The Red Cross is assisting a family of 3 who were displaced from their north side home early this morning.   According to the Milwaukee Fire Department, the fire was reported just after 2 AM in a two story, wood framed duplex at N 47^th and W Chambers Streets.  The three residents in the building were able to exit the building unassisted, without injury.   The fire was confined to the exterior of the building on a second floor porch.   Damage is estimated at $21,200 to the building and contents.   The cause of the fire is under investigation.  There were working smoke detectors in the structure.