A house fire that displaced 12 Northwestern students and caused about $100,000 worth of damage might have been started by undetermined smoldering materials, a fire department official said Wednesday.

Division Chief Alan Berkowsky of Evanston fire department said Tuesday night’s fire at 718-720 Foster St. probably started in a trash can located in a rear third-floor bedroom of 720 Foster.

The department is not entirely sure how the fire started because there was so little evidence left in the destroyed room, Berkowsky said. Officials evaluated burn patterns and used information from personal interviews to reach conclusions about the fire.

While residents of 718 Foster. could re-enter their homes soon, Berkowsky said, those at 720 Foster. might have to look for new permanent housing.

“You’re probably talking months for rehabbing that building,” Berkowsky said.

Firefighters had difficulty getting to the fire because they needed to walk up two different sets of stairs and contend with thick smoke.

“There was quite a bit of fire up there,” Berkowsky said.

The occupants of the third-floor apartment were not home at the time of the fire. University Police officers had to get them out of class.