Tom Shafer

Windows get a colonial look and modern insulation with 'muntins'

July 25, 2011

While reviewing glass options with one of my recent customers, I was puzzled when he asked if the windows were available with "railroad crossings." I admit I had no idea what he meant, but upon further questioning, I understood he was asking for muntins, which are dividers that give the appearance of splitting the glass in a window sash into smaller lites.

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Today, muntins are a design feature, but in the late 18th century, they were a vital, structural element for window glass. At the time, window glass was made in small batches, poured into flat molds that were cooled, and then polished. The only way to make a large window sash was to join the small panes together with strips of wood known as muntins. Usually these panes were squares, but there were other shapes, like sun rays and Gothic designs, often used in half-round, transom windows.

About 100 years later, the float glass process made large sheets of glass possible. Float glass is made by combining the ingredients for glass, melting and pouring them into a bath of molten tin. The materials float. A single ribbon of smooth glass forms as the melted mixture flows out of the tin pool.

Once large sheets of glass became possible, muntins grew obsolete. It was cheaper to manufacture a single sheet of glass for a window sash, than to use the more labor-intensive method of joining small pieces.

4 ways modern muntins are made

While the need for muntins may have disappeared with the advent of float glass, the demand for windows with a colonial look endured. To satisfy that demand, 21st century, single-pane, insulated windowscan be designed to simulate the appearance of small, individual lites of glass. Window manufacturers simulate muntins by doing the following:

  1. Externally applying the interior side of an insulated glass unit
  2. Placing grilles between the layers of insulated glass (GBG)
  3. Simulating divided lites (SDL), an external grille with a matching GBG, usually in a dark color
  4. Using true divided lites (TDL), which are small, individual panes like the originals with better insulation

"Railroad crossings" is just one term homeowners use for this popular design feature. Muntins have been called many things over the years: grilles, square bucks, bars, squares, dividers, grates, Georgian bars, cross bars, tic-tac-toes, griddles, sticks, criss-crosses and prison bars. If you definitely want this colonial look for your windows, you need only remember one funny name: muntins.

About the Author

Tom Shafer has decades of experience in window sales, marketing and product development. He's worked closely with window design engineers in testing, design, and building code interpretation. Past employers include United Windows and Doors and Norandex, MI Windows. He currently works at a home improvement retailer.


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