Window Sashes and Sash Windows

The terms ‘sash windows’ and ‘window sashes‘ are often thrown around a lot by window manufacturers, installers and even consumers, but the truth is that many consumers are usually not quite sure what the terms really mean. If you find yourself among that group, but have been afraid to ask what window sashes are for fear of looking stupid, here’s the quick tutorial you need so you can be “talking window” like a pro!

What Are Window Sashes?

Window sashes are a single panel of a window that consists of a frame within which a pane or panes of glass are inserted. Each window sash can be further divided into ‘lights’ by muntins. Multiple sashes are combined to form a sash window.

What Are Sash Windows?

Sash windows consist of a series of vertical or horizontal panels that form frames within which panes of glass are held (sashes). The panels are movable and can be moved vertically or horizontally to open the window. Glass panes within a sash window are often separated by muntins (narrow divider strips) to form individual panes of glass, also known as ‘lights’. Sash windows are sometimes referred to as ‘hung sash windows’ or single hung or double hung windows.

When Did Window Sashes First Come Into Use?

The original sash windows were first noted in the 1670’s in England. The window design is thought to have been invented by Robert Hooke, an English inventor and scientist.

What Types Of Homes Are They Most Often Used In?

A sash window can be used in most any type of home but is typically associated with Victorian and Georgian style architecture. These styles of homes often have windows with two sashes (like a double hung window) and each sash is divided by muntins into what is known as a “six over six” panel. This means that each single sash is divided into six lights or individual panes (2 rows of 3 lights each). The lights can be divided by actual muntins that separate the individual panes of glass, by interior muntins or by ‘fake’ or exterior muntins that simply give the illusion of divided glass.

How Do Sash Windows Operate?

Most sash windows operate by sliding the two sashes vertically up or down. This is why sash windows are often referred to as a hung sash window. Double hung windows consist of two sashes that are both movable. Single hung windows have only one movable sash and one stationary sash. In applications that require much taller windows, triple and even quadruple hung sash windows can be installed. Window sashes can also open horizontally, and are then referred to as sliding windows, but are not as common.

In hung sash windows, each sash slides in a separate vertical groove along the side jamb of the window. The side jambs contain sash weights to counteract and balance the weight of the window, which helps in the operation of moving the sash, as well as keeping it in place when open. Sash weights are typically made of lead, heavy steel or cast iron and are connected to the window sash by a cord that connects to a pulley system at the top of the window. The pulleys control the operation of opening and closing the sash. In some cases, spring balances are used instead of this system and compression weatherstripping can be used to keep a sash in place when open.

What Materials Can Window Sashes Be Made Of?

Most older sash windows are made from wood frames with single panes of glass. This single glazing is rather inefficient, so it is now more common to find sash windows with double glazing. In some cases, especially with double-glazed windows, the glass within each sash is made to look like it contains divided light with the use of exterior muntins, rather than the windows containing true divided light. Sash windows can also be constructed of vinyl, uPVC, fiberglass and other common window materials.

What Are Some Of The Benefits?

The most significant benefit of these windows is looks, especially in older homes with wood sashes. Another advantage is that sash windows provide a good deal of ventilation. Sashes can typically be opened the full length of the sash, providing an opportunity to fully open half of the window. In double sash windows, the top and bottom sashes can both be opened, allowing cooler air to be drawn inside through the lower opening and warmer air to escape through the upper opening. Sash windows are commonly found on many types of homes and are easily replaced.

Problems That Can Arise With Older Sash Windows?

Since most older sash windows are constructed with wood sashes, they can incur the same problems as any other type of window made of wood. Wood can swell or become distorted due to moisture and exposure to heat and sunlight, and can rot due to weather, water and insects. If the wood shrinks, windows can rattle in the wind, and this is especially apparent in windows with true divided light. The mechanisms that operate the sliding of the sashes up and down can also break, requiring repair or replacement. Wood sash windows also require periodic painting, staining or sealing to protect the wood and to keep it looking good, and careless applications of these coatings can affect the operation of the window.

Vinyl or uPVC sash windows do not have some of these issues due to the materials used in construction, but may still encounter some issues with the sliding mechanisms over time. Energy efficiency can be greatly enhanced or undermined based on the types of materials used in construction of sash windows.