The Window & Door Glossaries

Below are separate glossaries for windows and doors, which contain concise definitions and explanations for key terms associated with these products. Users can access definitions of terminology related to window types and components to door design and functionality. The definitions should provide a better understanding of the technical aspects and features of windows and doors.

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.

The following definitions are extracted from WDMA I.S.1A, Industry Standard for Architectural Wood Flush Doors and WDMA I.S.6A, Industry Standard for Architectural Stile and Rail Doors

Anatomy of a Flush Door

Anatomy of a Stile and Rail Door


Astragal- A molding or trim attached to the meeting edge of one door of a pair of door(s) which prevents swing-through and covers the gap where the doors meet when closed.

Balance Match- Two or more veneer components or leaves of equal size to make up a single face.

Barber Pole- An optical effect that often occurs when veneers are book matched, resulting in an alternating dark and light appearance. This is caused by slicing veneer, creating tight and loose sides that are placed adjacent to one another in the book matching process. The tight and loose sides reflect light differently, resulting in the varying appearance.

Bark Pocket- Bark around which normal wood has grown.

Bevel- A machine angle other than a right angle, i.e., a 3 degree bevel that is equivalent to a 1/8 inch drop in a 2 inch span (1 mm in 16mm).

Bird Peck- A mark or wound in a tree or piece of wood caused by birds pecking on the growing tree in search of insects.

Blended Repair Tapering- A repair referring to end splits, repaired with wood or filler similar in color to blend well with adjacent wood.

Blending- Color change that is detectable at a distance of 6 ft. to 8 ft. (1.8 m to 2.4 m) but which does not detract from the overall appearance of the door.

Blocking- A material used to replace core material in specific locations to provide improved screw holding for the attachment  of hardware or provide additional structural door reinforcement.

Bonded Core- Stiles and rails are securely glued to the core prior to application of crossbanding, door skins, veneers or laminate.

Book Match- Adjacent pieces of veneer from a flitch or log are opened like a book and spliced to make up the face with matching occurring at the spliced joints. The fibers of the wood, slanting in opposite directions in the adjacent sheets, create a characteristic light and dark effect when the surface is seen from an angle.

Bow- A curvature along the door height, or a deviation from a flat plane from end to end. A deviation, flatwise, from a straight line drawn from end to end or top to bottom of a piece as measured at the point of greatest distance from the straight line.

Burl- A figure created by abnormal growth or response to injury that forms an interwoven, contorted, or gnarly mass of dense woody tissue on the trunk or branch of the tree.

Burl, conspicuous- A swirl, twist or distortion in the grain of the wood which usually occurs near a knot or crotch. A conspicuous burl is associated with abrupt color variation and/or a cluster of small dark piths caused by a cluster of adventitious buds.

Butt Joint- A joint formed by square edge surfaces (ends, edges, and faces) coming together. Also referred to as a end butt joint, edge butt joint.

Cathedral Grain- A grain appearance characterized by a series of stacked and inverted "V"s, or cathedral type of springwood (earlywood) summerwood (latewood) patterns common in plain sliced (flat cut) veneer (see split heart).

Center Match- An even number of veneer components or leaves of equal size (prior to edge trimming) matched with a joint in the center of the panel to achieve horizontal symmetry.

Certified Wood- Wood products that have been qualified by an independent third party agency as satisfying their proprietary requirements for responsible environmental practices.

Checks- Small slits running parallel to grain wood, caused chiefly by strains produced in seasoning and drying.

Comb Grain- A rift cut veneer with exceptionally straight grain and closely-spaced growth increments resembling the appearance of long strands of combed hair

Compatible for color and grain- Components selected so that lighter-than-average color components are not adjacent to darker-than-average color components, no sharp contrasts in color exist between adjacent components, and grain of adjacent components does not vary widely and is similar in grain, character, and figure.

Compatible Species- Different species which are able to exist in a harmonious combination of color and grain.

Component (Of Face Veneer)- An individual piece of veneer that is joined to other pieces to achieve a full length and width face. Terms used interchangeably with component in the context of the face are piece and leaf.

Composite-  A composite whose ingredients include cellulosic elements. These cellulosic elements can appear in the form of, but are not limited to: distinct fibers, fiber bundles, particles, wafers, flakes, strands and veneers. These elements may be bonded together with naturally occurring or synthetic polymers. Also, additives such as wax or preservatives may be added to enhance performance.

Composite Panel- A panel composed of a wood derivative such as MDF. Used for opaque finishes.

Conspicuous- See burl, conspicuous and knots, conspicuous pin.

Core- The innermost layer or section in component construction. For typical constructions see:  Particleboard  Core, Medium Density Fiberboard Core, Structural Composite Lumber Core, Staved Lumber Core, Laminated Veneer Lumber Core, Fire Resistant Composite Core and other special core types.

Core, Fire Resistant- A door core material meeting fire listing requirements for fire protection of 20 minutes or greater.

Cross Bar (Veneer)- Irregularity of grain resembling a dip in the grain running at right angles, or nearly so, to the length of the veneer.

Cross Grain (Cross Figures)- Grain direction irregularity due to interlocked fibers, uneven annual rings, or to the intersection of a branch and stem forcing the visual line of the grain to run at an angle to the length of the wood. It is characterized by mild or dominant patterns across the grain in some faces. Also known as Cross Figures

Crossbanding- A ply placed between the core and face veneer in 5-ply construction or a ply placed between the back and face of a 3-ply skin in 7-ply construction, typically of hardwood veneer or engineered wood product.

Cup- A deviation in the face of a piece from a straight line drawn from end to end of a piece as measured at the point of greatest distance from the straight line.

Defect, Open- Checks, splits, open joints, knotholes, cracks, loose knots, wormholes, gaps, voids, or other opening interrupting the smooth continuity of the wood surface.

Discolorations- Stains in wood substances. Some common veneer stains are sap stains, blue stains, stain produced by chemical action caused by the iron in the cutting knife coming into contact with the tannic acid in the wood, and those  resulting from the chemical action of the glue.

Door Frame- A group of components (wood, composite, aluminum or steel) that are assembled to form an enclosure and support for a door. Also known as door jambs.

Door, Louver- A door assembly of stiles and rails where the interior is filled with slat or chevron louvers.

Doze- A form of incipient decay characterized by a dull and lifeless appearance of the wood, accompanied by a loss of strength and softening of the wood substance.

Edge Band- A strip along the outside edges of the two sides and/or top and bottom of the door (See stiles/vertical edges, rails/horizontal edges).

Edge Glued (Edge Joint)- When the edges of boards are glued together to increase the width.

End Match- Butting adjacent veneer leaves on one panel end to end in sequence. Veneer leaves are book matched end to end. Generally used for very long panels or for projects in which only short-length veneers are available.

Face Veneer- The outermost exposed wood veneer surface of a veneered wood door.

Few- A small number of characteristics (generally less than five) without regard to their arrangement in the panel.

Figure- The natural pattern produced in the wood surface by annual growth rings, rays, knots, and natural deviations. From the normal grain, such as interlock and wavy grain, and irregular coloration. 

Finger Joint- A series of interlocking fingers precision cut on the ends of two pieces of wood which mesh together and are held rigidly in place with adhesive.

Fire Rated Doors- A door complying with NFPA 80 that is listed and labeled by a qualified testing agency for fire-protection ratings. Ratings are indicated, based on testing at positive pressure, according to NFPA 252 or UL 10C, or at neutral pressure according to UL 10B. Doors can be rated as resisting fire for 20 minutes, 30 minutes, 45 minutes, 60 minutes, or 90 minutes. The door must be tested and carry an identifying label from a qualified testing and inspection agency.

Fire Resistant Composite Core- A core, typically incorporating minerals rather than wood fiber as the primary component, designed to improve fire resistance and thermal transmission,

Flake- See Fleck, Ray.

Flat-Cut- See Plain-Sliced.

Fleck, Ray (Flake)- Portion of a ray as it appears on the quartered or rift cut surface. Fleck is often the dominant appearance in oak.

Flitch-  A complete bundle of veneers sheets laid together in sequence as they are cut from a given log or section of a log.

Gaps- 1) An unfilled opening in a continuous surface or between adjoining surfaces. 2) An open slit in the inner ply or plies or improperly joined veneer when joined veneers are used for inner plies.

Grain- The direction, size, arrangement and appearance of the fibers in wood or veneer.

Grain Slope- Expression of the angle of the grain to the long edges of the veneer component.

Grain Sweep- Expression of the angle of the grain to the long edges of the veneer component over a 12 inch (300 mm) length from each end of the door.

Hairline- A thin, perceptible line showing at the joint of two pieces of wood.

Half-round Slicing- Veneer slicing method similar to rotary slicing, in which the piece being sliced is secured to a “stay log” device that permits the cutting of the log on a wider sweep than when mounted with its center secured in the lathe to produce rotary sliced veneer. Plain-sliced or flat-sliced veneer can be produced this way. A type of half-round cutting is used to achieve plain-sliced or flat-cut veneer

Hardboard- Homogeneous panels manufactured primarily from inter-felted lignocellulosic (wood) fibers consolidated under heat and pressure with density of 31 lb/ft3  (497 kg/m3) or more.

Hardwood- General term used to designate lumber or veneer produced from temperate zone deciduous or tropical broad- leaved trees in contrast to softwood, which is produced from trees which are usually needle bearing or coniferous. The term does not infer hardness in its physical sense.

Heartwood- The non-active center of a tree generally distinguishable from the outer portion (sapwood) by its darker color.

High Pressure Decorative Laminate (HPDL)- A high impact resistant surface material consisting of decorative surface paper impregnated with melamine resins pressed over multiple kraft paper layers saturated with phenolic resins, thermoset at high pressure and temperature.

High Density Fiberboard (HDF)- The generic name for a panel made out of exploded wood fibers that have been highly compressed and where the bonding of the wood fibers requires no additional materials, although resin is often added.

Holes, Worm- Holes resulting from infestation by worms greater than 1/16 inch (1.6 mm) in diameter and not exceeding 5/8 inch (16 mm) in length.

Intumescent- A material applied to the surface of flammable products to reduce flammability that expands when exposed to extreme heat or fire to fill any gap between the door and frame or between doors.

Joint- The common edge between two adjacent materials in the same plane.

Joint, Edge- Joint running parallel to the grain of the wood.

Joint, Open- Joint in which two adjacent pieces of veneer in the same plane do not fit tightly together.

Knife Cuts per inch (KCPI)- A measure of the smoothness of machined lumber. Can be determined by holding the surfaced board at an angle to a strong light source and counting the visible ridges per inch, usually perpendicular to the profile. The surface is smoother with more knife marks per inch.

Knife Marks- Very fine lines that appear across the panel veneer or wood solids that can look as though they are raised resulting from some defect in the lathe knife that cannot be removed with sanding.

Knot- Cross section of tree branch or limb with grain usually running at right angles to that of the piece of wood in which it occurs.

Knot Holes- Voids produced when knots drop from the wood in which they were originally embedded.

Knots, Blending Pin- Sound knots 6.4 mm (1/4 inch ) or less that generally do not contain dark centers. Blending pin knots are barely detectable at a distance of 1.8 m to 2.4 m. (6 ft. to 8 ft ), do not detract from the overall appearance of the panel, and are not prohibited from appearing in all grades.

Knots, Conspicuous Pin- Sound knots 6.4 mm (1/4 inch ) or less in diameter containing dark centers.

Knots, Open (Knot Holes)- Openings where a portion of the wood substance of the knot was dropped out, or where cross checks have occurred to produce an opening. (See Dead Knots)

Knots, Spike- Knots cut from 0o to 45o to the long axis of limbs.

Laminated Veneer Lumber Core (LVLC)- Manufactured by laminating veneer with all grain laid-up parallel. It can be manufactured by using various species of wood fiber in various thicknesses.

Lap (Veneer)- A condition where one piece of veneer in the same ply overlaps another piece.

Loose Side- In knife-cut veneer, that side of the sheet that was in contact with the knife as the veneer was being cut, and cutting checks (lathe checks) because of the bending of the wood at the knife edge.

Low Pressure Decorative Laminate (LPDL)- A decorative surface paper that is saturated with reactive resins. During hot press lamination, the resin flows into the surface of the substrate, creating a hard crosslinked thermosetting permanent bond and permanently changing the characteristics of both the paper and the board.

Louver- A panel constructed of slats installed in a door or openings to allowing various degrees of light, air, or sound passage. May be constructed as adjustable. Common types are slat and Chevron – an inverted "V” wood louver (vented or non-vented).

Medium Density Fiberboard (MDF)- A generic term for a composite panel product or core manufactured from lignocellulosic fibers and a bonding system cured under heat and pressure in a hot press by a process in which the added binder creates the entire bond. MDF is generally denser than plywood and particleboard

Medium Density Overlay (MDO)- Typically MDO is kraft paper saturated with resin and cured under high heat and pressure to make a hard, smooth, paintable surface.

Medium Density Fiberboard Core (MDFC)- Wood fiber and/or agri-fiber based materials that comply with ANSI A208.2.

Meeting Edges- Two adjacent door edges not separated by a mullion or transom bar. These are found in pair, Dutch door and door  & transom applications.

Mineral- See Streaks, Mineral.

Mineral Core- See Core, Fire Resistant.

Mineral Stain- Olive and greenish-black streaks believed to designate areas of abnormal concentration of mineral matter; common in hard maple, hickory, and basswood. Also called Mineral Streak.

Mineral Streaks- Sharply contrasting elongated discoloration of the wood substance.

Natural- When referring to color and matching, veneers containing any amount of sapwood and/or heartwood.

Neutral Pressure- A fire door test procedure where the neutral pressure plane is at or near the top of the door. Sometimes referred to as negative pressure.

Nominal- 1) A term that designates a stated dimension as being approximate and subject to allowances for variation. 2) The average sizes (width and thickness) of lumber just out of the sawmill before being processed into usable board stock. Always larger than finished dimensions.

Not Noticeable- Not readily visible without careful inspection (as a measurement of natural or machining characteristics).

Not Restricted- Allowed, unlimited.

Occasional- A small number of characteristics that arearranged somewhat diversely within the face.

Particleboard- A generic term for a composite panel primarily composed of cellulosic materials (usually wood), generally in the form of discrete pieces or particles, as distinguished from fibers, bonded together with a bonding system, and which may contain additives. Particleboard may be further defined by the method of pressing. When pressure is applied in the direction perpendicular to the faces as in a conventional multi platen hot press, they are defined as flat platen pressed. When the applied pressure is parallel to the faces, they are defined as extruded.

Particleboard Core- Wood fiber and/or agri-fiber based materials that comply with ANSI A208.1, minimum grade LD-1.

Pitch- An accumulation of resin that occurs in separations in the wood or in the wood cells themselves.

Pitch Pocket- A well-defined opening between the annual growth rings that contains pitch.

Pitch Streak- A well-defined accumulation of pitch in the wood cells in a more or less regular streak.

Pith- A small, soft core occurring in the center of the log.

Plain Slicing (Flat Cut)- Veneer sliced parallel to the pith of the log and approximately tangent to the growth rings to achieve flat cut veneer. Plain sliced veneer can be cut using either a horizontal or vertical slicing machine or by the half-round method using a rotary lathe.

Plank Matched- A face containing specially selected and assembled dissimilar (in color, grain and width) veneer strips of the same species, and sometimes grooved at the joints between strips, to simulate lumber planking.

Pleasing Match- A face containing components, which provide a pleasing overall appearance. The grain of the various components need not be matched at the joints. Sharp color contrasts at the joints of the components are not permitted.

Ply- A single sheet of veneer or several strips laid with adjoining edges that may or may not be glued, which forms one veneer lamina  in a glued panel. In some constructions, a ply is used to refer to other wood components such as particleboard or MDF.

Positive Pressure- A fire door test procedure where the neutral pressure plane is located at 40 inches (1 m) above the sill.

Quartered (Quarter-sliced, Quarter Cut)- unlimited straight grain appearance achieved through the process od quarter-slicing or through the use of veneer cut in any fashion that produces a straight grain effect. Cut is radial to the pith to the extent that ray fleck is produced, and the amount of fleck is not limited.

Rails/Horizontal Edges- Top and bottom edge bands of door.

Random Matched (Mismatched)- A panel having a face made up of  veneer strips of the same species which are selected and assembled without regard to color or grain, resulting in variations, contrasts and patterns of color and grain. Pleasing appearance is not required.

Ray Fleck- See Fleck, Ray.

Red/Brown- When referring to color and matching, veneers containing all heartwood, ranging in color from light to dark.

Repairs- A patch, shim, or filler material inserted and/or glued into veneer or a panel to achieve a sound surface.

Repairs, Blending- Wood or filler insertions similar in color to adjacent wood so as to blend well.

Rift Cut- A straight grain appearance achieved through the process of cutting at a slight angle to the radial on the half-round stay log or through the use of a veneer cut in any fashion that produces straight grain with minimal ray fleck.

Rotary Cut- Veneer produced by centering the entire log in a lathe and turning it against a broad cutting knife which is set into the log at an angle.

Rough Cut- Irregular shaped areas of generally uneven corrugation on the surface of veneer, differing from the surrounding smooth veneer and occurring as the veneer is cut by the lathe or slicer.

Running Match- The panel face is made from components running through the flitch consecutively. Any portion of a component left over from a face is used as the beginning component or leaf in starting the next panel.

Ruptured Grain- A break or breaks in the grain or between springwood and summerwood caused or aggravated by excessive pressure on the wood by seasoning, manufacturing, or natural processes. Ruptured grain appears as a single or series of distinct separations in the wood such as when springwood is crushed leaving the summerwood to separate in one or more growth increments.

Rustic- Lacking excessive refinement, having a rough surface or finish.

Sapwood- The living wood of lighter color occurring in the outer portion of a tree, sometimes referred to as sap.

Shake- A separation or rupture along the grain of wood in which the greater part occurs between the rings of annual growth. (See also RUPTURED GRAIN).

Sharp Contrast- For the purpose of this standard, this term means the veneer of lighter than average color should not be joined at  the edges with veneer of darker than average color, and that two adjacent pieces of veneer should not be widely dissimilar in grain, figure and natural character markings.

Show Through (Sanding)- A defect caused by excessive sanding such that the crossbanding is visible through the face veneer.

Show Through (Telegraphing)- See Telegraphing

Skin- The face layer, whether flat or contoured, of flush doors, stile-and-rail doors, bending laminations, etc., typically composed of hardwood plywood (usually 3 ply), hardboard, or composition pane.

Sliced- Veneer produced by thrusting a log or sawed flitch into a slicing machine, which shears off veneer in sheets.

Slight- Visible on observation, but does not interfere with the overall aesthetic appearance with consideration of the applicable grade and common species characteristics of the panel.

Slip Matching- A process in which a leaf from a flitch is slid across the leaf beneath and, without turning, spliced at the joint. This process results in a panel or door which consists of all either loose or tight sides, minimizing barber pole or metamerism.

Sound Transmission Class (STC)- A single number rating system derived from measured values of sound transmission loss or the acoustical performance of a building element, such as a door, window or wall. The higher the STC value, the better the rating and the better the acoustical performance value. Tested in accordance with ASTM E413 and E90.

Split Heart- A method of achieving an inverted "V" or cathedral type of springwood (earlywood)/summerwood (latewood), plain- sliced (flat-cut) figure by joining two veneer components of similar color and grain. A cathedral type figure must be achieved by a single component in AA grade; the split heart method is allowed in grades A and B. Each half of a split heart shall be subject to the minimum component width requirements for grade A and B faces.

Splits- Separations of wood fiber running parallel to the grain.

Splits, Hairline- A thin, perceptible line, separation, crack, or absence of wood fiber in the surface of a material or at the joint of two pieces of wood or veneer

Staved Lumber Core (SLC)- A door core made with any combination of blocks or strips of wood glued together.

Stiles/Vertical Edges- The upright or vertical pieces of the core assembly of a wood flush door. Measurement. The width of the vertical edge/stile is measured at its widest side (the wide side of a beveled door).

Streaks, Mineral- Sharply contrasting elongated discoloration of the wood substance.

Structural Composite Lumber Core (SCLC)- An engineered wood product that is made by fusing a network of wood strands together with a water-resistant adhesive to produce a strong, solid and stable product that has true structural properties with excellent screw holding properties and very high split resistance.

Sweep- See Grain

Tape- Strips of gummed paper or cloth sometimes placed across the grain of large veneer sheets to facilitate handling and sometimes used to hold the edges of the veneer together at the joints prior to gluing.

Telegraphing- In veneer or laminated work, a defect caused by outlines and/or surface irregularities, such as frame parts, core laps, voids, extraneous core matter, etc., that are visible through the face veneers, applied top veneer, or laminate sheet following pressing and/or finishing. Also known as Show Through.

Thermally Fused Decorative Laminate Panel- A polyester or melamine resin-impregnated paper, thermally fused under pressure to a composite core.

Tight Side- In knife-cut veneer, that side of the sheet that was farthest from the knife as the sheet was being cut and containing no cutting checks (lathe checks).

Transom- An operable or non-operable fenestration product that is designed to be a companion product installed above a door system.

Twist- 1) A distortion in a wood piece caused by freed tension in the grain as the wood was drying. The surface appears to twist as the four corners of any face are no longer in the same plane. 2) In passage doors, any distortion in the door itself and not its relationship to the frame or jamb in which it is hung, measured by placing a straight edge or a taut string on the concave face

Veneer (wood)- A thin layer or sheet of wood rotary-cut, sliced, or sawed from a log or flitch. Thickness may vary from, but not exceed, 0.3mm [.012”] to 6.4mm [.252”] thick.

Vine Marks- Bands of irregular grain running across or diagonally to the grain, which are caused by the growth of climbing vines.

Voids- See Gaps.

Warp- 1) Any deviation from a true or plane surface, including bow, crook, cup, twist, or any combination thereof. Warp restrictions are based on the average form of warp as it occurs normally. 2) In passage architectural wood doors, any distortion in the plane of a door itself and not its relationship to the frame or jamb in which it is to be hung. (See also BOW, CROOK, CUP, TWIST)

White- When referring to color and matching, veneers containing all sapwood, ranging in color from pink to yellow.

Wood Filler- An aggregate of resin and strands, shreds, or flour of wood, which is used to fill openings in wood and provide a smooth, durable surface.

Wood Flush Door- An assembly consisting of a core and one or more edgebands, with at least two plies of overlay on each side of the core assembly. All parts are composed of wood, wood derivatives, fire-resistant composites, or decorative laminates.

Wormholes- Holes resulting from infestation of worms.

Worm Track (Scar)- A natural mark caused by various types of wood-attacking larvae. Worm tracks often appear as sound discolorations running with or across the grain in straight to wavy streaks. Sometimes referred to as “pith flecks” in certain species of maple, birch, and other hardwoods because of a resemblance to the color of the pith.