Crews responded to a report of a blaze at a two-story apartment building over a garage in the 500 block of North Civic Drive at about 1:45 a.m., Fire Marshal Lewis Broschard said.
The Boulders apartment homes are in that block of North Civic Drive.
Upon arrival, Broschard said crews took a defensive, exterior attack on the fire with the building heavily involved in roughly four units.
A second alarm was called shortly after, and eventually crews made their way inside the building, Broschard said.
The fire was out at about 2:40 a.m., he said.
Broschard said that four units were heavily damaged, with another two sustaining moderate damage.
Four families were displaced, including seven adults and five children, due to the damage caused by the blaze, the fire marshal said.
The American Red Cross is assisting those families with temporary housing, he said.
No one was injured.
"Luckily everyone was able to be alerted (by working smoke alarms) and get out," Broschard said.
The cause remains under investigation, but Broschard said the blaze, which originated in a second-floor end unit, does not appear suspicious.