Post 691 –by Gautam Shah
The word sash, derives from the French chassis, which means a frame or a window shutter that holds a glass pane. Technically sash windows refer to an opening system where the framed glazed panels are opened by sliding vertically, or horizontally, against casement windows where shutters are hinged and open sideways. Sash windows, when opened, have no shutters projecting out, so resist rains better and pose lesser fire risk. Sash windows are less susceptible to warping due to moisture, as the shutter is bounded by a frame. Sash windows open by remaining within their frames, so do not distract, as do the hanging shutters of the casement windows. The casement shutters had to be of small-width, or tended to ‘drop at the free edge’. The small shutter width required many mullions to divide the opening. The wrought-iron hinges and lead cames of the casement windows were dark and heavy, compared to the clean image of the sash windows.
Sash windows allow control over air ventilation, as it can be opened to a small slit to nearly 50 % of the opening. By keeping open both the top and bottom of a sash window by equal amounts (in double hung sash window), it allows warm air to leave at top and cool air to enter through the bottom. This facility of controlled ventilation saw major drive for use of Sash windows replacing the Casement windows.
The earliest-known use of sash windows was in the later part of the 17th C. Sash windows with their better proportions and elegance compared to casement windows, soon became the most important visual element in buildings of the 18th and 19th C. Sash windows became so popular that people who could afford, replaced the leaded-light casement windows. Many 16th and 17th C houses have ‘replacement sash windows’. Such changes, however, were affected on the main facade only, less prominent facades and side faces continued with the original casement shutters.
The window tax (during 1696 – 1861, in England) forced people to wall-up unnecessary windows to save tax, and also add fictitious windows for the sake of composing a facade. In spite of the taxation (window tax and a heavy excise duty on glass in 1746) discouragements, this was the period when windows design saw some of the most innovative changes.
Windows were initially positioned flush with the front face of the building, but great fire of London forced authorities, in 1907, to set back all windows by 4″ from the outer face of masonry. To further reduce the risk of fire, in 1774, the exposed wood box containing the cord and weight mechanism was required to be concealed in the side masonry.
The first sash windows of 17th C were glazed with very heavy glass requiring thick oak frames and glazing bars. However, with the availability of thinner cylinder glass from 18th C onward during Georgian period, sash windows became lighter and elegant. Production of plate glass, from 1850 onward allowed, larger panes of glass. Larger and thinner glass panes required no or fewer glazing bars. The reinforcement offered by the glazing bars was eliminated, and so horns had to be added to strengthen the junction of the meeting rail with the frame. In more expensive work, the glazing bars were made of iron or brass and painted to appear like wood.
To slide open a sash shutter by sliding up or down, its weight is balanced by counterweight concealed within the window frame. The counter weight bar of lead, wrought steel or cast iron is connected to the window by a sash cord or chain running over a pulley at the top of the frame. The wheels were of wood or brass. In later versions spring balances were used. In earlier versions the weight boxes, set flush with the outer wall, seemed very heavy, but in later versions due to fire laws the weight boxes were concealed in side masonry, making the sash windows look much lighter.
The glass used in early sash windows was not very clear, so the view through was fuzzy. The divided pane divided and framed the view into smaller bearable units. The presence of glazing bars, was a ‘relief’. As glass technology developed larger panes, free of the blur and blemishes were available requiring thinner or no mid glazing bars.
The earliest sash windows were of natural wood colour, with brass and cast steel hones, joggles, weight covering plates etc. Curved horns, multi-arched heads, intricate mouldings, leaded lights and latticework started to appear in the sashes, which were often grouped into impressive bays and offset with ornate stone reveals. The shutter and the side box were made from different quality of wood. The sash window was a strange mix of materials and finishes. White painted sash windows provided single finish effect, very well contrasted by the brick masonry. The white colour over glazing bars also reduced their presence against the glass, making the windows look more elegant. The preference for white colour sash windows has continued till today even though materials have changed from wood to plastics, steel and aluminium.
Before 1887 buildings tended to be painted in one colour, usually white, beige or gray. But later people began to paint their houses in lighter and brighter colours. The vibrant colours became a key identifiable feature of Victorian architecture. The latter part of the 19th C brought a new attitude toward colour, but sash windows continued to be painted in the Queen Anne style of white.
Sash windows originated as an opening system with two distinct sections: the top was of fixed glazing (divided into smaller lites) and the bottom section had a casement or sliding (vertical) sash. Some exceptional buildings had exterior-wall flushed windows with sash sliding horizontally and parking on the side wall.
The bottom and top sashes (two are not necessarily of the same size) were divided into 3 x 2 =6, 3 x 3 =9 or 4 x 2 =8 glass panes. Each vertical rectangle reflected the proportion of the whole window. The 3 x 2 = 6 glass pane divisions have been accepted as the classical pattern for sash windows.
Windows with one movable sash are called single-hung sash windows, to contrast from double-hung sash windows, where both sections open by sliding against one another. Alternatively, one shutter opens by sliding and the other opens out or inward with simplex hinges. Simplex hinges allow the shutter to get locked on one side while the other side is freed for opening for escape or easy cleaning of shutters from both sides. Typical double-hung windows of Georgian architecture feature the lower sash in front of the upper sash. The fixed sash at the top allowed it to match the curvilinear arched openings.
Triple and quadruple hung windows are used for tall openings, common in New England churches. Among the numerous types of 18th C sash windows, the tripartite or Venetian consisted of a central sash with two side lights, one pane wide. The side lights were often fixed, with the sash cord running over their heads from the central sash into the weight boxes.
In tropical climates, double-hung sash windows were covered from outside by fixed louvered shutters. Some double-hung windows have a full window screen that needs to be positioned suitably over the open section. Sash windows were also built to appear as casements in Gothic and Tudor Revivals. These often involved elaborate detailing with moulded mullions and even concealing the boxes for pulleys and weights.
The growth in use of the casement increased during the Edwardian period, and by 1910 many houses were built with timber casements, with sash windows relegated to less important elevation. By 1939, the use of sash windows was confined to neo-Georgian buildings, particularly post offices, banks, public houses and local housing estates.
Georgian Windows are classical double-hung sash windows. Early in the 18th C, Georgian window of 3 x 2 =6 panels per sash matured. This basic configuration of ‘six panes over six panes’, remained in use even after the advent of larger panes in the 19th C. Georgian sash wood windows remained widely used form till the use of steel casement windows, as a cheaper and functionally superior option.
Horizontal Sliding Sash Windows have two or more sashes that overlap slightly but slides horizontally within the frame. In UK, these are sometimes called Yorkshire sash windows, presumably because of their traditional use in that area.
Box-head Sash Windows have shutters sliding vertically into the wall space above the header. Guillotine Windows have only one of the two sashes, usually the top one dropping down. The early versions of windows were without the counterweights or balancing system, and so had a tendency to come slamming down. Hanging Sashes are hung on a cord connected to counterweights.