Your Guide to the Parts of a Window

Let’s face it—until a window breaks or needs to be replaced, you probably don’t spend a lot of time in your day thinking about windows and how they work. Unless you’re a window expert, these picturesque panes are simply a way to let light into your home and enjoy the scenery in happy contemplation.

But when the time comes to replace your window, you need to know your stuff. Even if you’re paying for a professional installation, you must figure out what parts of your current window are damaged and what style, glass, and frame you want to replace them. 

Join us for a quick tour of window vocabulary and see just how many fascinating components go into each window in your home.  

Window Parts Names

Parts of a window frame

Let’s start by breaking down the window frame components. In window part anatomy, the window frame is the support system for your window. Windows that open and move will have both a frame (the stationary support) and a sash (the moveable support). 

Now, let’s take apart the pieces. 


The apron is a decorative beam that sits below the window sill. It’s not necessary for window function, but many people like them for aesthetics. 


The head is the top beam of the window frame. Some have decorative additions that stick out from the wall and frequently match the design of the apron. 

Drip Cap

The drip cap is an optional addition to a window frame. It sits on top of the head and adds another layer of water protection in high-rain areas. 


The jambs are the left and right vertical sides of the window frame.

Jamb Extension

Jamb extensions are thin pieces of window frame material (wood, aluminum, etc) that widen the sides of the jamb in order to hit the wall and create a sealed surface. 

Locking Handle

A locking handle or window lock is the lock that seals a sash (or two sashes) shut. These are only found on windows that open. Windows without opening mechanisms have no need for locks.


The window sill is the bottom piece of the window frame. It’s sometimes referred to as a window stool, but usually only by professionals. 

Weep holes 

The weep holes are small man-made pores in the bottom of certain window frames. They allow drainage from any rain, snow, or other moisture to protect the frame. 

What is a Window Sash?

Now that we’ve broken down the parts of the main window frame, let’s take a look at the sash. The window sash functions very similarly to a frame, but supports the moving pane of glass as it slides or hinges.

Parts of a window sash

A window sash will include:


Balances are the spring and pulley mechanisms in a window that make the sashes easier to open and keep them from slamming shut. Depending on the window style, balances can be found in the frame or in the sash itself. 


A lift is a handle that lets you open and close the window. Generally, the sash will include a “lift” if your window is double hung and can be lifted up to open.

Nailing Fin

A nailing fin is a temporary window framing device that holds the window in place during installation. Some fins also help prevent water and wind infiltration during installation. 


The pane is your window glass. Different types of windows can have any number of panes depending on their design. 


Rails are the horizontal beams of a sash. In single and double-hung windows, the rails that meet in the middle of the window are called check rails. 

Sash Lock

The sash lock is the window locking mechanism. It seals the window shut to keep out inclement weather and unwelcome intruders.

Sash Stop

The sash stop is a stationary piece that defines how much a window sash can open and prevents a window sash from closing past the designated sealing point. 


Spacers live between panes of glass to help increase insulation and soundproofing. 


Stiles are the vertical beams of a sash that run perpendicular to the rails. 

Storm Sash

Storm sashes are added sashes made to windows in areas with high-risk weather. Some modern windows come pre-equipped with storm sashes or the equivalent strength.


Weatherstripping refers to strips of material (such as metal, felt, foam, or vinyl) that can be secured around the window frame and sash to provide extra protection from extreme weather. Some weatherstripping is seasonal, while other types can be installed semi-permanently.

Window rail

The window rails are the tops and bottoms of the sash. There may be multiple rails depending on how many moving parts your window has. 

Other Parts of a Window to Know

This next list of terms may not fit into a specific category, but they are still very useful window terms for your vocabulary list. Let’s dive in.  


An architrave is an aesthetic molding that frames the wall surrounding the window. They serve decorative purposes and add visual aesthetics. 

Argon gas 

Argon gas isn’t visible, but it’s a smart add-on for any window with more than one pane. For homeowners looking to improve their window insulation, gas fills (such as argon) are one option. This neutral gas sits in between the panes of glass to decrease sound transmission, heat transfer, and (ultimately) utility bills.


A casing is a decorative frame, just like an architrave, that covers the ugly space between the window frame and the wall. Your window will function without it but may be a bit of an eye sore.

Fixed panel

A fixed panel is a stationary window pane that doesn’t open or close. Picture windows are an example of a window made entirely with fixed panels.


Grilles are decorative additions to your window glass that can make one sheet of glass look like multiple, smaller panes. They can be placed between the glass (in double- or triple-paned windows) or you can apply them directly to the interior side of the window. They’re not necessary for function, but they add a lovely and affordable stylistic touch. 

Low-E glass

Low-E glass is treated with a type of window coating that increases energy efficiency. Low-E frequently costs more than standard window glass, but many people invest in it to save money on energy bills down the line. It filters up to 90% of UV light and goes a long way towards temperature regulation in your home.


A mullion is a large beam that can run horizontally or vertically in order to join multiple windows together. Sometimes, the mullion is part of the existing frame, but it can also be an added piece on a custom design. 

Muntin Bars

Muntin bars are small beams that connect multiple, smaller panes of glass to create one large pane of window glass. They are no longer used in new windows, but historical buildings may still have them and historical preservation regulations may require that replacements have them as well. 


A reveal is a small piece of wood that you attach the frame to during the installation process. It supports the window while you’re securing it and is eventually replaced by the window sill. 

Rough Opening

The rough opening is the hole in the wall where your window frame is installed. Most rough openings will run larger than their measured window size to allow room for insulation and/or additional framing. 


A screen is an optional addition to any window that opens and closes. The screen acts as a porous shield between your home and the outside world so that you get all the fresh air without any of the bugs. Screens also protect animals and small children from accidental (or adventurous) escapes. 


A transom is a large beam that runs horizontally and divides one window from another located above or below it. They’re usually found in rooms with high ceilings or in bathrooms. 

Still have window vocabulary questions? Ask the window experts. 

If there’s one thing you can take away from this list, it’s that there are a lot of window parts to learn. Luckily, you don’t have to learn them all. Whether you need window replacements, professional installations, or home improvement advice, Window Nation is here to help. 

Contact Window Nation today for efficient, friendly window expertise.

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