Helpful glossary for any window replacement or door replacement project for your home.

Apron A piece of window trim attached to the wall underneath the interior stool (interior sill).

Argon Gas An inert, nontoxic gas (denser than air) used between window panes to insulate by reducing heat transfer.

Astragal A component fastened to one sash/panel of a gliding window or patio door that becomes the closing shoulder of the operating sash/panel. Its function is similar to a mull post.

Awning Window Hinged at the top, opens outward from the bottom with a crank, push bar, or manually operated using pressure hinges.

Balance Also called balancer. Mechanical device used on double-hung windows to counterbalance the weight of each sash during opening and closing. There are four balances in a double-hung window.

Bay Window Three or more window units attached together to project outward from a building wall. Bay angles vary; most common are 30°, 45° and 90°. Units can be the same or a combination of stationary and operating windows.

Bottom Rail The bottom horizontal component of a window sash that supports the weight of the glass.

Bow window A composite of four or more window units in a radial or bow formation.

Brickmould A milled wood trim piece that covers the gap between the window frame and the exterior of the building. On traditional wood windows, the brick mould is nailed through to attach the window to the wall.

Capstock Various materials used to coat wood, vinyl, metal, composite or other building materials. Provides a durable layer that protects against environmental exposure such as ultraviolet light.

Casement Window Hinged top and/or bottom, may pivot inward or outward, and opens with a bar or manual crank. 

Casing Brickmould Trim, usually milled wood, attached to the interior wall around a window to cover the space between the window frame and the wall.

Check Rail The horizontal middle rails that meet where the sash come together and lock on a double-hung window. Upper check rail refers to the bottom rail of the upper sash and lower check rail refers to the top rail of the lower sash. Also called meeting rail.

Coil Stock A sheet (usually prefinished aluminum), commonly packaged 12 to 30 inches wide on a 50-foot roll. Used for external covering and trim, shaped and cut using a brake.

Composite A solid material composed of two or more substances.

Condensation Water vapor from the air deposited on any surface having a temperature below the dew point, e.g., humid indoor air on cold window glass.

Conduction The transfer of heat through a solid material, where heat flows to a lower-temperature area from a higher-temperature area.

Convection The transfer of heat through a fluid material such as air due to differences in fluid density and the effects of gravity.

Divided Light A window having several small glass panes held in place by muntins within the window sash.

Double Glazing Two panes (or lites) of glass separated by an insulating space in a window or patio door. They may be individual panels or a sealed unit. The dry, airtight space between the panes minimizes condensation and provides excellent insulation properties.

Double-Hung Two movable sash that slide up and down independently.

Drip Cap A Type of flashing, often made from sheet metals, installed at the head of a window or door and extending to the exterior claddings. Used to divert water to the exterior or block the flow of water into the gap between the head jamb of a window or door and the wall. (See Flashing.)

Egress A window opening providing a secondary means of escape or rescue in an emergency. Various state or local codes have restrictions affecting the clear opening height and width a window must possess if it is a designated egress window.

Energy Rating Energy performance as affected by the energy efficiency of the framing, weatherstrip, and window glazing. Set by the National Fenestration Rating Council.

ENERGY STAR® Certification Program An Environmental Agency (EPA) and Department of Energy (DOE) certification program for NFRC windows that are 30% or more energy efficient above Model Energy Code standards. Renewal by Andersen® windows are rated ENERGY STAR qualified.

Extension Jamb A wood trim accessory that fills the space between the innermost edge of the window and the interior wall face.

Extrusion The process of forcing heated materials such as aluminum or vinyl through a die to produce specified shapes.

Fenestration Term used to refer to window and door products and accessories.

Fibrex® Material An Andersen patented structural composite of wood fiber and specially formulated thermoplastic polymer. Polymer surrounds and coats each fiber, providing moisture resistance and superior strength and rigidity.

Fixed Light A glass pane installed in a non-operational frame.

Fixed Panel A non-operational panel in a gliding window or a href="http://www.renewalbyandersen.com/windows-doors/patio-doors/contemporary-sliding-doors.aspx">sliding glass door.

Fixed Window A window having no operational sash. (i.e. a picture window)

Flanker A window set on either or both sides of a center unit (usually a picture unit).

Flashing Material such as sheet metal installed to shed water away from joints.

Full-Frame Replacement Replacement method where the entire old window is removed and replaced with a Renewal by Andersen® window.

Fusion Weld A manufacturing process for fusing sash or frame components together. The lineal ends are thermally softened with a hot plate, then welded to form a structural bond. Used in vinyl window manufacture and the manufacture of Renewal by Andersen products.

Gas Fill Gas, typically argon or krypton, is placed between glazing panels to suppress conduction and convection (reduce the U-Factor).

Glass An inorganic material composed of sand (silica), soda (sodium bicarbonate), and lime (calcium carbonate). Also includes small quantities of alumina, boric, or magnesium oxides.

Glass Stop Removable trim piece holding the glass in place on traditional windows. Also referred to as a glazing bead. (Renewal by Andersen uses this only on picture windows.)

Glazing Usually refers to the glass system used by a window, including the glass, glass coating, insulating spacer, and glass sealants.

Glazing Bead A molding or stop around the stiles and rails of the sash which holds the glass in place.

Gliding Window Window style with two or more independent sash. One or more of the sash travel horizontally for ventilation. Also called glider.

Grilles Decorative element that visually divides the glass into a desired pattern. Also called muntins. (Renewal by Andersen offers aluminum grilles between-the-glass (GBG) or wood snap-on grilles (removable) for interior glass surface.)

Head Jamb The topmost component of the window or door frame. The window sash seats against it.

Head Track The head member and track along the top of a sliding glass door or gliding window.

Header The horizontal structural framing component forming the top of the rough opening in the wall or door.

Heat Gain Heat transfer from the outside to the inside of a structure by conduction, convection, and radiation through all surfaces.

Heat Loss Heat transfer from the inside of a house to the outside due to conduction, convection, and radiation through all surfaces.

High-Performance™ Low-E4® Glass Andersen Corporation's brand name for their Low E (low emissivity) insulated glazing system.

High-Performance™ Low-E4® Sun Glass Andersen Corporation's brand name for a slightly gray-tinted low emissivity glazing system designed for southern climates or windows in rooms where heat buildup (solar heat gain) is a factor.

Infiltration The term used to describe the tendency of a window to allow air or water to move into or out of the building through or around the product's weather stripping or joints. Organizations such as WDMA, AAMA, and NFRC have adopted test standards for measuring acceptable levels of air and water infiltration for specific grades of product performance.

Insect Screen Woven metal or plastic mesh stretched over a screen frame. Allows window ventilation while keeping insects out.

Insert Replacement Window replacement method where a complete frame/sash unit is inserted inside the jamb area (pocket) of the original window frame.

Inside Stop On an older wood window, a piece of wood trim attached to each side jamb that defines the inner edge for the lower sash channel.

Installation Flange A fin of vinyl or metal that extends outward perpendicular from the frame of a window, which allows the window to be suspended within a rough opening.

Insulating Glass Two or more pieces of glass with a space between them that are hermetically sealed to provide insulating characteristics.

Insulation Any type of material used to prevent the passage of heat, cold, fire, or noise.

Interlock The place where a mechanism of one panel/sash connects tightly with the corresponding mechanism of an adjacent panel/sash, as in patio doors, gliding and double-hung windows.

Jamb The members that make up the sides and head of a window frame.

Jamb Cover (Liner) Material used to trim off visible surfaces on windows and doors. Often used to create travel channels and weatherstrip shoulders; can hide and protect functional hardware such as double-hung balancers.

Keeper The hardware piece where the lock engages on the sash. Jamb Cover

Laminated Glass A type of safety glass; two or more sheets of glass with an inner layer of plastic which holds the glass pieces if the glass is broken.

Lift The handle attached to the rail on a double-hung or gliding window.

Light (Lite) A window; an individual pane of glass installed in a window. Also one section of the glass pane when visually divided by grille bars.

Lineal Long length of extruded window material; includes wood, aluminum, vinyl, or Fibrex composite extrusions.

Low-E Abbreviation for low emissivity, a glass coating process that allows most of the sun's visible spectrum to pass through to the interior and reflects most heat energy back to its source (in cold weather, a low-E coating reflects radiant energy back into the house; in hot weather, it reflects the sun's heat energy back to the outside). A variety of low-E coatings are offered by glass manufacturers, with varying degrees of efficiency.

Meeting Rails The two horizontal members of a double-hung sash that meet and are locked together when the window is closed. Also called check rail.

Meeting Stile Either vertical-edge member in a pair of gliding window sash or door panel that meet and lock when the sash/panel are closed. Comparable to the meeting rail on a double-hung window.

Miter A method of cutting and joining two pieces of trim. The edge of a material beveled to make a miter joint; usually at a 45° angle.

Mortise and Tenon A slot (mortise) made in a piece of wood to receive an extension (tenon) of another piece of wood. Renewal by Andersen® gliding and double-hung windows provide the interior appearance of a traditional hand-crafted mortise and tenon joint via a patented sash welding method.

Mullion/Mull A member between two separate windows being attached together. May be vertical or horizontal, structural or integral.

Mull Post/Muntin A strip of wood or metal separating and holding panes of glass in a window.

NFRC National Fenestration Rating Council. An independent agency established in 1992 to test and rate window and door products. Also see Energy Rating.

WDMA  Organization established by window and door manufacturers to create industry standards and advocate self-monitoring.

Obscure Glass One of several types of specialty glazings that are textured for privacy, light diffusion, or decoration (frosted, etched, etc.).

Operable Window Window that can be opened and closed.

Operator A device for opening and closing windows. Usually refers to a crank-operated mechanism found on casement and awning windows.

Outside Stop On an older wood window, a piece of external wood trim attached to each side jamb that defines the outer edge for the upper sash channel. Also called blind stop.

Pane A sheet of glass; a compartment in a door or window containing a sheet of glass.

Panel A sliding or fixed unit consisting of a frame containing a light of glass.

Panning A type of metal flashing system used under the door or window sill to channel water away from the framing and siding.

Parting Stop A narrow strip that separates and secures two sash in the window frame. It provides a channel in which the sash can move.

Passive A sash that can be operated if necessary but usually is not, e.g., the left-hand sash of a gliding window.

Perma-Shield® Andersen Corporation's trademark name for a system of products that provides next-to-no maintenance through vinyl wrapping of wood, high durability paint finishes, and other techniques. It originally referred to Andersen's use of the process for extruding a vinyl sheath completely around a wood component.

Picture Window Fixed window with no opening sash.

Plumb
 Vertically straight up/down. As an installation term, it refers to the importance of making sure that the window sides are perfectly perpendicular to the earth.

Profile The end view shape of a lineal piece of the extruded or milled material.

R-Value A measure of resistance to heat flow; a higher value indicates better heat-insulating property.

Rail Horizontal member of a window sash or door panel. There are four rails on a double-hung window: the bottom rail, two meeting rails or check rails, and the top rail.

Rough Opening
 The opening in a wall where a window or door will be installed.

Safety Glass Also called tempered or wire-mesh glass, it meets a variety of industry and government safety standards. See Laminated Glass.

Sash Lock The lock that connects with the keeper. Used on double-hung, casement, awning, and gliding windows.

Sash Pack A window replacement system using a sash and jamb liner components applied to an existing window frame.

Sealant Various materials used to seal openings or the junctions between parts. May be liquid or solid, depending upon the application.

Shim A thin slip of material for straightening jambs and leveling window and door frames. Shims are also used to adjust hardware positioning. Term is also used to describe the action of bringing to a level by inserting a shim.

Side Jamb The left and right sides of the window frame. See Jamb.

Sill Angle Slope of the outside window sill.

Simulated Divided Lights A single unit of insulating glass with a simulated grille installed on the glass surface or between the glass panes that gives the appearance of small panes separated by muntins.

Simulated True Divided Light A single unit of insulating glass with three sets of grilles: on the exterior and interior surfaces, and between the glass panes.

Single-Hung A variation of the double-hung window style where the upper sash does not operate. Typically less expensive than a true double-hung window.

Sliding Glass Door A door fitted with two or more panels that move horizontally on a track or in grooves.

Solar Heat Gain Coefficient (SHGC) The fraction of solar radiation admitted through a window (directly transmitted and absorbed) and then released inward. The lower the SHGC, the less solar heat it transmits and the greater the shading ability.

Stationary A glazed sash or panel that cannot be operated.

Stile The vertical-edge framing components of a window sash.

Stool The interior window trim applied horizontally at 90 degrees to the wall at the base of a window (normally double-hung), commonly called the window sill.

Stop See Inside Stop, Outside Stop, Parting Stop.

Storm Door A seasonal second door installed in front of an exterior access door to provide additional insulation or protection from bad weather and allow ventilation.

Storm Window A seasonal second window installed on the outside or inside of a window to provide additional insulation or protection from bad weather and allow ventilation.

Tempered Glass Treated glass strengthened by reheating and then sudden cooling; upt to 4 times stronger than normal glass. (See Safety Glass.)

Thermal Break An element (space or other material) placed between other elements to reduce conduction. (Andersen uses a vinyl thermal break on patio door sills.)

Thermal Conductivity Refers to a physical property that affects the extent to which heat or cold is transferred by a material. For example: aluminum has 1,000 times the thermal conductivity of Fibrex™ material, making it a far more efficient insulating window material.

Thermal Expansion A term that describes the expansion a material exhibits when exposed to high temperature, or the shrinkage (contraction) that results when exposed to low temperatures.

Threshold The piece (wood, stone or other material) placed beneath a door to trim off the inside of the door sill.

Tilt-Wash Double-hung window design that pivots or tilts for ease of cleaning.

Tinted Glass Glass that is colored using a mineral admixture; sometimes a silver coating applied to the glass surface. Used to reduce radiation transmission.

Transom A crosspiece separating a door from a window above it.

Transom Window Also called a transom light, the window located above a door or other window.

Triple Glazing Three panes with two air spaces between.

TruScene® Insect Screen A nearly invisible micro-fine stainless steel mesh insect screen that is one-third the diameter of a standard screen wire and allows over 50% more clarity than an Andersen conventional insect screen.

U-Factor Sometimes called U-Value. A measure of the thermal efficiency of a window or a window component. Measures the amount of heat transferred through windows. The mathematical reciprocal of the same component or window R-Value.

Ultraviolet Light (UV) Invisible rays of the spectrum at its short-wavelength violet end; the invisible solar radiation that can cause heat buildup and fading of wood, fabrics and other surfaces. (Low-E coatings are added to window glazing to moderate or eliminate harmful undesired UV wavelengths of light.)

United Inch Term used to describe a method of calculating the size of a window, by adding the height to the width and expressing the sum in inches. Used for price estimating.

Unit Dimension (UD) The UD is the precise size of the window (unit) when measured in width and height from the outermost edge of the window frame, not including any installation flange or brick mould.

Vinyl-Clad Window A window with exterior wood parts covered with extruded vinyl.

Weatherstripping A narrow strip of material placed between window sash or door panels and frame to keep out rain, air, etc. May take many different forms, depending on product design and usage.

Welding The fusing or melting together of two or more individual components to form a solid bond. For example, Renewal by Andersen window sash stile and rails, and many frame components are welded together.

Window Hardware
 Mechanical devices and attaching hardware such as locks, hinges, pivots, catches, lifts and pulls, and stays.

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