A sash window can be adapted for motorised operation using a rack and pinion drive. A preassembled motor unit (24) with a drive pinion (34) is mounted within one window stile (16). A rack (38) engages with the pinion and slides in a track (66) in the window stile. The window sash (14) which is to be driven up or down is connected to the rack through upper and lower hook mountings (48, 50), and the opposite side of the sash is free to travel between vertical guide surfaces.
