Replacement Window Basics

Learn how a window is constructed 

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Window Construction and Terminology

The first step in any replacement window project is knowing how a window is constructed and the industry’s terminology.    Starting from the middle of a window and working our way to the perimeter:

Glazing refers to the glass in a window or the process of fitting glass into a window.  

Lite also means a piece of glass, but specifically refers to separately framed pieces of glass, or the simulation or look of separately framed pieces of glass.

Sash is the part of the window that holds the glass panes together.  It can be operable or stationary.  The sash fits inside the window frame and consists of stiles, rails, and check rails.  

Stiles are the upright or vertical perimeter pieces of a sash, panel or screen.

Rails are the cross or horizontal pieces of the framework of a sash. 

Check rail or meeting rail is used in a double hung window.   It is the top and bottom horizontal sashes of a double hung window meet in the middle and lock. In a glider window, the two vertical pieces  that meet in the center are also called the check rail or meeting rail. 

Parting Stop or parting bead is used in a double hung window  This long narrow strip between the upper and lower sashes enables them to slide past each other.  

Blind stop is also used on a double hung window.  It is located between the jambs and the casing to form a groove that supports either a storm sash or screen.     

Jambs form the top, sides, and bottom of the window frame.  The Head Jamb is the horizontal piece forming the top of the window frame.   

Casings are the moldings around the window frames.  Installed to the exterior of the house, casings seal the window frame to the house and block air from entering the interior.  Interior casings finish the window creating a frame around the window.  

Sill is the sloped horizontal piece that forms the bottom of the exterior of a window.  

Stool is a horizontal trim piece that laps the windowsill above the apron and extends beyond the interior casing.  

Apron is a decorative trim installed against the interior wall immediately below the stool. 

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