To help everyone to get on the same page, we’ve assembled this glossary of terms:
Air infiltration This test measures air infiltration through a window or door, excluding air which passes between the frame of the unit and the wall. The units are tested as specified in AAMA/NWWDA 101/I.S.2-97: cfm (cubic feet/minute) per square foot of overall frame dimension.
Argon An inert, nontoxic gas used in insulating windows to improve the insulating value of sealed glass units.
Astragal The vertical trim attached to one of the sash of a French casement window or one of the panels of a French door that bridges the gap between the sash/panels when closed to provide weather and overswing protection.
Awning Window A window with a sash that is hinged at the top and opens from the bottom.
Balance System The system in the side jambs of a single or double-hung window that controls the tension and balance for smooth operation of the sash.
Bar Hinge Hardware that connects the bottom and top rails of a casement or awning sash to the window frame and slides back and forth allowing the sash to open and close; bar hinges are composed of the hinge track and the bar assembly.
Bay Window A bay window is made up of three or more windows. The side or flanker units project out from the building in 30, 45, or 90 degree angles. The center is parallel with the building wall and is made up of one or more windows. All the units can be stationary, operating, or any combination of the two. Typically, the center section is stationary, while the side units are operating.
Bottom Rail A horizontal rail at the bottom of a sash, door, blind or other panel assembly.
Bow Window A series of four or more adjoining window units, commonly five in number, projecting 10°-20° from the wall of the building, forming a radius.
Brickmould A form of exterior casing for windows and doors that serves as an aesthetic boundary between the siding and the frame.
BTU An abbreviation for British Thermal Unit — the heat required to increase the temperature of one pound of water one degree Fahrenheit.
Butt Hinge A typical door hinge. One hinge plate is fastened to the door frame and the other is fastened to the panel.
Cam Lock A single-point locking mechanism that uses a cam action to lock and to pull the window sash against the frame forming a tight weather seal; large windows may have more than one cam lock.
Cam Pivot (also known as pivot pin or torx pin) The pins on the bottom corners of single and double-hung sash that engage the balance and also allow the sash to pivot for easy removal and reinstallation.
Casement Window A window that opens from the side like a door. Historically, casements were the first working windows. They were strategically placed throughout a house to capture breezes and direct them through the rooms. Screens are hung internally to prevent bugs and dirt from entering the house.
Casing Trim around door and window openings. Interior casing is shaped, decorative moulding that covers the inside edges of the jambs and the rough opening between the window unit and the wall. Exterior casing is an alternative to brickmould.
Checkrail In a double-hung window, this is the bottom rail of the upper sash (upper checkrail) and the upper rail of the lower sash, where the lock is mounted (lower checkrail). It is also known as a meeting rail.
Clutch A part of the balance system into which the cam pivot is inserted or engaged.
Condensation Condensation occurs when excess humidity in warmer air is released in the form of water droplets onto a colder surface such as a pane of glass.
Daylight Opening The visible or touchable area of glass in a window or patio door.
Decorative Entry System An entryway made up of a door in a frame, one or two sidelights, and a transom.
Dew Point The temperature at which condensation occurs.
Dimensional Stability The ability of a material to stay put or to resist changes in its dimensions due to temperature, moisture or physical stress variations; stability of a material.
Direct-Set The window’s glass is secured directly into the window frame without the stiles and rails of a sash (e.g. picture window).
Divided Lite A window opening divided into smaller sections by a grid system on the interior or exterior of the glass, between the glass panes, or any combination of these three.
Door An assembly of stiles, rails and glass panels that swings or slides, in a wall.
Door Frame The assembly of structural members (head, sill, jambs) used to fasten the door system to the structure.
Door Jamb The upper horizontal and the two vertical frame members that house the door panel. Jambs may be classified as head or side jambs.
Double Glazing Two panes of glass separated by an air space to form insulating glass; double glazing may also be accomplished by adding a storm panel.
Double-Hung Window A window with two sash, upper and lower, that slide vertically past each other.
Dual-Arm Operator A window-opening mechanism used on casement windows that is composed of two arms; one pulls the sash while the other pushes.
Dual-Pull Operator A window-opening mechanism on awning windows that uses a scissor action and has two keepers.
Egress Dual-Arm Operator A dual-arm operator with a shorter, jointed arm that allows the window to open wider to serve as an exit.
Egress Hinge A hinge used in conjunction with certain casement windows to allow a wider opening to meet emergency exit requirements.
Extrusion A form produced by forcing material through a die.
Fenestration The placement (or arrangement) and design of the windows and exterior doors of a building. In Greek architecture, windows began as simple openings in temples. These openings began to contain glass in the 13th century, when clear glass was available for buildings such as Westminster Abbey. Another important shift in fenestration occurred in the 20th century when large windows became important components in commercial buildings.
Fixed Refers to a window or door that is non-venting or inoperable.
Frame The assembly of structural members (head, sill, jambs) used to fasten a window sash or a door panel to a structure.
French Door A style of door in which two panels open to provide a clear opening which is approximately twice as wide as one panel. In the 19th century,glass was being added to door construction, mainly in French and German homes, on internal doors leading to rooms containing more natural light, such as conservatories, glass houses and vestibules.
French Casement Window A window unit comprised of a single frame in which two sash (hinged at the side jambs) may be opened outward from the center of the frame. This creates an unobstructed opening which spans nearly the complete width of the frame.
Geometric Window Specialty windows of various shapes including: rectangles, triangles, trapezoids, octagons, pentagons, half-rounds, quarter-rounds, full rounds, sectors and ellipses.
Glass Stop The trim that covers the edge of the glass.
Glazing The process of mounting glass into windows and doors. The purpose of glazing is to retain the glass adequately under the design load, provide an effective weather seal, prevent loads or pressure points on the glass resultingfrom building movement, prevent glass-to-metal contact, and minimize glass breakage from mechanical or thermal stress.
Grid (see grille)
Grille A decorative grid on the interior or exterior of the glass, between the glass panes, or in any combination of these locations that divides a window opening into smaller openings to create simulated divided lite or true divided lite. Grilles may or may not be removable.
Guide Bar Operator A window-opening mechanism that has a track along the interior bottom rail of an awning sash. It allows the operating arms to slide as the window opens and closes.
Head Jamb The horizontal frame member at the top of a window or door assembly.
Header Track The track in the head jamb of a sliding/gliding window or door that guides the sash/panel as it opens and closes.
Hinge A jointed or flexible device on which a door or window turns. The earliest known hinges were T-shaped devices called strap or cross-garnet hinges. They were made of wrought iron with a crossbar fixed vertically to the door frame, and attached with nails to the door. In the 18th century, hinges for interior doors were H-shaped or L-shaped, and attached to the door with nails.
Hinge Track The part of a bar hinge that allows the pivot point of an awning or casement sash to slide as the window opens and closes.
Horizontal Sliding Window Two or more sash that slide horizontally past each other; one or more of the sash may be fixed or inoperative or all the sash may operate; in a closed position, the sash come together to form a vertical meeting rail.
Insulating Glass Unit An insulating glass (IG) unit is two or three glass panes separated by a spacer and sealed. IG glass is offered in clear (no special coating) and high performance, which has a special low-emissivity coating for exceptional energy efficiency.
Jamb The vertical frame members of a window or door assembly.
Level A condition that exists when a surface is exactly horizontal.
Lite (also Light) A framed opening in the glass within a sash or door panel; frequently used in reference to glass divided by a grid into multiple smaller openings.
Low-E (Low-Emissivity) insulating glass Low-E insulating glass provides the best year-round performance and lowers energy costs by at least 15 percent (based on savings over clear glass). Low-E glass features transparent microscopic layers of silver placed between layers of anti-reflective metal oxide coatings. These coatings block 83 percent of harmful UV rays and 96 percent of the sun’s infrared heat, so homes stay cooler in the summer and interior furnishings fade less. In the winter, Low-E helps keep homes warmer for improved comfort and reduces condensation. It also delivers greater visible light transmittance than tinted glass.
Mulled Unit Two or more window units structurally joined together.
National Fenestration Rating Council (NFRC) The NFRC is an independent third-party certification organization with industry-accepted standards for evaluating and certifying energy performance. The NFRC Certificate contains U-factor, SHGC (Solar Heat Gain Coefficient), and VT (Visible Transmittance) values. These values form the basis for the ENERGY STAR® Door and Window Program.
Operator The hardware mechanism used to open and close a window, excluding the hinges.
Operating Sash An assembly comprised of stiles (vertical pieces), rails (horizontal pieces), and a window’s glass that opens and closes.
Operator Track The metal track at the bottom of the sash where the roller on the end of the operator arm slides to open and close the sash.
Pane A piece of glass.
Patio Door A mainly glass door that opens onto a patio, deck or backyard of a house. The door panel is comprised of stiles, rails and glass to allow for viewing. Originally homeowners asked for glass doors from a glazer, or someone who handles glass. This specialty product was created by distributors in small shops. In the 1960s when aluminum sliding doors became very popular, window manufacturers realized they could make patio doors to fill the openings that used to be filled by solid doors. At that point, the window companies started heavily promoting patio doors, made in aluminum, vinyl and wood. Door companies now also make them in wood, composites and steel.
Picture Window A fixed window typically of a large size in relation to adjacent windows.
Pivot Pins The pins on the bottom corners of single- or double-hung sashes that engage the balance and also allow the sash to pivot for easy removal and installation.
Rail The horizontal members on the framework of a sash or panel.
Relative Humidity The ratio of the amount of water vapor in the air compared to the maximum amount that could be present (usually expressed in a percentage); 100 percent is when the air is totally saturated with moisture.
Reveal The space between the window sash or door panel and the frame.
Roto-Operator A window-opening mechanism that has a handle that turns in a circular pattern; used on awning windows.
Rough Opening The framed opening in a wall where a window or door is to be installed.
R-value Refers to the resistance a window has to thermal transfer or heat flow. The higher the value, the better the insulation.
Sash An assembly of stiles and rails that forms a frame for holding the glass in a window.
Sash Lift A handle built into or attached to the rail of the sash on a double-hung or single-hung window for easy opening.
Sash Track The track on the sill of a sliding or gliding window that guides the sash as it opens and closes.
Setting Block Small pieces of vinyl or rubber in the bottom rail to protect and support the insulating glass unit.
Side Jamb The vertical frame member on either side of the window or patio door.
Side Light or Side-lite A fixed, usually rectangular window placed on either side of a door.
Sill A main horizontal member forming the bottom of the frame of a window or door.
Sill Track The track on the sill of a sliding or gliding window or door that guides the sash or panel as it opens and closes.
Single-Hung Window A window with a fixed upper sash and movable lower sash that slides vertically.
Single-Pull Operator A window-opening mechanism that uses a scissor action and has one keeper; used on awning windows.
Sliding Patio Door A door with one or more panels that slide horizontally.
Solar Heat Gain Coefficient (SHGC) Solar heat gain coefficient is a measurement of the amount of solar radiation through a piece of glass or door material. The lower the SHGC, the fewer UV rays that cause heat gain come through the glass.
Spacer A component (usually metal) that separates the panes of glass to create the airspace in an insulating glass (IG) unit.
Square A condition that exists when two surfaces are perpendicular (90° angle).
Stationary Sash or Panel A window sash or door panel, often used in combination with other types of window and sash units, that is fixed to the frame and intended primarily for viewing purposes and for admitting light.
Stile The vertical frame members of a sash or door.
Sunburst A semi-elliptical area, the lower center of which contains a sun-like figure with radiating rays; may consist of a wood panel or a glazed sash.
Tempered Glass Glass that is treated with heat in its manufacturing, creating a product that can withstand abnormal force or pressure on its surface, and which does not break into sharp pieces; code requires tempered glass in all doors (including patio doors) and in windows that are located near doors, bathtubs or showers.
Tilt Window A double-hung window designed in such a way that the sashes tilt inward for easy cleaning of the outside of the glass.
Top Rail The top rail of a sash, door, blind or other similar panel assembly.
Transom A window, usually rectangular, placed over a door or window. Transoms, or fanlites, were first used in the 18th century on exterior doors. They increased the amount of light let into the front hall, and because of them, the size of the front door could be reduced.
Trim Millwork, primarily mouldings, that finishes off window and door openings.
Triple Glazing Three panes of glass with an airspace between each pane.
U-factor/U-value U-factor or U-value is a number that represents the rate of heat loss through a window or door. The lower the number, the greater a window resists the transfer of heat. A U-factor of 0.35 or lower represents good insulating value.
Visible Transmittance (VT) Visible transmittance (VT) describes how much available light comes through a window, and is expressed as a percentage. The higher the VT, the more daylight a product lets in. A good VT is about 55%.
Weatherstrip Variously shaped metal, vinyl, plastic or molded fiber strips that fit tightly against the window or door frame parts to prevent air infiltration through cracks. Cold air entering the house in winter can account for up to 35% of the heating load. Weatherstripping can reduce the load to 20%.
Weep Hole The visible exit or entry part of a water drainage system used to drain water out of a window or patio door.
Window Casing May be interior or exterior; an exterior window casing is most commonly installed on window frames for wood sided exterior walls.
Window Frame A group of parts machined and assembled to form an enclosure and support for a sash.
Window Jamb The upper horizontal and vertical frame members that house the window sash. Jambs may be classified as head or side jambs.
Window A wall opening in a building added for the purpose of letting in light and air, usually sealed from the elements in some way, using a frame and sash containing glass or another type of transparent material, and usually able to be opened and shut.
Window Unit A combination of the frame, sash, weatherstripping, sash opening mechanism and, at the option of the manufacturer, screens and/or storm sash assembled as a complete and properly operating unit.