The Sash Through History
Upper Cheyne Row, Chelsea; C18 Sash Window. Source: Le Lay Architects
An Elizabethan Problem
Despite the images of romance conjured up by casement windows of the medieval era; think Romeo’s proclamation of love at the foot of Juliet’s balcony, practically they were of less benefit. With glass production limited to small sizes, window frames from that period were usually filled with lead tracery (strips of lead holding the glass in place- usually diamond in form) limiting the amount of light coming in, and obscuring views out. The casements themselves (side hinged, outward opening sections of the window), were usually limited in size. The only method of regulating the temperature of an Elizabethan house was by perpetually opening and closing the casement, each time lodging its long handle on the fixed pegs along the window frame. Together the casements and frame formed thick, clumsy squares on the building’s elevation.
A Welcomed Change
Then along came the invention of the sash window, comprising one or more movable, glazed panels (sashes), usually vertically sliding. First introduced in the mid 1600s, the sash window literally came as a breath of fresh air to the medieval home. With the ability to open the window top and bottom, a home could now be far more efficiently ventilated (warm stale air could escape through the top sash, cooler fresh air could enter through the bottom), and the temperature could be regulated by altering the height of each sash opening accordingly, and with little effort. Consequently, the turn of the 17th Century saw the mass replacement of casement windows for sashes. Some of the oldest surviving sash windows can be found at Ham House, Richmond and Chatsworth House, Derbyshire dating from 1670.
Development of the Sash
The first sashes, heavy and stately in nature, typically had 9, 12, or 16 panes of glass (or ‘lights’) per sash and only the bottom sash moved. As manufacturers developed larger sizes of glass throughout the 17th and 18th Centuries, the number of lights per sash was reduced, and the sashes became more slight. A classic early 19th century Regency window includes three lights across by two down (known as ‘six over six’, referring to both sashes). The invention of larger, cylinder-sheet glass in 1832 saw the Victorians introduce the ‘two over two’ sash. A typical Edwardian window can be identified by a ‘two over one’ formation. It is worth noting that reducing the number of glazing bars (wooden horizontal and vertical divides between window panes) weakens the window frame and so the Victorians’ solution to this was the inclusion of small downward protrusions, known as ‘horns’, fixed to the underside of the lower top sash rail to provide additional strength- a helpful tidbit when dating a building.
The sash window was dominant all the way up to the 19th Century, with most remaining sashes either Georgian or Victorian. The lowly casement has made a comeback more recently, when the Arts and Crafts movement of circa 1890 encouraged a return to Old England.