Window Terminology (a-j)

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.


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.


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


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.


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.


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.


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.


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


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.


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.


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.


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.


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.


The arrangement, proportioning and design of windows and doors in a building.


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.


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.


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.


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.


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.


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.


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.

By: Charlie McCurry

About the Author:

S&K Roofing, Siding and Windows is Maryland's leading company in roofing and maintenance-free home exteriors. Family-owned and operated since 1980, S&K Roofing, Siding and Windows provides high-quality exterior home workmanship and customer service that is among the best in the industry. We offer maintenance-free home exteriors including roofing, siding, windows, doors, gutters and downspouts, custom trim/wrap, and decks.

To learn more visit