Glossary of Window and Door Terms

Alpine - A lite breakup layout consisting of a single horizontal muntin placed significantly above center, along with one or more vertical muntins extending from the horizontal muntin to the top of the sash. This creates one larger lite in the lower portion of the window, and two or more small lites in the upper portion.

Annealed - Heating above the critical or re-crystallization temperature, then controlled cooling of metal, glass, or other materials to eliminate the effects of cold-working, relieve internal stresses, or improve strength, ductility, or other properties.

Apex - Denotes the highest point of the radius at the top of a flat-arch or true-arch door or window.

Astragal - Vertical member attached to the inactive door of a pair that seals them where the two lock stiles meet.

Awning Sash - A frame in which the panes of a window are set. The frame is built in such a way that the bottom swings outward in a window frame.

Butt Hinge - A standard barrel-type hinge, mounted by mortising the leaves into the sash and frame of a window. Butt hinges are also commonly used as door hinges.

Casement - A window in which the frame is built in such a way that the sash can open out like a door when installed in a window unit.

Crossbuck - Horizontal bars used in place of rails on a true plank door. Crossbucks are bolted across the vertical planks of the door in order to strengthen the assembly.

Direct Set - A window in which the glass is stopped directly to the frame, without utilizing a sash.

Double-Glazed - See Dual-Glazed.

Double-Hung Window - Two sashes, top and bottom, that slide vertically past each other, joined by a meeting rail and held in any open position by means of weights or one of several types of balancing devices.

Dual-Glazed - In general, two thicknesses of glass separated by an air space within an opening to improve insulation against heat transfer and/or sound transmission. In factory-made dual-glazed units, the air between the glass sheets is thoroughly dried and the space is sealed airtight, eliminating possible condensation and providing superior insulation properties. Dual-glazing, compared to single-glazing, cuts heat loss in half due to the insulating air space between the glass layers. Also called double-glazed.

Dutch Door - Originating in the Netherlands during the early 1600s, this unique design features top and bottom halves that operate independently. The bottom can be closed for some privacy, while the top is left open for fresh air and neighborly chats. Or, when locked together, the two sections can work as a standard door. Dutch doors were first used on front entryways and were later placed at secondary doorways to the kitchen or scullery. These doors also provided ventilation to barns and stables. Dutch doors lend a country charm to rear entrances and outbuildings such as potting sheds.

Dyad Operator - A crank-operated device, having a scissor-type arm anchored to a window sash, used to open and close a window.

Egress Hinge - A hinge utilizing a scissor-type bar at the bottom, allowing the window to open wider than perpendicular to the frame and providing an avenue of escape in case of emergency.

Elliptical - A door or window having a top rail with an egg-shaped radius, ending in a rounded point at its apex.

Finish - Various compounds (paint, varnish, stain, oil, and/or wax) applied to the surface of wood or metal to enhance its appearance, as well as to provide protection from the elements and for ease of maintenance.

Fixed - Refers to windows that are non-venting or inoperable. Also see Stationary Sash.

Flat-Arch - A window or door whose top is curved in a radius equal to the width of the product; for example, a flat-arch window having a width of 3' would have a top rail outsid3e radius of 36". To calculate the distance from the springline to the apex, multiply the products width by .134. (Example: the distance from springline to apex of a 3' wide flat-arch window would be 4.824".)

Flush Bolt - Sliding bolt mortised into the edge of a door or astragal that typically engages into the jamb head and sill to secure the door. Commonly used on the inactive door of a pair.

French Casement Window - Two casement sashes, each hinged on one stile and opening in the middle with no center mull but with a half lap connection. This allows a smaller rough opening to make egress since there is a large unobstructed opening. French windows are of the out-swing (sashes swing toward the exterior of the structure) type.

Friction Hinge - A window hinge which remains open in any position by means of friction in the hinge.

Glazing - The insertion of glass into sashes and doors. The purpose of glazing is to retain the glass adequately under the design load, provide effective weather sealing, prevent loads or pressure points on the glass resulting from building movement, prevent glass-to-metal contact, and minimize glass breakage from mechanical and thermal stress.

Heartwood - The older, harder nonliving central portion of wood that is usually darker, denser, less permeable, and more durable than the surrounding sapwood.

Hopper Window - Similar to a pivot window, but with the pivot points located near the bottom of the sash. Advantages include: allows warmer air near the ceiling to escape, brings in fresh replacement air at the sides, helps to minimize drafts at sill levels, and provides easy cleaning access to interior and exterior surfaces.

Jamb - The part of the window frame that surrounds and contracts the window or sash the frame is intended to support. In doors, it's a surface forming the sides of the opening.

Kelly Stay - A scissor-type window hinge; used in combination with a butt or pivot hinge. A Kelly stay does not allow a sash to open beyond 90 degrees.

Laminated Glass - Two or more layers of glass with a transparent plastic interlayer between each pair, to which the glass adheres if broken. Used for safety glazing and sound reduction.

Lite (also Light) - A framed opening in a door or sash containing a pane of glass.

Lite Breakup - The configuration or layout of lites contained in a door or window.

Moulding - A relatively narrow strip of wood, usually shaped to a curved profile throughout its length; used to accent and emphasize the ornamentation of a structure and to conceal surface or angle joints. Sometimes spelled molding.

Mull - A wood or metal part used to structurally join two window or door units. Also called a mullion.

Muntin - A short vertical or horizontal bar used to separate panes of glass in a window or panels in a door. The muntin extends from a stile, rail, or bar to another bar. This tern is often confused with mullion.

One Lite - A single pane of glass contained within the sash of a window. It has no mulls or muntins.

Panel - Material (wood, latilla, louvers, etc.) inserted into the frame formed by stiles, rails, and mulls of a door.

Panel Breakup - The configuration or layout of panels contained in a door or sidelite.

Patina - A metal finish, caused by oxidation or corrosion, giving the piece a "weathered" look. Patina imparts an attractive sheen or color to the metal.

Picture Window - The same as a stationary or fixed sash, a picture sash or window usually implies a relatively large-sized sash.

Pivot Window - A window that opens by means of pivot points between the sash and frame. These pivot points are normally located at the midpoint of the horizontal members. Advantages include maximum ventilation from a single window. It also provides for easier cleaning of both glass surfaces from the interior.

Rail - A horizontal member on the framework of a sash, door or other panel assembly.

Raised Panel - A door panel on which the edges have been contoured or shaped to provide an aesthetically appealing, three-dimensional effect.

Sapwood - The younger, softer living or physiologically active outer portion of wood that is more permeable, less durable and usually lighter in color than the heartwood.

Sash - A single assembly of stiles and rails in a frame for holding glass, with or without dividing bars or muntins to fill a given opening. It may be either open or glazed.

Sidelite - An assembly of stiles and rails, with or without a wood panel, containing a single row of glass panels or lites. They are installed on one or both sides of an exterior doorframe, especially a front entrance doorframe. Also used in older houses to frame interior doors. Also spelled sidelight.

Sill - A main horizontal member forming the bottom of a window or door assembly.

Simulated Divided Lite - Windows or doors that contain one piece of glass with internal spacer bars which provide the illusion of a true divided lite.

Single-Glazed - Single thickness of glass in a window or door. Also see Dual-Glazed.

Slider - Two or more sashes or doors that slide horizontally past each other. One or more of the sashes may be fixed or inoperative, or all the sashes may operate. In a closed position, the sashes come together to form a vertical meeting rail.

Springline - An imaginary horizontal line across a flat-arch or true-arch door or window, between the points where the top radius begins and ends.

Square-Top Door - A door with a flat top rail; i.e., not containing a radius. Also known as a standard-top door or a flat-top door.

Stationary Sash - A fixed or inoperative sash, often used in combination with other types of window and sash units. It's intended primarily for viewing purposes and for admitting light. Also see Fixed.

Stile - The upright or vertical outside pieces of a sash, door, window, or screen.

Stop - A moulding used to hold, position, or separate window parts.

Surface Bolt - Hardware that projects into the head of the doorjamb, or into the doorsill. Typically used to secure the inactive leaf in a pair of doors.

System - An arrangement of door or window units, combined for a particular application. An example of this would be multiple doors, with or without sidelites, transoms, and sunbursts. A window system may contain a particular grouping of windows, arranged in a certain order.

Tempered Glass - Treated glass that is strengthened by reheating it to just below the melting point, and then suddenly cooling it. When shattered, it breaks into small pieces. Approximately five times stronger than standard annealed glass; it is required as safety glazing in patio doors, entrance doors, sidelites, and other hazardous locations.

Textured Glass - Any glass with a surface texture (frosted, etched, fluted, ground, etc.) used for privacy, light diffusion, or decorative effects.

Tinted Glass - Glass colored by incorporation of a mineral admixture. Any tinting reduces both visual and radiant transmittance.

Top Rail - The rail located at the top of a door or window.

Top-Rail Arch - A top rail with a squared top edge and an inside radius bottom edge. The radius of a top-rail arch varies depending upon the width of the door, but the distance between the high point of the radius and the top edge of the rail will always be the width of the stile.

Transom - A small opening above a door or window separated by a horizontal member that usually contains a sash or louver panel hinged to the transom bar. Transoms were first used in the 18th century on exterior doors. Because of the increased amount of light they allowed into the interior of a building, the size of the front door could be reduced.

Triple-Glazed - Three panes of glass with an air space between each pane. Also see Dual-Glazed and Single-Glazed.

True Arch - A window or door whose top is curved in a radius equal to half the width of the product, for example, a true-arch window having a width of 3' would have a top rail outside radius of 1'6".

True Divided Lite (TDL) - Windows and doors that contain individual panes of glass and are assembled in the sash using muntins.

Weatherstripping - A strip of resilient material for covering the joint between the window's sash and frame in order to reduce air leaks and prevent water from entering the structure.

Window Frame - A group of wood parts machined and assembled to form an enclosure and support for a window or sash.

Window Unit - A combination of the frame, window, weatherstripping, sash activation device, and screen, assembled as a complete operating unit.