Abstract: This invention relates to a window assembly with a window frame having a first window sash mounted fixedly in the frame and a second window sash mounted for movement between a closed position and at least one open position in parallel relation to the first sash. The window frame has a main frame and an auxiliary frame that mates with the main frame to define a common frame outline and to combine with at least one of the sash to define guideways to guide the second sash as it moves between the closed position and an open position.