What are the parts of a window frame?

Written by carol owens
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What are the parts of a window frame?
Window frames are made in many styles. (Jupiterimages/Comstock/Getty Images)

The windows are the eyes of a home. They can add or detract from the look of the structure, depending on the architectural style chosen. The window frame is the structure that holds the window panes (or glass) together. A window seems to be a simple structure but upon further inspection there is more than meets the eye. Many parts make the whole. A window frame must allow in light, views and ventilation while keeping out the weather.

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The main part of a window frame is the outer frame. An open structure that encases, holds or borders the glass. Window frames are made from a variety of materials, including wood, vinyl and aluminium. Each type of material provides a benefit as well as drawbacks. Wood is the traditional choice since it is great looking and has a good insulation value but must be painted every few years. Metal and vinyl frames are more durable and maintenance free, but not as attractive as wood. Another option is the clad frame of wood over metal or vinyl. These offer the best of both types but can cost a premium.


Jambs are the upright side part of the frame. The head is the horizontal top of the frame. The sill is the bottom or horizontal part of the frame and the stile is the vertical or side of the sash. The stool is the horizontal trim on the inside of a window sash. The sash is the moving part of the window. The apron is the inside flat trim under the stool at the bottom of the window. The top rail is the top of the sash while bottom rail is the bottom horizontal part of the sash. Casing is the flat decorative moulding covering the inside or outside edge of the jambs and the rough openings between window and wall. Glazing is the glass panes. Glazing also refers to the installation of the panes. Light or lite is the glass framed by the sash or windowpane. The muntin bar or grille, also called the windowpane, is a decorative strip of wood glued to the pane.


The finishing or architectural details are what distinguish a window frame's style. The moulding is one element that determines architectural style. The moulding is the ornamental exterior trim that goes around the outside of the frame.

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