Window Terminology
Argon gas: Argon is a safe, odorless, colorless, non-toxic, non-flammable
inert gas that is commonly used in place of air between the
glass panes of an insulated Low-E glass unit to reduce temperature transfer.
Astragal: The center member of a double door, which is attached to the fixed or inactive door panel.
Awning window: A window unit in which the bottom of the sash swings outward.
Bay window: A composite of three windows, usually made up of a large center unit and two flanking units at 30-,45- or 90- degree angles to the wall.
Bow window: A composite of four or more window units in a radial or bow formation.
Brickmold: A type of external casing which frames windows and doors.
Casement window: A window unit in which the single sash cranks outward, to the right or left.
Casing: Molding of various widths, thickness and shapes applied to the framework of window and door units.
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.
Circlehead: A generic term referring to any of a variety of window units with one or more curved frame members, often used over another window or door opening.
Cladding: Any material locked to the outside faces of doors and windows to provide a durable, low-maintenance exterior surface.
Cottage double-hung: A double-hung window in which the upper sash is shorter than the lower sash.
Dormer: A space which protrudes from the roof of a house, usually including one or more windows.
Double-hung window: A window unit that has two operable sashes which move vertically in the frame.
Drip cap: A molding placed on the top of the head brickmold or casing of a window frame.
Double or dual glazing: Use of two panes of glass in a window to increase energy efficiency and provide other performance benefits.
Extrusion: A form produced by forcing material through a die. Most window frames are clad with extruded vinyl or aluminum.
Fenestration: An architectural term referring to the arrangement of windows in a wall. From the Latin word, "fenestra," meaning window.
Fixed window: Non-venting or non-operable window. Also known as picture window.
Flashing: A thin strip of metal or synthetic material that diverts water away from a window or skylight.
Foam Spacer: Foam material placed in the airspace of the insulating glass in a window to enhance the appearance and improve the performance of the window.
Frame: The enclosure in which window sash or door panels are mounted.
French hinged door: Hinged door(s) which have wider panel members around the glass.
French sliding door: A sliding door which has wider panel members around the glass, giving the appearance of a French hinged door.
Glass Pane: In the window shown at right there are two panes of glass, one in the top sash and one in the bottom sash
Glazing: Glass in a window or door; the act or process of fitting with glass.
Glazing bead: A plastic or wood strip applied to the window sash around the perimeter of the glass.
Grille: A term referring to windowpane dividers or muntins, usually a type of assembly which may be detached for cleaning.
Head: The main horizontal member forming the top of the window or door frame.
Header: A horizontal framing member placed over the rough opening of a window to prevent the weight of wall or roof from resting on the window frame.
Head Jamb: Groove at the top of the window which allows the window sashes to slide into place and seat inside the window frame
Hopper: A window unit in which the top of the sash swings inward.
Insulating glass (IG): A combination of two or more panes of glass with a hermetically sealed air space between the panes of glass. This space may or may not be filled with an inert gas, such as argon.
Jalousie window: Louver blades open to maximize airflow through opening.
Jamb: The main vertical members forming the sides of a window or door frame.
Jamb liner: In a modern double-hung window, the track installed inside the jambs on which the window sashes slide.
Lift: A handle or grip installed on the bottom rail of the lower sash of a double-hung window to make it easier to raise or lower the sash.
Light or lite: Glazing framed by muntins and/or sash in a window or door.
Low-E glass: A common term used to refer to glass which has low emissivity due to a film or metallic coating on the glass or suspended between the two lights of glass to restrict the passage of radiant heat.
Lower Sash: The bottom portion of the window comprised of a pane of glass set inside a frame. Is fixed in a single hung window and slides up and down in a double hung window.
Masonry opening: The space in a masonry wall left open for windows or door.
Mullion: A wood or metal part used to structurally join two window or door units.
Muntin: Applies to any short or light bar, either vertical or horizontal, used to separate glass in a sash into multiple lights. Also called a windowpane divider or a grille.
Muntin Bar: Any small bar that divides a windows glass. Also called a grille or windowpane divider.
Nail-on: Windows with nail-on frames are for new construction.
Parting stop: In a double-hung window, a strip of wood applied to the jamb to separate the sash.
Passive solar collector: Any glazed area in the walls or roof of a building pointed to the south to take maximum advantage of the sun's heat without a mechanical (or active) method of storage or distribution of the heat.
Picture: Non-venting or non-operable window. Also know as a fixed window.
Rail: The top and bottom horizontal members of the framework of a window sash.
Rough opening: The framed opening in a wall into which a window or door unit is to be installed.
R-Value: Resistance to thermal transfer or heat flow. Higher R-value numbers indicate greater insulating value.
Pane: A framed sheet of glass within a window.
Sash: A single assembly of stiles and rails made into a frame for holding glass.
Sash balance: A system of weights, cords and/or coiled springs which assist in raising double-hung sash and tend to keep the sash in any placed position by counterbalancing the weight of the sash.
Sash cord: In double-hung windows, the rope or chain which attaches the sash to the counter balance.
Sash lift: A protruding handle screwed to the inside bottom rail of the lower sash on a double-hung window.
Sash weights: In older double-hung windows, the concealed cast-iron weights which are used to counterbalance the sash.
Seat board: A flat board cut to fit the contour of a bow or bay window and installed between the sills and the flat wall surface, providing a seat or shelf space.
Shims: Wood wedges (often wood shingles) used to secure the window or door unit in the rough or masonry opening in a square, level and plumb position during and after installation.
Sidelights: Narrow fixed units mulled or joined to door units to give a more open appearance.
Side Jamb: Grooves in window that allows the window sashes to slide up and down or side to side
Sill: The main horizontal member forming the bottom of the frame of a window or door.
Simulated divided light: A method of constructing windows in which muntins are affixed to the inside and outside of a panel of insulating glass to simulate the look of true divided light.
Single glazing: Use of single panes of glass in a window. Not as energy-efficient as double glazing.
Single-hung: A double-hung type of window in which the top sash is fixed or inoperable.
Sloped Sill Adapter: Used to cover the gap between the old sloped sill window and the new block frame window. It adapts a new window to the existing sloping sill.
Solar gain: The process of providing a net heat gain within a structure, over and above the normal heat loss, by passive collection of the sun's heat through windows and other glazed areas.
Stile: The main vertical members of the framework of a sash.
Stool: An interior trim piece on a window which extends the sill and acts as a narrow shelf.
Stop: A molding used to hold, position or separate window parts.
Tempered glass: Glass manufactured to withstand greater than normal forces on its surface. When it breaks, it shatters into small pieces to reduce hazard. Standard on all doors and large fixed windows.
Thermal break: The addition of a thermal insulating material between two thermally conductive materials.
Transom: A small window that fits over the top of a door or window, primarily for additional light and aesthetic value.
Trim: The trim extends beyond the end of the window frame on the outside of the window. This allows the window to fit flush with the exterior wall when the window in installed.
True divided light: A term which refers to windows in which multiple individual panes of glass or lights are assembled in the sash using muntins.
U-value: Rate of heat flow-value through the complete heat barrier, from room air to outside air. The lower the U-value, the better the insulating value.
Unison lock: A casement locking system which secures the window at two locking points by operation of one handle.
Upper Sash: The top portion of the window comprised of a pane of glass set inside a frame. Is fixed in a single hung window and slides up and down in a double hung window.
Vapor barrier: A watertight material used to prevent the passage of moisture into or through floors, walls and ceilings.
Vent Unit: A window or door unit that opens or operates.
Vinyl: A plastic material used for cladding or entire window units.
Weatherstripping: A material or device used to seal the openings, gaps or cracks of venting window and door units to prevent water and air infiltration.
Windload: Force exerted on a surface by moving air.
