A blaze which "devastated" a college boarding house started accidentally and the cause was electrical, says South Wales Fire and Rescue Service.
The fire started in an upstairs room in Atlantic College's Sunley house in the Vale of Glamorgan.
About 50 students have been relocated to St Donat's Castle.
The college said education will continue as normal and next year's intake will not be affected, and insurance assessors were investigating.
Although both floors and the building's roof were damaged, a complete rebuild may not be necessary, according to the college.
Nobody was injured in the blaze, which was doused using water from a swimming pool.
A college spokeswoman said some students had managed to save their personal belongings, while others had lost everything.