What Is A Window Sash?

window sash


At a glance a window certainly isn’t complex and, in simplest terms, consists of a glass unit enclosed in a frame. Any part of that window frame that operates by opening or closing is called a sash. In fact, the word sash is derived from the French word “châssis” which means “frame”. Window sashes have been around for as long as windows since, long before air conditioning, it was vital that a window could be opened for the circulation of fresh air in addition to letting natural light.

Window sashes are not limited to any one type of window construction and can be found in windows made of vinyl, clad wood, fiberglass, or aluminum. Since most homes being built today will have a climate control system, operating windows have become more of a feature than a necessity. With the exception of bedrooms which require an operating window for egress code windows are not required to operate.

Functions Of A Window Sash

  • Ventilation: A sash provides one with the ability to open and close a window to regulate fresh air flow throughout a building. This was especially important before the advent of climate control systems.
  • Insulation: Being a movable part of the window also means that there is potential for air infiltration so window sashes need to be insulated and incorporate weather-stripping to retain the efficiency of the window.
  • Structural Integrity: Sashes house a glass unit that operates freely of the fixed frame so it’s critical that they be structurally sound to keep the glass from flexing and failing. This is especially important with certain types of windows which will cover shortly.
  • Aesthetics: As well as functional, window sashes can be used to incorporate design elements into the overall appeal of a home or building.

Types Of Windows With Sashes

  • Hung Windows
  • Casement Windows
  • Slider Windows
  • Awning Windows
  • Hopper Windows

Hung Windows

hung window

By far the most common and familiar type of window sash is the hung window. Any window that has a sash that moves vertically up or down is referred to as a hung window. If one sash operates it’s called “single-hung”, if both move it’s a “double-hung” window.

Hung windows are the most common because they are among the simplest configuration to produce so you get the most bang for your buck. Since the sash remains within the window frame there really isn’t a need for additional structural consideration.

Hung windows do require the use of “balancers” to offset the weight of the window so it can stay in place when opened. Most balancers consist of a coil spring concealed in the window frame and have to be selected based on the weight of the sash. If a set of balancers isn’t strong enough the sash won’t stay open, too strong and the sash would be difficult to push back down to latch.

Casement Windows

casement sash

A casement window opens like a typical door, swinging out to one side or the other. A sash on a casement window needs to be much more structurally sound than a hung window since the glass unit is actually moved out of the frame and, in addition to the weight of the glass, needs to stand up to the forces and stresses of the wind.

Casement windows can be found in two different configurations, crank-operated and push-out. Crank-operated make use of a mechanical crank to open the window with the push-out simply being hinged. Since casement windows open outwards it is necessary for the screens to be mounted inside which means that to open a push-out casement one would need to remove the screens first.

Casement windows tend to be the most costly class of operating windows because of engineering considerations. They are desirable because the way that they operate allows for an unobstructed and the way the sash closes against the frame allows for gasket seals which make them extremely efficient as well.

Slider Windows

slider window

Sliders (or horizontal sliders) are windows that have one or more sashes that open horizontally using rollers to move along a track system located at the bottom of the frame. They are typically found in windows that are wider than they are tall or incorporated into a large fixed window to provide some ventilation without detracting from the open view of a picture window.

Sliders are the simplest form of an operable window. They don’t use balancers and just ride on rollers. However, they also hold the distinction of being the least efficient window configuration because their need to slide freely prevents them from being tightly sealed against the elements.

During heavy rainfall, it is possible to see water in the track at the bottom of the window. This is normal and as long as the weeping system is not clogged up the water will evacuate as designed.

Awning Windows

An awning window is very much like a casement window in its operation but it is hinged at the top of the sash and is tilted out to provide ventilation. Awning windows are typically wider than they are tall and are most often used above other windows or doors (which are called transoms). Because of this, they don’t use crank handles and instead require a pole with a hook on the end to operate the window.

Being mounted closer to the ceiling they are excellent at letting out the heat in a room all while ensuring that the cat won’t manage to find his way out of the house.

Hopper Windows


Hopper windows are almost exactly like awning windows except, whereas awning window sashes are hinged at the top and swing out a hopper window is hinged at the bottom and will swing into the home. They are almost exclusively used in basements to allow fresh air circulation.

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