Window Terminology
Keeper:

The hook-shaped piece of hardware that it is mounted on the inside sash stile of a casement window in which the sash lock engages.
Knocked-down:

Not assembled. Parts for a window frame pre-manu?factured for assembly later on a job site.
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.
Labeled window:

Windows bearing fire-rating labels of Underwriters? Laboratories (UL).
Laminated glass:

Similar to the construction of car windshields, this technique sandwiches a piece of transparent film or plastic between two panes of glass. Typically used for safety reasons because of its resistance to shattering. Also reduce noise transmission to the interior.
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.
Lift:

A handle or grip installed on the bottom sash rail of a double-hung window to assist in the raising or lowering of the sash.
Light (also lite):

A window; a pane of glass within a window. Double-hung windows are designated by the number of lights in the upper and lower sash, as in 6-over-6.
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 Roman?esque Revival architecture.
Low-E Glass:

A term used to refer to glass which has low-emissiv?ity due to a film or metallic coating on the surface of the glass. Usually constructed of dual, sealed panes of coated glass filled with pure inert gas to block ultraviolet heat, for cooling purposes, while reflecting room heat back into the room for heating purposes.
LVL:

Laminated Veneer Lumber ? A combination of many pieces of veneered lumber glued together to give added structural capabilities. Often used in window or door frames.
Masonry Opening:

The space in a masonry wall left open for the window or door.
Meeting rail (also lock rail):

One of the two horizontal members of a double-hung sash which come together. A check rail.
Meeting stile:

The vertical member in a pair of stiles, as in abutting casement windows.
Mold stone (also jamb stone):

A stone that serves as a window jamb.
Mortise:

A slot or rectangular cavity cut into a piece of wood to receive another part.
Mortise and tenon:

A strong wood joint made by fitting together a mortise in one board and a matching projecting member (tenon) in the other.
Mullion:

A vertical member (usually wood or metal) to structurally join two window or door units.
Muntin:

Vertical or horizontal bars used to separate glass in a sash into multiple lights. Often called a grille.
Nailing Fin:

A vinyl or aluminum extension attached to the frame of a window or door which creates a positive seal be?tween the window and the framed wall. Acts as an additional barrier against air and water leakage. Screws or nails are fastened through the fin to hold the unit in the opening.
NFRC label:

NFRC stands for the National Fenestration Rat?ings Council. This non-profit trade group sets energy standards for windows – the NFRC label shows everything you need to know about the window you?re

considering.
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 window:

Window which can be opened for ventilation.
Operator:

A metal arm and gear attached to a window which al?lows for easy operation.
Palladian window:

A large, arch-top window flanked by smaller windows on each side.
Panel:

Usually refers to the glazed panel or panels in a door frame.
Parting slip:

A thin wood strip separating the sash weights in the weight box of each jamb of old double-hung windows.
Parting stop:

A vertical strip on each jamb that separates the sash of a double-hung window.
Picture window:

Large fixed windows.
Pivot window units:

Window units in which the sash hardware is located near the midpoint of the stile or rail to permit sash rotation.
Prime sash:

Balanced or moving sash of a window unit.
Prime window:

Window with single or multiple glazing. A storm sash may be installed.
Projected window:

Awning type window that swings either inwards or outwards at the top or the bottom. The window usually may be cleaned from the inside.
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 l870s.
Rail:

Horizontal member of a window sash or door panel.
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.
Rough Opening:

A framed opening in which the unit will be installed.
R-Value:

The measurement of resistance to heat transfer in a material. The higher the R-Value, the greater the insulation value.
Sash:

Framework of stiles and rails in which the glass of a window or door is set.
Saddle bar:

Light steel bar placed horizontally across a window to stiffen leaded glazing.
Saddle bead:

Glazing bead for securing two panes.
Sash lock:

A lock applied to the window to pull the sash tightly against the frame (casement) or to pull the check rails together (double-hung) in order to seal the sash from weather and for security.
Single-hung window:

Window similar to double-hung window, except the top sash is stationary.
Seat board:

A flat board cut to fit the contour of a bow or bay window and installed between the sill and the wall surface, providing a seat or a shelf space for plants, etc.
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.
Side light: A fixed, often narrow glass window next to a door opening or window opening.
Sill: Horizontal member at the bottom of the window frame.
Simulated divided lights: A method in constructing windows or doors in which muntins are fixed to the inside and outside of the insulated glass panel to simulate the look of a true divided light. Modern Divided Light? in EAGLE terminology.
Single glazing: Use of single panes of glass in a window sash or door panel. Not as efficient as double glazing.
Single-hung window: Window similar to double-hung window, except the top sash is stationary.
Slide-by window: Windows which slide horizontally.
Smartwindow: Generic term that refers to windows with switchable coatings to control solar gain.
Solid frame: Window frame made from a single piece of lumber.
Sound-insulating glass (also sound-resistive glass): Double glass fixed on resilient mountings and separated so as to reduce sound transmission.
Splayed window: Window unit set at an angle in a wall.
Stacked windows: Combined grouping of awning, casement, or non-operative windows to form a large glazed unit.
Stile: Vertical member of a window sash or door panel.
Stile Lug or Horn: One of two extensions of the sash stiles to support the upper sash of a double-hung window.
Storm clip: Device attached to the muntin of a metal sash to stop the pane from moving outwards.
Stool: An interior trim on a window which extends the sill and acts as a narrow shelf. Often seen on double-hung window.
Stop: A wood trim member nailed to a window frame to hold, position or separate window parts.
Tandem lock: A locking system which secures the window at two locking points by the operation of one lever.
Tempered glass: Special heat-treated, high-strength safety glass which shatters into pebble-sized particles and not in slivers.
Tenon: A rectangular projection cut out of a piece of wood for insertion into a mortise.
Thermal break: A thermal insulating barrier between two thermally conductive materials.
Transom joint: Horizontal member separating a door from a window panel above the door, or separating one window above another.
Transom: Small window located above a door or another window.
Top hung-in window: An awning window pivoted at the top and with the bottom swinging-in.
Transom (also transom bar):

Horizontal member separating a door from a window panel above the door, or separating one window above another.
Triple glazing:

Three panes of glass with two air spaces between, com?monly consisting of an insulating glass with a separate storm sash. Also available in an insulating window in a single frame.
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.
U-Value:

Measurement of heat transfer through a given mate?rial. The lower the U-Value, the better the insulation value.
Venetian window:

Same as Palladian window.
Vertical sliding window:

One or more sash that move in a vertical direction.
View sash:

Picture window with the lights divided by muntins.
Venting unit:

A window or door that operates or opens for ventilation.
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.
Weather-stripping:

A strip of resilient material applied to the perimeter of the sash and/or frame of a window or door to minimize the potential for water and air infiltration.
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.
Windload:

The force exerted on a surface by moving air.

Window Terminology

Aluminum-clad windows and doors:

Windows or doors of wood construction covered on the exterior with extruded (EAGLE windows) or roll-formed aluminum. Has a factory-applied finish to deter the elements. The extruded aluminum adds structural capabilities to the product and helps eliminate warping and damage through handling.
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.
Argon:

An odorless, colorless, tasteless, nontoxic gas that is six times denser than air. Replacing the air between two panes of glass with argon gas reduces temperature transfer, making the surface of the glass inside the house closer to the inside temperature.
Astragal:

The center member of a double door, which is attached to the fixed or inactive door panel.
Apron:

Inside horizontal trim located under the window stool at the bottom of a unit.
Auxiliary frame window:

EAGLE?s version of a fixed, direct set window frame where glass is set directly into a frame without a sash. Is used in the creation of geometric and radius windows.
Awning window:

Hinged at the top, this window has a single sash that swings outward from the bottom.
Backband (also Backbend):

Millwork around outside edge of the window casing, usually installed when the casing consists of flat boards.
Balance:

Device for counterbalancing a sliding sash, usually associated with a double-hung window, so sash may be held open at any given position. Usually a system of cords, weights, springs, spiral devices or block and tackle hardware.
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.
Basement window (also sash, cellar sash):

Wood or metal in-swinging sash that is hinged at either the top or bottom.
Bay window:

A composite of 3 or more windows that project out from the wall. Usually consists of one large center window with two flanking fixed or operating windows at 30, 45, or 90 degree angles to 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.
Bottom rail:

Bottom horizontal member of a window sash.
Bow window:

A composite of 3 or more windows in a radial or bow formation. Typically consists of casement win?dows both fixed and operating assembled at 10 degree angles from the wall.
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.
Brickmold:

Standard outside casing around the window to cover the gap between the window frame and the opening. Nails are driven through the molding to install the window to the framed opening.
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.
Caming (Cames):

Lead strips which bond small pieces of decorative glass in windows.
Cap:

Decorative molded projection, or cornice, covering the lintel of a window.
Casement:

A window with side hinges that cranks outward from either the right or left.
Casement operator:

A hardware device used to operate a casement window to any open position.
Casing:

Molding or trim available in many widths, thicknesses and profiles applied to the frame around a window or door to cover the space between the window frame and 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.
Check rail:

On a double-hung window, the bottom rail of the upper sash and the upper rail of the lower sash, where the lock is mounted.
Chicago window:

A large fixed sash flanked by a narrow, often mov?able, sash on either side. First used by Chicago School architects in the late l9th and early 20th Century.
Circle top:

A generic term referring to a variety of window units with one or more curved frame members, often used over another window or door.
Cladding:

Usually an aluminum or vinyl material fixed to the outside faces of wood windows and doors to provide a durable, low-maintenance surface.
Clerestory window:

A venting or fixed 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 l2-lite, 16-lite and so on.
Combination window unit (also combination storm sash and screen:

Window assembly containing a half screen and two glass storm panels; in summer the bottom storm panel is stored in the top frame, exposing the screen panels.
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. Is controlled by limiting the amount of humidity inside of a room relative to the outdoor temperature.
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.
Cottage double-hung window:

A double-hung window in which the upper sash is shorter than the lower sash.
Crank handle:

A handle that attaches to an awning or casement operator, used to open the venting 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:

A space which projects from the roof of a house, usually including one or more windows.
Double-hung window:

A window with two vertically moving sashes, each closing a different part of the window.
Double windows (also double glazing):

Two windows, such as a regular window plus a storm sash; also an insulating window with air space between glass panes.
Drip cap:

Horizontal exterior 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 casement hinge:

Hinge for a casement window which provides clearance for cleaning the two sides of the sash from the inside.
Extension jamb:

A board used to increase the depth of the jambs of a window frame to fit a wall of any given thickness.
Extrusion:

A form produced by forcing metal or vinyl through a die. Window and door frames are often clad with extrusions.
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 rabbetted frame.
Fanlight (also sunburst light; fan window; circle-top transom):

A half-circle window over a door or window, with radiating bars.
Fenestration:

The arrangement, proportioning and design of windows and doors in a building.
Finger-jointing:

A wood end-joint formed by a set of interlocking fingers, coated with adhesive and meshed together under pressure.
Fire window:

Window with fire-endurance rating specified for the location.
Fixed light (also fixed sash):

Window or sash which is non-operative or non-venting.
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.
Frame:

An enclosure or combination of parts which surround a window sash or door panel.
French sliding doors:

A sliding door which has wider panel members around the glass, thus giving it the appearance of a hinged French door.
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.
Geometric window:

A fixed framed window made up of 2 or more angles (i.e., pentagon or trapezoid).
Georgian window:

A double-hung window.
Glazing:

The glass panes or lights in the sash of a window. Also the installation of glass in a window.
Glazing bead (also glass stop):

Removable trim that holds glass in place.
Glazing clip:

Metal clip for holding glass in a metal frame while putty is applied.
Glazing channel:

Groove cut into sash for acceptance of glass.
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.
Grille (or muntin bar):

Usually removable for easy cleaning, grilles give the appearance of a divided window pane.
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.
Head casing:

Top or upper member of any element or structure. In windows, it refers to the top of the frame.
Head flashing:

Flashing installed in a wall over a window.
Header:

Supporting member or beam above window opening which transfers building weight above to the supporting wall structure on each side of the window.
Head jamb (also head):

All of the horizontal members that make up the top of the window or door frame.
Hinged French doors:

Hinged door(s) which have wider panel members around the glass.
Hit-and-miss window:

Two-part window with the lower sash containing movable ventilation panels.
Hopper light (also hopper vent and hopper ventilator):

Inward-opening ash hinged at the bottom.
Impact resistant glazing:

Glass specifically manufactured to withstand impacts from airborne objects or forced entry. Usually a type of laminated glass often used in coastal areas impacted by hurricanes.
Insulating glass:

A combination of 2 or more panes of glass with a hermetically sealed air space between the panes. The space may be filled with an inert glass such as argon.
Interior glazes:

Glazing installed from inside of the building structure.
Jal-awning window (also awning window):

Windows with several out-swinging, awning type units that pivot near the top of the glass and operate in unison.
Jalousie:

A shutter-type window with slats, which are either fixed or adjustable.
Jalousie windows (also louvered windows):

A window composed of overlapping narrow glass, metal, or wooden louvers, operated with a crank handle for adjusting the louver angles.
Jamb:

The vertical members at the side of the window or door frame.
Jamb depth:

Width of the window frame from inside to outside.
Jamb liner:

The plastic or metal track installed in the jambs of the window in which the window sash slide.