Glossary of Common Glass Terminology

At Dedicated Glass Works, we believe in educating our customers as a fundamental part of our service. This glossary provides definitions for common terms used in the glazing industry, supplementing our Basic Guide to Glazing.

Glazing Definitions

Argon Gas: A gas injected between the layers of a double pane, insulated glass unit (IGU) to improve thermal performance.

Awning Window: A type of window that opens from the bottom, usually operated by a push or crank mechanism.

Balance: A mechanism that regulates the placement and force needed to hold up single and double hung windows, typically hidden inside the window’s sash.

Bay Window: A three-sided window that protrudes from the house, creating a three-dimensional effect.

Bow Window: A curved version of a bay window, usually consisting of smaller windows.

Casement Window: A window attached to the frame by hinges on one side, similar to a door, and typically opened by a crank.

Casing: Decorative trim around the interior frame of a window.

Compression Jambs: Liners in a window jamb that allow the window sash to tilt, maintaining a weather-tight seal.

Cottage Style Window: A double or single hung window where the bottom sash is larger than the top sash.

Crank Handle: An opening mechanism used for hopper, casement, and awning windows.

Double Hung Window: A window with both the top and bottom sash that move up and down, typically featuring more balances than single hung windows.

Egress: The size opening a window creates for access, especially for emergency exits.

Fixed/Picture Window: A window with no moving parts or sashes.

Grilles/Muntins: Dividers used for window decoration or home security, preventing intruders from entering through the window.

Grilles-Between-The-Glass: Grids inserted between two pieces of glass, making the window pane easier to clean.

Head: The horizontal member forming the top of the window frame.

Jamb: The vertical members of the window frame.

Jambliner: The internal frame part that holds the sash in place.

Keeper: Part of the lock system on a double hung window that engages the lock latch for a secure fit.

Low-E: Stands for "low emissivity," a coating on a window pane that lets light in while reflecting heat and blocking harmful UV rays.

Mulled: The combination of individual pieces of glass attached together.

NFRC Rating: The National Fenestration Rating Council (NFRC) provides unbiased energy performance ratings for windows, doors, and skylights.

Rail: The horizontal part of a sash.

Rough Opening: The opening in a wall where a window is to be installed, measured before the window installation.

R-Value: A measure of a window’s resistance to heat loss or gain. The higher the R-value, the better the window reduces heating and cooling bills.

Sash: The frame that holds the glass in place, commonly made from wood, aluminum, or vinyl.

Silicone: A sealant used to fill gaps and keep moisture out. It is elastic, can expand and contract significantly, and is suitable for outdoor applications due to its resistance to UV light.

Sill: The horizontal piece forming the bottom of the window frame.

Simulated True Divided Lites (Grids): Grilles attached to the interior and exterior of a window, with a bar between the window panes, to give the appearance of true divided lites.

Single Hung Window: A window with only one sash—usually the lower one—that moves up and down.

Spacer Material: Material along the perimeter of the sash, sandwiched between two pieces of glass.

Stile: The vertical part of a sash.

Tempered Glass: Glass that, when broken, shatters into small pieces to prevent injury.

Thermal Break: A part of a window or door that reduces the transfer of cold or heat from one surface to another.

Tilt Latch: A locking mechanism that, when released, allows the sash to tilt inward.

Tilt Pins: Pins on a tilt double-hung window that rotate the sash when it opens into the home.

True Divided Lites: Muntins in a cross-hatch pattern creating one window with several small separate windows within.

Urethane: A sealant used in glazing that is elastic and can move with temperature changes. It is best used indoors or in areas with limited UV exposure due to its susceptibility to UV decomposition.

UV (Ultraviolet) Rays: Rays of the sun that can filter through windows and heat up a room. UV reflective glass coatings can protect your home from these rays.

U-Value: A measure of the amount of heat entering or escaping through a window. The lower the U-value, the better the insulation value.

We hope this glossary helps you better understand the terminology used in the glazing industry. For more information or if you have any questions, feel free to contact Dedicated Glass Works.