AAMA: American Architectural Manufactures Association. A national trade association that establishes voluntary standards for the window and door industry.

Air Infiltration: The amount of air leaking in and out of a home through cracks in walls, windows and doors.

Aluminum-Clad Window: A window with wood construction covered with aluminum sheet that has a factory-applied finish.

Architrave: The molded frame or ornament surrounding a window, door or other square opening.

Argon Gas: An inert, nontoxic gas used in insulating glass units to reduce heat transfer.

ASTM: American Society for Testing and Materials. An organization that develops methods for testing of materials.

Astragal: An interior molding attached to one of a pair of doors, or side-hinged windows in order to prevent swing through, often on older casements. Can also be used with sliding doors to ensure a tighter fit where the doors meet. 

Awning Window: A window hinged at the top, the sash swings outward from the bottom.

Balance Cover: A snap in vinyl that covers the balance system in the window frame to keep dirt out.

Balance System: A mechanical device used in double-hung windows as a means of counterbalancing the weight of the sash.

Basement Window: (Basement Sash or Cellar Sash) A wood or metal in-swinging sash that is hinged at either top or the bottom.

Bay Window: Window consisting of three or more units that angle out beyond the wall, often configured with a large center unit and two flanking units.

Bottom Rail: The bottom horizontal member of a window sash.

Bow Window: Window consisting of three or more units projecting out from the wall to form a radius.

Boxed Mullion: A hollow mullion between two double-hung windows to hold the sash weight.

Brickmold: A molding used as an exterior door or window casing. 

BTU: An abbreviation for British Thermal Unit, the heat required to increase the temperature of one pound of water one degree Fahrenheit, about the heat from burning one wooden match.

Butyl: A rubber material that seals the glass to the spacer system; used to create an airtight and water-tight insulated glass unit.

Casement Window: A window that opens outward a full 90° with a durable crank mechanism. Can be mulled with one or more casements. Often found in bay and bow windows.

Casing: (trim) Exposed molding or framing around a window or door, on either the inside or outside, to cover the space between the window frame or jamb and the wall.

Caulking: A mastic compound for filling joints and sealing cracks to prevent leakage of water and air; commonly made of silicone, bituminous, acrylic, or rubber-based materials.

Celsius: A centigrade scale of temperature measurement based on 0° as the freezing point and 100° as the boiling point of water. Abbreviated °C.

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: (Meeting Rail or Lock Rail) The horizontal members of a double-hung window which come together.

Circle Top Transom: See Fanlight.

Clerestory: (Clearstory or High-Light Window) A window in the upper part of a lofty room that admits light to the center of the room.

Coated Glass: A window glass with an outside surface provided with a mirror reflective surface; the shading coefficient ranges from 20% to 45%. See Shading Coefficient.

Colonial Grids: Windows with small rectangular panes, or divided lites, designated as 12-lite, 16-lite, etc.

Combination Window Unit: (Combination Storm Sash and Screen) A window assembly containing a half screen and two-glass storm panels; in frame, exposing the screen panel.

Comfort Foam: Expanding polyurethane insulation foam fills critical spaces in extrusions and greatly improves the overall thermal performance.

Commercial Standard: A voluntary set of rules and regulations covering quality of product or installation, method of testing, rating of the product, certification, and labeling of manufactured products.

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

Convection: See Natural Convection and Forced Convection. A heat transfer process resulting from the circulation or movement of fluids, such as air.

Cove Molding: Trim molding with a concave face.

Crack Perimeter: The total length of the crack around a sash through which outdoor air could leak into the room. In a double-hung window, the total crackage is three times the width plus two times the height of the sash.

Dado: A rectangular slot or groove (with 3 surfaces) cut across the grain of a wood member, into which another board is fitted.

Decorative Glass: A variety of colors, shapes and patterns used to accent a window or door.

Degree-Day: A measure of heating demand, based on the difference between the daily outdoor temperature and 65°F. Cumulative totals for the month or heating season are used by engineers for estimating heating energy requirements.

Desiccant: A drying agent, such as silica gel, used by some manufacturers between the panes of insulating glass to prevent fogging between the panes.

Design Heat Loss: The calculated values, expressed in units of BTU per hour for the heat transmitted from a warm interior to a cold outdoor condition, under some prescribed extreme weather conditions. The values are useful for selecting heating equipment and for estimating seasonal energy requirements. 

Design Pressure: A numerical value that defines the structural wind load requirements for a building as well as the components of the building.

Dew Point Temperature: The temperature of the air at which the water vapor in the air starts to condense in the form of liquid or as frost.

Double-Hung Window: Window with two vertically moving sashes, each closing a different part of the window.

Double-Strength Glass: Sheet glass with a thickness between 0.115″ to 0.133″ (3 to 3.38mm).

Double Window: Two windows separated by a mullion, forming a unit. Also called a coupled window.

Drip Cap: A horizontal molding to divert water from the top casing so that the water drips beyond the outside of the frame.

Dry Glazing: A form of glazing in which the glass is secured in the frame with a dry gasket, wood stops, or metal stops, instead of by a glazing compound.

Dual Glazing: Two layers of glazing material mounted in a common frame and/or sash, separated by a space and sealed or non-sealed.

Dura-Sill: Consists of Soft Seal: Q-Lon Neoprene, structural interlock in the bottom sash and tight mortise-cut, double walled sill dam penetrates inside the jamb.

Emergency Exit Window: (Egress Window) Fire escape window large enough for a person to climb out; each bedroom should be provided with exit windows.

Endura-Force Balance System: State-of-the-art balance system that provides smooth operation and never needs lubrication or adjustment.

ENERGY STAR: A program run by the United States Department of Energy and Environmental Protection Agency that helps protect the environment through greater energy efficiency.

Extension Jamb: (Jamb Lining or Jamb Extender) A board used to increase the depth of the jambs of a window frame to fit a wall of any given thickness.

Fixed Panel: An inoperable panel of a sliding glass door or sliding window.

Fixed Window: A window with no operating sashes.

Flashing: Water resistant material that directs water away from your windows.

Forced Entry Resistance: The ability of a window or door in the locked position to resist entry under a specified load and conditions.

Frame: Outer structure of a window or door that holds the sash or panel in position.

Full Screen: A screen that covers the entire opening of a window unit.

Fusion-welded: The process of joining materials by melting them together with extreme heat, resulting in the materials combining into a one-piece unit.

Garden Window: A window that extends from the wall to the exterior of the home. It is built in a square or rectangular shape at right angles. The two side lites often operate for added ventilation.

Gas Fill: A gas placed between glass panes in an insulated glass unit to decrease the U-Factor.

Glazing: The process of sealing a piece of glass to a sash or frame.

Glazing Bead: A molding or stop around the inside of a window frame to hold the glass in place.

Grids: Components used to simulate individual pieces of glass within a sash or panel to help create the look of a divided window design.

Half Screen: Insect screen that only covers the lower sash area of a double-hung window.

Hardware: All the necessary equipment to retain, operate, and lock or unlock the sash or panel within the frame.

Head Expander: A vinyl cap used on the head of the window as a filler to accommodate the gap between the unit and the rough opening.

Heat Gain: The transfer of heat from the outside of the home to the inside of the home.

Hopper Window: A bottom-hinged sash window that opens inward for ventilation.

Impact Glass: Laminated glass used mainly in hurricane areas for protection from wind and debris.

Insulating Glass Unit: Two or more glass panes that are sealed together to increase energy efficiency.

Interlock: A construction feature that enables the sash of a unit to lock into each other for a tighter seal.

Jamb: Window or door frame that forms the top and sides of a unit.

J-Channel: Component that surrounds a window to hide the seam between the window and siding.

Laminated Glass: Layered glass that resists breakage and holds together when broken.

Lift Rail: Rail on the bottom of a double-hung window sash that makes it easier to raise and lower the window.

Lite: Individual unit of glass.

Lock: Mechanism used to secure windows and doors into a closed position.

Low-E Glass: Glass with a low-emissivity coating that restricts heat loss to help reduce the U-Factor rating.

Mainframe: The combination of the head, jamb, and sill portion of a window.

Meeting Rail: Central location on a single-hung, double-hung and sliding window or patio door where the two panels meet.

Mulled Units: Two or more windows joined with a mullion to make one unit.

Mullion: The vertical or horizontal joint between individual window units that form together.

Nailing Fin: An integral extension of a window or patio door frame that laps over the stud construction which nails are driven to secure the frame in place.

NFRC: National Fenestration Rating Council is a non-profit organization that provides accurate energy performance ratings for window and door products.

Obscure Glass: Glass with a texture of patterns (frosted, etched, etc.) that limits visibility through a window or patio door.

Operable Window: Windows that can be opened for ventilation.

Operator: Cranking device used to open and close hinged windows.

Patio Door: A glass door with at least two panels that slide back and forth to open with adjustable rollers in a track.

Performance Grade: (PG) An industry rating for a unit that has been tested for air, water, structural, and forced entry performance. Used to determine compliance with code required design pressures.

Picture Window: A large, fixed window that does not move or operate.

Pivot Pin: Component on the bottom corner of an operable sash in a single- or double-hung window that allows that sash to be tilted in.

Plumb: When a surface is exactly vertical.

There are no terms for this letter available.

Radiation: The transfer of heat in the form of electromagnetic waves from one separate surface to another.

Reinforcement: The material added to the individual sash, panel, or frame members to increase strength.

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

R-Value: A measure of how well a barrier such as a window resists conductive flow of heat. It is the inverse of the U-Value (R=1/U). R-Value, the greater the resistance and better thermal insulating properties.

Sash: The portion of a window that includes the glass and the framing section directly attached to the glass.

Screen: Woven mesh stretched over a window opening to permit air to pass through, but not insects.

Sealant: A compressible material used to seal any opening such as between the glass and a sash, commonly made of butyl.

Sill: The lowest horizontal member in a door, window, or sash frame.

Sill Extender: A vinyl piece used on the sill of the window as a filler to accommodate the gap between the unit and the rough opening.

Single-Hung Window: A window consisting of two sashes of glass, the top one is stationary, and the bottom is movable.

Sliding Window: A window fitted with one or more sashes opening by sliding horizontally. Available in 2- and 3-lite configurations.

Sloped Sill: A window sill with a downward slope design that aids in allowing water to run away from the home.

Solar Heat Gain Coefficient: (SHGC) The fraction of solar radiation admitted through a window or door. The lower a window’s solar heat gain coefficient, the less solar heat it transmits.

Spacer: Is placed between two or more pieces of glass which helps to maintain a uniform width between the glass and prevents seal failure.

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

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.

Tilt Latch: A mechanism that engages the sash into the frame of the window but can disengage to allow the sash to tilt into the home.

Tilt Window: A single-hung or double-hung window that has an operable sash(es) that can be tilted into the room for easy cleaning.

Transom: A window placed over a door or window.

Triple-Pane: Glass construction consisting of three distinct layers of glass and two air spaces.

U-Value: Commonly used measurement of heat transmission through a window and door. The lower the U-Value, the better the insulating value.

UV Protection: Percentage of Ultra-Violet (UV) transmission from the sun’s energy. The lower the number, the potential for reduced fabric fading.

Vinyl: Polyvinyl chloride (PVC) material that is very durable and resistant to corrosion.

Visible Light Transmission: The fraction of the light allowed to enter through a window.

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.

Weatherstripping: A flexible component used to reduce air leakage, water penetration, or both between the sash and frame.

Weep Hole: An opening that allows water to drain.

Window Opening Control Device: (WOCD) An option available for some windows designed to restrict the opening of a sash to less than 4″ to reduce the risk of accidental falls by children.