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The Millwork Industry has numerous terms which could confuse or frustrate someone that may not be familiar with all the intricacies. Here is a list of terms designed to assist you with questions you may have.

Air Chambers - Small honeycomb spaces within the sash and frame which help to insulate and strengthen the window.

Air Infiltration - The amount of air that passes between a window sash and frame. In windows it is measured in terms of cubic feet or air per minute, per square foot of area. The lower the number, the less air the window lets pass through.

Air Latch - Latch mechanism on the interior face of the sash that retains the window in a partially open position for ventilation.

Alpine - A light 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 light in the lower portion of the window, and two or more small lights in the upper portion.

Angled Exterior- A sloped extension from the frame that adds an aesthetically-pleasing dimension to the exterior of the window.

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.

Argon Gas - An odorless, colorless, tasteless, non-toxic gas which is six times denser than air. It is used to replace air between the glass panes to reduce temperature transfer.

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

Awning window - A top-hinged window that swings outward for ventilation.

Baguette — Thin, half-round molding, smaller than an astragal, sometimes carved, and enriched with foliages, pearls, ribbands, laurels, etc. When enriched with ornaments, it was also called chapelet.[2]

Balance System - Device for holding vertically sliding sash in any desired position through the use of a spring or weight to counterbalance the weight of the sash.

Bandelet — Any little band or flat molding, which crowns a Doric architrave. It is also called a tenia.[2]

Baseboard, "base molding" or "skirting board" — used at the junction of an interior wall and floor to protect the wall from impacts. The so called speed base (a 163 base cap on top of a 1x board and the Victorian base (feathered edge) are the most common baseboards.

Batten or board and batten — a symmetrical molding that is placed across a joint where two parallel panels or boards meet

Bay window - An angled combination of three windows that project out from the wall of the home. The windows are commonly joined at 30- or 45-degree angles.

Bead molding — narrow, half-round convex molding, when repeated forms reeding

Beading or bead — molding in the form of a row of half spherical beads, larger than pearling

Beak — Small fillet molding left on the edge of a larmier, which forms a canal, and makes a kind of pendant.[2] See also: chin-beak

Bed molding — a narrow molding used at the junction of a wall and ceiling. Bed moldings can be either sprung or plain.

Beveled Exterior - An angled extension from the frame that adds an aesthetically-pleasing dimension to the exterior of the window.

Block frame window - Used when replacing the wood sash of an old double hung wood window.

Bolection — a moulding which is raised, projecting proud of the face frame. It is located at the intersection of the different surface levels between the frame and inset panel on a door or wood panel. It will sometimes have a rebate (or rabbet) at the back, the depth of the difference in levels, so that it can lay over the front of both the face frame and the inset panel and can in some instances thus give more space to nail the moulding to the frame, leaving the inset panel free to expand or contract in varying climates, as timber is prone to do.

Bow Window - An angled combination of windows in 3-, 4- or 5-lite configurations. The windows are attached at 10-degree angles to project a more circular, arched appearance.

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.

Butyl - A rubber material that seals the glass to the spacer, creating an airtight and water-tight IG unit. Butyl has the lowest gas permeability of all rubbers.

Cabled fluting or cable — Convex circular molding sunk in the concave fluting of a classic column, and rising about one-third of the height of the shaft[2]

Cam Lock and Keeper - The mechanisms which pull the sash together when placed in the locked position.

Capillary Tubes - Small hollow tubes which penetrate the spacer system of an insulating glass unit. They allow pressure equalization between manufacturing locations, shipping, and installation locations. Since the insulating glass unit is not permanently sealed, the air space cannot be filled with Argon gas.

Cartouche (French) escutcheon) — Framed panel in the form of a scroll with an inscribed center, or surrounded by compound moldings decorated with floral motifs

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.

Casement window - A window with a side-hinged sash that opens outward for ventilation.

Casing — Final trim or finished frame around the top, and both sides of a door or window opening

Cavetto(Italian) cavare: "to hollow", concave, quarter-round molding sometimes employed in the place of the cymatium of a cornice, as in the Doric order of the theatre of Marcellus. It forms the crowning feature of the Egyptian temples, and took the place of the cymatium in many of the Etruscan temples.

Center of Glass U- and R-values - The U- and R-values measured from the center of the glass to 2-1/2" from the frame.

Chair rail — Horizontal molding placed part way up a wall to protect the surface from chair-backs, and used simply as decoration

Chamfer — Beveled edge connecting two surfaces

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.

Chin-beak — Concave quarter-round molding. There are few examples of this in ancient buildings, but is common in more recent times.[2]

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.

Condensation Resistance Factor - A measure of the effectiveness of a window or glazing system to reduce the potential for condensation. The higher the condensation resistance factor, the more efficient the window and glazing system.

Conduction - Energy transfer from one material to another by direct contact.

Convection - Heat transfer by currents that flow from a warm surface to a colder one.

Corner guard — Used to protect the edge of the wall at an outside corner, or to cover a joint on an inside corner.

Cottage double hung - A double hung window in which the upper sash is shorter than the lower sash.

Cove molding — A concave-profile molding that is used at the junction of an interior wall and ceiling

Coved Exterior - An arced extension from the frame that adds an aesthetically-pleasing dimension to the exterior of the window.

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.

Crown molding — A wide, sprung molding that is used at the junction of an interior wall and ceiling. General term for any molding at the top or "crowning" an architectural element.

Cyma — Molding of double curvature, combining the convex ovolo and concave cavetto. When the concave part is uppermost, it is called a cyma recta but if the convex portion is at the top, it is called a cyma reversa, When the crowning molding at the entablature is of the cyma form, it is called a cymatium.

Dead-air space - The space between the panes of glass of an I.G. Unit.

Dentils — Small blocks spaced evenly along the bottom edge of the cornice

Desiccant - A material used in insulating glass to absorb water vapor which causes fogging.

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

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

Double glazing - Use of two panes of glass in a window to increase energy efficiency and provide other performance benefits.

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.

Double-strength Glass - Glass with a thickness of approximately 1/8".

Drip cap — This is placed over a door or window opening to prevent water from flowing under the siding or across the glass

Dry glazing - An alternative method of placing glass in a door or window. No glazing mastic is used. Dry glazing is recommended whenever reflective coatings are glazed to first surface.

Dual-durometer - An elastomeric material with two different degrees of hardness.

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.

Echinus — Similar to the ovolo molding and found beneath the abacus of the Doric capital or decorated with the egg-and-dart pattern below the Ionic capital[3]

Egress Code - The code that requires a minimum opening of a window for persons to exit or firefighters to enter a building.

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

ENERGY STAR® - ENERGY STAR® is an independent U.S. government program establishing a standard set of guidelines to recognize the energy efficiency of various products. ENERGY STAR® guidelines are used in conjunction with a variety of building materials, including windows and patio doors. Over the past ten years, ENERGY STAR® guidelines have helped double the efficiency of windows they endorse.

Extruded screen frame - Different from a Rollformed frame, this frame is pressed through a form or die.

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.

Fillet — Small, flat band separating two surfaces, or between the flutes of a column

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 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.

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.

Fluting — Vertical, half-round grooves cut into the surface of a column in regular intervals, each separated by a flat astragal. This ornament was used for all but the Tuscan order

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 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.

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.

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

Fusion-welded - The process of joining materials by melting them together with extreme heat (over 500ºF), resulting in the materials uniting into a one-piece unit.

Geometric - Specially designed windows classified as either straight line geometrics such as rectangles, triangles, trapezoid, octagons, pentagons, etc., or radius geometrics which include half-rounds, quarter-rounds, full-rounds, sectors, ellipses, eyebrows, etc.

Glass - An inorganic transparent material composed of sand (silica), soda (sodium bicarbonate), and lime (calcium carbonate) with small quantities of alumina, boric or magnesia oxides.

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.

Glazing bead - A strip of vinyl which surrounds the edge of the glass and holds it in place in conjunction with other sealants. Could also be a wood strip applied to the window sash around the perimeter of the glass.

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

Godroon or Gadroon — Ornamental band with the appearance of beading or reeding, especially frequent in silverwork and molding. It comes from the Latin word Guttus, meaning flask. It is said to be derived from raised work on linen, applied in France to varieties of the, bead and reel, in which the bead is often carved with ornament. In England the term is constantly used by auctioneers to describe the raised convex decorations under the bowl of stone or terracotta vases. The godroons radiate from the vertical support of the vase and rise half-way up the bowl.

Grids - Decorative horizontal or vertical bars installed between the glass panes to create the appearance of the sash being dividing into smaller lites of glass.

Grille - A term referring to windowpane dividers or muntins, usually a type of assembly which may be detached for cleaning.

Guilloche — Interlocking curved bands in a repeating pattern often forming circles enriched with rosettes and found in Assyrian ornament, classical and Renaissance architecture.[3]

Head - The horizontal top portion of the main frame.

Head expander - A vinyl shape cut the width of a product and placed on the head, fitting over it snugly. This piece is used as a filler to expand or lengthen the unit from the head and take up the gap in the opening between the unit and the opening in the unit.

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

Hook accessory - Accessories that snap to the hook frame and provide easy installation.

Hopper - A window with a bottom-hinged sash that opens inward for ventilation.

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.

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.

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.

J-channel - Integral extension on the outside of a new construction window that eases installation on siding applications.

Keel molding — With a sharp edge, resembling in cross-section the keel of a ship. It is common in the Early English and Decorated styles.

Keeper Rail - The horizontal section of the sash where the keeper is attached.

Keeper Stile - The vertical section of the sash where the keeper is attached.

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.

Krypton Gas - An inert, odorless, colorless, tasteless, non-toxic gas which is about 12 times more dense than air. It is used to replace air between the glass panes to reduce temperature transfer and deter convection. Used when a higher performance is desired than that produced with Argon gas.

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.

Lift Handle - A handhold for raising and lowering the sash. Handle implies that the handhold is not continuous across the sash.

Lift Rail - A handhold for raising and lowering the sash. Rail implies that the handhold is continuous across the sash.

Light - A framed opening in a door or sash containing a pane of glass.

Light Breakup - The configuration or layout of lights contained in a door or window.

Light - Glazing framed by muntins and/or sash in a window or door. A unit of glass in a window.

Lock Rail - The horizontal section of the sash where the cam lock is attached.

Lock Stile - The vertical section of the sash where the cam lock is attached.

Low-E (Emissivity) Glass - Glass with a transparent metallic oxide coating applied onto or into a glass surface. The coating allows short-wave energy to pass through but reflects long-wave infrared energy which improves the U-value.

Main Frame - The head, sill and jambs sections of a window.

Mechanically Fastened Frame - Refers to frames fastened with screws.

Meeting Rail - The horizontal sections of a pair of sash that meet when the sash are closed.

Meeting Stile - The vertical section of a pair of sash that meet when the sash are closed.

Mesh - Fabric made of either fiberglass or aluminum, used in the making of screens.

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.

Mullion - A vertical or horizontal wood or metal part used to structurally join two or more windows or door units.

Muntin Bar - Any small bar that divides a windows glass. Also called a grille or windowpane divider.

Nailing Fin - An extrusion attached to the main frame of a window used to secure the unit to the rough opening.

Obscure Glass - Glass that has been made translucent instead of transparent.

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

Oriel - A window with the meeting rail located off center of the frame. Most oriels have a 60/40 configuration.

Ovolo — Simple, convex quarter-round molding that can also be enriched with the egg-and-dart or other pattern

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

Pane - A framed sheet of glass within a window.

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 sidelight.

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.

Patio door - A glass door that slides open and close on adjustable tandem rollers.

Picture Rail - Functional molding installed 7–9 feet above the floor from which framed pictures and paintings are hung using picture wire and picture rail hooks.

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.

Power Seal Spacer System or True-dual Seal - A high-performance spacer system based on four independent designs featuring a U-channel Intercept spacer dual-sealed with urethane adhesive and a hot melt butyl and an additional desiccant matrix.

Pull Handle - A handhold for sliding the sash back and forth. Handle implies that the handhold is not continuous across the sash.

Pull rail - A handhold for sliding the sash back and forth. Rail implies that the handhold is continuous across the sash.

Pull Stile - A handhold for sliding the sash back and forth. Stile implies that the handhold is continuous across the sash.

Radiation - Wave energy transmitted directly from one object to another through the atmosphere or through transparent or translucent materials. The energy radiated is either transmitted, absorbed, reflected or a combination of all three.

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

Raised Exterior - An angled extension from the frame that adds an aesthetically pleasing dimension to the exterior of the window.

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

Relative Humidity Condensation Point - The relative humidity level at which visible water vapor or other liquid vapor begins to form on the surface of the sash or frame, based on an inside temperature of 70E F and an outside temperature of 0E F. The higher the percentage, the more moisture the air can hold before condensation will occur.

Rollformed Screen Frame - A method of fabrication in which a flat (usually metal) material is placed on a machine where the material is formed into shape using differently shaped rollers and pressure.

Rosette — Circular, floral decorative element found in Mesopotamian design and early Greek stele. Part of revival styles in architecture since the Renaissance.[3]

R-value - Resistance a material has to heat flow. Higher R-value numbers indicate greater insulating value.

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.

Sash Alignment System - An exclusive hinge-type system used on hung windows. This system attaches the sash to the balance, creating perfect alignment between the sash and frame, while allowing the sash to tilt inward for cleaning.

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.

Scotia — Concave molding with a lower edge projecting beyond the top and so used at the base of columns as a transition between two torus moldings with different diameters[3]

Screen molding — This is a small molding that is used to hide the area where a screen is attached to the frame.

Shading Coefficient - The ratio of solar heat that is transferred through a glazing material relative to the solar heat transferred through 1/8" clear glass. The lower the number, the more efficient the window is at reducing solar heat gain.

Shoe molding, toe molding or quarter-round — often used at the bottom of the baseboard to cover a small gap or uneven edge between the flooring and the baseboard.

Sidelight - An assembly of stiles and rails, with or without a wood panel, containing a single row of glass panels or lights. 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.

Sill Extender - An extrusion that is attached to the bottom of the window to cover the gap between the sill and the rough opening.

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

Single Hung - A window in which one sash slides vertically and the other sash is fixed (usually the top).

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

Single-strength Glass - Glass with a thickness of approximately 3/32".

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.

Sloped sill - The sill of the window that has a downward slope to the outside. This sill has sufficient degree of slope to aid in water runoff.

Solar Heat Gain - The percentage of heat gained from both direct sunlight and absorbed heat. The smaller the number, the greater the ability to reduce solar heat gain.

Spacer - Material placed between two or more pieces of glass in order to maintain a uniform width between the glass, and prevent sealant distortion.

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.

Stepped Sill - An exclusive triple-stepped, sloped sill design.

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

Stop - A molding 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 sidelights, transoms, and sunbursts. A window system may contain a particular grouping of windows, arranged in a certain order.

Tape Glazing - Two-sided tape used to secure and seal the glass to the sash.

Tempered Glass - Glass with a surface compression of not less than 10,000 psi, or an edge compression of not less than 9,700 psi. When broken, the glass breaks into pebbles instead of shards. Standard on all doors and large fixed windows.

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

Thermal break - The addition of a thermal insulating material between two thermally conductive materials.

Tilt Latch - Mechanism that unlocks the sash and allows it to tilt in from the main frame.

Tilt-in/lift-out sash - A sash that can be tilted to the interior and removed for cleaning and is manufactured by welding.

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.

Torus — Convex, semi-circular molding, larger than an astragal, often at the base of a column, which may be enriched with leaves or plaiting

Total Unit U- and R-values - The U- and R-values of the window calculated from the average of the center of glass, edge of glass and frame U- and R-values. It is the reciprocal of the R-value.

Transom - A small window that fits over the top of a door or window, primarily for additional light and aesthetic value.

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

Unison lock - A casement locking system which secures the window at two locking points by operation of one handle.

UV Block - The percent of ultraviolet rays blocked from being transmitted through the glass. The higher the number the lower the percentage of ultraviolet rays transmitted through the window.

U-value - Amount of heat transferred through a material. The lower the U-value, the slower the rate of heat flow and the better the insulating quality.

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.

Visible Light Transmittance - The percentage of light that is transmitted through glass in the visible light spectrum (380 to 720 nanometers). The higher the number the higher the percentage of visible light transmitted through the window.

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.

Weep flaps - A weep hole that is covered with vinyl flap that allows water to escape, while keeping insects out.

Weep Holes - Small openings designed to allow water to escape that might otherwise accumulate in a window's sill.

Weep Slots - Slots or holes in the sill (bottom) member of the sash frame that provides an outdoor release of infiltrated rainwater.

Wet Glazing - A silicone-based substance used to secure and seal the glass to the sash.

Windload - Force exerted on a surface by moving air.

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.

Wood blocks - Pieces of plywood that come in different thickness, depending on the depth of the hook of the frame. They are used to make the window flush with the opening it is filling. They are also used to assist in pre-mulling windows together and give the screw more to bite into when joining the windows.

Wood jamb strips - Strips of wood that run along the jamb used to shim up the window


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