A Charnwood was extensively damaged in a fire started by a radiator, the ACT Emergency Services Agency says.
ACT Fire and Rescue was called to Nivison Place just after 2.30am Sunday, and was dealing with the fire until about 5am.
"Damage was extensive with a portion of the roof collapsing and significant smoking logging in each room," the agency said in a statement.
"The fire was caused by an electrical radiator. A working smoke alarm alerted the two people home at the time to the fire and they safely evacuated."
No one was hurt.