A fire at a Somerville condo complex last week may have caused nearly $1 million in damage, according to fire officials. The fire started in the basement at 106 Walnut St. at about 5:30 a.m. on June 27 and spread up the three-story building through the walls, District Fire Chief Jay Keane said. Every floor received smoke and water damage, according to Keane, and the fire displaced 24 residents. The American Red Cross has provided aide to residents of the complex. There were no reports of injuries. Damage estimates included about $700,000 to the building itself and about $200,000 to contents, Deputy Fire Chief Charles Breen said. The cause of the fire is still under investigation, according to Somerville fire investigator Vincent Lampley.