The following definitions are extracted from AAMA/WDMA/CSA 101/I.S.2/A440, NAFS — North American Fenestration Standard/Specification for windows, doors, and skylights.

Adjustable — accessible without major reconstruction of the window, door, TDD, SSP, roof window, or unit skylight to bring the parts of the product to a true or more effective relative position.

Air leakage — the flow of air that passes through fenestration products.

Airspace — the space between adjacent layers in a multi-layer glazing system.

Architectural terrace door — a door primarily used for terrace access in high-rise applications/buildings.
Note: Architectural terrace doors consist of one or more glazed panels contained within one master frame. The operable panels will be hinged on either jamb and can swing either to the exterior or interior (not both). The door is not used as a primary entrance door because of the nature of the sill/threshold design used to meet performance requirements.

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.

Awning window — see Awning, hopper, projected window.

Balance — a mechanical device used in hung windows as a means of counterbalancing the weight of the sash.

Basement window — any window type intended for ventilating or illuminating a basement or cellar.

Bite — the dimension by which the inner or outer edge of the frame or glazing stop overlaps the edge of the glazing.

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.

Building envelope — the assembly or assemblies of materials and components that enclose building spaces and are exposed to exterior space or separate conditioned interior space from unconditioned interior space.

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.

Cellulosic composite material — a composite material whose ingredients include cellulosic elements.
Note: These cellulosic elements appear in the form of, but are not limited to, distinct fibers, fiber bundles, particles, wafers, flakes, strands, and veneers.

Certification — a process that indicates a representative sample of a product line has been tested, that the product meets specified requirements, and that the product is subject to ongoing inspections by an outside certification agency.

Check rail — see Meeting rail.

Chemically bonded (when related to a welded corner) — a process where the two polymer profiles or pieces are heated and fused together with the aid of a chemical reaction. The reaction and bonding is similar to the original extrusion process.

Cladding — see Fenestration cladding.

Closing force — see Operating force and Force to latch door.

Combination assembly — an assembly formed by a combination of two or more separate fenestration products whose frames are mulled together utilizing a combination mullion or reinforcing mullion.

Commercial entrance system — a system of products used for ingress, egress, and rescue generally in non-residential buildings.
Note: Commercial entrance systems typically utilize panic hardware, automatic closers, and relatively large amounts of glass. Commercial entrance systems are often site assembled. They are typically subject to high use and possibly abuse and are designed to withstand such use and abuse.

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.
Note: Composite units are not to be confused with products made from cellulosic composite materials.

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.

Conditioned space — an area or room within a building that (a) is heated or cooled by any equipment or appliance; (b) contains uninsulated ducts; or (c) has a fixed opening directly into an adjacent area or room that is heated or cooled by any equipment or appliance or contains uninsulated ducts.

Corrosion — the deterioration of a material by chemical or electrochemical reaction resulting from exposure to weathering, moisture, chemicals, or other agents or media.

Curtain wall — a non-load-bearing exterior wall cladding that is hung to the exterior of the building, usually spanning from floor to floor.
Note: Curtain wall systems can be factory-glazed or designed to accommodate field fabrication and glazing, including optional structural glazing. Curtain wall employs deep rectilinear framing profiles (approximately 150 mm [6 in] or greater), which are often made available in "stock lengths”. Curtain wall vertical framing members run past the face of floor slabs, and provision for anchorage is typically made at vertical framing members only. In contrast to combination assemblies and composite units, non-residential curtain wall systems often need to meet additional performance requirements for interstory differential movement, seismic drift, dynamic water infiltration, etc. Operating vents and entrance doors are provided as separate inserts.

Deflection — displacement due to flexure of a member under an applied load.

Design pressure (DP) — a rating that identifies the load, induced by wind and/or static snow, that a product is rated to withstand in its end-use application.
Note: Design pressure (DP) is not to be confused with Performance Grade (PG) or structural test pressure (STP). Loads induced by static snow are applicable only to TDDs, roof windows, and unit skylights.

Design wind load — the wind load pressure a product is required by the specifier to withstand in its end-use application.
Note: When other loads such as snow load are included, a "design load” results.

Divider — a member that divides glazing into separate vision areas. Dividers are either structural or decorative. Other common terms are muntin, true divided lite (TDL), simulated divided lite (SDL), grill, grid, or bar-in-glass.

Door — a means of access for the purpose of ingress and egress. See also Commercial entrance system, Dual-action side-hinged door, Folding door system, Interior door, Passive door, Revolving door, Secondary storm product, Side-hinged door system, Sliding door, Storm door, and Vehicular-access door.

Double-hung window — a hung window with two sash in which both sash are operable.

Dual-action side-hinged door — a door system consisting of one or more leaves contained within an overall frame and designed such that one of the leaves is operable in a swing mode and can be tilted inward from the top for ventilation.

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.

Dual mode — the primary and secondary window/door, or both primary windows/doors, are closed, the primary windows/doors are locked, and the insect screen (when offered or specified by the manufacturer) is in the stored position.

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.

Fenestration 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. This use of cladding should not be confused with the definition of "Components and Cladding — Elements of the building envelope that do not qualify as part of the main wind-force resisting system” found in ASCE/SEI 7.

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.
Note: This category does not include non-operable unit skylights or TDDs, or products fabricated from curtain wall or storefront systems that are used in window openings.

Float glass — flat glass that has been formed on molten metal, commonly tin. The surface in contact with the tin is known as the tin surface or tin side. The top surface is known as the atmosphere side or air side.

Folding door system — a door system that has, at a minimum, a hinge or pivot attachment of any type between two leaves and three vertical axes about which the leaves rotate. The leaves can be folded to the interior or exterior of the opening. These systems are either top hung or bottom supported by hardware that attaches to a single track system and include, at a minimum, two pivoting/folding leaves, a frame, and a track and roller assembly. The frame has vertical and horizontal members that are joined at the intersections that fully encompass the operating and inactive leaves in a closed position. A flush set track assembly can exist in place of a sill assembly. Additional hinged and pivoting/folding leaves and/or a single-side hinged leaf can be included in the door system.

Forced-entry resistance (FER) — the ability of a window or door in the locked position to resist entry under a specified load and conditions.

Force to latch door — the force required to close a door and fully engage the latch.

Frame — the enclosing structure of a window, door, TDD, roof window, SSP, or unit skylight which fits into or attaches to the wall or roof opening and receives glazing, sash, panels, leaves, or vents.

Fully tempered glass — glass that has been heat treated to a high surface and/or edge compression to meet the requirements of ASTM C1048 (kind FT) or CAN/CGSB 12.1.
Note: Fully tempered glass, if broken, will fracture into many small pieces (dice) which are more or less cubical. Fully tempered glass is approximately four times stronger than annealed glass of the same thickness when exposed to uniform static pressure loads.

Fusion welded — see Welded.

Garage door — see Vehicular-access door.

Garden window — see Greenhouse window.

Gateway performance requirements — the requirements for minimum gateway test size, air leakage resistance, structural design load and overload testing, water penetration testing, forced-entry resistance, and auxiliary testing which are the conditions permitting a product entry into a Performance Class.

Gateway test size — the minimum test specimen size specified to enter a Performance Class.

Glass — a hard, brittle substance, usually transparent, made by fusing materials such as soda ash (NA2CO3), limestone (CaCO3), and sand under high temperatures.

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.

Grade — see Performance Grade (PG).

Greenhouse window (garden 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.

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.

Heat-strengthened glass — glass that has been heat treated to a specific surface and/or edge compression range to meet the requirements of ASTM C1048 (kind HS).
Note: Heat-strengthened glass is approximately two times as strong as annealed glass of the same thickness when exposed to uniform static pressure loads. Heat-strengthened glass is not considered safety glass and will not completely fracture into many small pieces (dice) as with fully tempered glass.

Heat treated — see Fully tempered glass and Heat-strengthened glass.

Hinged rescue window — any window that is mounted into a stationary perimeter frame and is permanently hinged at one jamb.

Hopper window — see Awning, hopper, projected window.

Horizontally pivoted window — see Pivoted window.

Horizontal sliding window — 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).

Hung window — a window consisting of vertically sliding sash which utilize counterbalancing devices to allow the sash to be opened to any variable position between its fully open and fully closed limits. See also Vertical sliding window.
Note: Common types are single hung, double hung, and triple hung.

Inoperable — no longer opening, closing, locking, or unlocking as originally designed.

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.

Integral ventilating system/device — an apparatus that is independent from but installed into a window, door, or unit skylight product for the purpose of controlling the transfer of air through the window, door, or unit skylight product.

Interior accessory window (IAW) — a glazed frame and/or sash, attached inboard of existing prime windows, curtain wall, or storefront, in commercial buildings, to enhance control of thermal transmittance, solar heat gain, sound, air leakage, and/or daylight. IAWs are not intended for occupant operation or to be used with the exterior windows in the open position, nor are they intended to provide any specific resistance to air leakage or water penetration, or withstand structural load.
Note: The IAW frame is typically anchored to surrounding construction, to the existing window frame, or to the curtain wall or storefront interior frame. Unlike SSPs and multiple glazing panels, interior accessory windows are intended for use by trained custodial personnel only and are fitted with limited-access custodial locks to hinge or lift out for periodic cleaning of the non-hermetically sealed air space created. If IAWs are intended for regular occupant operation, or used with the exterior windows in the open position, the product should instead be rated as a prime window or SSP.

Interior door — a door system not intended for use in exterior applications.

Interior window — a window system not intended for use in exterior applications.

Jal-awning window — a window consisting of a multiplicity of top-hinged sash arranged in a vertical series within a common frame, each operated by its own control device which swings the bottom edges of the sash outward. See also Jalousie window and Tropical awning window.

Jalousie window — a window consisting of a series of overlapping horizontal frameless louvers which pivot simultaneously in a common frame and are actuated by one or more operating devices so that the bottom edge of each louver swings outward and the top edge swings inward during operation.

Jambs — the upright or vertical members forming the side of the frame.

Laminated glass — two or more lites of glass permanently bonded together with one or more polymer interlayers.

Leaf — a part of a side-hinged door system, glazed or unglazed, surrounded by a frame. Leaves can be fixed in place (non-operable) or movable (operable).

Limited water (LW) (as a designation) — that the water penetration resistance performance is achieved by testing at a pressure less than the minimum test pressure required for the indicated Performance Class and Performance Grade (PG).

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.

Manufacturer — a company which fabricates and/or assembles one or more parts, components, and/or accessories or supplies entire fenestration systems.

Meeting rail or check rail — one of the two adjacent horizontal sash members that come together when in the closed position.

Meeting stile — one of the two adjacent vertical leaf, sash, or panel members that come together when in the closed position.

Minimum gateway test size — the test specimen size specified to enter a Performance Class at the lowest or minimum level.

Moisture content — the percentage of dry weight that is composed of water, such as in wood.

Mullion assembly

Combination mullion — a horizontal or vertical member formed by joining two or more individual fenestration units together without a mullion stiffener.

Integral mullion — a horizontal or vertical member which is bounded at either end or both ends by crossing frame members.

Mullion stiffener — an additional reinforcing member used in a reinforcing mullion. Mullion stiffeners carry the entire load or share the load with adjacent framing members.

Reinforcing mullion — a horizontal or vertical member with an added continuous mullion stiffener and joining two or more individual fenestration units along the sides of the mullion stiffener.

Multiple glazing panel (MGP) — a glazed panel that can be installed in or on a sash, leaf, or panel on either the interior side or exterior side of the primary glazing. An MGP is tested only in conjunction with a specific primary window or door.

Muntin — see Divider.

Negative pressure — pressure acting in the outward direction.

Non-hung window — a window consisting of vertically sliding sash which utilize mechanical retainers or slide bolts to allow the sash to be opened to any one of the pre-selected positions between its fully open and fully closed limits. See also Vertical sliding window.

Non-operable — intended to not open or close.

Normal use (pertaining to windows, doors, secondary storm products, operable unit skylights, and roof windows) — intended for operation for reasons in addition to cleaning and maintenance of the window(s), door(s), secondary storm product(s), operable unit skylight(s), or roof window(s) in question.

Operable — intended to be opened and closed.

Operating force — the force required to initiate or maintain a sash, leaf, or panel motion in either the opening or closing direction.

Outdoor-indoor transmission class (OITC) — a single-number rating calculated in accordance with ASTM E1332, using values of outdoor-indoor transmission loss, that provides an estimate of the sound insulation performance of a facade or building elements.
Note: The frequency range used is typical of outdoor traffic noises.

Overall dimensions — the external height and width of the product, expressed in millimeters or inches.

Panel — the members of a sliding door or sliding door side lite within a frame which are designed to accommodate the glazing.

Parallel opening window — a window consisting of an operable sash that moves outward in a horizontal direction perpendicular to the plane of the frame for the purpose of ventilation. The sash remains parallel to the frame throughout its range of motion.

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.

Performance Class — one of the five Performance Classes (R, LC, CW, AW, and SK) within the classification system that provides for several levels of performance.
Note: This allows the purchaser or specifier to select the appropriate level of performance depending on climatic conditions, height of installation, type of building, etc.

Performance Grade (Grade or PG) — a numeric designator that defines the performance of a product in accordance with this Standard/Specification.
Note: Performance Grade (Grade or PG) is not to be confused with design pressure (DP) or structural test pressure (STP). Performance Grade (PG) is achieved only on successful completion of all applicable tests specified

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.

Plastic glazing — plastic infill materials (including, but not limited to, acrylic, co-polyester, fiberglass-reinforced plastic, and polycarbonate) that are glazed or set in a frame or sash.

Positive pressure — pressure acting in the inward direction.

Primary door — that door in a dual-door system so designated by the manufacturer, capable of protecting the building’s interior from climatic elements (as opposed to a secondary door used mainly for performance enhancement).

Primary window — that window in a dual-window unit so designated by the manufacturer, capable of protecting the building’s interior from climatic elements (as opposed to a secondary window used mainly for performance enhancement).

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.

Revolving door — an exterior door consisting of two or more leaves that pivot about a common vertical axis within a cylindrically shaped vestibule.

Roof window — a sloped application of a fenestration product that provides for in-reach operation.
Note: Roof windows used for emergency escape and rescue usually have a balanced sash.

Rough opening — the opening in a wall or roof into which a window, door, TDD, roof window, or unit skylight is to be installed.

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, secondary storm product, or unit skylight 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.

Secondary door — that 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.

Secondary storm product (SSP) — a door, window, or skylight product intended to be used only in conjunction with a primary door, window, or skylight product for the purpose of enhancement of performance in a system with the primary product. A secondary storm product can be attached to the internal or external frame or sash of the primary product. A secondary storm product is also considered a secondary door or window.

Secondary 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.

Serviceable — accessible without major reconstruction of the window, door, SSP, TDD, roof window, or unit skylight.

Setting block — a device or member that supports the weight of the glazing and is in direct contact with an edge of the glazing after final installation.

Side-hinged door system — a door system having, at a minimum, a hinge attachment of any type between a leaf and jamb, mullion, or edge of another leaf but having a single, fixed vertical axis about which the leaf rotates between open and closed positions. These systems include, at a minimum, a single operating leaf, surrounding frame, and components. The surrounding frame has vertical and horizontal members that are joined at the intersections and fully encompass the operating and/or fixed leaf/leaves.
Note: Additional operating, passive and/or fixed leaves, side lites, transoms, framing, and mullions are often included.

Side-hinged (inswinging) window — a window that consists of sash hinged at the jambs that swings inward using exposed butt hinges or concealed butt hinges, and in some cases friction hinges. It is used primarily for cleaning or emergency escape and rescue purposes, but not for ventilation other than in the case of emergency. The gateway test size is larger than for casement windows, but otherwise the same requirements are met. See also Hinged rescue window and Top-hinged window.

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.

Single mode — the primary window/door is closed and latched, the secondary window/door or outer primary window/door is opened fully, and the insect screen (when offered or specified by the manufacturer) is in the functional position.

Slider — see Horizontal sliding window.

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).

Sloped glazing (other than unit skylights) — a glass and framing assembly that is sloped more than 15° from the vertical and which forms essentially the entire roof of the structure.
Note: Generally, this is a single slope construction.

Sound transmission class (STC) — a single-number rating calculated in accordance with ASTM E413, using sound transmission loss values, that provides an estimate of the sound insulation performance of an interior partition in certain common sound insulation problems.
Note: The frequency range used is typical of indoor office noises.

Spacer — the linear material that separates and maintains the space between the glass surfaces of insulating glass units.

Span — the clear distance measured parallel to the length of a mullion or divider between support points.

Spandrel — the opaque areas of a building envelope which typically occur at locations of floor slabs, columns, and immediately below roof areas.

Specification — a written document often accompanying architectural drawings, giving such details as scope of work, materials to be used, installation method, required performance, and quality of work for work under contract.

Stile — a vertical member of a sash, leaf, or panel.

Storefront — a non-residential, non-load-bearing assembly of commercial entrance systems and windows usually spanning between the floor and the structure above, designed for high use/abuse and strength.
Note: Storefront systems are typically designed to accommodate field fabrication and glazing and employ exterior glazing stops at one side only. Storefront employs shallow rectilinear framing profiles (approximately 150 mm [6 in] or less), which are often made available in "stock lengths”. Vertical framing members run between the top of the floor slab and structure above, with provision for anchorage at all perimeter conditions. Operating vents and entrance doors are provided as separate inserts.

Storm door — see Secondary door.

Storm window — see Secondary window.

Structural test pressure (STP) — the pressure differential applied to a window, door system, TDD, roof window, SSP, or unit skylight.
Note: Structural test pressure (STP) is not to be confused with design pressure (DP) or Performance Grade (PG).

Sunroom — a multi-sided structure consisting of a high percentage of glazed area versus framing area.
Note: Usually a non-conditioned area attached to the exterior of an existing building.

System — the parts, components, hardware, and/or accessories that yield a complete, fully functional assembly.

Tempered glass — see Fully tempered glass.

Test specimen — a complete, fully functioning window, door, SSP, TDD, roof window, or unit skylight supplied by the applicant and fitted in the test apparatus in accordance with the manufacturer’s written installation instructions (including the manufacturer’s instructions for clearance, shimming, and anchoring).

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.

Thermal break — see Thermal barrier.

Thermoplastic — a polymer material that turns to liquid when heated and becomes solid when cooled and is able to repeat these processes.

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.

Tributary width — the width of wind-bearing area contributing to the load on a mullion or divider.

Tropical awning window — a window consisting of one or more top-hinged or pivoted sash that swing outward at the bottom edge and are operated by one control device that securely closes them at both jambs without the use of any additional manually controlled locking devices.

Tropical window — see Jal-awning window, Jalousie window, and Tropical awning window.

True divided lite (TDL) — a lite in which dividers (muntins) separate the glazing into individual smaller glazing lites.

Tubular daylighting device (TDD) — a non-operable fenestration unit primarily designed to transmit daylight from a roof surface to an interior space via a closed-end tubular conduit. The basic unit generally consists of an exterior glazed weathering surface, a light-transmitting tube with a reflective inner surface, and an interior closure glazing in a retainer frame. The interior closure glazing is generally sealed. A TDD product line can be tested and rated in either or both of the following configurations: (a) Closed ceiling (CC): the tubular conduit passes through unconditioned space. (b) Open ceiling (OC): the tubular conduit is suspended in conditioned space.

Turn-tilt window unit — see Dual-action window.

Unit skylight — a complete factory-assembled glass- or plastic-glazed fenestration unit consisting of not more than one panel of glass or plastic installed in a sloped or horizontal orientation primarily for natural daylighting. Unit skylights are either fixed (non-operable) or venting (operable).

Vehicular-access 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.

Vertical fenestration — fenestration products that are installed at an angle less than 15° from vertical.

Vertically pivoted window — see Pivoted window.

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 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.

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.

The Language of Windows

Below are some additional terms which have been used to describe windows or doors or their component parts. These definitions are not included in current industry standards.

Anchor strip — board around a window frame nailed to house framing. It also serves as windbreak. In newer windows, anchor strip may be plastic or metal.

Angle brace — wood member nailed across window frame at upper corners while frame is in a squared position in order to maintain squareness before installation.

Apron — horizontal trim board under a window stool.

Backband (also Backbend) — millwork around outside edge of the window casing, usually installed when the casing consists of flat boards.

Barn sash — plain sash for farm or cottage, used as a fixed, sliding, or casement window; generally installed in a rough frame for utility or temporary structures.

Bay window — windows that project out from the wall and extend to the ground. An "angle bay window" refers to the angle of departure from the plane of the wall.

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.

Bedding — method of glazing in which a thin layer of putty or glazing compound is placed in the glass rabbet, the glass pressed into the bed, the glazier's points (metal tabs) driven, and the sash is face-puttied over the points.

Blank window — see false window.

Bottom rail — 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.

Box-head window — window made so the sash can slide vertically into the wall space above the header.

Cabinet window — projecting window for the display of goods, as in a retail store.

Cameo window — fixed oval window, generally with surrounding moldings and ornaments, often found on Colonial Revival Houses.

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 adjuster — device to hold a casement window in any open position.

Casement stay — bar for holding a casement window in any of several fixed open positions.

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.

Center-hung sash — a sash that pivots on pins in the middle of the sash stiles and sides of the window frame to allow access for cleaning from the inside.

Chicago window — a large fixed sash flanked by a narrow, often movable, sash on either side. First used by Chicago School architects in the late 19th and early 20th Century.

Clerestory (also clearstory; high-light window) — a window in the upper part of a lofty room that admits light to the center of a room.

Colonial windows — windows with small rectangular panes, or divided lites, designated as 12-lite, 16-lite and so on.

Corner window — two windows meeting at a corner of a structure.

Coupled window — two separate windows separated by a mullion. Also called a double window.

Diffusing glass — glass with an irregular surface for scattering light; used for privacy or to reduce glare.

Diocletian window — semi-circular window divided by wide mullions into three lights (lites). This ancient Roman style was later used by Palladio in the 16th century. Also called a Therm. Used in Classical Revival buildings of the early 1900s.

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.

Drip cap — horizontal molding to divert water from the top casing so water drips beyond the outside of the frame.

Drop window — vertical window in which the sash can descend into a cavity in the wall below the sill.

Extension blind stop — molded window frame member, usually the same thickness as the blind stop and united with it, thus increasing the width of the blind stop, in order to close the gap between the window frame and the rough opening in the house frame. Used to attach the window frame to the wood framing. Also known as blind stop extender or blind casing.

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.

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 rabbeted frame.

Fanlight (also sunburst light; fan window; circle-top transom) — a half-circle window over a door or window, with radiating bars.

Fire window — window with fire-endurance rating specified for the location.

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); quatre-foil (4), etc. Foils are found in windows of Gothic Revival churches and houses.

Folding casement — casement windows hinged together so they may fold into a confined space.

French window — two casement sash hinged on the sides to open in the middle; sash extends to the floor and serves as a door to a porch or terrace.

Georgian window — a double-hung window.

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.

Glazing gasket — special extruded plastic shape for attaching window glass to metal or masonry wall openings. It also serves as a cushion and insulator.

Gothic-head window — window topped with a pointed arch. It is not as tall and narrow as the pure Gothic Lancet window.

Guillotine window — the first double-sash window, with only one movable sash and no counterweights or balancing system. A peg was inserted through a hole in the movable sash and into a corresponding hole in the frame. Its tendency to come slamming down led to the colorful name.

Hanging sash (also hung sash) — sash hung on a cord connected to a counterweight.

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.

Head flashing — flashing installed in a wall over a window.

Hit-and-miss window — two-part window with the lower sash containing movable ventilation panels.

Inset dormer (recessed, internal) — see dormer window.

Interior glazed — glazing installed from inside of the building structure.

Jamb depth — width of the window frame from inside to outside.

Label — a projecting molding by the sides and over the top of an opening.

Label stop — ornamental projection on each end of a label, sill, or sill course. Often takes the shape of a gargoyle or other decorative carving.

Lancet window — tall, narrow window with a pointed-arch top, often with leaded diamond shaped lights; characteristic of Gothic architecture.

Lattice window (also lozenge) — window with glazing bars set diagonally.

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.

Lintel — horizontal member (wood, steel, or stone) over a window opening to support the weight of the wall above. A header.

Loop window (also Balistraria) — a long and narrow vertical opening, usually widening inward, cut in a medieval wall, parapet, or fortification for use by archers. Modifications appear in Romanesque Revival architecture.

Mold stone (also jamb stone) — a stone that serves as a window jamb.

North-light roof — sawtooth roof with north-facing clerestory windows.

Ogee curve (also ogee molding) — reverse flex curve commonly found in window moldings and trim pieces.

Operable transom — panel usually glazed over a door which may be opened for ventilation.

Operable window — window that can be opened for ventilation.

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.

Panel window — a form of picture window consisting of several sash or fixed glazings, separated by crossbars or mullions--or both.

Palladian window — tripartite window by the 16th century Italian architect Andrea Palladio.

Parting bead (also parting strip and parting stop) — a vertical strip on each jamb that separates the sashes of a double-hung window.

Parting slip — a thin wood strip separating the sash weights in the weight box of each jamb of old double-hung windows.

Picture window — large fixed windows.

Prime sash — balanced or moving sash of a window unit.

Projected window — awning type window that swings either inwards or outwards at the top or the bottom.

Quarrel — a diamond- or square-shaped glass piece set diagonally. A medieval term for small panes of glass set diagonally in Gothic windows.

Queen Anne window — a window with small glass windows or lights arranged in various forms, usually only on the upper sash. Appeared 1870s.

Reglet — plastic or wood molding put in a concrete or masonry opening for a uniform groove for a spline-type gasket to hold window glass.

Reversible extension blind stop — an extension blind stop that is rabbetted to receive l/2 or 25/32-in. sheathing.

Saddle bar — light steel bar placed horizontally across a window to stiffen leaded glazing.

Saddle bead — glazing bead for securing two panes.

Shading coefficient — decimal value which is the solar gain of a window, divided by the solar gain for a clear single-glass window of the same size. The shading coefficient of clear, double-glazing is about 0.85 to 0.9.

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.

Solid frame — window frame made from a single piece of lumber.

Splayed window — window unit set at an angle in a wall.

Storm clip — device attached to the muntin of a metal sash to stop the pane from moving outwards.

Transom light — window sash located above a door.

Triple window — generally refers to any tripartite group of windows with square heads. Found on Colonial Revival houses. Units suggest Palladian windows but are less expensive to construct.

Venetian window — same as Palladian window.

View sash — picture window with the lights divided by muntins.

Wash cut — beveled cut in a stone sill to divert water.

Water drip — molding sometimes used on exterior surfaces of an in-swinging casement sash to prevent water from being driven over the sill.

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

Yoke — head window jamb in a box window frame.

Yorkshire light — window with one or more fixed sash and a horizontally moving sash.