English sash window

The sash window was developed in France around 1550 and improved with a system of weights by the architect Robert Hooke in England in the 1660s.

A sash window is a sliding window with one or two sashes that slide vertically in a frame.

English sash windows balance the lower, operable sash with wires and lead weights in the hollowed jambs so the lower sash can easily be lifted and lowered. Compared with side-hung windows, sash windows have the disadvantage of weak lateral and central seals.