Abstract: A support frame for a window frame is provided to address the problem of unwanted entry of moisture, such as condensation, into a building in which the window frame is mounted. The support frame includes four sections of flashing. Each section of flashing has a window frame support plate that has a window frame side and building framework side. A first longitudinal wall extends from the window frame side of the support plate. One or more longitudinal stiffening box sections continuous with the plate are provided for imparting rigidity to the flashing. Two of the sections comprise sill and header flashings spaced apart at either end by the remaining two sections, which comprise jamb flashings. Joiners connect adjacent ends of the four sections.