Janesville firefighters are looking into the cause of a Friday afternoon house fire.  Firefighters say when they arrived at the single story home in the 200 block of Valley Drive a little before 3:00 p.m. Friday, they found smoke coming from the basement.  Officials say the two occupants and their pets had already escaped.  A small fire in the basement was quickly extinguished.  No injuries were reported at the scene.  The Red Cross is assisting the residents.  Damage is estimated at about $30 thousand.