Window Glazing Terminology | Glossary of Terms Used in the Window Industry

August 19, 2018

We assembled this list of Window Glazing Terminology for visitors as well as ourselves. It’s amazing to think that as many years as we have been in the Window Repair industry that we still come across a new phase from time to time. While the list below may not encompass the entire gamut of window glazing terminology known to man, it seems to cover the basics. If your favorite window term isn’t on the list let us know and we’ll add it.

Window Glazing Terminology

Apron: Nope, not your mom’s kitchen apron, this is the decorative piece of wood trim that is installed directly beneath the window stool.

Argon Gas: This is the most common gas used to fill the gap between the inner and outer layers of glass in Low E windows.

Authentic Divided Lites: Also known as “True Divided Lites,” both are windows that are divided into smaller panes of glass. Most windows today are constructed with a large solid piece of glass that is divided into smaller panels using fake muntin’s. “Authentic Divided Lite” & “True Divided Lite” windows consist of smaller window panes separated by a solid muntin.

Bay Window: A window assembly that protrudes outward from the wall and is flanked by a window on either side. The end windows angle outward toward the center window, which is often a large picture window.

Balance: This is the block & tackle type system incorporated into double hung windows to counterbalance the lower window sash.

Blindstop: The wood section located between the casing and jambs on double hung windows.

Bow Window: Often confused with the Bay Windows above, if the protrusion forms an arc, then the assembly is actually called a “Bow window.” In most cases there will be 5 individual window panels in a Bow Window installation.

Cam Locks: A latch mounted to the upper and lower sashes to prevent entry into your home.

Capillary Tubes: A small tube with a tiny hole that is installed in insulated glass assemblies to equalize the pressure between the panes. This is necessary if the windows are to be used at high altitudes.

Casement Windows: A complete window assembly that swings outward using a crank handle.

Cottage Window: A window assembly with upper and lower sashes that are unequal in height.

Direct Glaze Window: Glass that is mounted directly into a fixed opening.

Divided Lites: When muntin bars are used to break up a larger window into smaller segments.

Double Hung Windows: Windows with 2 vertical, movable sashes.

Drip Cap: A section of flashing that is installed above the window assembly to direct water away from the window.

French Casement Window: A pair of crank-out, casement windows fitted with muntins.
Window Glazing Terminology
Glazing: The action of installing window glass into the assembly.

Grilles: Removable dividers installed on the face of a window to replicate the look of authentic window muntins.

Krypton Gas: Like argon, Krypton is an inert gas often used to fill the air space between the inner and outer layers of glass used in Low E windows. I bet your thought this one belonged in the Superman Blog instead of our post about window glazing terminology?

Low E Glass: The term “Low E” refers to Low Emissivity Glass. The glass is coated with a microscopic layer of metallic oxide that reduces the U-Value of the glass.

Mulling: Connecting two windows together in an assembly. The gap between the two windows is filled with a vertical member called a mullion.

Mullion: The vertical member located between two window assemblies.

Muntins: The small dividing bars to produce the effect of smaller window lites.

Obscure Glass: Textured glass that provides privacy and security.

Sash: In the case of a double hung window, the Sash is the portion of the window that moves up and down freely within the frame. You may be surprised to learn that a sash can also be stationary.

Sash Bars: Dividing bars spanning from stile to stile to separate authentic dividing lites.

Sash Rails: The horizontal members of a window sash.

Sash Stiles: The vertical members of a window sash.

Sash Lock: The latch that keeps the window closed. Some larger windows require two sash locks.

Side Jamb: The vertical side component of the window frame.

Side-Lite: Stationary window panels installed adjacent to an entrance door.

Sill: The horizontal member of a window frame situated below the window, resting on the bottom of the frame opening.

Sill Horn: The portion of the window sill that extends left and right to meet the outside edge of the window casing.

Single Hung Window: This looks like a double hung window, however the top sash is fixed and does not open.

Stool: The horizontal trim section that overlaps the window sill, extending to the right and left of the interior casing.

Storm Sash: An additional fixed window sash that can be placed over the exterior of the windows during the winter months.

Tempered Glass: Also referred to as safety glass, tempered glass is roughly four times stronger than ordinary annealed glass. The most notable benefit is that when broken, tempered glass fractures into small, somewhat harmless pieces. Unlike standard glass which breaks into sharp shards.

Transom Window: A small window located above a door or window. The window is usually stationary of fixed, but in some cases can be operating.

U-Factor: The rate at which heat flows through a window. The lower the number the better the insulating capability.

Do you have questions about window glazing terminology? Contact our support team at (815) 634-8922.