A simulated architectural component such as a framed window or vent is formed by vacuum molding, and includes an undercut or recess on the laterally outer edges of a surrounding frame portion. The undercut is adapted to receive and conceal the abutting edges of aluminum or plastic siding panels of an exterior wall into which such component is installed. The undercut is formed during the vacuum molding process by the use of a split ring which is removed from the mold with the finished part and is thereafter separated from the part as permitted by its split construction.
