A Chicago window is a large fixed glass panel flanked by two narrower sashes of the same height, filling a structural bay. The large pane is a single panel of plate glass, and the flanking elements are vertical double-hung sash windows with no dividing muntins. The fenestration was first used by architect William LeBaron Jenney in the 1884 Home Insurance Building, and immediately after by several of the Chicago School architecture firms such as Holabird and Root in their Marquette Building (Chicago), Daniel Burnham's Fisher Building (Chicago), and Louis Sullivan's Carson Pirie Scott department store. The window design was made possible by advances in glass-making technology and steel structural framing, and became a defining feature of the Chicago school style. The design offered both abundant natural light and practical ventilation. Projecting oriel bays are a common variant of the Chicago window, as seen here in the Reliance Building (1895) by Burnham and Root.
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Muntin in the context of Paned window (architecture)
In architecture, a paned window is a window that is divided into panes of glass, usually rectangular pieces of glass that are joined to create the glazed element of the window. Window panes are often separated from other panes (or "lights") by lead strips, or glazing bars, moulded wooden strips known as muntins in the US.
Paned windows originally existed because of the difficulty of making large flat sheets of glass using traditional glassblowing techniques, which typically did not produce flat sheets larger than 8 inches square. Modern glass manufacturing process such as float glass make window panes unnecessary, but paned windows are still used as an architectural feature for aesthetic reasons.
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