The pilot reported he was flying in visual meteorological conditions for most of the flight. As he approached the airport, he inadvertently entered an area of instrument meteorological conditions that resulted in a buildup of ice on the airframe and windscreen. He attempted to make a 180 degree turn to exit the conditions, but was unable to maintain sufficient airspeed for flight, and the airplane descended and collided with terrain. The impact resulted in substantial damage to the fuselage, empennage, and wings.