Window Terms & Definitions

Glossary of Window Terms

Argon Gas: injected between layers of glass to increase the insulation value of the window. Argon gas is non-toxic, has no smell or color, and is heavier than oxygen.

Awning Window: similar to a casement window, but the window opens at the bottom by turning a hand-held crank.

Balance: the mechanism that holds up sash units on single and double hung windows. It also helps control the force needed to raise and lower sash.

Bay Window: a three-sided window that is three-dimensional, protruding from the house.

Bow Window: a curved window created by smaller windows mulled together.

Casement Window: window that opens from one side, like a door, by turning a hand-held crank.

Casing: decorative trim around interior frame of window.

Compression Jambs: liner in window jamb that can be pushed in, allowing you to tilt the window sash. Assists in maintaining weather-tight seal between window sash and jamb.

Cottage Style Window: on a double-hung window, the bottom sash is larger than the top sash.

CPVC: cellular polyvinyl chloride. A composite material more rot resistant than wood.

Crank Handle: opening mechanism for the casement and awning window.

Double Hung Window: a window in which both the top and bottom sash move up and down.

Egress: the size opening a window creates for access.

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

Grilles/Muntins: decorative window dividers installed on the exterior or interior of the window or sandwiched between the glass (see GBG). Offered in variable widths.

Grilles-Between-The-Glass (GBG): grilles 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: vertical members of the window frame.

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

Keeper: on a doublehung window, this is part of the lock system that engages the lock latch for a secure fit.

Krypton Gas: injected between layers of glass to increase the insulation value of the window to a level greater than windows using Argon gas. Krypton gas is non-toxic, has no smell or color, and is heavier than oxygen.

Low-E: stands for “low emissivity”. Low-E coating on a window pane lets light in, yet reflects heat and keeps harmful UV rays out in the summer and keeps heat inside during the winter.

Mulled: the way windows are attached together to create a combination.

Nailing Flange/Fin: piece extended from the window frame to make installation easier. Premium windows will offer an integral nailing fin for more secure installation, with predrilled holes for easy nailing.

NFRC Rating: National Fenestration Rating Council (NFRC) provides unbiased energy performance ratings for windows, doors and skylights. Independent NFRC ratings provide the basis for the Energy Star’s® window performance requirements.

Rail: horizontal part of a sash.

Rough Opening: framed opening in wall in which a window is installed.

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

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

Simulated True Divided Lites (STDL): 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 along the perimeter of the sash, sandwiched between two pieces of glass.

Stile: vertical part of a sash.

Tempered Glass: type of glass that, when broken, shatters into small pieces to protect you from injury.

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

Tilt Latch: a locking mechanism that, when released, enables the sash to tilt inward.

Tilt Pins: on a tilt double-hung window, tilt pins 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.

UV (Ultraviolet) Rays: the rays of the sun that can filter through windows and heat up a room, as well as fade furniture, rugs, etc.

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