A rough window opening is an unfinished wall or ceiling opening that is intended to be filled by a window. The rough window opening is surrounded by studs on the left and right sides, a rough sill on the bottom and a header on top.
A new window mounts onto the rough window opening. Before installing a new set of windows, refer to the manufacturer's instructions to ensure that the window fits the rough window opening. There is a difference between replacing the operating portion of a window or the entire window including the frame. Replacing the full window including the jambs requires measurement of the entire rough window opening.