Industry Glossary

Window and Door Glossary


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Air Chambers
Small honeycomb spaces within the sash and frame which help to insulate and strengthen the window.
Air Infiltration
The amount of air that passes between a window sash and frame. In windows it is measured in terms of cubic feet or air per minute, per square foot of area. The lower the number, the less air the window lets pass through.
Air Latch
Latch mechanism on the interior face of the sash that retains the window in a partially open position for ventilation.
Angled Exterior
A sloped extension from the frame that adds an aesthetically-pleasing dimension to the exterior of the window.
Argon Gas
An odorless, colorless, tasteless, non-toxic gas which is six times denser than air. It is used to replace air between the glass panes to reduce heat transfer.
Awning Window
A top-hinged window that swings outward for ventilation.

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Balance Covers
Covers the balance cavity holding the coil-spring balance system inside the jamb.
Balance System
Device for holding vertically sliding sash in any desired position through the use of a spring or weight to counterbalance the weight of the sash.
Bay Window
An angled combination of three or more windows that project out from the wall of the home. The windows are commonly joined at 30- or 45-degree angles.
Beveled Exterior
An angled extension from the frame that adds an aesthetically-pleasing dimension to the exterior of the window.
Block Frame Window
Used when replacing the wood sash of an old double hung wood window.
Bow Window
An angled combination of windows in 3-, 4-, 5-, 6- and 7-lite configurations. The windows are attached at angles of varying degrees, to project a more circular, arched appearance.
A rubber material that seals the glass to the spacer, creating an airtight and water-tight IG unit. Butyl has the lowest gas permeability of all rubbers.

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Cam Lock and Keeper
The mechanisms which pull the sash together when placed in the locked position.
Capillary Tubes
Small hollow tubes which penetrate the spacer system of an insulating glass unit. They allow pressure equalization between manufacturing locations, shipping, and installation locations. Since the insulating glass unit is not permanently sealed, the air space cannot be filled with Argon gas.
Casement Window
A window with a side-hinged sash that opens outward for ventilation.
Molding of various widths, thickness and shapes applied to the framework of window and door units.
Center of Glass U-Factors and R-values
The U-Factors and R-Values measured from the center of the glass to 2-1/2″ from the frame.
Check Rail
On a double-hung window, the bottom rail of the upper sash and the upper rail of the lower sash, where the lock is mounted.
A generic term referring to any of a variety of window units with one or more curved frame members, often used over another window or door opening.
Any material locked to the outside faces of doors and windows to provide a durable, low-maintenance exterior surface.
Condensation Resistance Factor
A measure of the effectiveness of a window or glazing system to reduce the potential for condensation. The higher the condensation resistance factor, the more efficient the window and glazing system. For the Northeast US, a CRF of 50 or higher is strongly recommended.
Energy transfer from one material to another by direct contact.
Heat transfer by currents that flow from a warm surface to a colder one.
Cottage Double Hung
A double hung window in which the upper sash is shorter than the lower sash.
Coved Exterior
An arced extension from the frame that adds an aesthetically-pleasing dimension to the exterior of the window.

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Dead-air Space
The space between the panes of glass of an I.G. Unit.
A piece of glass or IGU with a sash profile around it; not set within the main frame of a window unit.
A material used in insulating glass to absorb water vapor which causes fogging.
A space which protrudes from the roof of a house, usually including one or more windows.
Double Hung Window
A window that has two operable sashes which slide vertically in the frame.
Double Glazing
Use of two panes of glass in a window to increase energy efficiency and provide other performance benefits.
Double-strength Glass
Glass with a thickness of approximately 1/8″.
Drip Cap
A molding placed on the top of the head brickmould or casing of a window frame.
Dry Glazing
An alternative method of placing glass in a door or window. No glazing mastic is used. Dry glazing is recommended whenever reflective coatings are glazed to first surface.
An elastomeric material with two different degrees of hardness.
Dual Glazing
See double glazing.

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Egress Code
The code that requires a minimum opening of a window for persons to exit or firefighters to enter a building.
Energy Star®
Energy Star is an independent U.S. government program establishing a standard set of guidelines to recognize the energy efficiency of various products. Energy Star guidelines are used in conjunction with a variety of building materials, including windows and patio doors. Over the past ten years, Energy Star guidelines have helped double the efficiency of windows they endorse.
Extruded Screen Frame
Different from a Roll-formed frame, this frame is pressed through a form or die.
A form produced by forcing material through a die.

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An architectural term referring to the arrangement of windows in a wall. From the Latin word, “fenestra,” meaning window.
Fixed Window
Non-venting or non-operable window. Also known as picture window.
A thin strip of metal or synthetic material that diverts water away from a window or skylight.
Foam Spacer
Foam material placed in the airspace of the insulating glass in a window to enhance the appearance and improve the performance of the window.
The enclosure in which window sash or door panels are mounted.
French Hinged Door
Hinged door(s) which have wider panel members around the glass.
French Sliding Door
A sliding door which has wider panel members around the glass, giving the appearance of a French hinged door.
The process of joining materials by melting them together with extreme heat (over 500ºF), resulting in the materials uniting into a one-piece unit.

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Specially designed windows classified as either Straight-Line Geometrics (such as rectangles, triangles, trapezoid, octagons, pentagons, etc.), or Radius-Geometrics (which include half-rounds, quarter-rounds, full-rounds, sectors, ellipses, eyebrows, etc.)
An inorganic transparent material composed of sand (silica), soda (sodium bicarbonate), and lime (calcium carbonate) with small quantities of alumina, boric or magnesia oxides.
The process of sealing the glass to the sash.
Glazing Bead
A strip of vinyl which surrounds the edge of the glass and holds it in place in conjunction with other sealants. Could also be a wood strip applied to the window sash around the perimeter of the glass.
Glazing Stop
The part of the sash or door panel which holds the glass in place.
Decorative horizontal or vertical bars installed between the glass panes to create the appearance of the sash being dividing into smaller lites of glass.
A term referring to windowpane dividers or muntins, usually a type of assembly which may be detached for cleaning.

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The horizontal top portion of the main frame.
Head Expander
A vinyl shape cut the width of an insert window and placed on the head, fitting over it snugly. This piece is used as a filler to expand or lengthen the unit from the head and take up the gap in the opening between the unit and the opening in the unit.
A window with a bottom-hinged sash that opens inward for ventilation.

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Insulating Glass (IG)
A combination of two or more panes of glass with a hermetically sealed air space between the panes of glass. This space may or may not be filled with an inert gas, such as argon.

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Integral extension on the outside of a new construction window that eases installation on siding applications.
The main vertical members forming the sides of a window or door frame.

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Keeper Rail
The horizontal section of the sash where the lock keeper is attached.
Keeper Stile
The vertical section of the sash where the lock keeper is attached.
Krypton Gas
An inert, odorless, colorless, tasteless, non-toxic gas which is about 12 times more dense than air. It is used to replace air between the glass panes to reduce temperature transfer and deter convection. Used when a higher performance is desired than that produced with Argon gas.

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Laminated Glass
Two or more pieces of glass bonded together over a plastic interlayer.
Lift Handle
A handhold for raising and lowering the sash. Handle implies that the handhold is not continuous across the sash.
Lift Rail
A handhold for raising and lowering the sash. Rail implies that the handhold is continuous across the sash.
Glazing framed by muntins and/or sash in a window or door. A unit of glass in a window.
Lock Rail
The horizontal section of the sash where the cam lock is attached.
Lock Stile
The vertical section of the sash where the cam lock is attached.
Low-E (Emissivity) Glass
Glass with a transparent metallic oxide coating applied onto or into a glass surface. The coating allows short-wave energy to pass through but reflects long-wave infrared energy which improves the U-value.

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Main Frame
The head, sill and jambs sections of a window.
Mechanically Fastened Frame
Refers to frames fastened with screws.
Meeting Rail
The horizontal sections of a pair of sash that meet when the sash are closed.
Meeting Stile
The vertical section of a pair of sash that meet when the sash are closed.
Fabric made of either fiberglass or aluminum, used in the making of screens.
A vertical or horizontal wood or metal part used to structurally join two or more windows or door units.
Multi-point Lock
A casement locking system which secures the window at two locking points by operation of one handle.
Applies to any short or light bar, either vertical or horizontal, used to separate glass in a sash into multiple lights. Also called a windowpane divider or a grille.
Muntin Bar
Any small bar that divides a windows glass. Also called a grille or windowpane divider.

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Nailing Flange
An integral part of the main frame extrusion of a window used to secure the unit to the rough opening.

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Obscure Glass
Glass that has been made translucent instead of transparent.
A window with the meeting rail located off center of the frame. Most oriels have a 60/40 configuration.

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Palladian Window
A large, arch-top window flanked by smaller windows on each side.
A framed sheet of glass within a window.
Usually refers to the separate panel or panels in a door frame.
Patio Door
A glass door that slides open and close on adjustable tandem rollers.
Picture Window
A window that has no moveable sash.  Also known as a fixed window.
Pull Handle
A handhold for sliding the sash back and forth. Handle implies that the handhold is not continuous across the sash.
Pull Rail
A handhold for sliding the sash back and forth. Rail implies that the handhold is continuous across the sash.
Pull Stile
A handhold for sliding the sash back and forth. Stile implies that the handhold is continuous across the sash.

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Resistance a material has to heat flow. Higher R-value numbers indicate greater insulating value.
Wave energy transmitted directly from one object to another through the atmosphere or through transparent or translucent materials. The energy radiated is either transmitted, absorbed, reflected or a combination of all three.
The horizontal sections of the sash.
Raised Exterior
An angled extension from the frame that adds an aesthetically pleasing dimension to the exterior of the window.
Relative Humidity Condensation Point
The relative humidity level at which visible water vapor or other liquid vapor begins to form on the surface of the sash or frame, based on an inside temperature of 70° F and an outside temperature of 0° F. The higher the percentage, the more moisture the air can hold before condensation will occur.
Rollformed Screen Frame
A method of fabrication in which a flat (usually metal) material is placed on a machine where the material is formed into shape using differently shaped rollers and pressure.

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A single assembly of stiles and rails made into a frame for holding glass. The part of the window which contains the glass.
Sash Alignment System
An exclusive hinge-type system used on hung windows. This system attaches the sash to the balance, creating perfect alignment between the sash and frame, while allowing the sash to tilt inward for cleaning.
Sash Balance
A system of weights, cords and/or coiled springs which assist in raising double-hung sash and tend to keep the sash in any placed position by counterbalancing the weight of the sash.
Sash Cord
In double hung windows, the rope or chain which attaches the sash to a counter balance located in the wall cavity.
Sash Lift
A protruding handle screwed to the inside bottom rail of the lower sash on a double-hung window.
Sash Weights
In older double-hung windows, the concealed cast-iron weights which are used to counterbalance the sash.
Shading Coefficient
The ratio of solar heat that is transferred through a glazing material relative to the solar heat transferred through 1/8″ clear glass. The lower the number, the more efficient the window is at reducing solar heat gain.
Narrow fixed units mulled or joined to door units to give a more open appearance.
The horizontal, bottom section of the main frame.
Sill Extender
An extrusion that is attached to the bottom of the window to cover the gap between the sill and the rough opening.
Single Hung
A window in which one sash slides vertically and the other sash is fixed (usually the top).
Single-strength Glass
Glass with a thickness of approximately 3/32″.
Slider Window
A window in which the sash move horizontally.
Sloped Sill
The sill of the window that has a downward slope to the outside. This sill has sufficient degree of slope to aid in water runoff.
Solar Heat Gain
The percentage of heat gained from both direct sunlight and absorbed heat. The smaller the number, the greater the ability to reduce solar heat gain.
Material placed between two or more pieces of glass in order to maintain a uniform width between the glass, and prevent sealant distortion.
The vertical sections of the sash.
A molding used to hold, position or separate window parts.

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Tape Glazing
Two-sided tape used to secure and seal the glass to the sash.
Tempered Glass
Glass with a surface compression of not less than 10,000 psi, or an edge compression of not less than 9,700 psi. When broken, the glass breaks into pebbles instead of shards. Standard on all doors and large fixed windows.
Thermal Break
The addition of a thermal insulating material between two thermally conductive materials.
Tilt Latch
Mechanism that unlocks the sash and allows it to tilt in from the main frame.
Tilt-in/Lift-out Sash
A sash that can be tilted to the interior and removed for cleaning and is manufactured by welding.
Total Unit U-Factor
The U-Factor of the window is calculated from the average of the conductivity of the center of glass, edge of glass and frame U-Factors. (It is approximately the reciprocal of the R-value.)
A small window that fits over the top of a door or window, primarily for additional light and aesthetic value.
True Divided Light
A term which refers to windows in which multiple individual panes of glass or lights are assembled in the sash using muntins.

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Amount of heat transferred through a material. The lower the U-factor, the slower the rate of heat flow and the better the insulating quality.
UV Block
The percent of ultraviolet rays blocked from being transmitted through the glass. The higher the number the lower the percentage of ultraviolet rays transmitted through the window.

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Vapor Barrier
A watertight material used to prevent the passage of moisture into or through floors, walls and ceilings.
Vent Unit
A window or door unit that opens or operates.
A plastic material used for cladding or entire window units.
Visible Light Transmittance
The percentage of light that is transmitted through glass in the visible light spectrum (380 to 720 nanometers). The higher the number the higher the percentage of visible light transmitted through the window.

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Material used to form a weather-resistant seal around operable sash.
Weep Flaps
A weep hole that is covered with vinyl flap that allows water to escape, while keeping insects out.
Weep Holes
Small openings designed to allow water to escape that might otherwise accumulate in a window’s sill.
Weep Slots
Slots or holes in the sill (bottom) member of the sash frame that provides an outdoor release of infiltrated rainwater.
Wet Glazing
A silicone-based substance used to secure and seal the glass to the sash.
Force exerted on a surface by moving air.
Window Opening Control Device. Safety latches that allow homeowner to limit the window opening. ASTM F2090-2010 standard requires that all windows, where young children are at risk of injury from falling, be equipped with a window opening control device.
Wood Blocks
Pieces of plywood that come in different thickness, depending on the depth of the hook of the frame. They are used to make the window flush with the opening it is filling. They are also used to assist in pre-mulling windows together and give the screw more to bite into when joining the windows.
Wood Jamb Strips
Strips of wood that run along the jamb used to shim up the window.

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