Abstract: A window frame assembly which comprises a first intermediate frame member and a second intermediate frame member adapted to be inserted from opposite sides of a window opening to embrace the edges of the window opening. The first frame member has a locking channel extending about the periphery of its inner end and the second intermediate channel has locking tongues projecting inwardly therefrom which are adapted to be inserted within the locking channel of the first intermediate member. The second intermediate frame comprises a plurality of frame lengths connected to one another at opposite ends to form corners of the second intermediate frame. A locking tongue formed on each length terminates short of the corners of the second intermediate frame so that the locking tongues are independently flexible to facilitate the insertion of the locking tongues within the locking channels when the second intermediate frame is interlocked with the first intermediate frame in use.

Abstract: A window assembly in which two window units are slidably mounted and in which one of the window units cannot be removed until the other has been removed. The removal of a first of the window units releases the sash locking member for lateral movement within the frame to permit overlapping lips of the other window unit and its associated frame to move out of overlapping engagement with one another.