Sash Window: Considerations for Sash Windows

A window sash is an individual panel or section of window frame that can hold separate panes of glass. A sash window, also known as a sliding sash window or a single-hung window, is a type of window that provides ventilation to a home with a moveable lower sash. A counterbalance or spring inside the window frame assists the movement of the bottom sash until it overlaps the fixed upper sash.

Although these window styles are less common today, you can still find sash windows in homes that are classic to the Victorian, Edwardian, and Georgian eras. Homeowners often confuse sash windows with double-hung windows or casement windows due to their similar appearances. However, sash window designs have distinctive opening mechanisms like hinges or an adjustable top sash.

Separate panes of glass are set into a window sash, the moveable section of the sash window frame. A window sash’s different components include the:

1. 1. Mullion: The vertical support of a window is the mullion or jamb. You can use this element as the main structural support that divides the glass or glazing of each sash panel. Mullions are also the dividers between commercial double doors, so the terminology can become confusing in a construction setting.
2. 2. Muntins: Glazing bars, also known as muntins, are vertical support structures between the glazings of a window sash. These perform the same purpose as mullions except they are smaller and will support individual panes of window glass. This design element allows remodelers to switch the single-pane windows of an older, listed building with double-glazing options rather than execute a total window replacement.
3. 3. Stiles: These are the outermost vertical support elements of the window sash. Whereas the mullions and muntins support the interior panes of glass, stiles serve as the outer frame that holds the entire sash in place.

Although sash windows are less common than more modern window models, there are still a few potential advantages to using this style of window.

1. 1. A wide variety of sash windows are available. Manufacturers craft sash windows in many different styles and materials. Popular sash window styles include the Queen Anne variations plus arched, round, or gothic head sashes. You can purchase sash windows that use synthetic unplasticized polyvinyl chloride (uPVC) or aluminum clad or natural wood sidings. Both the aluminum clad and uPVC options will typically last longer than a natural wood frame.
2. 2. Sash windows have a classic, traditional aesthetic. You can purchase sash windows for a higher price than other styles, but this investment will add value and curb appeal to your home. Since sash windows were fixtures of homes in the Edwardian and Victorian eras, you might associate the appearance of these windows with these older, charming structures.
3. 3. Sash windows feature exceptional security. You can add opening restrictors or window catches to your sash windows to prevent entry to the home from the exterior. Additionally, you can consider adding reinforced glass or plexiglass panes, which will increase the tensile strength of your window. All of these security options are simple yet effective anti-theft features that are compatible with sash windows.

Consider the drawbacks of sash windows before you select new windows for your home.

1. 1. Joinery on sash windows can expand, crack, or stick. If your sash windows are wood windows, they will have significantly less durability or moisture-resistance than synthetic options. Window manufacturers or craftsmen use thin, structural elements like mullions and muntins to hold the glazings of a sash window in place. These small pieces are tied together with fragile mortise and tenon joints at the corners where they meet. Moisture will cause these pieces to swell and crack, eventually leading to loose glazings and warped sashes that will stick in the window frame.
   
2. 2. The sash cord and pulleys can fail. The most obvious design flaw of sash windows is the counterbalance that rests inside the window frame. This counterbalance can assist the movement of the lower sash; however, if the cord or pulley breaks, there is no easy way to replace these mechanisms. You will have to remove the window framing and manually replace these items.
3. 3. Sash windows are less energy-efficient than modern window designs. Even well-insulated, double-glazed sash windows will provide limited temperature control for a home. Failed joinery and sealant can lead to increased airflow and drafts near windows. These leaks between the interior and exterior of the home will increase the amount of energy that a homeowner will use to heat or cool their home.

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