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A - M

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 60- or 45-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 levers outward, to the right or left.


Casing: Molding of various widths, thickness and shapes applied to the framework of window and door units.


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: An aluminum material locked to the outside faces of many Pella® products to provide a durable, low-maintenance exterior surface.


Clerestory window: A venting or fixed window above other windows or doors on an upper outside wall of a room.

Dormer: A space which protrudes from the roof of a house, usually including one or more windows.


Double glazing (STANDARD FEATURE): Use of two panes of glass in a window to increase energy efficiency and provide other performance benefits.


Drip cap: A molding placed on the top of the head brickmold or casing of a window frame.


Double Weatherstripping (STANDARD FEATURE): A material that has two or more levels of flexibility. An example is the weatherstripping used between the frame and sash of a casement window.

Extrusion: A form produced by forcing material through a die (if you think back to when you were a kid, this is similar to the spaghetti-like ‘extrusions‘ created by squeezing Play-doh through a mold). Pella window frames are clad with extruded aluminum.

Fixed: Non-venting or non-operable.


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 windows 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.

Glazing: Glass in a window or door; the act or process of fitting with glass.


Glazing stop: The part of the sash or door panel which holds the glass in place.


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.


Hopper: A window unit in which the top of the sash swings inward.

Insulating glass (IG) (STANDARD FEATURE): 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.

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.

Knocked down (KD): Unassembled window or door unit.

Light: A separately framed piece of glass in a window or door. A traditional double-hung window, for instance, often has several lights divided by muntins in each sash. Such windows are described as six-over-six, eight-over-one, twelve-over-twelve, etc., to indicate the number of lights in each sash. Sometimes spelled ‘lite.’


Low-emissivity (low-E) glass: A special type of glass having a transparent material fused into its surface which acts as a thermal mirror.

Masonry opening: The space in a masonry wall left open for windows or door.


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. Often used as a corner joint in window sashes.


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.

N - Z

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Panel: Usually refers to the separate panel or panels in a door frame.

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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.

Sash: A single assembly of stiles and rails made into a frame for holding glass.


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.


Sidelights (or sidelites): Narrow fixed units mulled or joined to door units to give a more open appearance.


Sill: The main horizontal member forming the bottom of the frame of a window or door.


Simulated divided light (SDL): 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 window: A double-hung type of window in which the top sash is fixed or inoperable.


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 (STANDARD): Glass manufactured to withstand greater than normal forces on its surface. When it breaks, it shatters into small pieces to reduce hazard.


Tenon: A rectangular projection cut out of a piece of wood for insertion into a mortise.


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.


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.

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Vent Unit: A window or door unit that opens or operates.


Vinyl: A plastic material used by some window manufacturers.

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.


Windowpane divider: See muntin.

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