Seattle fire spokesman Kyle Moore said flames broke out in the basement of the home in the 2900 block of S. Austin St. around 2:19 p.m.
Police believe the incident began when a man got into a verbal argument with his girlfriend at the home. The man assaulted his girlfriend, then retreated to a back room where he may have set the blaze, investigators said.
The unidentified man fled the scene and remains at large.
Fire crews had the blaze under control within an hour. One side of the home appeared heavily damaged through the roof, and heavy plumes of smoke were seen pouring out of the building.
Eight people were inside the home when the blaze broke out. No one was injured.
Damage is estimated at $250,000.