History of timber box sash windows

The sash window is often found in Georgian and Victorian houses, and the classic arrangement has three panes across by two up on each of two sashes, giving a “six over six” panel window, although this is by no means a fixed rule. Innumerable late Victorian and Edwardian suburban houses were built in England using standard sash window units approximately 4 feet (1.2m) in width, but older, hand-made units could be of any size, as the image illustrates. It consists of an upper and lower sash that slide vertically in separate grooves in the side jambs or in full-width metal weatherstripping.

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This type of window provides a maximum face opening for ventilation of one-half the total window area. Each sash is provided with springs, counterweights, or compliant weatherstripping to hold it in place in any location.

To facilitate operation, the weight of the glazed panel is usually balanced by a heavy steel, lead, or cast iron sash weight or counter-weight concealed within the window frame. The sash weight is connected to the window by a sash cord or chain that runs over a pulley at the top of the frame, although spring balances are sometimes used. Sash windows may be fitted with simplex hinges, which allow the window to be locked into hinges on one side while the counterbalance on the other side is detached, allowing the window to be opened for escape or cleaning.

The name “hung sash window” refers to a double-hung window with two sashes that can move up and down in the window frame. A single hung window has two sashes but normally the top sash is fixed and only the bottom sash slides. Triple and quadruple hung windows are used for tall openings.

Construction is usually of softwood, and units are generally single glazed; although double-glazed sashes are available it is more common for single-glazed sash windows to be replaced with top-hung casements when double glazing is retro-fitted.

Traditional problems

Traditional problems with wooden sash windows include rot, swelling or distortion of the woodwork, rattling in the wind (due to shrinkage of the wood), and problems brought on by careless application of paint. The sliding mechanism makes sash windows more vulnerable to these problems than traditional casement windows. Sash windows are relatively high maintenance, but offer advantages in return (looks, abides by-laws (relating to older houses and buildings), natural resources, etc.). It is also possible to clean all the glass from within the building by sliding the two panes to different positions.

Some top-hung double-glazed units are manufactured to give the appearance of sashes.

A significant advantage of sash windows is that they provide efficient cooling of interiors during warm weather. Opening both the top and bottom of a sash window by equal amounts allows warm air at the top of the room to escape.

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