A sash window is a window made of one or more glazed panels, or sashes, that slide within a frame to open and close. In the classic British vertical sliding sash, the sashes run up and down in a box frame, counterbalanced by weights hidden in the frame and hung on cords running over pulleys, while horizontal sliding sashes are known as Yorkshire sashes.
The sash window was introduced into England in the late seventeenth century and quickly became a defining feature of Georgian and later architecture. Early sashes were divided into many small panes by thick glazing bars, as glass could only be made in small sheets. During the eighteenth century, glazing bars became progressively finer and the classic six-over-six arrangement became standard on many houses. From the mid-nineteenth century, cheaper and larger sheets of glass allowed two-over-two and one-over-one designs, often with small projecting horns to strengthen the joints. Original sashes with old glass are valuable features of period buildings, and in listed buildings permission is normally required to replace them. Skilled joiners can often repair, draught-proof and re-cord existing sashes rather than replacing them. Rippled old glass and slender bars give period houses much of their character.
