Abstract: On June 25, 2005, an employee was installing audio and video wiring in the attic access of a new house under construction. The home was partially complete, so far as the drywall installation in the ceiling and walls. The wiring was being installed as a retrofit at the owner's request. The employee used a ladder for access through the attic opening in the master bedroom closet. He crawled on his knees on the plywood to reach the great room where he needed to drop the wiring. He crawled along on the plywood, until he reached the area in the master bedroom where the ceiling sloped upward and he had to place his knees on the trusses which were located over drywall. As he crawled along the trusses, he stopped and asked his coworker who was on the floor level, to send up more wire. As he rose up to pull on the wires, he lost his balance and his right knee came off the trusses. He fell through the drywall, 13-ft to the concrete floor. The employee was hospitalized at Northridge Hospital from June 25 through June 29 and treated for fractured vertebrae.