The Anatomy of a Window

Learning proper window terminology can be beneficial when fixing or installing new windows in your home. This way, you know how to talk to an expert when it’s time to pick out the ideal replacement windows or describe the specific components that might need replacing.

There are many different parts of a window to learn about, from interior to exterior components that can provide safety, energy efficiency and visual appeal. Here we’ll discuss the anatomy of a window to help you when it comes time to install new windows. 

How Does a Window Work?

It’s helpful to get an overview of how windows work before discussing the more minor details. When you hire experts, they can install high-quality windows that provide many benefits, such as:

  • Safety: Windows serve to protect you from extreme weather and break-ins. With window locks, you can protect your home and prevent your windows from opening too wide if you have pets or children.
  • Energy Efficiency: High-quality windows provide energy efficiency for your home. When you hire window experts, they can install them securely to prevent air transfer or utilize double-pane windows to insulate your home, keeping it warm in the winter and cool in the summer.
  • Aesthetics: Replacing your old windows with new ones can increase your home’s value. You can customize window features to match your style and provide a gorgeous look to the interior and exterior of your home. 

Exterior Window Components

We’ll discuss how your exterior window components work together to provide safety, energy efficiency and decoration for your home.

  • Sash: The sash is the glass framework of a window.
  • Rails: Rails are horizontal pieces on the top and bottom of a window
  • Stiles: Positioned on the sides of a window, stiles hold the sash together vertically. 
  • Frame: The window frame outlines the sash to keep all of its parts in place.
  • Head: The head is the top portion of the window that makes up the horizontal structure of the frame.
  • Jambs: These vertical side pieces form the window frame to keep it in place. 
  • Sill: The sill makes up the bottom portion of a window frame. 

What Is a Window Frame?

A window frame forms the surround of the window that includes the head, jamb and windowsill. The frame can be constructed of wood, vinyl, metal or fiberglass and weatherstripping material to prevent air from filtering around the sash. 

  • Head: The window head or the crown is the horizontal bar that lays at the top of the exterior window. It often incorporates beautiful architectural elements and is sometimes referred to as the first mullion. 
  • Jamb: Jambs hold the sash together, connected to the top and bottom of the window frame. They are very common to most windows, though not required for a functioning window. You can typically paint the jambs to match your aesthetic or replace them to fix leaks without having to install a new window or frame.
  • Sill: A window sill is the structural support for the window, located on the bottom exterior of the frame. Most people confuse sills with aprons, which is the correct term to describe the bottom interior portion of a window. 

What Is a Window Sash?

The window sash consists of stiles and rails that hold your window together and keep the glass in place. The sash fits into your window frame and may or may not be movable.   

Window sashes are essential to the structure and durability of the window. Some opt to replace the window sash to reduce leaks, although installing a high-efficiency window might offer better performance and energy savings in the long run. 

  • Rails: A rail describes the horizontal portion of the window sash that includes the lower, check and upper rail. The lower rail is the lower portion of the sash, while the upper rail makes up the top of the upper sash. 
  • Stiles: Stiles comprise the vertical edges that run up both sides of the stash. The stile and rails essentially hold the sash in place. 
Window Sash

Interior Window Components

You’ll see the interior side of your window most frequently, so you’ll want your new windows to function correctly and be aesthetically pleasing. Here we’ll discuss internal window terminology and the decorative touches that make them look beautiful in your home.

  • Stool: Often confused with the sill, the window stool attaches to your sill on the bottom portion of the interior window frame.
  • Apron: An apron is a decorative trim installed beneath the stool or the bottom of the window. 
  • Side casing and head casing: Casing refers to the horizontal and vertical molding surrounding a window. 
  • Operator: An operator is the crank mechanism that allows you to open and close casement or awning windows.
  • Latch: A latch is the locking device attached where two rails meet on a double-hung window.


The window stool refers to the piece of wood that juts out from the bottom interior of your window. Often you can customize your stool to match your home’s interior and rest objects upon it, such as houseplants and decorations. 


The apron is installed beneath the stool to accentuate it and add to your home’s style. The apron is another design element that you can paint and customize to your liking, depending on its materials. 


The side casing or head casing surrounds the window and covers the space between your window and the wall. You might install it on the inside of your home for a gorgeous finished look. The casing also acts as molding to seal your window and prevent air transfer around the edges.  


If you install casement windows, they’ll come with an operator handle. When you need some fresh air, you can crank the operator to push your window frame out and open the window. When you need to close the window, you’ll crank the operator in the opposite direction to contract the arm on the frame and pull the window shut. 


A window latch is a locking device that helps to secure and lock your windows. The latch ensures that your window stays firmly closed to prevent air filtering around the sash so that your home stays at a consistent temperature no matter the season.

Schedule Window Installation with Garrety Glass

Schedule Window Installation Today

Our windows consist of many components and functions to provide energy efficiency and visual appeal to our homes.  Now that you know the terminology, you can better repair or install new windows with your desired features.

When you’re ready to install replacement windows, trust the dedicated team at Garrety Glass for installation services. We’re a locally owned and operated business specializing in glass and windows, and we use high-quality materials at an affordable price to make your windows shine. 

For a free window estimate, contact us today or call 717-741-9949 today!