The following definitions are extracted from AAMA/WDMA/CSA 101/I.S.2/A440-11, NAFS — North American Fenestration Standard/Specification for windows, doors, and skylights
AAMA – American Architectural Manufacturers Association. A national trade association that establishes voluntary standards for the window, door, storefront, curtain wall, and skylight industries.
Air Infiltration – the amount of air leaking in and out of a building through cracks in walls, windows and doors.
Air leakage — the flow of air that passes through fenestration products. See air infiltration.
Airspace — the space between adjacent layers in a multi-layer glazing system.
Apron — horizontal trim board under a window stool.
Argon – an inert, nontoxic gas used in insulating glass units to reduce heat transfer.
Astragal – a molding attached to one or both meeting stiles of a pair of double doors in order to prevent drafts.
Awning, hopper, projected window — a window consisting of one or more sash hinged at the top or bottom which project outward or inward from the plane of the frame. An awning rotates about its top hinge(s) and projects outward. A hopper window rotates about its bottom hinge(s) and projects inward.
Backband (also Backbend) — millwork around outside edge of the window casing, usually installed when the casing consists of flat boards.
Balance — a mechanical device used in hung windows as a means of counter balancing the weight of the sash.
Basement window — any window type intended for ventilating or illuminating a basement or cellar.
Bay window — an arrangement of three or more individual window units, attached so as to project from the building at various angles. In a three-unit bay, the center section is normally fixed, with the end panels operable as single hung or casement windows.
Bead (also bead stop; stop) — wood strip against which a swinging sash closes, as in a casement window. Also, a finishing trim at the sides and top of the frame to hold the sash, e.g., a fixed sash or a double-hung window sash.
Bottom rail – the bottom horizontal member of a window sash.
Bow window (also compass, radial bay window) — rounded bay window that projects from a wall in the shape of an arc. It consists usually of five sash.
Boxed mullion — hollow mullion between two double-hung windows to hold sash weights.
Brickmold — a molding used as an exterior door or window casing.
British thermal unit (Btu) — the heat required to increase the temperature of 1 lb. of water 1°F.
Cames — lead strips which hold small pieces of glass in leaded windows.
Cap — decorative molded projection, or cornice, covering the lintel of a window.
Casement window — a window consisting of one or more sash hinged to open from the side (adjacent to the jambs), which project outward or inward from the plane of the frame in the vertical plane.
Casing — a trim. Exposed molding or framing around a window or door, on either the inside or outside, to cover the space between the window frame or jamb and the wall.
Caulking – a mastic compound for filling joints and sealing cracks to prevent leakage of water and air, commonly made of silicone, bituminous, acrylic, or rubber-based material.
Check rail – the bottom horizontal member of the upper sash and the top horizontal member of the lower sash which meet at the middle of a double hung window.
Cladding — the exterior components that cover the frame, sash, leaf, or sliding door panel members and constitute the weather-resistant surface. Note: Some claddings function only as an aesthetic covering, while others contribute partially to the structural strength of the product.
Closing force — the force required to initiate or maintain a sash, leaf, or panel motion in either the opening or closing direction.
Composite unit — a fenestration product consisting of two or more sash, leaves, lites, or sliding door panels within a single frame utilizing an integral mullion.
Concentrated load — a force applied to a fixed point on a window, door, TDD, SSP, roof window, or unit skylight component.
Condensation — the deposition of moisture (liquid water or frost) on the surface of an object caused by warm, moist air coming into contact with a colder object.
Corrosion — the deterioration of a material by chemical or electrochemical reaction resulting from exposure to weathering, moisture, chemicals, or other agents or media.
Diffusing glass — glass with an irregular surface for scattering light; used for privacy or to reduce glare.
Divided light – a window with a number of smaller panes of glass separated and held in place by muntins.
Door — a means of access for the purpose of ingress and egress.
Dormer window — window in a wall that either projects from a sloping roof, or is recessed (inset dormer) into the roof, or a combination of both.
Double-hung window — a window consisting of two sashes operating in a rectangular frame, in which both the upper and lower halves can be slid up and down. A counterbalance mechanism usually holds the sash in place.
Drip cap — horizontal molding to divert water from the top casing so water drips beyond the outside of the frame.
Dual-action window — a window consisting of a sash that tilts from the top and swings inward from the side for cleaning of the outside surface. Also referred to as a tilt-turn window.
Dual glazing — two layers of glazing material mounted in a common frame and/or sash, separated by a space, and sealed or non-sealed.
Egress – is defined as the act of coming or going out. Egress codes are laws about the size of operable windows for the purpose of escape. For example, an egress window cannot be higher than 44 inches from the floor and must have a minimum clear opening of 5.7 sq feet.
Extension jamb (also jamb lining and jamb extender) — a board used to increase the depth of the jambs of a window frame to fit a wall of any given thickness.
Extrusion – the process of producing vinyl or aluminum shapes by forcing heated material through an orifice in a die.
Eyebrow windows — low, inward-opening windows with a bottom-hinged sash. Usually attic windows built into the top molding of the house, the units sometimes are called “lie-on-your-stomach” windows or slave windows. Often found in Greek Revival and Italianate houses.
Face glazing — common glazing set with putty in a rabbited frame.
Fanlight (also sunburst light; fan window; circle-top transom) — a half-circle window over a door or window, with radiating bars.
Fenestration — openings in the building envelope, such as windows, doors, secondary storm products (SSPs) curtain walls, storefronts, roof windows, tubular daylighting devices (TDDs), sloped glazing, and skylights, designed to permit the passage of air, light, or people.
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.
Fire window — window with fire-endurance rating specified for the location.
Fixed door — one or more non-operable assembled leaves or sliding door panels within a door frame and threshold/sill.
Fixed window — a window that is designed to be non-operable and consists of a glazed frame or a non-operating sash within a frame.
Flashing – sheet metal or other material applied to seal and protect the joints formed by different materials or surfaces.
Foil — lobe on a leaf-shaped curve formed by the cusping of a circle or arch. The number of foils involved is indicated by a prefix, e.g., tre-foil (3); quarter-foil (4), etc. Foils are found in windows of Gothic Revival churches and houses.
Frame — the enclosing structure of a window, or door, which holds the sash or casement as well as hardware.
Garage door— a door that is used for vehicular traffic at entrances of buildings such as garages, loading docks, parking lots, factories, and industrial plants, and is not generally used for pedestrian traffic.
Garden window — (Greenhouse window) a window consisting of a three-dimensional, five-sided structure, with provisions made for supporting plants in the enclosed space outside the plane of the wall. Operating sash are allowed but are not required.
Gas fill – a gas other than air, usually argon or krypton, placed between window or skylight glazing panes to reduce the U-factor by suppressing conduction and convection.
Glass — an inorganic transparent material composed of silica, soda, and lime with small quantities of alumina, boric, or magnesia oxides..
Glazing — (n): an infill material such as glass or plastic. (v): the process of installing an infill material into a prepared opening in windows, doors, TDDs, roof windows, SSPs, or unit skylights.
Glazing bead (also glass stop and wood stop and sill bead) — removable trim that holds glass in place.
Glazing channel — groove cut into sash for acceptance of glass.
Glazing clip — metal clip for holding glass in a metal frame while putty is applied.
Handle — a component which enables the movement of a sash, leaf, or panel, or which activates a mechanism which locks or unlocks a sash, leaf, or panel.
Hardware — all the necessary equipment to retain, operate, and lock or unlock the sash, leaf, or panel within the frame.
Head — the horizontal member forming the top of the frame.
Head flashing — flashing installed in a wall over a window.
Header (also lintel; beam) — supporting member or beam above window opening which transfers building weight above to the supporting wall structure on each side of the window. The term header is generally in reference to a wood beam, whereas “Lintel” often refers to a steel beam.
Heat loss – the transfer of heat from inside to outside by means of conduction, convection, and radiation through all surfaces of a house.
Heat-strengthened glass — glass that has been reheat, after forming, to just below melting point, and then cooled, forming a compressed surface that increases its strength beyond that of typical annealed glass.
Hopper – window with sash hinged at the bottom.
Insulating glass unit (IG unit or IGU) — two or more lites of glass spaced apart and hermetically sealed to form a single unit with an air- or gas-filled space between each lite.
Interior door — a door system not intended for use in exterior applications.
Jalousie window — a window consisting of a series of overlapping horizontal frameless louvered glass slats that abut each other tightly when closed and rotate outward when cranked open.
Jambs — the upright or vertical members forming the side of the frame.
Jamb depth — width of the window frame from inside to outside.
Krypton – an inert, nontoxic gas used in insulating windows to reduce heat transfer.
Laminated glass — two or more lites of glass permanently bonded together with one or more polymer interlayers.
Lead light (also lead glazing; stained glass) — window with small panes of glass set in grooved rods of cast lead or came. The glass may be clear, colored, or stained.
Lift – handle for raising the lower sash in a double hung window.
Lintel — horizontal member (wood, steel, or stone) over a window opening to support the weight of the wall above. Also called a header.
Lite (light) — a pane of glass or an insulating glass (IG) unit used in a window, door, TDD, roof window, SSP, or unit skylight. Frequently spelled “lite” in industry literature to avoid confusion with visible light.
Low E (Low-emittance) coating – microscopically thin, virtually invisible, metal or metallic oxide layers deposited on a window or skylight glazing surface primarily to reduce the U-factor by suppressing radiative heat flow.
Meeting rail or check rail — one of the two adjacent horizontal sash members that come together when in the closed position.
Mullion — a horizontal or vertical member which is bounded at either end or both ends by crossing frame members.
Muntin — a member that divides glazing into separate vision areas. Muntins are either structural or decorative. Other common terms are divider, true divided lite (TDL), simulated divided lite (SDL), grill, grid, or bar-in-glass.
Nailing fin – a 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.
NFRC – National Fenestration Rating Council.
Non-operable — intended to not open or close.
Obscure glass – a textured glass (frosted, etched, fluted, ground, etc) used for privacy, light diffusion, or decorative effects.
Operable — intended to be opened and closed.
Operable transom — panel usually glazed over a door which may be opened for ventilation.
Operable window — window that can be opened for ventilation.
Operator – crank operated device for opening and closing casement or jalousie windows.
Oriel window — a window projecting from the wall and carried on brackets, corbels, or a cantilever. Unlike a bay window, the projection of an oriel does not extend all the way to the ground.
Overall dimensions — the external height and width of the product, expressed in millimeters or inches.
Pane – one of the compartments of a door or window consisting of a single sheet of glass in a frame.
Panel — the members of a sliding door or sliding door side lite within a frame which are designed to accommodate the glazing.
Passive door — one or more hinged leaves or sliding door panels that are normally held inactive by latching or locking hardware, but can become active on the release of the latching or locking hardware.
Picture window — large fixed windows.
Pivot — an axis or the hardware about which a window, sash, panel, or leaf rotates.
Pivoted window — a window consisting of a sash which pivots about an axis within the frame. The pivoting action of the window allows for easy access to clean the outside surfaces of the window. Two common types are the 180° compression seal pivoting window and the 360° pivoting window.
Projected window — awning type window that swings either inwards or outwards at the top or the bottom.
R-value – a measure of the resistance of a glazing material or fenestration assembly to heat flow. A high R-value window has a greater resistance to heat flow and a high insulating value than one with a low R-value.
Rail — a horizontal member of a sash, leaf, or panel.
Reinforcement — the material added to individual sash, leaf, panel, or frame members to increase strength and/or stiffness.
Rough opening — the opening in a wall or roof into which a window, door, TDD, roof window, or unit skylight is to be installed.
Saddle bar — light steel bar placed horizontally across a window to stiffen leaded glazing.
Saddle bead — glazing bead for securing two panes.
Safety glass — a strengthened or reinforced glass that is less subject to breakage or splintering, such as glass for doors, unit skylights, and some windows. See also Fully tempered glass and Laminated glass.
Sash — the members of a window that fit within a frame which are designed to accommodate the glazing.
Screen — a product that is used with a window, door, secondary storm product, or unit skylight, consists of a mesh of wire or plastic material used to keep out insects, and is not for providing security or retention of objects or persons from the interior.
Sealant — a compound used to fill and seal a joint or opening.
Side lite — an operable or non-operable product that is designed to be a companion product installed on one or both sides of an operable door or a fixed door. Side lites often have their own separate frame or are contained within the frame of a composite assembly.
Single glazing — glazing that is just one layer of glass or other glazing material.
Single-hung window — a hung window with only one operable sash.
Sill (also sill plate; inside sill; outside sill) — horizontal member at the bottom of the window frame; a masonry sill or sub-sill can be below the sill of the window unit.
Sill drip molding — sill member on a window frame serving as a screen stop; also the extension of the sill that contains the drip cut.
Simulated divided lights – a window that has the appearance of a number of smaller panes of glass separated by muntins, but actually is a lager glazing unit with the muntins placed between or on the surfaces of the glass layers.
Skylight – a roof window that gives light and ventilation
Slider — a window that consists of one or more sash that slide or roll horizontally within a common frame and can also contain fixed lites/sash. Note: Typically, operating sash are identified with an (X) and fixed lites or fixed sash are identified with an (O).
Sliding door — a door that consists of manually operated door panels, one or more of which slide or roll horizontally within a common frame, and can also contain fixed lites/panels. Note: Typically, operating panels are identified with an (X) and fixed lites or fixed panels are identified with an (O).
Solid frame — window frame made from a single piece of lumber.
Sound Transmission class (STC) – the sound transmission loss rating of a material over a selected range of sound frequencies. The higher the number, the less sound transmitted.
Spacer — the linear material that separates and maintains the space between the glass surfaces of insulating glass units.
Stile — one of the two adjacent vertical leaf, sash, or panel members that come together when in the closed position.
Stool – the shelf like board of the interior part of the window sill, against which the bottom rail of the sash closes.
Stop – the molding on the inside of a window frame against which the window sash closes. In the case of a double hung window, the sash slides against the stop.
Storm door — door in a dual-door system so designated by the manufacturer, used on the exterior of, or interior of, and in tandem with, a primary door designated by the manufacturer to be used for the purpose of performance enhancement, and not to be used by itself as a primary door.
Storm window — that window in a dual-window unit so designated by the manufacturer, used on the exterior of, or interior of, and in tandem with, a primary window for the purpose of performance enhancement, and not to be used by itself as a primary window.
Tempered glass — treated glass that is strengthened by reheating it to just below the melting point and then suddenly cooling it. when shattered, it breaks into small pieces. Approximately five times stronger than standard annealed glass and is required as safety glazing in patio doors, entrance doors, side lights, and other hazardous locations. It cannot be recut after tempering.
Thermal barrier — an element made of material with relatively low thermal conductivity, which is inserted between two members having high thermal conductivity, in order to reduce the heat transfer.
Threshold – the member that lies at the bottom of a sliding glass door or swinging door, the sill of a doorway.
Top-hinged window — a window consisting of sash hinged at the head which swings inward or outward using a continuous top hinge or individual hinges, primarily for cleaning or emergency escape and rescue purposes and not for ventilation.
Torsion — the twist induced in a product by the application of a static load to an extreme free corner of that product and normal to its plane.
Transom — an operable or non-operable product that is designed to be a companion product installed above a fenestration product. Note: Transoms often have their own separate frame or are contained within the frame of a composite unit.
Transom light — window sash located above a door.
True divided lite (TDL) — a lite in which dividers (muntins) separate the glazing into individual smaller glazing lites.
Turn-tilt window unit — see Dual-action window.
U-factor or U-value – a measure of the rate of non-solar heat loss or gain through a material or assembly. The lower the U-factor, the greater a window’s resistance to heat flow and the better its insulating value.
Ultraviolet light – the invisible rays of the spectrum that are outside of the visible spectrum at its short-wavelength violet end. Ultraviolet rays are found in everyday sunlight and can cause fading of paint finishes, carpets, and fabrics.
Vertical sliding window — a hung or non-hung window consisting of at least one manually operated sash that slides vertically within a common frame.
Water drip — molding sometimes used on exterior surfaces of an in-swinging casement sash to prevent water from being driven over the sill.
Water penetration — penetration of water beyond the plane intersecting the innermost projection of the test specimen, not including interior trim and hardware, under the specified conditions of air pressure difference across the specimen.
Weatherstrip (weatherseal) — a flexible component used to reduce air leakage, water penetration, or both between sash, leaf, panel, and/or frame.
Weep cut (also drip cut) — groove in the underside of a horizontal board or masonry unit which projects beyond the wall service below to prevent water from moving back toward the wall surface
Weephole (weep) — an opening that allows water to drain.
Welded — when materials are fused by heat to become one when cooled.
Window — an operable or non-operable assembly that is installed in an opening within an exterior wall or roof intended to admit light or air to an enclosure, and is usually framed and glazed. Note: Windows are typically designed to accommodate factory fabrication and glazing.
Window wall — a non-load-bearing fenestration system provided in combination assemblies and composite units, including transparent vision panels and/or opaque glass or metal panels, which span from the top of a floor slab to the underside of the next higher floor slab. Note: Window walls are available with separate or integral slab edge covers and can be fabricated from windows or curtain wall or storefront systems. Primary provision for anchorage occurs at head and sill conditions. Receptor systems can be designed as a part of drainage and movement accommodation provisions.
Yoke — head window jamb in a box window frame.
Z-bar – a steel bar with a Z shaped section used in construction.