Window terminology can be confusing when you’ve decided to replace some old drafty windows and are beginning to do your comparison shopping. You are quickly discovering that a replacement window has many parts, more than just glass and a frame, and the window terminology can get very confusing. In this article, we will go over a few of the more common window industry terms.
- Sash: The portion of a window that includes the glass and the framing sections directly attached to the glass, not to be confused with the complete frame into which the sash sections are fitted.
- Sill: The lowest horizontal member in a door, window, or sash frame.
- Frame: The fixed frame of a window which holds the sash or casement as well as hardware.
- Glazing: The glass or plastic panes in a window, door, or skylight.
- Header: The upper horizontal member of a window frame. Also called head.
- Bottom rail: The bottom horizontal member of a window sash.
- Lift: Handle for raising the lower sash in a double-hung window. Also called sash lift.
- Light: A window; a pane of glass within a window. Double-hung windows are designated by the number of lights in upper and lower sash, as in six-over-six. Also spelled informally lite.
- Muntin: A secondary framing member (horizontal, vertical, or diagonal) to hold the window panes in the sash. This term is often confused with mullion.
- Mullion: A major structural vertical or horizontal member between window units or sliding glass doors.
Energy Efficient Window Terminology
- Argon: An inert, nontoxic gas used in insulating glass units to reduce heat transfer.
- Gas fill: A gas other than air, usually argon or krypton, placed between window or skylight glazing panes to reduce the U-factor by suppressing conduction and convection.
- R-value: A measure of the resistance of a glazing material or fenestration assembly to heat flow. It is the inverse of the U-factor (R = 1/U) and is expressed in units of hr-sq ft-°F/Btu. A high-R-value window has a greater resistance to heat flow and a higher insulating value than one with a low R-value.
- U-factor (U-value): A measure of the rate of non-solar heat loss or gain through a material or assembly. It is expressed in units of Btu/hr-sq ft-°F. The U-factor may be expressed for the glass alone or the entire window, which includes the effect of the frame and the spacer materials. The lower the U-factor, the greater a window’s resistance to heat flow and the better its insulating value.
Educating yourself in window terminology and learning about all of your options is a great way to ensure that you are getting the best window for your budget and your home. To learn more window terminology, please visit our glossary at http://www.ThrushAndSon.com/glossary.