The Parts of a Window Explained

Window shopping is a real challenge—and not the kind that involves leisurely gazing through windows at all-too expensive items.  Actual window shopping is overwhelming if you’re unfamiliar with the parts of a window.

parts of a window

Manufacturers and salespeople alike throw out terms with ease, strapped with years of experience that sometimes blinds them to the fact that regular homeowners are left scrambling to translate whatever a sash or jamb is.

But now’s the time to brush up on this lingo to help you crack the code of this integral part of your home, whether you’re repairing windows, replacing it, or installing brand new ones.


The apron is the piece of vinyl, wood, or whatever material the windows are composed of that runs beneath the windowsill.  It is flush against the wall, creating a seamless look for the window unit.


A balance is used in both single and double-hung windows to help counteract the weight of the sash when windows are being open and closed.  Typically, the balance is comprised of a spring-loaded mechanism.


Starting off with the most basic of the basics, the frame is the framework that surrounds the entire window system.  The frame is comprised of other components like the head, jamb, and windowsill.


What would windows be without its sheet of glass?  The glass sits inside the frame, held in place by the frame’s components.


The head is the horizontal part of the window that creates the top of the frame.

Interior Casing

This is the finished trim or holdings that surround the window frame.  The purpose of the interior casing is to prevent cold air from penetrating the window unit by creating a tight seal.  The casing also adds a level of aesthetics to the windows, giving it a look of completion.


These are the vertical parts of the window frame that form the sides.

Jamb liner

This is the strip that is inserted on the sides of the windows, on the jambs, literally lining them to create a seal for the window sash.


Muntins are the parts of the window that hold the panes in place.  They can be bars or strips of wood or metal.  They’re what form the grid-like appearance of a window.


Windows that can open and close, specifically sing-hung and double-hung windows, have upper and lower sashes.  The sashes slide back and forth in tracks housed within the side jambs.  Window sashes can be fixed or operable.

Sash Lock

The sash lock sits in the middle of the window and when turned to its locked position, prevents the window from opening and engages with the sash lock strike to help reduce rattling effects.


Also called the stool of the window, the windowsill is the horizontal part of the frame, opposite the head, that forms the bottommost part.  The sill juts out, forming a ledge.

Sill Horn

The sill horn is the part of the windowsill that extends beyond past the frame.  Sill horns are a decorative choice, predominately used in colonial or classic trims.


Spacers are commonly made of aluminum and used to seal the two glass layers with its insulating effects, while also working to keep the glass panes apart.


These are the vertical parts of the window frame.  The stiles make up the sides of the window on the interior of the frame, next to the jambs.


Rails are located between the vertical components of a window and allow the unit to move.  On double-hung windows, there are three rails: the upper and lower rails, which make up the horizontal part of a window sash, and the check rail, which is located in the middle of the window.  Here, at the check rail, the bottom part of the upper sash comes into contact with the upper part of the lower sash during the window’s function.

Weep Hole

Small, individual openings located in the windowsill that allow water, condensation, or rain runoff to drain.  Weep holes are essential to the health of the windows as they allow for moisture to escape, preventing the numerous problems associated with water damage.

There’s a Lot of Parts That Make Up a Window

window frame

For windows, there’s more than glass panes and vinyl or wood, there’s an entire glossary of parts that make up its function.  Being able to navigate the anatomy of a window means understanding and knowing the terms that it’s comprised of, which will be tremendously helpful when purchasing new windows or fixing them.

Learning the terminology will save you on the time it takes investigating replacement windows as well as allowing you to speak the same language as your installers and manufacturers. As a homeowner, this will make it easier to inspect your windows to ensure they’re functioning properly. As a result, you’ll know exactly how they’re supposed to work and what needs to be replaced.  With the proper terms at hand, you’ll know the right questions to ask to help get you there.

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