Abstract: A door jamb extension apparatus is provided for filling a gap between a door-mounted box and a door jamb and includes an inner or first wall portion, an intermediate wall portion connected to the inner wall portion, and an outer or second wall portion connected to the intermediate wall portion. The inner wall portion and the outer wall portion are mounted on a portion of the door jamb, and the inner wall portion and the outer wall portion fill the gap between the door-mounted box and the door jamb. By filling the gap between the door-mounted box and the door jamb, a spreader bar cannot be used to damage the door-mounted box. Preferably, the door jamb includes a door jamb lip, and the inner wall portion and the outer wall portion are mounted on the door jamb lip.