Window and Door Glossary of Terms

Air ChambersThese are small spaces that look like honeycombs that are between the frame and the sash and help strengthen and insulate the window.
Active PanelPrimary operating door panel.
Air InfiltrationThe amount of air leaking in and out of a building through cracks in walls, windows and doors.
Air Leakage The flow of air that passes through fenestration products.
Air Leakage RatingA measure of the rate of air-leakage around a window, door, or skylight in the presence of a specific pressure difference. It’s expressed in units of cubic feet per minute per square foot of frame area (cfm /sq ft). Formerly expressed as cubic feet per minute per foot of window perimeter length (cfm /ft) but not now in use. The lower a window’s air-leakage rating, the better its airtightness
Airspace The space between adjacent layers in a multi-layer glazing system.
Alpha-10Exclusive combination of inert gases that enhances thermal performance of Bristol replacement windows
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.
Annealed GlassAnnealed glass has undergone a cooling treatment at a glass fabricator’s float plant as a way to improve durability.
ANSIAmerican National Standards Institute. Clearing house for all types of standards and specifications.
ApronA piece of casing or decorative trim installed against the wall immediately beneath the stool of a window.
Argon GasA colorless and odorless gas used to fill the airspace between insulating Low E glass. The addition of argon greatly increases the insulating performance of the Low E glass.
AssemblySingle units mulled together.
AstragalA moulding applied to one stile of a French Door, Sliding French Door or French Casement window unit which the other door panel or window sash strikes. Usually head and footbolt devices will be found on the astragal side.
Authentic Divided Lites (Adl)Also known as True Divided Lite. Permanent stationary muntins and bars separate the glass in a window or door sash to give the sash two or more lites of glass.
Awning Window UnitA combination of frame and sash, hinged at the top of the vertical jambs which allows the unit to pivot from the top with the sash opening to the exterior of the building.
Balance A mechanical device (normally spring loaded) used in single- and double-hung windows as a means of counterbalancing the weight of the sash during opening and closing.
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.
BarsA narrow rabbeted, horizontal or vertical sash or door member in an authentic divided lite unit, extending from rail to rail or stile to stile along the total length or width of the glass opening.
Basement Window Any window type intended for ventilating or illuminating a basement or cellar.
Bay WindowsA series of windows installed in a bay which is two flanker units and a center sash; a bay may be an arc or a polygon; when a bay is or closely approaches an arc, the window is termed a bow.•See Bow Windows.
Bead  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.
Bedding 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.
Beveled GlassRefers to a glass that has its edges cut and polished to a specific angle and size in order to produce a specific elegant look. This process leaves the glass thinner around the edges, while the large middle portion remains the normal glass thickness.
Bite The dimension by which the inner or outer edge of the frame or glazing stop overlaps the edge of the glazing.
BlindstopThe frame member on a double hung window located between the jambs and the casing. The blindstop forms a rabbet that supports either a storm sash or screen.
Bottom Rail Bottom horizontal member of a window sash.
Bow Window  Rounded bay window that projects from a wall in the shape of an arc. It consists usually of five sash.
Box-Head Window Window made so the sash can slide vertically into the wall space above the header.
Boxed Mullion Hollow mullion between two double-hung windows to hold sash weights.
BR50Exclusive warm-edge thermal spacer system for Bristol and Oxford Replacement windows.
Breather TubesCapillary tubes and breather tubes are used in insulating glass units to equalize the pressure between the sealed panes. The main reason for the use of capillary or breather tubes is for installation of windows at high altitudes.
Brick Mould Casing An exterior moulding of window and door frames that abuts the exterior facing material of the structure.
British Thermal Unit (BTU)  An abbreviation for British Thermal Unit, the heat required to increase the temperature of one pound of water one degree Fahrenheit.
Building Envelope The assembly or assemblies of materials and components that enclose building spaces and are exposed to exterior space or separate conditioned interior space from unconditioned interior space.
ButylA synthetic rubber prepared by co-polymerization of isobutylene with a small amount of isoprene (both ingredients are gaseous hydrocarbons). It can be used as a sealant and architectural glazing tape.
Cam LockA lever operated lock which is used to prevent intrusion through the sash. Cam locks and keepers were installed on the jambs and stiles of older Casement and awnings.
Cam PivotA zinc pivot pin attached to the top and bottom sash stiles of double hung units (bottom sash on single hung units). Cam pivots rest on the clutch system of the balance tube assembly which allow opening and closing of the sash.
Cames Lead strips which hold small pieces of glass in leaded windows.
Cap Decorative molded projection, or cornice, covering the lintel of a window.
Capillary TubesA tube inserted into the insulating glass spacer that allows the inside and outside air pressure to equalize in higher elevations.
Casement Adjuster Device to hold a casement window in any open position.
Casement Stay Bar for holding a casement window in any of several fixed open positions.
Casement WindowA combination of frame, sash, weather-strip, concealed hinges and operating device assembled as a complete and properly operating unit. Casements have a flat sill and a sub-sill; screens and/or energy panels are optional. Operating casements have a crank handle for smooth operation.
Casing A trim. Exposed molding or framing around a window or door, on either the inside or outside, to cover the space between the window frame or jamb and the wall.
CaulkingThe blocking of exterior air or moisture leaks by filling cracks around doors, windows, or anywhere else where two surfaces meet and have minimum movement with a “putty” compound. Large cracks can be stuffed with mineral wood and weather sealed with caulking.
Cellulosic Composite Material A composite material whose ingredients include cellulosic elements. Note: these cellulosic elements appear in the form of, but are not limited to, distinct fibers, fiber bundles, particles, wafers, flakes, strands, and veneers.
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.
Certification A process that indicates a representative sample of a product line has been tested, that the product meets specified requirements, and that the product is subject to ongoing inspections by an outside certification agency.
Chemically Bonded  A process where the two polymer profiles or pieces are heated and fused together with the aid of a chemical reaction. The reaction and bonding is similar to the original extrusion process.
Cladding See fenestration cladding.
ClerestoryA window in the upper part of a lofty room that admits light to the center of a room.
Closing Force See operating force and force to latch door.
ClutchThe plastic and metal assembly on which the cam pivots of a double hung or single hung sash rest. The clutch is attached to the block and tackle system of the balance tubes which allow opening and closing of the sash. The clutches are color coded for easy identification of balance strength.
Colonial Windows Windows with small rectangular panes, or divided lites, designated as 12-lite, 16-lite and so on.
Combination Assembly An assembly formed by a combination of two or more separate fenestration products whose frames are mulled together utilizing a combination mullion or reinforcing mullion.
Combination DoorA wood framed assembly containing an interchangeable storm panel and screen. The unit is installed on the exterior of the door, and is available for wood Inswing and Ultimate Inswing French doors.
Combination Mullion A horizontal or vertical member formed by joining two or more individual fenestration units together without a mullion stiffener.
Combination StormA wood or aluminum storm sash with self-storing screen and operating glass panels. Available for double hungs, gliders and wood swinging doors, these panels are removable.
Combination WindowA wood or clad wood frame storm sash with self-storing screen. Bottom glass panels such as those installed on a double hung unit operate by moving the plungers in and sliding the glass panel up to the desired position. Side glass panels such as those installed on gliders slide to the left or right to the desired position. All inserts are removable from the inside.
Commercial Entrance System A system of products used for ingress, egress, and rescue generally in non-residential buildings.
Composite Unit A fenestration product consisting of two or more sash, leaves, lites, or sliding door panels within a single frame utilizing an integral mullion. Note: composite units are not to be confused with products made from cellulosic composite materials.
Concentrated Load A force applied to a fixed point on a window, door, tdd, ssp, roof window, or unit skylight component.
Condensation The deposition of moisture (liquid water or frost) on the surface of an object caused by warm, moist air coming into contact with a colder object.
ConductionProcess of heat transfer through a material from a warm surface to a cool surface.
ConvectionHeat transfer by the movement of fluid or air.
Corner Window Two windows meeting at a corner of a structure.
Corrosion The deterioration of a material by chemical or electrochemical reaction resulting from exposure to weathering, moisture, chemicals, or other agents or media.
Cottage WindowA window with unequal sash, top and bottom.
Coupled Window Two separate windows separated by a mullion. Also called a double window.
CRFCondensation Resistance Factor. Gives an indication of a window’s ability to resist condensation. The higher the CRF, the less likely condensation is to occur.
Curtain Wall A non-load-bearing exterior wall cladding that is hung to the exterior of the building, usually spanning from floor to floor.
Daylight Opening (Dlo)The width and the height of the visible glass.
DesiccantAn extremely porous crystalline substance used to absorb moisture from within the sealed air space or an insulating glass unit.
Deflection Displacement due to flexure of a member under an applied load.
Delta-8Exclusive combination of inert gases that enhances thermal performance of Oxford replacement windows
Depth Of The JambThe point where the exterior casing ends to the point where the interior casing begins. On clad units, the point from the backside of the nailing fin to the interior of the frame.
Design Pressure  (DP)a rating that identifies the load, induced by wind and/or static snow, that a product is rated to withstand in its end-use application.
Note: Design pressure (DP) is not to be confused with Performance Grade (PG) or structural test pressure (STP). Loads induced by static snow are applicable only to TDDs, roof windows, and unit skylights.
Design Wind Load The wind load pressure a product is required by the specifier to withstand in its end-use application.
Dew PointThe temperature at which the condensation of water vapor in a space begins, at a given state of humidity and pressure, as the temperature is reduced. Used in testing sealed insulating glass. The lower the number, the higher the resistance to forming condensation.
Diffusing Glass Glass with an irregular surface for scattering light; used for privacy or to reduce glare.
Direct GlazeRefers to a window with no sash. The glass is glazed directly into the frame and is stationary.
Divided LitesDivision of light by the use of muntin bars.
Divider A member that divides glazing into separate vision areas. Dividers are either structural or decorative. Other common terms are muntin, true divided lite (tdl), simulated divided lite (sdl), grill, grid, or bar-in-glass.
Door A means of access for the purpose of ingress and egress. See also commercial entrance system, dual-action side-hinged door, folding door system, interior door, passive door, revolving door, secondary storm product, side-hinged door system, sliding door, storm door, and vehicular-access door.
Dormer Window Window in a wall that either projects from a sloping roof, or is recessed (inset dormer) into the roof, or a combination of both.
Double GlazingIn general, any use of two lites of glass, separated by an air space, within an opening, to improve insulation against heat transfer and/or sound transmission. In factory-made double glazing units the air between the glass sheets is thoroughly dried and the space is sealed airtight, eliminating possible condensation and providing superior insulating properties.
Double-Hung Window A hung window with two sash in which both sash are operable. Double hung windows have two movable sash which operate vertically.
Drip CapA formed aluminum or vinyl piece which is installed at the top of windows and doors that allows water to run off the casing of the unit instead of seeping around the casing and into the unit.
Drop Window Vertical window in which the sash can descend into a cavity in the wall below the sill.
Dry GlazingA method of securing glass in a frame by use of a dry, preformed resilient gasket, without the use of a compound.
Dual Glazing Two layers of glazing material mounted in a common frame and/or sash, separated by a space, and sealed or non-sealed.
Dual Mode The primary and secondary window/door, or both primary windows/doors, are closed, the primary windows/doors are locked, and the insect screen (when offered or specified by the manufacturer) is in the stored position.
Dual-Action Side-Hinged Door A door system consisting of one or more leaves contained within an overall frame and designed such that one of the leaves is operable in a swing mode and can be tilted inward from the top for ventilation.
Dual-Action Window A window consisting of a sash that tilts from the top and swings inward from the side for cleaning of the outside surface. Also referred to as a tilt-turn window.
Electric OperatorAn electrically operated device which will open casements or awnings units by using a switch. This is used in lieu of a roto gear crank or pole crank.
EmissivityThe ability of a material to radiate energy.
Energy Panel (Ep)Formerly called an RDG – removable double glazing, is a piece of glass annealed or tempered, and finished on the edges by a surround. Eps are applied to windows or doors and rest on the glazing stop. Eps offer the homeowner added energy efficiency.
Energy StarEnergy Star is a government-backed program that uses specific criteria to ‘grade’ the efficiency of replacement windows. You should always check for products that are “Energy Star” rated.
EPDMA weathering compound with good resistance to ultra-violet radiation. Good memory and weathering characteristics.
EscutcheonA decorative door handle plate attached to the stile directly behind the handle(s). Generally square or rectangular shaped.
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 JambA board used to increase the depth of the jambs of a window frame to fit a wall of any given thickness.
ExtrusionAn article or product of vinyl or metal-made by the process of extruding. Extrusions include vinyl sill and head jamb tracks, vinyl jamb liners and aluminum cladding used on the exterior of clad units.
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 rabbeted frame.
Factory MulledTwo or more window units attached together at the manufacturing facility.
Fading FactorThe measure of the ability of a glazing to reduce fading or damage to interior fabrics and materials. The ISO Damage Weighted Transmittance (Tdw-ISO) calculation assigns a specific damage weighted factor to each wavelength of UV or visible light (from 300nm to 680nm), based on its contribution to fading. Tdw-ISO is expressed as a number between 0 and 1. The lower the value, the lower the risk of fading to interior fabrics and materials.
FanlightA half-circle window over a door or window, with radiating bars.
Fenestration Openings in the building envelope, such as windows, doors, secondary storm products (ssps) curtain walls, storefronts, roof windows, tubular daylighting devices (tdds), sloped glazing, and skylights, designed to permit the passage of air, light, or people.
Fenestration Cladding The exterior components that cover the frame, sash, leaf, or sliding door panel members and constitute the weather-resistant surface.
FiberglassA composite material made by embedding glass fibers in a polymer matrix. May be used as a diffusing material in sheet form, or as a standard sash and frame element.
Field Measurement GuideA form that is filled out prior to ordering to ensure the correct sized unit is assembled at the factory.
Finger-JointA series of fingers machined into the ends of two pieces of lumber to be joined together. They are then held firmly in position by adhesive. Finger jointed wood is very strong and has a lesser chance of warping than does a clear piece of wood the same length.
Fire Window Window with fire-endurance rating specified for the location.
Fixed Door One or more non-operable assembled leaves or sliding door panels within a door frame and threshold/sill.
Fixed Window A window that is designed to be non-operable and consists of a glazed frame or a non-operating sash within a frame. A window which is stationary, also known as a picture window. 
FlankerA former term used to describe a side or lateral part. Also previously used to describe a 3-wide picture unit or bay. See two-wide entry.
Flat CasingFlat, surfaced on four sides, pieces of pine of various widths and thicknesses for trimming door and window openings. The casing serves as the boundary moulding for siding material and also helps to form a rabbet for screens and/or storm sash or combination doors.
Float Glass Flat glass that has been formed on molten metal, commonly tin. The surface in contact with the tin is known as the tin surface or tin side. The top surface is known as the atmosphere side or air side.
Foil 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.
Folding Door System A door system that has, at a minimum, a hinge or pivot attachment of any type between two leaves and three vertical axes about which the leaves rotate. The leaves can be folded to the interior or exterior of the opening. These systems are either top hung or bottom supported by hardware that attaches to a single track system and include, at a minimum, two pivoting/folding leaves, a frame, and a track and roller assembly. The frame has vertical and horizontal members that are joined at the intersections that fully encompass the operating and inactive leaves in a closed position. A flush set track assembly can exist in place of a sill assembly. Additional hinged and pivoting/folding leaves and/or a single-side hinged leaf can be included in the door system.
FootboltA locking rod device installed vertically in the stile or astragal of a door or screen which when activated secures the panel or screen in a stationary position.
Force To Latch Door The force required to close a door and fully engage the latch.
Forced-Entry Resistance  The ability of a window or door in the locked position to resist entry under a specified load and conditions.
FrameThe window frame is the head, jambs and sill that make up the exact opening where the window sash will fit. Window frames are available in a variety of different materials including wood, clad wood, aluminum, vinyl and fiberglass.
Frame ExpanderA flat aluminum extrusion used in conjunction with the 90 degree frame expander to provide a flat casing appearance for clad units.
French CasementA casement styled unit with two sash in one frame providing a sense of openness unrestricted by a vertical mullion or stiles when both sash are open.
French DoorFrench Doors are available in either inswinging or outswinging rectangular or arch top style choices.
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.
Fully Tempered Glass Glass that has been heat treated to a high surface and/or edge compression to meet the requirements of astm c1048 (kind ft) or can/cgsb 12.1.
Fusion Welded A generic term for welding processes that rely upon melting in order to join materials of similar compositions and melting points. Due to the high-temperature phase transitions inherent to these processes, a heat-affected zone is created in the material.
Garden Window A window consisting of a three-dimensional, five-sided structure, with provisions made for supporting plants in the enclosed space outside the plane of the wall. Operating sash are allowed but are not required.
Gas FillingA gas other than air, usually argon or krypton, placed between window or skylight glazing panes to reduce the U-factor by suppressing conduction and convection.
Glass A hard, brittle substance, usually transparent, made by fusing materials such as soda ash (na2co3), limestone (caco3), and sand under high temperatures.
Glass Size (Gs)The measurement of the actual glass, not the visible glass.
Glazing An infill material such as glass or plastic. The process of installing an infill material into a prepared opening in windows, doors, tdds, roof windows, ssps, or unit skylights.
Glazing BeadStrips of profiled wood or vinyl used to hold the glass in position in the sash. Wood glazing bead is attached to the rails and stiles of the sash using staples, small nails or vinyl barbs. A vinyl bead is held in place by extruded barbs positioned in the kerf. Aluminum caps may be used over the vinyl bead in some cases.
Glazing Channel Groove cut into sash for acceptance of glass.
Glazing Clip Metal clip for holding glass in a metal frame while putty is applied.
Glazing Gasket Special extruded plastic shape for attaching window glass to metal or masonry wall openings. It also serves as a cushion and insulator.
Glazing TapeA two sided adhesive tape placed between the glass rabbet and the glass and/or the glazing bead and glass of some unit types.
Glider/SliderHorizontal operating units which have one sash fixed while the other glides open and shut horizontally.
Gothic-Head Window Window topped with a pointed arch. It is not as tall and narrow as the pure gothic lancet window.
Grade See performance grade (pg).
Garden/ Greenhouse Window  A window consisting of a three-dimensional, five-sided structure, with provisions made for supporting plants in the enclosed space outside the plane of the wall. Operating sash are allowed but are not required.
GridsA window or door option where grids are placed between panes of insulating glass.
GrillesRemovable wood dividers made to simulate authentic divided lites. Grilles are often rectangular or diamond shaped and are easily removed for cleaning purposes. Grilles can be purchased for nearly all Marvin products.
HandingA term used to describe the right or left hand operation of a window or door.
Handle A component which enables the movement of a sash, leaf, or panel, or which activates a mechanism which locks or unlocks a sash, leaf, or panel.
Hanging Sash Sash hung on a cord connected to a counterweight.
Hardware All the necessary equipment to retain, operate, and lock or unlock the sash, leaf, or panel within the frame.
HDRExclusive solid composite creating strength comparable to that of titanium.
Head The horizontal member forming the top of the frame.
Head Flashing Flashing installed in a wall over a window.
HeadboltA locking rod device installed vertically in the stile or astragal of a door or screen which when activated secures the door in a stationary position.
HeaderSupporting member or beam above window opening which transfers building weight above to the supporting wall structure on each side of the window. The term header is generally in reference to a wood beam, whereas “lintel” often refers to a steel beam.
Heat GainThe similar transfer of heat from outside to inside. Both heat loss and heat gain are measured in terms of the fuel consumption required to maintain a comfortable indoor temperature.
Heat LossThe transfer of heat from inside to outside by means of conduction, convection, and radiation through all surfaces of the house.
Heat Treated See fully tempered glass and heat-strengthened glass.
Heat-Strengthened Glass Glass which is reheated, after forming, just below melting point and then cooled. A compressed surface is formed which increases its strength. Used for spandrel glass.
Hermetically Sealed UnitAn insulating glass unit made up of two lites of glass, separated by a roll formed aluminum spacer tube (at the full perimeter) which is filled with a moisture absorbing material. The unit is then completely sealed, creating a moisture-free, clean dead air space.
Hinged Rescue Window Any window that is mounted into a stationary perimeter frame and is permanently hinged at one jamb.
HistoricalA term used to define a window or door product meeting the requirements of historical renovation standards.
Hopper Window A combination of frame and sash, hinged at the bottom of the vertical jambs which allows the unit to pivot from the bottom with the sash opening to the exterior of the building.
Horizontal Sliding Window A window that consists of one or more sash that slide or roll horizontally within a common frame and can also contain fixed lites/sash.
Hung Window A window consisting of vertically sliding sash which utilize counterbalancing devices to allow the sash to be opened to any variable position between its fully open and fully closed limits. See also vertical sliding window.
IGCCInsulating Glass Certification Council
Inactive PanelSecondary operating door panel.
Inoperable No longer opening, closing, locking, or unlocking as originally designed.
Insulating GlassInsulating glass refers to two pieces of glass spaced apart and hermetically sealed to form a single-glazed unit with an air space between. Heat transmission through this type of glass may be as low as half that without such an air space. It is also called Double Glazing
Insulating Glass Unit  Two or more lites of glass spaced apart and hermetically sealed to form a single unit with an air- or gas-filled space between each lite.
Inswing French DoorA French door with panels that swing to the inside. One, two, three and four panel units available as stationary or operating.
Integral Mullion A horizontal or vertical member which is bounded at either end or both ends by crossing frame members.
Integral Ventilating System/Device An apparatus that is independent from but installed into a window, door, or unit skylight product for the purpose of controlling the transfer of air through the window, door, or unit skylight product.
InterlockAn upright frame member of a panel in a window which engages with a corresponding member in an adjacent panel when the window is closed. An interlock on a window or door provides a hooking action between the sash rails reducing air infiltration and increasing security. (an overlap)
Interior Accessory Window  A glazed frame and/or sash, attached inboard of existing prime windows, curtain wall, or storefront, in commercial buildings, to enhance control of thermal transmittance, solar heat gain, sound, air leakage, and/or daylight. Iaws are not intended for occupant operation or to be used with the exterior windows in the open position, nor are they intended to provide any specific resistance to air leakage or water penetration, or withstand structural load.
Interior CasingThe casing trim used on the interior perimeter of the window or door. Generally supplied by others except in the case of round top casing which is factory supplied.
Interior Door A door system not intended for use in exterior applications.
Interior Glazed Glazing installed from inside of the building structure.
Interior Window A window system not intended for use in exterior applications.
Jal-Awning Window A window consisting of a multiplicity of top-hinged sash arranged in a vertical series within a common frame, each operated by its own control device which swings the bottom edges of the sash outward. See also jalousie window and tropical awning window.
Jalousie Window A window consisting of a series of overlapping horizontal frameless louvers which pivot simultaneously in a common frame and are actuated by one or more operating devices so that the bottom edge of each louver swings outward and the top edge swings inward during operation.
Jamb Depth Width of the window frame from inside to outside.
Jamb ExtensionA jamb-like member, usually surfaced on four sides, which increases or extends the depth of the exterior or interior window or door frame; jamb extensions imply a larger depth than “wood jamb liners.”
Jamb LinerThin strips of wood attached to the head jamb, side jambs and sill to accommodate various wall thicknesses. Common jamb depths are: 4 9/16″, 4 13/16″, 5 1/16″ and 5 3/16″.
Jambs The upright or vertical members forming the side of the frame.
Keyed Cylinder LockA lock providing an exterior entry and locking convenience.
Krypton GasInert gas known for its ability to provide insulating properties in a small air space.
Label A projecting molding by the sides and over the top of an opening.
Label Stop Ornamental projection on each end of a label, sill, or sill course. Often takes the shape of a gargoyle or other decorative carving.
Laminated GlassGlass composed of two sheets of glass fused together with a sheet of transparent plastic between the sheets. When broken laminated glass will generally not leave the opening.
LaminatingA method of gluing strips of thin clear wood to the lengthwise surfaces of finger jointed material to provide the appearance of clear stock.
Lancet Window Tall, narrow window with a pointed-arch top, often with leaded diamond shaped lights; characteristic of gothic architecture.
Lattice Window  Window with glazing bars set diagonally.
Lead Light  Window with small panes of glass set in grooved rods of cast lead or came. The glass may be clear, colored, or stained.
Leaf A part of a side-hinged door system, glazed or unglazed, surrounded by a frame. Leaves can be fixed in place (non-operable) or movable (operable).
Lever LockA lever handle and lever arm operator available as an option on awning units.
Lift RailThe bottom part of the sash on a double or single hung window designed with an integrated method of lifting the operating sash.
Limited Water   That the water penetration resistance performance is achieved by testing at a pressure less than the minimum test pressure required for the indicated performance class and performance grade (pg).
Lintel Horizontal member (wood, steel, or stone) over a window opening to support the weight of the wall above. A header.
Lite  A pane of glass or an insulating glass (ig) unit used in a window, door, tdd, roof window, ssp, or unit skylight. Frequently spelled “lite” in industry literature to avoid confusion with visible light.
LocksetA complete door lock system comprised of the lock mechanism together with knobs, keys, plates, strikes and other accessories.
Loop Window  A long and narrow vertical opening, usually widening inward, cut in a medieval wall, parapet, or fortification for use by archers. Modifications appear in romanesque revival architecture.
Long Wave InfraredA hot automobile dashboard or a hot sidewalk or roadway where you can often see heat radiating from the surface is an example of long wave infrared.
Low-conductance SpacersAn assembly of materials designed to reduce heat transfer at the edge of an insulating window. Spacers are placed between the panes of glass in a double- or triple-glazed window.
Low E GlassLow E stands for low emissivity. The lower the emissivity the higher the percentage of long-wave radiation blocked thereby improving thermal performance. Low E glass is coated with a thin microscopic, virtually invisible, metal or metallic oxide layer. The primary function is to reduce the U-value by suppressing radiative heat flow. A secondary feature is the blocking of short wave radiation to impede heat gain. There are two basic types of Low E glass. The first, vacuum or sputter coated Low E, is referred to as soft-coat (See Low E II definition). The second is pyrolytic Low E, commonly referred to as hard-coat. (See pyrolytic definition.)
Low E Ii GlassA high performance Low E glass, providing the best winter U-value and warmest center glass. It offers significant improvement in reducing solar heat gain coefficient values, providing customers one of the coolest summer glass temperatures of all Low E products. Additionally, ultraviolet light transmission is greatly reduced. The Low E II coated glass products are specifically designed for insulating glass units normally as a second surface coating. See Low E and pyrolitic definitions.
Manufacturer A company which fabricates and/or assembles one or more parts, components, and/or accessories or supplies entire fenestration systems.
Masonry OpeningA brick, stone or block opening into which a window or door unit is installed including the outside casing.
Meeting Rail One of the two adjacent horizontal sash members that come together when in the closed position.
Meeting Stile One of the two adjacent vertical leaf, sash, or panel members that come together when in the closed position.
Minimum Gateway Test Size The test specimen size specified to enter a performance class at the lowest or minimum level.
Moisture Content The percentage of dry weight that is composed of water, such as in wood.
Mold Stone  A stone that serves as a window jamb.
MullingThe act of attaching two or more window or door units together. The joint is then finished with a mullion center cap or mull trim.
MullionAn intermediate connecting member used to “marry” two or more windows or patio doors together in a single rough opening without sacrificing air or watertight performance. A mullion also can give added strength to the connection for structural stability.
Mullion ReinforcementThe 3/8″ mullion reinforcement is designed to be used on wood or clad multiple casement, awning and direct glaze assemblies to improve structural performance.
Mullion Stiffener An additional reinforcing member used in a reinforcing mullion. Mullion stiffeners carry the entire load or share the load with adjacent framing members.
Multi-Lock HardwareAn adjustable lock system used on the French Casement to ensure a tight seal of the sash frame components. It also provides a secure locking system.
Multi-Point Locking SystemA line of standard or optional multiple point locking mechanisms installed on the operative panel(s)/ sash of various Marvin products to enhance security and performance.
Multiple Glazing Panel  A glazed panel that can be installed in or on a sash, leaf, or panel on either the interior side or exterior side of the primary glazing. An mgp is tested only in conjunction with a specific primary window or door.
Muntins A decorative design in cut-ups of glass lites, such as painted muntin grids (enamelite) applied to an interior lite of glass in a sealed insulating glass unit to simulate cut-ups of glass lites either in colonial or diamond patterns, or use of aluminum muntin bar between lites of glass in a sealed insulating glass unit to simulate glass cut-ups, or use of actual vertical and horizontal bars to divide windows into smaller lites of glass. The bars are termed muntin bars.
Nailing FinAn integral extension of a window or patio door frame that generally laps over the conventional stud construction and through which nails are driven to secure the frame in place.
Negative Pressure Pressure acting in the outward direction.
New ConstructionWindows or doors designed for installation in new construction.  Windows typically have a nailing fin.
NFRCThe National Fenestration Rating Council gives consumers energy performance ratings and other useful information about windows, doors, and skylights.
Non-Hung Window A window consisting of vertically sliding sash which utilize mechanical retainers or slide bolts to allow the sash to be opened to any one of the pre-selected positions between its fully open and fully closed limits. See also vertical sliding window.
Non-Keyed CylinderA handle without a keyed cylinder. The door cannot be locked from the exterior.
Non-Operable Intended to not open or close.
Obscure GlassGlass formed by running molten glass through special rollers. These rollers have a pattern on them causing the glass to become patterned and thus obscure.
Ogee Curve  Reverse flex curve commonly found in window moldings and trim pieces.
One-Wide (1W)The current term used to describe one frame with single or multiple sash or panels.
Operable Intended to be opened and closed.
Operable Transom Panel usually glazed over a door which may be opened for ventilation.
Operable Window Window that can be opened for ventilation.
Operating Force The force required to initiate or maintain a sash, leaf, or panel motion in either the opening or closing direction.
OperationOur drawings always illustrate the window sash or door panels as if you are looking at it from the exterior. X means operating, O means stationary.
OperatorAn operating sash, panel or unit.
Oriel Window This is a double or single hung window with an unequal top and bottom sash where the top sash is greater in height than the lower sash.
OSMOutside measurement.
Outdoor-Indoor Transmission Class  A single-number rating calculated in accordance with astm e1332, using values of outdoor-indoor transmission loss, that provides an estimate of the sound insulation performance of a facade or building elements.
Outswing French DoorA French door with panels that swing to the outside. One, two, three, or four panel units available as stationary or operating.
Overall Dimensions The external height and width of the product, expressed in millimeters or inches.
OXThe letters OX or XO identify the operation of window or door units as viewed from the exterior. The letter O stands for stationary while the letter X stands for operating.
Palladian Window Tripartite window by the 16th century italian architect andrea palladio.
PaneOne of the compartments of a door or window consisting of a single sheet of glass in a frame; also, a sheet of glass.
Panel The members of a sliding door or sliding door side lite within a frame which are designed to accommodate the glazing.
Panel Window A form of picture window consisting of several sash or fixed glazings, separated by crossbars or mullions–or both.
PanningA term used to describe the aluminum covering extrusion components (i.e. Jambs, sill and head jamb.
Parallel Opening Window A window consisting of an operable sash that moves outward in a horizontal direction perpendicular to the plane of the frame for the purpose of ventilation. The sash remains parallel to the frame throughout its range of motion.
Part StopA strip of wood with weather-stripping attached which prevents air and water infiltration. Part stops are commonly found at the head jamb of a double hung unit.
Parting Bead  A vertical strip on each jamb that separates the sashes of a double-hung window.
Parting Slip A thin wood strip separating the sash weights in the weight box of each jamb of old double-hung windows.
Passive Door One or more hinged leaves or sliding door panels that are normally held inactive by latching or locking hardware, but can become active on the release of the latching or locking hardware.
Performance Class One of the five performance classes (r, lc, cw, aw, and sk) within the classification system that provides for several levels of performance.
Performance Grade  A numeric designator that defines the performance of a product in accordance with this standard/specification.
Picture Window The picture window is stationary and framed so that it is usually, but not always, longer horizontally than vertically to provide a panoramic view.
Pivot An axis or the hardware about which a window, sash, panel, or leaf rotates.
Pivoted Window A window consisting of a sash which pivots about an axis within the frame. The pivoting action of the window allows for easy access to clean the outside surfaces of the window. Two common types are the 180° compression seal pivoting window and the 360° pivoting window.
Plastic Glazing Plastic infill materials (including, but not limited to, acrylic, co-polyester, fiberglass-reinforced plastic, and polycarbonate) that are glazed or set in a frame or sash.
Plate GlassPolished plate glass is a rolled, ground and polished product with true flat parallel plane surfaces affording excellent vision. It has less surface polish than sheet glass and is available in thickness varying from 1/4″ to 1-1/4″. Now replaced by float glass.
Plinth BlockA decorative wood block placed between the vertical casing and the top casing of a unit to provide an elegant interior casing profile.
Pole CrankAn aluminum extension pole used to open or close roof windows or awnings which would be inaccessible because of their height.
PolygonA high level term used to describe triangles, trapezoids, pentagons, hexagons and octagons.
Polyvinylchloride (PVC)An extruded or molded plastic material used for window framing and as a thermal barrier for aluminum windows.
Positive Pressure Pressure acting in the inward direction.
Primary Door That door in a dual-door system so designated by the manufacturer, capable of protecting the building’s interior from climatic elements (as opposed to a secondary door used mainly for performance enhancement).
Primary Window That window in a dual-window unit so designated by the manufacturer, capable of protecting the building’s interior from climatic elements (as opposed to a secondary window used mainly for performance enhancement).
PrimeThe first coat of paint in an application that consists of two or more coats; also refers to the paint used for such an initial coat – primer.
Prime Sash Balanced or moving sash of a window unit.
Projected Window Awning type window that swings either inwards or outwards at the top or the bottom.
PultrusionLineal profiles of constant cross section manufactured by combining plastic resin and continuous glass fiber reinforcement. These thermally insulating and structural components are ideally suited for applications where strength, thermal stability and weather resistance are required, such as in patio door frames and commercial windows.
Pyrolytic Low E Glass (Hardcoat)Pyrolytic Low-E is designed to be used either in non-insulating applications such as energy panels that have exposed surfaces or for insulating glass applications. In some northern climatic situations where an application or customer requires increased solar heat gain, over Low E II performance, this is a desirable option. This increased solar heat gain which is desirable in winter may increase summer energy costs if the home is air conditioned. The pyrolytic coating is typically applied to the second surface, but can be applied to the third surface to provide increased solar heat gain.
Q-IV Locking SystemThe system of incorporating a 4-point steel locking mechanism in Winchester Bristol windows.
Queen Anne Window A window with small glass windows or lights arranged in various forms, usually only on the upper sash. Appeared 1870s.
R-ValueThe resistance a material has to heat flow. Higher numbers indicate greater insulating capabilities. A measure of resistance to heat gain or loss. R-Values rather than thicknesses can be compared for different materials, since 6″ of fiberglass (R-19) might compare with 12″ of wood or 18′ of stone.
RadiusThe length of an imaginary line from the center point of a circle to the arc or circumference of a circle.
RailsThe cross or horizontal members of the framework of a sash, door or other panel assembly.
Reglet Plastic or wood molding put in a concrete or masonry opening for a uniform groove for a spline-type gasket to hold window glass.
Reinforcement The material added to individual sash, leaf, panel, or frame members to increase strength and/or stiffness.
Reinforcing Mullion A horizontal or vertical member with an added continuous mullion stiffener and joining two or more individual fenestration units along the sides of the mullion stiffener.
Relief KerfKerfs machined into the frame parts of a unit. Relief kerfs inhibit warping.
ReplacementWindows and doors designed to replace and exsisting unit.
RESFENA computer program used to calculate energy use based on window selection in residential buildings.
Retro-SizingRefers to units which are sized for replacement purposes.
Revolving Door An exterior door consisting of two or more leaves that pivot about a common vertical axis within a cylindrically shaped vestibule.
Rolled AluminumA term used to describe aluminum profiles for screen and energy panel surrounds which are fabricated by the use of a roller or series of rollers to produce a desired profile. All other Marvin profiles are fashioned by the extrusion method.
Roller CamsThe adjustable roller devices of the Multi-Lock hardware installed on the sash of the French Casement unit. When adjusted properly with an Allen wrench, they ensure a tight seal between the sash and frame members.
Roof Window A sloped application of a fenestration product that provides for in-reach operation. Note: roof windows used for emergency escape and rescue usually have a balanced sash.
RoseA circular cover plate attached to the stile directly behind a knob or door handle. May be plain or have a decorative design embossed into the cover.
Roto-GearA term used to describe the steel drive worm, gears and crank device used for opening awnings and casements.
Rough OpeningThe opening in the wall where a window or door unit is to be installed. Openings are larger than the size of the unit to allow room for insulation and to shim the unit square.
Round TopGenerally a semicircle window which is mulled to the top of another window or door, thus forming the round top appearance. There are full round tops, separated round tops, ellipticals, transoms, inverted corners, ovals and Gothic heads, etc. Round tops can be used separately or combined with other units to create a seemingly endless selection.
Saddle Bar Light steel bar placed horizontally across a window to stiffen leaded glazing.
Saddle Bead Glazing bead for securing two panes.
Safety Glass A strengthened or reinforced glass that is less subject to breakage or splintering, such as glass for doors, unit skylights, and some windows. See also fully tempered glass and laminated glass.
Sash The members of a window, secondary storm product, or unit skylight that fit within a frame which are designed to accommodate the glazing.
Sash LimiterAn optional metal device which attaches to a casement sill and bottom rail which limits the sash to a specified opening -5, 10, 15 or 20 degrees.
Sash LockA locking device which holds a window shut, such as a lock at the check rails of a double hung unit. Larger units utilize two locks.
Sash Opening (SO)The opening between wood frame members for both height and width (disregarding any jamb hardware tracks)
Sash Retainer PlateA nylon retainer plate used on double hung and Magnum Double Hung sash to secure the bottom sash.
Sash WidthHorizontal measurement across the face of a sash.
Screen A product that is used with a window, door, secondary storm product, or unit skylight, consists of a mesh of wire or plastic material used to keep out insects, and is not for providing security or retention of objects or persons from the interior.
Screen OM (Outside Measurement)The width and the height of a screen including wood or metal surrounds.
ScreensA close-mesh woven screen material of metal or fiberglass attached to an aluminum or wood surround. Screens inhibit entry of insects, yet permit light, air and vision.Window and door products utilize full or Half-screens.
Sealant A compressible plastic material used to seal any opening or junction of two parts, such as between the glass and a metal sash, commonly made of silicone, butyl tape, or polysulfide.
Secondary Door That door in a dual-door system so designated by the manufacturer, used on the exterior of, or interior of, and in tandem with, a primary door designated by the manufacturer to be used for the purpose of performance enhancement, and not to be used by itself as a primary door.
Secondary Storm Product  A door, window, or skylight product intended to be used only in conjunction with a primary door, window, or skylight product for the purpose of enhancement of performance in a system with the primary product. A secondary storm product can be attached to the internal or external frame or sash of the primary product. A secondary storm product is also considered a secondary door or window.
Secondary Window That window in a dual-window unit so designated by the manufacturer, used on the exterior of, or interior of, and in tandem with, a primary window for the purpose of performance enhancement, and not to be used by itself as a primary window.
Sequential Locking SystemAn exclusive Marvin design used on casements for locking the sash to the frame. The action is sequential where the lower lock activates first moving the sash to the weatherstrip; the top then engages to snug the sash to the frame.
Serviceable Accessible without major reconstruction of the window, door, ssp, tdd, roof window, or unit skylight.
Setting Block A device or member that supports the weight of the glazing and is in direct contact with an edge of the glazing after final installation.
Shading Coefficient (SC) Decimal value which is the solar gain of a window, divided by the solar gain for a clear single-glass window of the same size. The shading coefficient of clear, double-glazing is about 0.85 to 0.9.
Short Wave InfraredShort wave infrared energy comes directly from the sun, but is not felt as heat. It converts into heat when it strikes something.
Side JambThe side (vertical) member of a frame.
Side Lite An operable or non-operable product that is designed to be a companion product installed on one or both sides of an operable door or a fixed door. Side lites often have their own separate frame or are contained within the frame of a composite assembly.
Side-Hinged  Window A window that consists of sash hinged at the jambs that swings inward using exposed butt hinges or concealed butt hinges, and in some cases friction hinges. It is used primarily for cleaning or emergency escape and rescue purposes, but not for ventilation other than in the case of emergency. The gateway test size is larger than for casement windows, but otherwise the same requirements are met. See also hinged rescue window and top-hinged window.
Side-Hinged Door System A door system having, at a minimum, a hinge attachment of any type between a leaf and jamb, mullion, or edge of another leaf but having a single, fixed vertical axis about which the leaf rotates between open and closed positions. These systems include, at a minimum, a single operating leaf, surrounding frame, and components. The surrounding frame has vertical and horizontal members that are joined at the intersections and fully encompass the operating and/or fixed leaf/leaves. Note: additional operating, passive and/or fixed leaves, side lites, transoms, framing, and mullions are often included.
SideliteAn operable or non-operable product that is designed to be a companion product installed on one or both sides of an operable door or a fixed door. Side lites often have their own separate frame or are contained within the frame of a composite assembly.
SillThe horizontal member forming the bottom of a window or exterior door frame; the lowest member of the frame of a structure, resting on the foundation and supporting the frame.
Sill Drip Molding Sill member on a window frame serving as a screen stop; also the extension of the sill that contains the drip cut.
Sill ExtenderThe sill extender, also called the apron, is attached to the bottom of the window to cover the gap between the sill and the opening.
Sill-HornThe extension of the lip of a window sill to the outside edge of the casing.
Sill TrackThe track provided at the sill of a sliding glass door. Also, the sill member incorporating such a track.
Single Glazing Glazing that is just one layer of glass or other glazing material.
Single Hung WindowA window very similar to a double hung window, except that the top sash is stationary or non-operable.
Slider See horizontal sliding window.
Sliding Door A door that consists of manually operated door panels, one or more of which slide or roll horizontally within a common frame, and can also contain fixed lites/panels. Note: typically, operating panels are identified with an (x) and fixed lites or fixed panels are identified with an (o).
Sliding French DoorA sliding door utilizing French door style panels.
SlopeThe measure of the tilt of a line; rise over run.
Sloped Glazing  A glass and framing assembly that is sloped more than 15° from the vertical and which forms essentially the entire roof of the structure.
Smart WindowGeneric term for windows with switchable coatings to control solar gain.
SnubberAn interlocking metal bracket attached at the center of the hinge side of a casement sash and frame with a call number height of 40″ or more and both sides of an Awning sash and frame with a call number height of 48″ or more. It pulls the sash tightly against the frame weather-strip to maximize performance.
Soft Coat Solar Ban 60The coating is applied to pre-cut glass (usually in stock sheets for further fabrication) in a vacuum chamber at ambient plant temperatures. MSVD coatings such as Sungate® 400 and Solarban® 60 low-e glasses offer lower emissivity and superior solar control versus pyrolytic (hard coat) coatings.
Solar Heat Gain Coefficient (SHGC) Measures how well a window blocks (or shades) the heat from sunlight. SHGC is the fraction of solar radiation transmitted through a window or skylight, as well as the amount that is absorbed by the glass and re-radiated to the interior. SHGC is expressed as a number between 0 and 1. The lower a window’s SHGC, the less solar heat it transmits and the greater its shading ability. The SHGC is similar to the SC, but also accounts for absorbed, convected, and inwardly radiated solar energy.
Solid Frame Window frame made from a single piece of lumber.
Sound Transmission Class  (STC)A single-number rating calculated in accordance with astm e413, using sound transmission loss values, that provides an estimate of the sound insulation performance of an interior partition in certain common sound insulation problems. Note: the frequency range used is typical of indoor office noises.
Spacer The linear material that separates and maintains the space between the glass surfaces of insulating glass units.
Span The clear distance measured parallel to the length of a mullion or divider between support points.
Spandrel The opaque areas of a building envelope which typically occur at locations of floor slabs, columns, and immediately below roof areas.
Specification A written document often accompanying architectural drawings, giving such details as scope of work, materials to be used, installation method, required performance, and quality of work for work under contract.
Spectrally Selective CoatingA coated or tinted glazing with optical properties that are transparent to some wavelengths of energy and reflective to others. Typical spectrally selective coatings are transparent to visible light and reflect short-wave and long-wave infrared radiation.
Splayed Window Window unit set at an angle in a wall.
Square FootFor measuring the area of a unit. RO width (in inches) x RO height (in inches) divided by 144 equals the area in square feet of a unit.
Stabilizer ArmAn optional piece of hardware for the Tilt-Turn window which is attached to the header and top rail corner drive on the handle side to limit the travel of the sash when operated in the tilt mode. It is automatically disengaged when the sash is swung in the turn mode.
StarburstA semi-elliptical area, the lower center is the point where the dividing spokes meet and radiate outward. May be constructed of glazed sash, removable grilles, ADL or SDL.
StationaryA non-operating sash, panel or unit.
Stationary Sash BracketA 90 degree L bracket used to secure stationary casement and awning sash to the frame. The sash can be removed for replacement by removing the wood stops and bracket screws.
StilesThe upright or vertical perimeter pieces of a sash, panel or screen.
StoolA horizontal trim member that laps the window sill above the apron and extends beyond the interior casing. See apron entry.
Storefront A non-residential, non-load-bearing assembly of commercial entrance systems and windows usually spanning between the floor and the structure above, designed for high use/abuse and strength.
Storm Clip Device attached to the muntin of a metal sash to stop the pane from moving outwards.
Storm Door See secondary door.
Storm SashA wood framed assembly containing non-removable glass. The storm sash is removed during the summer and replaced with a wood framed screen.
Storm Window See secondary window.
Structural Masonry BracketsAn installation bracket used with multiple high/wide window units or large doors for added structural support. The brackets are also used to attach the unit in the rough opening in lieu of nailing through the casing, thus eliminating unsightly nail holes.
Structural Test Pressure  The pressure differential applied to a window, door system, tdd, roof window, ssp, or unit skylight.note: structural test pressure (stp) is not to be confused with design pressure (dp) or performance grade (pg).
Sub-SillThe supplemental member of a frame used under most awning and casement units as an additional sill with the primary purpose being to hold multiple units together at the sill.
Summer Day U-ValueThe calculation of U-Value using Summer Daytime environmental conditions of a hot outside temperature and direct sunlight.
SunburstA semi-elliptical area, the lower center of which contains a sun-like figure with sun rays radiating therefrom. May be constructed of glazed sash, removable grilles, ADL or SDL.
Sunroom A multi-sided structure consisting of a high percentage of glazed area versus framing area.
SurroundAn attractive, protective trim which is secured to an energy panel by an adhesive or vinyl barb to give the glass panel a safe finished edge. Also the aluminum framework for most standard screens.
System The parts, components, hardware, and/or accessories that yield a complete, fully functional assembly.
Tempered GlassFloat glass panels heated and then cooled rapidly in a controlled environment. This process makes the glass several times stronger than regular glass. It also makes it safer because when broken it yields small pebble-like fragments.
TemplateA pattern of a window unit from which dimensions and measurements can be determined. Round Tops require templates for replacement units.
Test Specimen A complete, fully functioning window, door, ssp, tdd, roof window, or unit skylight supplied by the applicant and fitted in the test apparatus in accordance with the manufacturer’s written installation instructions (including the manufacturer’s instructions for clearance, shimming, and anchoring).
Tilt LatchMechanism at the top of each sash which allows for inward movement for cleaning as well as removal purposes.
Thermal Barrier An element made of material with relatively low thermal conductivity, which is inserted between two members having high thermal conductivity, in order to reduce the heat transfer.
Thermoplastic A polymer material that turns to liquid when heated and becomes solid when cooled and is able to repeat these processes.
Three-Wide (3W)Current term referring to any product or unit when three frames (i.e. Separate jambs) are mulled together as a multiple unit.
ThresholdThe member that lies at the bottom of a sliding glass door or swinging door; the sill of a doorway.
Tinted GlassA mineral admixture is incorporated in the glass, resulting in a degree of tinting. Any tinting reduces both visual and radiant transmittance.
Top-Hinged Window A window consisting of sash hinged at the head which swings inward or outward using a continuous top hinge or individual hinges, primarily for cleaning or emergency escape and rescue purposes and not for ventilation.
Torsion The twist induced in a product by the application of a static load to an extreme free corner of that product and normal to its plane.
TransmittanceThe fraction of radiant energy that, having entered a layer of absorbing matter, reaches its farther boundary.
Transom An operable or non-operable product that is designed to be a companion product installed above a fenestration product. Note: transoms often have their own separate frame or are contained within the frame of a composite unit.
Tributary Width The width of wind-bearing area contributing to the load on a mullion or divider.
TrimlineA wood or clad patio door having two or three glass panels; one panel operates. Formerly known as a Wood Retro (WR) or Clad Retro (CR) door. The door features a multi-point locking system.
Triple GlazingThree panes of glass or suspended film with two air spaces between.
Triple Window Generally refers to any tripartite group of windows with square heads. Found on colonial revival houses. Units suggest palladian windows but are less expensive to construct.
Tropical Awning Window A window consisting of one or more top-hinged or pivoted sash that swing outward at the bottom edge and are operated by one control device that securely closes them at both jambs without the use of any additional manually controlled locking devices.
True Divided Lite  A lite in which dividers (muntins) separate the glazing into individual smaller glazing lites.
Tubular Daylighting Device  A non-operable fenestration unit primarily designed to transmit daylight from a roof surface to an interior space via a closed-end tubular conduit. The basic unit generally consists of an exterior glazed weathering surface, a light-transmitting tube with a reflective inner surface, and an interior closure glazing in a retainer frame. The interior closure glazing is generally sealed. A tdd product line can be tested and rated in either or both of the following configurations: (a) closed ceiling (cc): the tubular conduit passes through unconditioned space. (b) open ceiling (oc): the tubular conduit is suspended in conditioned space.
Turn ButtonA vinyl or aluminum button and screw. Buttons are used to secure wood combinations, storm sash and wood screens to the exterior casing or energy panels to the sash or door panel.
Two-Wide (2W)Current term referring to any product or unit when two frames (i.e. Separate jambs) are mulled together as a multiple unit.
U-FactorA measure of total heat flow through a window or door barrier from room air to outside air. Lower numbers indicate greater insulating capabilities.
U-ValueA measure of the insulating characteristics of the glass or how much heat gain or loss occurs through the glass due to the difference between indoor and outdoor temperatures. The lower the number, the better the insulating performance. This number is the reciprocal of the R-Value.
Ultraviolet (UV)The invisible rays of the spectrum which are outside of the visible spectrum at its violet end. U.V. rays are found in everyday sunlight and can cause fading or chalking of dark paint finishes. Extreme U.V. exposure can cause certain plastic materials to distort.
UnitOne single product such as a one wide casement.
Unit Skylight A complete factory-assembled glass- or plastic-glazed fenestration unit consisting of not more than one panel of glass or plastic installed in a sloped or horizontal orientation primarily for natural daylighting. Unit skylights are either fixed (non-operable) or venting (operable).
V-GrooveA decorative pattern which is “grooved” into the glass using a special process.
Vehicular-Access Door A door that is used for vehicular traffic at entrances of buildings such as garages, loading docks, parking lots, factories, and industrial plants, and is not generally used for pedestrian traffic.
Venetian Window Same as palladian window.
Vertical Fenestration Fenestration products that are installed at an angle less than 15° from vertical.
Vertical Sliding Window A hung or non-hung window consisting of at least one manually operated sash that slides vertically within a common frame.
View Sash Picture window with the lights divided by muntins.
VinylPolyvinyl chloride material that can be both rigid and flexible, used in glazing channels, weather stripping and/or frame materials of both windows and doors.
Vinyl Glazing BeadA vinyl extrusion used on clad units which serves the same purpose as a wood glazing bead for wood units.
Visible Light Transmittance (VLT)The percentage of the visible spectrum of sunlight that is passing through a piece of glass. It is expressed as a figure between 0 and 100 – a glass with a VLT of 0 would transmit no sunlight whatsoever, while a glass with a VLT of 100 would transmit all of the sun’s light.
Warm-edge Technology The use of low-conductance spacers to reduce heat transfer near the edge of insulated glazing.
Wash Cut Beveled cut in a stone sill to divert water.
Water Drip Molding sometimes used on exterior surfaces of an in-swinging casement sash to prevent water from being driven over the sill.
Water Penetration Penetration of water beyond the plane intersecting the innermost projection of the test specimen, not including interior trim and hardware, under the specified conditions of air pressure difference across the specimen.
Weatherstrip  A strip of resilient material for covering the joint between the window sash and frame in order to reduce air leaks and prevent water from entering the structure.
Weep Cut  Groove in the underside of a horizontal board or masonry unit which projects beyond the wall service below to prevent water from moving back toward the wall surface
Welded When materials are fused by heat to become one when cooled.
Weephole  A small opening in a wall or window member through which water may drain to the building exterior.
Weep SystemA system of tiny holes in the windowsill that allows water condensation to escape outside rather than inside the house.
Wet GlazingA method of sealed glass in a frame by use of a knife or gun-applied glazing compound or sealant.
Window An operable or non-operable assembly that is installed in an opening within an exterior wall or roof intended to admit light or air to an enclosure, and is usually framed and glazed. Note: windows are typically designed to accommodate factory fabrication and glazing.
Window & Door Manufacturers Association (WDMA)The Window & Door Manufacturers Association defines the standards of excellence in the residential and commercial window, door and skylight industry and advances these standards among industry members while providing resources, education and professional programs designed to advance industry businesses and provide greater value for their customers. (see
Window Wall A non-load-bearing fenestration system provided in combination assemblies and composite units, including transparent vision panels and/or opaque glass or metal panels, which span from the top of a floor slab to the underside of the next higher floor slab.
Winter Night U-ValueThe calculation of U-Value using Winter Nighttime environmental conditions of a cold outside temperature and no sunlight.
Yoke Head window jamb in a box window frame.