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VOL. 6, NO. 1 -- SPRING 2004


Windows are one of the most noticeable details on a building. They are functional elements that allow for unlimited expression, be it through paint colors, molding styles or pane configurations. Yet they often provide the telltale sign that a building is not carefully designed. The stock window designs available today run the range from elegant to unskilled. The best way to be able to discern between the two is to learn the elements that make up a traditional window; with this knowledge, you will know which windows are careful representations of traditional window design and which are shoddy substitutes.

Windows are generally one of three types: fixed, hung and casement. Fixed windows do not open, hung windows slide up or down, and casement windows open outwards. Windows were single-glazed until the 19th century, meaning that the panes of windows were a single thickness of glass. With industrialization came innovations in energy conservation, and window manufacturers began to use double-glazing, with the sealed space between the two layers of glass acting as insulation.

This innovation is still important today; what many stock windows have gained in advanced energy efficiency, they have lost in design quality. Often lost in the pursuit of improved efficiency are elements intrinsic to traditional windows: proper rails, stiles, stops and mullions. The snap-in variety and the even less skilled taped mullions are a clear indication of poor window design; they do not provide for the depth of profile, for the separation (or implied separation) of panes that traditional windows express. In contrast, True Divided Lite (TDL) or Simulated Divided Lite (SDL) windows replicate the overall look of traditional windows while still allowing for the energy efficiency advancements available.

The major components of a traditional window are the following.

Apron/Skirt: A flat piece of trim immediately below the stool of the window frame.

Casement Window: A window sash that swings open along its entire length; usually on hinges fixed to the sides of the opening into which it is fitted and with fixed lites.

Casing: The exposed trim molding, framing or lining around a window; may be either flat or molded.

Fixed Lite: A window or area of a window that does not open; glazed directly in a fixed frame that does not open.

Hung Window: A pair of window sashes designed to close a portion within the window frame; the bottom sash (as in a single-hung window) or both sashes (as in a double-hung window) slide up and down.

Jamb: One of a pair of vertical posts or pieces that together form the sides of a window frame.

Lite: A pane of glass, a window, or a compartment of a window.

Lintel: A horizontal structure member (such as a beam) over an opening, which carries the weight of the wall above it, as in the case of a window; often of stone or wood.

Mullion/Muntin: A secondary framing member that separates and supports panes within a window.

Rail: A primary framing member that extends horizontally between supports.

Sash: A frame in which the panes of a window or door are set; may slide in a vertical plane (as in a hung window) or may be pivoted (as in a casement window).

Sill: The horizontal member that bears the upright portion of a frame, especially the horizontal member that forms the base of a window.

Stile: An upright structural member of a window frame, along the outside edge of the frame.

Stool: A horizontal member that forms the base of the interior of a window frame.