Glossary

40 window and door terms in plain English.

A

Air leakage rating: The air leakage rating shows how much air passes through a closed window or door, measured in cubic feet per minute per square foot. Lower is tighter.
Aluminum-clad: Aluminum-clad describes a wood window or door whose outside face is covered with a layer of aluminum that resists weather and fading.
Argon gas fill: Argon gas fill replaces the air between the panes of an insulated glass unit with an inert gas that slows heat transfer.
Awning window: An awning window is hinged at the top and opens outward from the bottom, like a shade over the glass.

Bifold door: A bifold door has hinged panels that fold flat and stack to one or both sides of the opening.

Casement window: A casement window is hinged on one side and swings outward like a door, usually with a crank.
Certificate of Appropriateness: A Certificate of Appropriateness is City of Dallas approval for exterior work on a landmark or in a landmark district, issued before the work starts.
Corner window: A corner window joins two glass units at a corner with no post, so the view wraps around the room.

Egress: Egress is a window or door opening large enough, and easy enough to open, that a person can escape through it in an emergency.
ENERGY STAR climate zone: An ENERGY STAR climate zone is a region of the country with its own limits for the U-factor and SHGC a window must meet to qualify.

Fixed (picture) window: A fixed window does not open. It gives the largest clear view and the thinnest frame for its size.
Flashing: Flashing is waterproof material, such as metal or tape, that directs water away from the edges of a window or door opening.
French door: A French door is a pair of glazed, hinged doors that open from the center with no post between them.

IGU (Insulated Glass Unit): An insulated glass unit, or IGU, is two or more glass panes held apart by a spacer and sealed around the edge with an air or gas space between.
Impact-resistant glass: Impact-resistant glass is laminated glazing built to stay in the frame after a hard strike, such as hail or windborne debris.

Jamb: The jambs are the vertical side parts of a door or window frame. The head jamb runs across the top.

Laminated glass: Laminated glass bonds two panes around a plastic interlayer, so the glass cracks but stays in one piece instead of falling out.
Lift-and-slide door: A lift-and-slide door has a handle that lifts the panel off its seals so it glides easily, then lowers to lock tight.
Low-E coating: A low-E coating is a thin, nearly invisible metal layer on glass that reflects heat while letting daylight through.

Mullion: A mullion is the vertical or horizontal bar that joins two window or door units side by side or stacked.
Multi-slide door: A multi-slide door has several large panels that slide past each other or tuck into a wall pocket to open a whole wall.
Muntin: A muntin is a slim bar that divides one pane of glass, or one sash, into smaller panes called lites.

NFRC label: The NFRC label is the sticker on a window or door that shows independently rated U-factor, SHGC, visible transmittance, air leakage and condensation resistance.

Pivot door: A pivot door turns on a hinge point set in the floor and head instead of side hinges.
Pivot hinge: A pivot hinge is the hardware at the top and bottom of a pivot door that carries its weight and sets its swing.

Rough opening: The rough opening is the framed hole in the wall, before trim, where a window or door is set.

Sash: The sash is the movable frame that holds the glass in a window. On a fixed window, it is the frame around the glass.
SHGC (Solar Heat Gain Coefficient): SHGC is a number from 0 to 1 that shows how much of the sun's heat passes through a window. A lower number blocks more heat.
Sightline: A sightline is the visible width of frame, sash or bar you see between the glass and the wall; slimmer sightlines mean more glass and more view.
Sill: The sill is the bottom horizontal part of a window or door frame. It sheds water away from the opening.
Slim-profile (thin-frame) window: A slim-profile window uses very narrow frames and sashes to maximize the glass area and the view.
Storm rating (windborne debris): A windborne debris rating shows that a window or door passed a test for resisting flying debris and pressure from high winds.

Tempered glass: Tempered glass is heat-treated to be stronger than ordinary glass, and when it breaks it crumbles into small, blunt pieces instead of sharp shards.
Thermal break: A thermal break is an insulating barrier built into a metal frame so heat cannot flow straight through the metal.
Thermally broken steel: Thermally broken steel is a steel window or door profile with a built-in insulating barrier, so it keeps slim lines and better efficiency.
Tilt-and-turn window: A tilt-and-turn window opens inward two ways: tilted from the top for air, or swung open like a door.

U-factor: U-factor measures how fast heat flows through a window or door. A lower number means better insulation.

Visible transmittance (VT): Visible transmittance, or VT, is a number from 0 to 1 that shows how much daylight passes through a window. A higher number is brighter.

Warm edge spacer: A warm edge spacer is the low-conductivity strip at the perimeter of an insulated glass unit that cuts heat loss and lowers the chance of condensation.
Wood-clad window: A wood-clad window has a real wood interior and a metal or other protective cladding on the outside that shields the wood from weather.

Send your plans or a few photos of the openings. We will help you choose the system, the brand and the glass.