The fire started at around 8:30 Sunday morning in the 900-block of North Trumbull.
Investigators say 12 people lived in the building and one of them suffered a minor injury.
The building quickly filled with smoke.
"I looked at the house, and there started to be so much smoke just coming up out of the basement," said resident Ulysses Davis. "So I'm like, just get my grandma out of the house, get my grandma out of the house. We got my grandma out of the house. I just didn't go back in there after that and everybody else started coming out."
Davis said he believes a space heater in the basement sparked the fire, but an official investigation is still underway.