Air Infiltration/Air Tightness

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/WDMA/CSA 101/I.S.2/A440-S1-09.

Awning Window

A window with a sash that is hinged at the top and opens from the bottom.

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° 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.

Bow Window

A series of four or more adjoining window units, commonly five in number that project 10°-20° from the wall of the building, forming a radius.


A form of exterior casing for windows and doors that serves as an aesthetic boundary between the siding and the frame.

Cam Lock

A single-point locking mechanism that uses a “cam” action to lock and 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 sashes 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.


The trim around door and window openings. Interior casing is shaped, decorative molding 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 brickmold.

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 Casing

The trim around an interior or exterior door. Exterior door casings are installed only on the outside of exterior door frames, especially on wood facing wood-frame exterior walls. Interior casing covers the inside edges of the jambs and the rough opening between the door unit and the 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 two vertical frame members that house the door panel. Jambs may be classified as head or side jambs.

Door Panel

An assembly comprised of stiles (vertical pieces), and rails (horizontal pieces) inserted into the door frame.

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 sashes, upper and lower, that slide vertically past each other.

Dual-Arm Operator

A window-opening mechanism used on casement windows. It is composed of two arms; one pulls the sash while the other pushes.

Entrance Door

A door that serves as the main entrance of a structure. It may be single or paired.


A form produced by forcing material through a die.

Finger Joint

A joint between two pieces created by machining a series of interlocking groves. It is used to create a longer section of wood. The joints are firmly held in place with an adhesive.


The final, protective treatment of a surface (paint, stain, etc.).


Refers to a window or door that is non-venting or inoperable.

Flat Door Panel

A door panel consisting of a flat piece of plywood, solid wood or other material in contrast to a raised door panel

Flush Door

A door consisting of a core, cross-banding and flat-face veneers, or a door consisting of a core and flat-face veneers only.

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 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.

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.


The process of mounting glass into windows and doors. Glazing also refers to the lowest quality of plate glass. 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 resulting from building movement, prevent glass-to-metal contact, and minimize glass breakage from mechanical or thermal stress. An insulating glass (IG) unit is two 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-emissive coating for exceptional energy efficiency.


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 a simulated divided lite or true divided lite. Grilles may or may not be removable.


A term describing the swinging direction of a window or door. Window or door hardware may also be left or right-handed.

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


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.

Insulating Glass Unit

A sealed assembly of two or more panes of glass separated by a spacer. Manufacturing of insulating glass began in 1930.

Horizontal Sliding Window

Two or more sashes that slide horizontally past each other. One or more of the sashes may be fixed or inoperative or all the sashes may operate. In a closed position, the sash come together to form a vertical meeting rail.


The vertical frame members of a window or door assembly.

Kick Plate

A thin, polished metal plate applied to the bottom rail or bottom of a door to prevent denting and soiling of the wood surface caused by the kicking action of persons opening the door; kick plates may be applied to one or both sides of a door.

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.

LoE2 (“Low-E Squared”) Glass

Window City uses LoE2, which provides the best clarity and highest performance of all solar gain Low-E glass products. Ordinary Low-E provides 14% air-conditioning savings when compared to single pane clear glass, whereas LoE² provides 31%. The end result is windows that provide the ultimate in comfort, because they reduce window heat gain by 50% or more when compared to ordinary glass.

Low-Emissive (Low-E) Glass

Low-E glass is manufactured by depositing a microscopically thin, transparent metal or metallic oxide layer on the glass. Low-E coatings reduce radiant heat loss, and can reduce the passage of UV rays. Use of heat-resistant (or absorbing) glass began in the 1950s, as did the use of reflective (or mirror) glass.


A strip of wood, usually shaped to a curved profile, used to accent and emphasize the ornamentation of a structure and to conceal surface or angle joints.


A wood or metal part used to structurally join two window or door units.


The individual pieces of a decorative grid that help divide a window opening into smaller sections.

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.


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.


A framed sheet of glass within a window or door frame.

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.

Rough Opening

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.


This refers to the resistance a window has to thermal transfer or heat flow. The higher the value, the better the insulation.


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.

Sidelite (Light)

A fixed, usually rectangular, window placed on either side of a door.


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 Glazing

The use of a single pane of glass in a window.

Single-Hung Window

A window with a fixed upper sash and movable lower sash that slides vertically.

Sliding Patio Door

A door with one or more panels that slide horizontally.


The vertical frame members of a sash, door, blind or screen.

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.


A component that separates the panes of glass to create the airspace in an insulating glass (IG) unit.

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 does not break into sharp pieces. Building 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.


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.

Triple Glazing

Three panes of glass with an air space between each pane.

True Divided Lite

A window opening comprised of multiple individual smaller panes of glass separated by muntins.


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%.

Warm-edge Spacer

A spacer designed to minimize heat transference between two layers of insulating glass.


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%.

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 uPVC 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 Unit

A combination of the frame, sash, weatherstripping, sash opening mechanism and, at the option of the manufacturer, screens and/or storm sashes assembled as a complete and properly operating unit.