Exterior Casing (Outside Casing)

casing to trim the exterior of window and exterior door frames, to serve as the boundary moulding for the siding material, and to form a rabbet with the blind stop or jamb for the screen, storm sash, blind, shutter or combination door; exterior casing is most commonly used on wood facing wood frame exterior walls; three pieces of exterior casing are used for each frame, namely two side and one head; also exterior or outside lining.