Terminology

Below we have provided some helpful terminology relating to our specific window and door products as well as general industry standard fenestration terms.

Sash: Refers to the operable/venting portion(s) of a window assembly. Comparable to a door panel.
Awning: Window hinged at the sill that swings outward from the bottom. Vents from the bottom.
Hopper: Window hinged at the head that swings outward from the top. Vents from the top.
Bay: Multiple windows mulled together and projects out beyond the exterior wall/facade. Typically, these systems consist of three (3) mulled windows.
Casement: Window hinged at the jamb that swings open to the side.
French (Double) Casement: Casement window with two (2) sashes hinged at either jamb.
Single-hung: One vertically sliding frame that vents from the lower sash while the upper panel remains inoperable.
Double-hung: Two vertically sliding frames that vent from the upper and lower sash.
Lift and Slide Window: A bottom loaded window that slides on dedicated carriages. The term ‘lift’ refers to the window lifting off its track when the user engages the handle to ‘slide’ the panel(s). Also called a ‘lift and lock’ window.
Tilt and Turn Window: A dual-use window that features the operability of an awning window and an inswing single casement window.
Bi-fold (Folding): A top hung window that folds open like an accordion.
Egress: A window typically required by building codes for emergency escape and/or rescue.
Fixed: Non-operable and non-venting window.
Window Wall: A large non-load bearing wall assembly consisting of multiple windows which may, or may not, be of the same size, type, or operability.
Curtain wall: A non-load bearing exterior window wall spanning floor to ceiling or floor to floor. Learn more about our thermally broken curtain wall here.
Storefront: A non-residential curtain wall with integrated entrance systems.
Sidelight: A non-operable window installed on the side of a window or door.
Transom: An additional window positioned on top of another window or door.
Venting unit: An operable window.
Bulls Eye: Another name for a circular window. A Bulls Eye window can be operable or fixed.

Panel: Refers to the operable portion(s) of a door assembly. Comparable to a window sash.
Leaf: Part of a side-hinged door assembly. Leaves can be fixed or operable.
Single Door: Also called a “single casement door”, it consists of one (1) operable panel hinged at the jamb and swings opens to the side.
French (Double) Door: Also called a “double casement door”, it consists of two (2) operable panels hinged at the jambs and opens from the center.
Fixed Door: One or more non-operable panels within a single frame.
Bi-fold (Folding): A top hung door that folds open like an accordion. Each leaf of the door is hinged together to create a large, unobstructed opening.
Pocket Door: Typically used with sliding door configurations, this door type has one or more panels that sliding into a wall pocket.
Lift and Slide Door: Bottom loaded door that slides on dedicated carriages. The term ‘lift’ refers to the door lifting off its track when the user engages the handle to ‘slide’ the panel(s). Also called a ‘lift and lock’ door.
Top Hung Slider: Unlike a lift and slide door, a top hung slider is top loaded and slides on an upper track instead of bottom mounted carriages. Top hung sliders are often pocketing doors.
Barn Door: A large, single panel top hung slider. Typically, barn doors have visible decorative tracks and bearings to emphasize the style of traditional barn doors. Since they do not offer water or air seals, these are used for interior applications.
Pivot door: Unlike a casement door, pivot door’s swing on a dedicated pivot point aligned on top and bottom. This means that the door is bottom loaded on the bottom pivot instead of being sideloaded (i.e. jamb loaded) like most swinging doors.

Single Glazing: A glass pane consisting of a single layer of glass.
Insulating glass unit (IGU or IG): Two or more glass panes hermetically sealed with a cavity between each pane.
Dual (Double) pane glass: Consists of two panes of glass with an air-filled space/cavity between them. Specialty gas, such as argon gas, may be used instead of air.
Triple pane glass: Consists of three panes of glass with two (2) air-filled spaces/cavities between them. Specialty gas, such as argon gas, may be used instead of air.
Lite: Individual glass panes within a window sash or door panel.
Simulated Divided Lite (SDL): Please visit our Frequently Asked Questions page for a full description.
True Divided Lite (SDL): Please visit our Frequently Asked Questions page for a full description.
Argon gas: Colorless gas used in the airspace of a dual or triple pane, Low-E glass to increase the insulating/thermal performance.
Glazing: The act of installing glass in a window or door frame.
Glazing Pocket (Glazing Channel): The channel in the frame that the glass is placed into. The width of this channel determines the maximum glass thickness.
Safety glass: The two types of safety glass are Laminated and Tempered.
Laminated glass: Glass that is layered/bonded together by a plastic inner layer known as polyvinyl butyral (PVB) which prevents the glass from shattering when broken. Glass that is not laminated is more prone to shattering into small pieces that can be extremely harmful.
Heat Strengthened glass: Glass that is heat treated to be approximately twice as strong as annealed glass. Unlike tempered glass, heat strengthened glass is not considered safety glass.
Fully Tempered glass: During the manufacturing process, tempered glass is heated to over 1,100 degrees. It is then shot with cold air, which rapidly cools the glass. That process causes the outer surface to become much harder than the inner material. As a result, tempered glass shatters into tiny fragments with rounded edges when broken. Tempered glass is approximately four times stronger than annealed glass and therefore is commonly used in large windows where added strength is a required.
Annealed glass: Annealed glass tends to break into irregular, sharp pieces when broken. Glass which has not been annealed is liable to crack or shatter when subjected to a relatively small temperature change or mechanical shock. Annealing glass is critical to its durability but not comparable to tempering glass.
Impact-resistant glass: Impact glass is specially engineered, laminated, glass used for protection from wind-borne debris during a hurricane or severe storm.
Low-E glass: Glass with a low-emissivity coating that enhances the thermal efficiency of the glass by reducing heat loss. Also known as ‘heat-reflecting’ glass.
Tinted glass: Glass that has a tinted (i.e. colored) exterior pane which absorbs solar energy instead of reflecting it like Low-E glass. Typically, tinted glass is noticeably darker in color. Also known as ‘heat-absorbing’ glass.
Low Iron glass: Noticeably clearer and color neutral than standard float glass due to its significantly lower iron content.
Monolithic glass: Thick glass that has no airspace.
Obscure glass: Glass with that has a texture or pattern of various degrees of opacity that limits visibility.
Spandrel glass: Non-transparent glass designed to conceal building elements.
Cap seal: A continuous bead of exposed silicone between the glass and frame edge.
Dry Glazing: Glazing achieved using preformed gaskets between the glass and glazing bead.
Wet Glazing: Glazing achieved by a combination of butyl tape and silicone sealant cap seals. Offers a more watertight seal compared to dry glazing, which may move or shrink with time.
Structural Silicone Glazing (SSG): Glass that is bonded to a structure using structural sealants, typically curtain wall, without the use of continuously gasketed pressure plates or caps.
Capillary Tubes: Small tubes used in insulating glass units to equalize the pressure between the sealed panes to accommodate for changes in elevation. Also called ‘breather tubes’.
Desiccant: Absorbent material in the IGU that prevents it from fogging up.

Glazing bead: Steel or aluminum profiles attached to the inside perimeter of the frame. Although these beads can be decorative shape, they play an essential role in securing the glass in the frame.
Closer: An additional component that assists in pulling a window or door closed without the user having to manually shut it. Closers can be mounted at the head or sill and can be either concealed or visible depending on the application.
Hinge: Provides swing operability to a window sash or door panel.
Pivot Hinge: Allows action of the vent to rotate in the frame.
Operator: Handle, lever, arm and/or gear used to operate hinged windows.
Electric operator: A motorized device that provides for remote (hand-free) operation of windows, doors, screens, shades and much more.
Peg Stay: Also known as a ‘Casement Stay’, a Peg Stay is a metal bar that holds the window open in different positions.
Roto Operator: A rotary crank that operates the vent on an outswing casement window.
T-Handle: A small handle used to operate a roto operator. As its name suggests, it is shaped like a “T”.
Cam Handle: A surface mounted handle that rotates in front of its strike plate to locks the window sash. Commonly associated with ‘cockspur’ handles.
Lock: The keyed mechanism used to secure windows and doors into a closed position to prevent operation.
Passage Lock: Lock that engages the frame at one (1) location. Commonly used for interior door applications.
Multi-point Lock: Lock that engages the frame along multiple locations along the edge of the window or door.
Threshold: Material, mostly decorative, used as a transitional sill between interior and exterior flooring.
Kick-panel: Also called a ‘kick-plate’, this is an area at the bottom of a door that has no glass. Instead, there is an insulated panel or plate so that if you ‘kick’ the door open, your foot doesn’t damage the door.
Escutcheon plate: Decorative plate that mounts on the door lockbox under the handle.
Grilles/Muntins/Dividers/Grids: Frame components used to simulate a true division been individual glass pieces within a window or door.
Insect screen: A tightly woven mesh attached to a frame which allows outside air ventilation while keeping undesired insects out.
Mullion: The vertical or horizontal frame member between two (2) or more individual units. Integral Mullions are horizontal or vertical mullions within a frame structure while Stiffener Mullions are separate from the frame and add reinforcement to the adjoining frames.
Mulling: The act of using a “mullion” to join two or more window or door units together.
Shim: A thin wedge used to plumb and/or level the frame in the rough opening. Different shim materials and thicknesses are used depending on the application (i.e. glass, frames, or hardware).
Setting Block: An important glazing material that is set between the frame and IGU. Setting blocks are important for protecting the IGU from vibrations during normal use, accommodating for frame and glass expansion, and maintaining the glass position within the frame to prevent sagging.
Weather-stripping: Compressible material designed to insulate and weather-proof window or door frames.
Sill: A horizontal member that forms the bottom of a window or door frame.
Jamb: The left or right-side frame members of a window or door.
Stile: The vertical frame member of a panel or sash.
Rail: The horizontal frame member of a panel or sash.
Weephole (weep): Small holes located on the exterior of a window or door to allow for water drainage.
Track: Traveling surface for sliding window and door carriages. Tracks can either be mounted on the floor or hung on the wall or ceiling depending on the application.
Drip cap: Metal flange installed above a window or door that directs water away from the unit.
Fusible link: A component that consists of two (2) strips of metal soldered together with a fusible alloy that is designed to melt at a specific temperature, and thus close a window or trigger a sprinkler system in the case of a fire.
Astragal: Also known as the “meeting stile seal”, astragals are commonly used to close the clearance gap at the center of a double door for privacy, waterproofing, sound insulation and sometimes decoration.

Tolerance: The allowed limit of variation in a physical dimension or measured value.
Design Pressure (DP): The load pressure that the assembly is required to meet for the specified application. For window and doors, the critical DP is the design wind load which is typically specified in force (PSF) and speed (MPH).
Outdoor/Indoor Transmission Class (OITC): Measurement standard used to indicate the rate of sound transmission.
Sound Transmission Class (STC): A single-number rating of a material’s or an assembly’s ability to resist airborne sound transfer at the frequencies ranging between 125-4000 Hz. A higher STC rating blocks more noise from transmitting through a partition. In the case of a window or door, it measures the unit’s ability to resist sound from transferring through.
Solar Heat Gain Coefficient (SHGC): A measurement of the sun’s heat energy that passes through the entire window or door assembly. The SHGC is expressed as a number between 0 and 1. The lower a window’s solar heat gain coefficient, the less solar heat it transmits.
Shading Coefficient (SC): Equal to 1.15 times the Solar Heat Gain Coefficient (SHGC).
UV protection: Percentage of ultra-violet (UV) rays being blocked.
Visible Light Transmission (VLT): Measures the amount of daylight (i.e. visible light) allowed through a glazing system.
Performance Grade (PG): An industry rating for a window or door that has been tested for air, water, structural, and force entry performance. Used to determine compliance with code required design pressures and building regulations.
Yield Strength: The force required to cause a material to yield (i.e. permanently deform.
Tensile Strength: The force required to cause a material to break. This will be equal to or greater than the yield strength. Also called ‘ultimate strength’.
Coefficient of Expansion: Measures the amount of thermal energy that can be conducted.
Adhesion Coefficient: For sealants, it measures how long the sealant will remain adhered to the surface type to which it is applied.
U-Factor: Also called the “U-Value” or “Thermal Transmittance”, it is a frequently used measurement of heat transmission through a window or door assembly. The lower the U-Factor, the better the insulating value. The nationally recognized rating method by NFRC is for the whole window, including glazing, frame, and glass. High-performance double-pane windows can have U-Factors of 0.30 or lower, while some triple-pane windows can achieve U-Factors as low as 0.15.
R-Factor: Also called the “R-Value”, it is used for insulation in most other parts of the building envelope (walls, floors, roofs, etc…). Since thermal resistance is the reciprocal of thermal conductance, to compare R-Factor and U-Factor, divide 1 by the U-Factor (e.g. [U-Factor]=1/[R-Factor]). For example, a 0.25 U-Factor equates to an R-Factor of 4. In contrast to a U-Factor, the higher the R-Factor, the best the instating qualities.
Concentrated load: A measurable force on a fixed point.
Deflection: Measurable displacement due to flexure of a component or material under load.

Cladding: Covering attached to the exterior frame or wall surface. To learn about of thermally broken cladding please see our Facade Cladding brochure.
Condensation: Water vapor that collects as droplets or fog on the glass or frame surface. Please visit our Frequently Asked Questions page for a full explanation of why this occurs.
Flashing: Water resistant material/membrane that directs water to a drainage system or to the exterior surface of a building.
Clear opening (CO): The effective clear opening is the unobstructed area when a window or door is fully open.
Daylight opening (DO): The visible, unobstructed glass area.
Rough opening (RO): Total opening size, including installation clearances, that the window or door will occupy.
Inactive panel/sash: A window sash or door panel that will open only after active panel or sash is opened.
X, O, P Sliding Identification: ‘X’ stands for operable, ‘O’ stands for stationary, and ‘P’ stands for pocketing.
Fenestration: Fenestration refers to the construction, design, or existence of openings in a building. Some types of fenestration include: windows, doors louvers, vents, wall panels, skylights, storefronts, and curtain walls.
Girder: A beam made of steel, wood, or reinforced concrete, used as a main horizontal support in a building or structure.
Header / Lintel: A structural beam, commonly steel or wood, extended across the top of the rough opening. This is a crucial load-bearing structural member responsible for holding a majority of the weight from the roof or walls above. Without a strong header, the weight would be transferred to the window or door frame.
NFRC: National Fenestration Rating Council. A non-profit organization that provides accurate and credible energy performance ratings for windows, doors, and skylights. Visit their official website here.
IRC: International Residential Code. A comprehensive residential code that creates minimum regulations for one- and two-family dwellings of three (3) stories or less. Visit their official website here.
Building envelope: The physical separators between the interior and exterior of a building. Separators include: walls, floors, roofs, and various fenestration.
Corrosion: Deterioration of a metal resulting from chemical reactions between it and the surrounding environment.
Extrusion: A refinement process used to produce objects of a fixed cross-sectional profile.
Profile: The resulting finished geometry of an extrusion process.
Anodize: A finishing process that increases corrosion resistance and allows for varying dyeing (i.e. coloring) of the metal or alloy.
Powder Coating: A very durable dry finish painting process that uses polymer resin systems, combined with curatives, pigments, leveling agents, flow modifiers, and other additives. For more information on this process, visit the Powder Coating Institute website.
RAL: A standardized color matching system for powder coating and varnishes used throughout Europe.
Backer-Rod: A flexible polyurethane foam product that is compressed into gaps behind caulking to increase elasticity, reduce sealant consumption and provide a depth limit so that uniform seal is achieved.
Activeage™: A proprietary silver finish on AGB hardware with a very high resistance to corrosion. Visit the AGB Product Page for a detailed overview.
Interior casing: Typically, made from wood, this is the interior trim around the window.