Abstract: A finish mounted framed building element such as a window or doorway sidelight or the like is mounted in a space provided in rough framing structures in a wall, by inserting facing sheets, preferably of sheet metal, into the framing jambs up to a variable depth in slots provided at the perimeters of the door or window frame opening. The space between the sheets can be substantially confined as a foaming composition is injected and permitted to expand and cure in place. The foam locks the sheets to the framing jambs of the window or doorway sidelight, etc. This provides a wall panel with a correctly sized and correctly positioned internal opening, for example to receive a window frame or doorway sidelight or other insert structure. The invention also supports or reinforces the window or doorway generally, for example to support the hinged side of a door jamb adjacent to a door sidelight.