what is window sash

What Is A Window Sash? Why Is It Important?

The total of a window sash’s parts truly makes it. A window sash would probably look completely different if all of its components were separated. While the parts of newer windows are more often factory-built and sealed than those of older windows, older windows can still be disassembled.

When it comes time to repair or replace your home’s windows, you might not be ready if you are unfamiliar with their layout and operation. We’ll explain what a window sash is in this post and why they’re significant to the window’s design.

What Is A Window Sash?

A window’s moving component that holds the glass panes together is called a sash. The window frame, which is attached to the house, is large enough to accommodate the sash.

Depending on the type of window, the sash will vary slightly. For instance, a double-hung window has an upper and lower sash that can be raised and lowered. The double-hung window is the simplest to use and maintain because it has two sashes. Additionally, both sashes can tilt in so that you can clean the window’s exterior from inside your house.

Unlike a double-hung window, which has two sashes, a slider window has just one sash and glides from left to right. Additionally, casement windows have a single sash. Casement windows slide into the window frame, but the sash is operated by a crank handle.

What Does A Window Sash Look Like?

Homeowners occasionally struggle to distinguish between the sash and other parts of the window. On a typical double-hung or single-hung window, look at the wooden, aluminum, or vinyl casing around the glass to identify the sash. This casing will become lodged in the window frame and adhere to the window frame with tracks. The sash is contained by this casing.

The Importance Of A Window Sash

To ensure the overall strength and durability of the window, window sashes are crucial. Vinyl window sashes must be reinforced, fusion-welded, and multi-chambered in order to prevent distortion over time. A distorted window sash can make the window leak and fail to lock securely. The strength of the structure governs the window’s quality.

How Does A Window Sash Operate?

In a typical window, there will typically be a top and a bottom sash, which is the name given to the frame that houses the glass. If we are going to be specific, the full title of a sash window is a ‘vertical double-hung box-framed sliding sash window’! Since it’s a mouthful, most people just call them “sash windows.”

You can open the window by using spiral balances, weights, and cords, or sliding sashes. The top and bottom sashes will be locked together at the mid rail when closed to prevent sliding. Depending on the window’s design, the sashes may have handles to aid in opening.

Depending on whether you have a single or double-hung window, you can open it by sliding the bottom sash upwards. Double-hung windows are great for encouraging airflow and ventilating a building.

Understanding Sash Windows – The Individual Parts

A sash window is made up of a number of components that keep it functioning properly. In addition to making sure the window is thermally efficient and can open and close as needed, they give this type of window its distinctive appearance.

These are the main components that make up a traditional, weight and cords sash window:


A double-paned window is made of two sheets of glass. Occasionally, this is referred to as glazing, as in double-glazed or triple-glazed windows. Double-paned windows are more typical than single-paned windows were in years past.

Insulated Glass Unit (IGU)

what is window sash

The central component of a modern window is the insulated glass unit. A double- or triple-paned assembly of glass, gas, seals, and gaskets is referred to as an IGU in the window industry. An IGU does not come with a window frame or any other ancillary items.

Window Frame

The parts that hold the glass together are referred to as window frames and can be made of wood, fiberglass, vinyl, or metal. Rails and stiles, which are horizontal and vertical pieces, make up the window frame in older windows.

Window Grille

Smaller window segments that go by different names but are collectively referred to as grillework may be contained within the window frame. True mullions, or windows with wood between the panes, are a feature of older, single-pane windows. Double-pane windows that are more recent might look like mullions.

GBG, or grille-between-glass, is the technical term for this situation, in which fictitious mullions are inserted in between the glass sheets without providing any structural support. GBGs make the glass more aesthetically pleasing and make it simpler to clean.


The framework for the glass must be sealed. For this, rubber or TPV (thermoplastic vulcanizate) gaskets are used.


Krypton and argon are odorless, colorless gases that are injected between the gas sheets to provide insulation. There is no gas in single-pane windows. Seals enable the balancing of gas pressure and atmospheric pressure. The gas is already inside IGUs when they are shipped.


Because of the difference in pressure between the IGU and the exterior, seals are built into the IGU to equalize the pressure.

Some window sashes will also have these additional features, which might alter the appearance or improve the functionality in some way:

  • For the purpose of giving the appearance of smaller panes of glass, astragal bars are applied across the glass. They will be fastened to a single pane of glass on the inside and outside of the sash of a contemporary window. Multiple panes of glass held together by glazing bars would have made up a traditional Victorian or Georgian window. The reason for this was that glass used to be so expensive; if one pane broke, only that needed to be replaced. The astragal bar is used in its place to provide the appearance without adding to the cost because it is now much less expensive to produce a single pane of glass.
  • Sill. The majority of sash windows may have a sill either inside or outside the window. Although primarily decorative, this element might also help shield the window from rot and moisture.
  • The thermal performance of a sash window can be increased by installing draught-proof strips. They frequently come with a parting or staff bead, so your window may already have them (especially if the parting or staff bead or the window is brand-new).

How To Know If You Have Problems With Your Window Sash?

The functionality of window sashes is crucial because they play a significant role in window design. A problem with alignment might be the cause of a window that is stuck and unable to open or close. If this cannot be fixed with minor adjustments, you might have to have your windows or window sashes replaced.

It might be wise to buy replacement windows for your home if you haven’t had them replaced in a number of years. New windows may be expensive up front, but they could reduce your energy costs and raise the overall value and curb appeal of your house.

Wooden Windows

Wooden windows may start to absorb moisture from the environment if they have been exposed to air for a long time. Maintaining a tight seal around the wood with paint or sealant will stop this from happening.

what is window sash

In contrast, exposed wood will expand and contract in response to changes in humidity if the seal starts to deteriorate. When this occurs, the window might get jammed or stuck in the frame. To get the window working again, replace the sash.

The sash may develop rot, mold, or other types of deterioration in addition to the window’s potential for natural swelling and shrinkage.

The wood may occasionally become stained as a result of this damage. Other times, this damage can be seen by sticking a screwdriver into the wood. A replacement sash is necessary if the screwdriver penetrates the wood.

Aluminum Windows

Older aluminum windows encouraged sweating and condensation, which in turn accelerated the rotting of the window frame. On extremely chilly days, check the windows to see if there’s a problem.

Check the window’s interior for moisture and water droplets. The window sash may need to be replaced, but ultimately the window may need to be replaced.

Vinyl Windows

While installing new, energy-efficient windows will provide the best performance over time, replacing window sashes may only be a temporary solution. The custom-milled sash design typically offers a precise fit and is frequently 100% maintenance-free.

When Do Windows Need Replacement?

Windows need to be replaced if more than just the sash is rotten or if the window itself has defects that require regular sash replacement. The entire window needs to be replaced if the upper sash of a single-hung window is rotten.

It can be challenging for homeowners to identify when this is an issue. A builder or window installer can aid in the situational analysis.

How Should The Window Sash Be Maintained?

In general, window sashes don’t need to be maintained frequently. But as the paint or sealant on wooden windows starts to wear off, they do need to be resealed.

An annual inspection of the window sashes can aid in problem prevention. Start by looking for mold, mildew, scratches, softwood, and deterioration when inspecting a window sash.

The window is then raised and lowered to see if everything looks okay visually. The window is probably fine if the sash slides open and shut easily, without sticking or exerting much effort.

Installing a second window latch is advised in order to aid in window security and offer a firmer seal to prevent air leakage. This will tightly cinch the two sashes together.

Read More: Does A Painted Black Window Block Light?

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