Investigators in Sioux City are trying to determine what caused a house to explode. Fire Department spokesman Brian Thiele says neighbors reported the blast this morning just before three.Thiele says there was debris spread all over from the explosion as the front of the house blew out and the roof collapsed.A neighbor’s home also suffered minor damage. Thiele says the State Fire Marshal was already in town on a visit and is helping with the investigation. He says it could involve a gas line.The rental home was unoccupied at the time of the explosion. A family was scheduled to move in this weekend.