Whether you’re a homeowner looking to enhance your understanding of window components, a DIY enthusiast tackling a renovation project, or a professional in the construction industry, this glossary is designed to shed some light on terms associated with windows, doors, and more.
A
Argon Gas
An inert, nontoxic gas (denser than air) used between windowpanes 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.
B
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.
C
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.
D
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 Window
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.)
E
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.
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.
F
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 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.
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.
G
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.
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 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.
H
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.
I
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.
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.
J
Jamb
The members that make up the sides and head of a window frame.
Jamb Cover
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.
K
Keeper
The hardware piece where the lock engages on the sash. Jamb Cover
L
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).
M
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.
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.
N
NFRC
National Fenestration Rating Council. An independent agency established in 1992 to test and rate window and door products. Also see Energy Rating.
O
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.
P
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.
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.
Q
Quarter Round
Trim molding that is one-quarter of a full circle in cross-section.
R
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.
S
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.
T
Tempered Glass
Treated glass strengthened by reheating and then sudden cooling; up 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.
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.
U
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.
V
Vinyl-Clad Window
A window with exterior wood parts covered with extruded vinyl.
W
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.
Window Hardware
Mechanical devices and attaching hardware such as locks, hinges, pivots, catches, lifts and pulls, and stays.
X
X-bar
A horizontal or vertical bar that divides a window or door into sections.
Y
Yield Strength
The stress level at which a material begins to deform, undergoing a significant and permanent change in shape.
Z
Z-bar
Typically refers to a type of flashing or trim that is shaped like the letter “Z.