What is a Window Sash & Why is it Important?

In this article, we’ll teach you what a window sash is, why it’s a critical part of your window, and how to properly evaluate your sash to prevent expensive repairs. 

When your car breaks down, what’s the first thing you do? 

Do you call AAA? A friend? Or do you dust off your mechanic knowledge and dive into fixing the problem yourself? 

If you chose the third answer, chances are, you know a bit about cars—or at least enough to know not to take the entire thing apart to fix a flat tire. If you didn’t know anything, you’d never know where to start tinkering. Even worse, you might not notice when there’s a problem in the first place.

Windows may not evoke the same excitement as the auto world, but understanding your window can be the difference between a ten-minute pitstop and a multi-week overhaul when things go awry. 

In this piece, we’ll take you through the purpose, parts, and pitfalls of the window sash—and why you should care about them as much as we do!

What is a window sash? 

A window sash is the moveable framework that holds glass panes in place within a window. It’s usually made up of vertical or horizontal rails and stiles that are joined together to create a rectangular framework.

The sash can be designed to move up and down or side to side within the window frame to allow for ventilation or to open and close the window. A single-hung window, for example, has one stationary sash and one movable sash, while a double-hung window has two movable sashes.

It’s important to distinguish sash frames from the basic window frame or box frame. “Window frame” refers to the encircling frame that attaches the window to your wall. Sashes, on the other hand, refer to the interior framework connected directly to the glass panels.

This distinction becomes especially important when looking for a replacement window sash or a replacement window frame. You can replace both at the same time, but it’s essential to know the difference if you’re only looking to replace one or the other.  

What are the parts of a window sash? 

Let’s take a look at the different parts of a window sash from A-Z. 

Box Frame

The box frame is the exterior frame of the window that connects to the wall and holds the sash pieces in place. All windows have a box frame, though windows that do not open may not have sashes.

Check rail

On a double-hung window, the check rail refers to the middle bar of the window where the bottom of the upper sash and the top of the lower sash meet. This is typically where you’ll find window locks.


A crank is a method of opening a window that occurs in casement sash windows. Rather than sliding a casement sash open, you usually use a crank that rotates to open and close the window on hinges like a door.


Glass, also called glazing, refers to the glass pane or panes that make up a window’s sash(es). Glass panes are found in all windows, but can come in different varieties, including double- and triple-pane Low-E glass for energy savings.  


Grilles are thin bars of sash frame material that divide a piece of glass into smaller, decorative sections. Nowadays, grilles are applied to a large, single pane of glass for decoration. Historically, however, they held smaller pieces of glass together to create a full window pane. 


Window jambs refer to the vertical sides of a box frame. The window sash slides along the window jambs when it is opened or closed. In non-opening windows, the jambs directly touch the glass and hold the window together.


The lift is a handle found on single- and double-hung sash windows that allows the user to open and close the window. In casement sash windows, the lift is replaced by a crank.  


The sash is the moveable part of the window that opens and closes. Sashes are found in multiple window styles, including single-hung, double-hung, casement, and bay. Larger homes or buildings might also feature sash windows in Georgian, Victorian, or Edwardian styles. 

Sash cord

The sash cord allows the window sash to open by creating leverage with a pulley system. It balances the weight of the window with the sash weight, allowing you to open the window without struggling. The sash cord is attached to the side of the sash but is rarely visible once you’ve installed the window. 

Sash locks

Sash locks are small pieces of hardware that, quite literally, lock the sash window in place. For single- and double-hung windows, sash locks are generally found on top of the check rails and are only operable from the inside. For crank/casement windows, the sash lock may be on the crank mechanism itself. These locks ideally create an air-tight seal when your window is closed to prevent drafts and water damage.

Sash weight

The sash weight pulls on the sash cord to counterbalance the weight of the window sash, allowing you to easily open your window. Like the sash cord, the sash weight is rarely visible once the window is fully installed.

Sash stops

Sash stops are small pieces of wood or vinyl that are affixed to the window jamb or sill to prevent the window sash from opening beyond a certain point. They’re normally only found in single and double-hung windows and typically act as a safety feature to prevent upper-floor windows from opening wide enough for a person to accidentally fall out. If you’ve ever struggled to open your sash window all the way, there’s a strong chance it’s because your window has sash stops. 


The window sill is the bottom portion of the box frame. Sash windows have a bottom piece of the sash frame that fits snuggly onto the sill and seals tightly when you lock the window.  


The stiles are the vertical sides of the sash frame. They are comparable to the jambs on your box frame.  

Window hinge

The window hinge allows casement-style sash windows to open and close like a door.

Why is a window sash important? 

Window sashes are important because they allow you to open and close your windows. While closed windows provide your home with natural light and a sense of openness, being able to open your windows allows for fresh air, ventilation, and important fire escape routes. 

Within the window itself, sashes keep your glass safe and allow you to experience the open air without risk of water damage or burglary. Additionally, sashes divide your windows into smaller moving pieces, making replacements or repairs much simpler than for non-sash windows.  

When should you replace your window sash?

Fortunately, window sashes are designed to last years with proper maintenance. Most repairs on sashes tend to be caused by glass cracks or frame issues rather than the sash itself. 

That said, there are two primary reasons you may want to have your window sash(es) replaced: 

  1. The sash no longer opens and closes easily. Sashes are designed to open and close with little-to-no effort. If you can’t open or close your sash, it’s time to call in backup. Ideally, this problem stems from misaligned hardware, which is relatively simple to fix. However, there’s a chance it could be the result of moisture buildup and a warped frame—in which case you need a replacement as soon as possible. 
  2. The sash doesn’t seal properly. Open windows may allow for refreshing breezes in the summertime, but a window that doesn’t seal properly in a blizzard is a problem. If you can feel air or water coming in through the top or bottom of your sash, you likely have a seal problem. Seals are essential to window function, so it’s advisable to call in a professional. 

Replacing window sashes is a task best left to the experts, but there are replacement window sash kits available for intrepid DIY homeowners. 

Feel confident in your window sash selection and installation with Window Nation

At Window Nation, we understand the value of a job well done. Our technicians are always ready to share their expertise—whether through a full-scale window installation or a simple piece of advice. 

If you need a window sash replacement or you’re looking at choosing new sash windows, we’ve got your back. Contact Window Nation today for a free quote and a helping hand! 

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