Crews were called to the units at Holland and Chestnut Avenues Tuesday afternoon.
They say a resident smelled smoke and heard the smoke alarm going off in a neighbor's apartment and called 911.
Officials say the fire was burning in a small attic shared among the units.
They were able to put it out safely but 13 people are now displaced.
Officials say wiring and ceiling repairs will need to be done before the residents can return home.