Air Chambers
Small honeycomb spaces within the sash and frame which help to insulate and strengthen the window

Air-leakage (air infiltration)
The amount of air leaking in and out of a building through cracks in walls, windows, and doors.

Argon gas
Argon is a safe, odorless, colorless, non-toxic, non-flammable inert gas that is commonly used in place
of air between the glass panes of an insulated Low-E glass unit to reduce temperature transfer.

Awning window
A window unit in which the bottom of the sash swings outward for ventilation.

Balance
A mechanical device (normally spring-loaded) used in single- and double-hung windows as a means of
counterbalancing the weight of the sash during opening and closing.

Bay window
A composite of three windows, usually made up of a large center fixed unit and two flanking units at
30-,45- or 90- degree angles to the wall.

Beveled Exterior
An angled extension from the frame that adds an aesthetically-pleasing dimension to the exterior of the
window.

Bow window
A composite of four or more window units in a radial or bow formation.

Brickmold
A type of external casing which frames windows and doors.

Casement window
A window unit in which the single sash cranks outward, to the right or left.

Casing
Molding of various widths, thickness and shapes applied to the framework of window and door units.

Composite frame
A frame consisting of two or more materials for example, an interior wood element with an exterior
fiberglass element.

Condensation
The deposit of water vapor from the air on any cold surface whose temperature is below the dew point, such as a cold window glass or frame that is exposed to humid indoor air.

Conduction
Energy transfer from one material to another by direct contact.

Convection
Heat transfer by currents that flow from a warm surface to a colder one.

Double-hung window
A window unit that has two operable sashes which move vertically in the frame.

Double or dual glazing
Use of two panes of glass in a window to increase energy efficiency and provide other performance benefits.

ENERGY STAR® windows program
A voluntary partnership between the U.S. Department of Energy (DOE) and the fenestration industry to promote sales of energy-efficient windows, doors and skylights. The program establishes three climate regions with one recommended product designation for each region. All ENERGY STAR® windows must be NFRC-rated, certified and labeled for both U-factor and solar heat gain coefficient.

ENERGY STAR® label
A label that indicates a window meets ENERGY STAR® program energy-efficiency requirements for a specific region, and is at least 40% more efficient than products required under the most common national building codes.

Fanlight
A half-circle window over a door or window, with radiating bars. Also called circle top transom.

Fenestration
The placement of window openings in a building wall, one of the important elements in controlling the exterior appearance of a building. Also, a window, door, or skylight and its associated interior or exterior elements, such as shades or blinds.

Fiberglass
A composite material made by embedding glass fibers in a polymer matrix. May be used as a diffusing material in sheet form, or as a standard sash and frame element.

Fixed window
Non-venting or non-operable window. Also known as picture window.

Flashing
A thin strip of metal or synthetic material that diverts water away from a window or skylight.

Frame
The enclosure in which window sash or door panels are mounted.

French sliding door
A sliding door which has wider panel members around the glass, giving the appearance of a French hinged door.

Glass
An inorganic transparent material composed of silica (sand), soda (sodium carbonate), and lime (calcium carbonate) with small quantities of alumina, boric, or magnesia oxides.

Glazing
Glass in a window or door; the act or process of fitting with glass.

Grids/Grilles
Also called "muntins." The decorative bars that divide the glass part of a window up and create a pattern.

Hinged windows
Windows (casement, awning, and hopper) with an operating sash that has hinges on one side. See also Projected window.

Horizontal slider
A window with a movable panel that slides horizontally.

Infrared radiation
Invisible, electromagnetic radiation beyond red light on the spectrum, with wavelengths greater than 0.7 microns.

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.

Jamb
The side and head trim of a door or window frame.

Laminated glass
Two or more sheets of glass with an inner layer of transparent plastic to which the glass adheres if broken. Used for safety glazing and sound reduction.

Low-E glass
A common term used to refer to glass which has low emissivity due to a film or metallic coating on the glass or suspended between the two lights of glass to restrict the passage of radiant heat.

Metal-clad windows
Exterior wood parts covered with extruded aluminum or other metal, with a factory-applied finish to deter the elements.

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

Muntin
A secondary framing member (horizontal, vertical, or diagonal) to hold the window panes in the sash. This term is often confused with mullion.

Nail fin
An integral extension of a window or patio door frame which generally laps over the conventional stud construction and through which nails are driven to secure the frame in place.

Obscure glass
Any textured glass (frosted, etched, fluted, ground, etc.) used for privacy, light diffusion, or decorative effects.

Operable window
Window that can be opened for ventilation.

Pane
One of the compartments of a door or window consisting of a single sheet of glass in a frame; also, a sheet of glass.

Panel
Usually refers to the separate panel or panels in a door frame.

Picture
Non-venting or non-operable window. Also know as a fixed window.

Radiation
The transfer of heat in the form of electromagnetic waves from one separate surface to another. Energy from the sun reaches the earth by radiation, and a person's body can lose heat to a cold window or skylight surface in a similar way.

Rail
Horizontal member of a window sash.

Rough opening
The framed opening in a wall into which a window or door unit is to be installed.

R-Value
Resistance to thermal transfer or heat flow. Higher R-value numbers indicate greater insulating value.

Safety glass
A strengthened or reinforced glass that is less subject to breakage or splintering.

Sash
A single assembly of stiles and rails made into a frame for holding glass.

Screen
Woven mesh of metal, plastic, or fiberglass stretched over a window opening to permit air to pass through, but not insects.

Sealant
A compressible plastic material used to seal any opening or junction of two parts, such as between the glass and a metal sash, commonly made of silicone, butyl tape, or polysulfide.

Sidelights
Narrow fixed units mulled or joined to door units to give a more open appearance.

Sill
The main horizontal member forming the bottom of the frame of a window or door.

Single-hung
A double-hung type of window in which the top sash is fixed or inoperable.

Skylight (operable or pivot)
A roof window that gives light and ventilation.

Sliding glass door
A door fitted with one or more panels that move horizontally on a track and/or in grooves. Moving action is usually of rolling type (rather than sliding type). Also called gliding door, rolling glass door, and patio sliding door.

Sliding window
A window fitted with one or more sashes opening by sliding horizontally or vertically in grooves provided by frame members. Vertical sliders may be single- or double-hung.

Sloped Sill Adapter
Used to cover the gap between the old sloped sill window and the new block frame window. It adapts a new window to the existing sloping sill.

Spacer
A material placed between two or more panes of glass in an insulated glass unit to bond and seal the glazing unit.

Stop
Small molding strips attached to side and head jambs to guide and stop moving sashes and swinging doors.

Storm windows
A second set of windows installed on the outside or inside of the primary windows to provide additional insulation and wind protection.

Tempered glass
Glass manufactured to withstand greater than normal forces on its surface. When it breaks, it shatters into small pieces to reduce hazard. Standard on all doors and large fixed windows.

Thermal expansion
Change in dimension of a material as a result of temperature change.

Tilt window
A single- or double-hung window whose operable sash can be tilted into the room for interior washability.

Tinted glass
Glass colored by incorporation of a mineral admixture. Any tinting reduces both visual and radiant transmittance.

U-value
Rate of heat flow-value through the complete heat barrier, from room air to outside air. The lower the U-value, the better the insulating value.

Vapor barrier
A watertight material used to prevent the passage of moisture into or through floors, walls and ceilings.

Vent
The movable framework or sash in a glazed window that is hinged or pivoted to swing open.

Vinyl
Polyvinyl chloride material, which can be both rigid or flexible, used for window frames.

Vinyl-clad window
A window with exterior wood parts covered with extruded vinyl.

Window
A glazed opening in an external wall of a building; an entire unit consisting of a frame sash and glazing, and any operable elements.

Window hardware
Various devices and mechanisms for the window including catches, fasteners and locks, hinges, pivots, lifts and pulls, pulleys and sash weights, sash balances, and stays.