Agency and Defra on Burghill Road, Brentry, for one year.
With the exception of its sixth form building, the 1, 250-capacity secondaryschool, which was originally built for 500 students in the 1950s, needs a complete rebuild, according to deputy head teacher Steve Ostler.
They say the issue has been ignored for too long, and accuse Labour of "wasting vast sums" on bureaucracy in its Building Schools for the Future (BSF) programme of secondaryschool rebuilds.