Window Glossary

We’ve compiled this glossary to serve as a handy reference for window and door industry terminology.


ACCESSORY GROOVE: A serrated groove extruded into the window frame that is designed to receive a number of accessory profiles typically used to complete or aid installation of the window.

ANNEALED GLASS: Sheet glass used as a glazing product. Further processing is required to transform annealed glass into safety glass.

APRON: A piece of horizontal sash or window trim applied against the wall immediately below the stool; serves to conceal the joint between the window frame sill and the plaster on interior finish surface.

AWNING WINDOW: A projecting window, hinged at the top, opening up and out like an awning.

ASTRAGAL: An interior moulding (molding) attached to one of a pair of doors or sash in order to prevent swinging through; also used with sliding doors to insure tighter fitting where the doors meet; also a small semi-circular molding or bead encircling a column or post below the capital or cap.

  • Flat astragal – a non-rabbeted astragal applied to swing doors; the astragal is applied to the face of the meeting stile of one of the doors.
  • Sliding astragal – an astragal so worked so as to cover the meeting joint of sliding doors.
  • T-astragal – an astragal, T-like in shape, which is rabbeted to the approximate thickness of the swinging door.

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BACKER ROD: A material placed into a joint, primarily to control the depth of the sealant. Also serves as a bond breaker.

BALANCE SHOE: Part attached to bottom of balance that attaches balance to sash. A bar or pin on the sash fits in a “slot” in the shoe.

BALANCE SPRING: A device for counterbalancing a sliding vertical sash, generally associated with a double-hung or single-hung window, so that it can be held open at a position. See Sash Balance.

BASEMENT SASH UNIT: (cellar sash unit) – A sash unit, usually of the in swinging or hopper sash type, used for basement or cellar sash openings; usually consists of one, two or three glass lites (lights); may include screens and storm panels.

BAY WINDOW: Composed of three or more individual windows, generally with the side or flanker units at 45° or 30° angles to the wall of the structure.

BEAD: A sealant after application in a joint irrespective of the method of application, such as sealant bead, glazing bead, etc. Per ASTM E 631, n – in glazing, (1) a strip of metal, wood or plastic used around the periphery of a pane of glass to secure it in place. (2) a strip of sealant, glazing compounds or putty.

BEVEL: A machine angle other than a right angle, i.e., a 3 bevel is equivalent to a 1/8-inch drop in a 2-inch span (1mm in 16mm).

BLIND STOP: A sash or window frame member applied to the exterior vertical edge of the side and head jamb in order to serve as a stop for the top sash and to form with the brick moulding and/or casing a rabbet for the storm sash, screens, blinds and shutters.

BOTTOM RAIL: The bottom horizontal member of a window sash.

BOW WINDOW: Composed of three or more individual windows in a gently curved contour. Bow windows also project from the wall of the structure.

BUCK: A jamb stud or header; wood buck. Rough framework to which a window or door is installed.

BUCK OPENING: The opening in a wall formed by the rough framing members; also stud opening.

BUTT JOINT: A joint formed by square edge surfaces (ends, edges, faces) coming together; end butt joint, edge butt joint.

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CAMING: Grooved, usually H-shaped, rod of cast lead used, as in stained glass, to hold the panes or pieces of glass together.

CAP / CAPPING: Cosmetic covering, usually found on the exterior of the window or door to achieve aesthetic sight lines or to integrate the window or door system into the building surface or weatherproofing system. If panning is being used for weatherability, the panning is not considered cosmetic, but part of the window system.

CASEMENT WINDOW: A projecting window with a single sash hinged at the sides and usually opening outward like a door and operated by a (crank) handle, which turns to open or close the unit.

CASING (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.

CHLORINATED PVC: Produced by the post chlorination of polyvinyl chloride resins. Used extensively in pipe, fittings, and valves in water piping systems.

CIRCLE TOP WINDOW: A window having a curved (radius) top and a flat bottom. The shape of the window is an exact half-circle with the height being usually one-half of the width. Also called circle head, half-circle and half-round.

CIRCLE TOP TRANSOM: A half-circle window over a door or window usually with radiating bars.

CO-EXTRUSION: The technique of extruding two or more materials through a single die being fed by separate extruders.

COMBINATION STORM SASH AND SCREEN: A frame assembly of stiles and rails containing a half screen and two glass storm panels; in summer the bottom storm panel is stored in the top of the combination frame and replaced by the screen panel; sometimes called “combination storm sash and screen unit” or simply “combination window unit”.

COMPOSITE MATERIALS: Window and door members which are comprised of two or more materials, which are structurally combined or connected so as to perform structurally as a singular material; i.e., poured and debridged aluminum shapes, fiberglass and man-made wood products, etc.

CORE: Insulating or other center material used in the door.

COTTAGE-STYLE WINDOW: Hung Window (Single or Double) that has a larger bottom sash (lite) than the top sash (lite).

CRIPPLE STUD: A short stud above or below a window or door opening.

CRYSTAL SHEET GLASS: Sheet glass with a thickness between 0.180″ to 0.199″ (4.50 to 5.50 mm) or approximately 3/16″ thick. Used in very large window units.

CYLINDER LOCK: Lock in which keyhole and tumbler mechanism are contained in a cylinder separate from the lock case.

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DADO: Rectangular groove recessed into a wood doorframe.

DESICCANT: A drying agent usually in granular form (similar to silica gel) used by some manufacturers between the panes of insulating glass (in edge spacer) to prevent “fogging” between the panes.

DOOR JAMB: The part of a door frame which surrounds and contacts the edges of the stiles and top rail of a door; jambs may be classified as (1) “head or “side” jambs and (2) “plain” or “rabbeted”.

DOOR SKIN: Sheet of material (wood, steel, fiberglass, PVC, etc.) that forms the exterior faces of the door.

DOOR SLAB: A door without lites or sweep installed.

DOUBLE HUNG WINDOW: Two sash which move vertically, by-passing each other in a single frame. Sash may be counter-balanced by weights or springs.

DOUBLE-STRENGTH GLASS: Sheet glass with a thickness between 0.115″ to 0.133″ (3 to 3.38 mm) or approximately 1/8″ used in larger window units.

DOUBLE WINDOW: Two windows separated by a mullion, forming a unit. Also called a twin window unit.

DRIP CAP: A molding or flashing commonly installed over windows and doors to direct water away from the building in order to prevent seepage; also called a drip molding. A rounded or beveled metal strip attached to the bottom of an exterior door to prevent water from drainage or blowing under the door.

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ESCUTCHEON: Ornamental shield or plate mounted behind the knob, “surrounding” the lock base.

EXTENSION CASEMENT HINGE: A hinge for a casement window, which provides clearance for cleaning the two sides of the sash from the inside.

EXTENSION JAMBS: Flat parts made of vinyl, wood or other materials which are attached to the inside edges of a window jamb to extend it in width to adapt to a thicker wall.

EXTRUDER, COMPOUNDING: The basic functions of a compounding extruder are to melt the polymer and evenly disperse and distribute additives or fillers to obtain the specifications of the end product. Large-scale compounding is done on either single or twin-screw extruders. Single screws are used for basic operations where little variation in material formulation and viscosity is expected. Twin-screw compounders offer better conveyance characteristics.

EXTRUDER, SINGLE SCREW: Basic machine consists of a screw, barrel, drive mechanism, resin feed arrangement, and controls. The constantly turning screw augurs the resin through the heated barrel where it is heated to proper temperature and blended into a homogeneous melt. Before the melt can leave the barrel, it must pass through a breaker plate and screen pack. This unit builds up backpressure in the barrel, filters out contaminants, and tends to convert turbulent melt flow into more laminar flow. The melt is then extruded through the die into the desired shape.

EXTRUDER, TWIN SCREW: Two screws, side by side, is placed within the extruder barrel, and they are either co-rotating or counter-rotating. Counter-rotating twin-screw extruders are used primarily for processing PVC products such as pipe, siding, sheet, pellets, and film. The co-rotating units are used for compounding materials where thorough mixing and high output rates are important. The twin-screw unit resembles a positive displacement screw pump. It conveys the material at low speeds with controlled shear. The positive action assures that all portions of the material experience a uniform residence time.

EXTRUSION: Compacting and melting a plastic material and forcing it through an orifice in a continuous fashion. In the extrusion process, the material is conveyed through the heated machine barrel by a helical screw where it is heated and mixed to a homogeneous state and then forced through a die of the shape required for the finished product.

EYEBROW WINDOW: Today, used to identify certain arch-topped or radius-topped windows that have a curved top like the shape of a human eyebrow. In older homes, low, inward-opening windows with a bottom-hinged sash. These attic windows built into the top molding of the house are sometimes called ‘lie-on-your-stomach’ windows or slave windows. Often found on Greek Revival and Italianate houses.

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FACE PANELS: The hardwood plywood, high-pressure laminate, hardboard, or composition panels or combination thereof, whether flat or configured, which are used for the faces of flush doors.

FENESTRATION PRODUCT: Any transparent or translucent material plus any sash, frame, mullions, dividers, in the envelope of a building, including but not limited to: windows, sliding glass doors, french doors, skylights, curtain walls, and garden windows.

FIRE-RATED DOORS: A door which has been constructed in such a manner that when installed in an assembly and tested it will pass ASTM E-152 “Fire Test Of Door Assemblies,” and can be rated as resisting fire for 20 minutes, 30 minutes, 45 minutes (C), 1 hour (B), or 1-1/2 hours (B). The door must be tested and carry an identifying label from a qualified testing and inspection agency.

FIXED LIGHT (Fixed Sash): Window, which is non-operative (does not open).

FIXED PANEL: In a two-door swinging or sliding door, the panel that is non-operating.

FLASHING: Sheet material that protects and bridges the joint between the window or door frame members and the adjacent construction for the purpose of preventing water penetration by draining water away from the window or door to the exterior. See also Through-wall flashing.

FRAME: Outside member of a window (or door) unit which encloses the sash.

FRENCH DOOR: An interior or exterior door consisting of stiles, top and bottom rail and divided glass panels or lights; often used in pairs; “casement” or “terrace” door.

FRICTION HINGE: A window hinge, which remains open at any position by means of friction in the hinge.

FUSION WELDING: The process of heating mitered corners to over 200°F and bringing the heated corners into contact until they fuse together into a single piece of vinyl.

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GLASS (Insulating): Two sheets of glass bonded together in a unit to enclose a captive air space. In the case of Xi welded glass, the edges are melted together and the air space is filled with an inert gas. Organic units have a hollow metal spacer around the perimeter and edges are sealed with an organic substance. These spacers must be filled with a desiccant, which is a chemical to absorb and hold any moisture trapped in the air space. The latest insulating units use Butyl, Silicone Foam and other non-conductive spacers at the edge for reduced thermal conduction. (Also called warm-edge.)

LEADED GLASS: Small, usually irregular panes of glass, sometimes vari-colored, joined together by lead or zinc muntins and bars and used primarily for decorative purposes; zinc bar glazing.

PLATE GLASS: Glass from which grinding and polishing have removed surface irregularities so that the surfaces are approximately plane and parallel; also polished plate glass.

GLAZING: The glass panes or “lites” (lights) in the sash of a window. Also the act of installing the glass in a window sash.

GLAZING (Single): A single sheet of glass installed in a window sash.

GLAZING (Double): A single glazed sash with an additional glass panel installed on the sash to provide an air space between the two lites of glass. The second glass can either be removable (RDG) or fixed and can be installed on either the inside or outside of the sash. Double glazing differs from insulating glass in that there is no positive seal around the edges of the two lites of glass to provide a true dead air space and there’s no desiccant within the unit to absorb and hold moisture.

GLAZING, (Triple): A sash glazed with three lites of glass, enclosing two separate air spaces.

GLAZING BEAD: A removable trim that holds the glass in place in a window sash.

GLAZING BLOCK: A small, hard rubber block placed around the edges of the glass unit in a window sash to position the glass and prevent it from shifting.

GLAZING COMPOUND: A pliable substance applied between the window sash and the lites of glass to seal against the elements and sometimes to adhere the glass to the sash.

GLAZING TAPE: Double-sided tape used to adhere glass to sash and form an airtight, watertight seal.

GLIDING WINDOW OR DOOR: Same construction as a sliding window. The moving sash generally travels on rollers.

GRILLES: Ornamental or simulated muntins and bars which don’t actually divide the lites of glass. Generally made of vinyl or wood and fit on the inside of the sash against the glass surface for easy removal. Grilles or grids between the glass are usually made of aluminum and sealed inside the insulating glass unit.

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HALF SCREEN: A screen, which does not cover the entire opening of a window. Used on the bottom half of single hung units and on the operating sash side of single sliders.

HEAD: The top or upper member of any elementary structure; in windows, it refers to the top of the frame, as in Round Head Window, head jamb or header.

HEAD BOARD: A flat board cut to fit the contour of a bay or bow window and used to affix the top of the window units.

HEAD EXPANDER: An inverted U-channel installation accessory that may be fitted to the head of a replacement window to accommodate differences between rough opening and window heights.

HEAD JAMB: Also called “header” or “head”: Cross or horizontal jamb member forming the top of the frame.

HEAT MIRROR®: A thin transparent insulating film that is inserted between double glazing which permits transmission of visible light but reflects far-infrared radiation. Heat Mirror® is a registered trademark of Southwall Technologies.

HEAT TRANSFER COEFFICIENT (U-VALUE): A value indicating the rate of heat flow through a building construction, expressed in units of ‘Btu/h per square foot of surface per degree F. difference between indoor and outdoor air temperature.’ This is numerically equal to the ‘inverse of the sum of R-values’ for the construction.

HEAVY FLOAT GLASS: Used in furniture, tabletops, and storefronts.

HINGE MORTISE: The area cut away to accept the hinge leaf for mounting on the doorframe or door edge.

HINGE STILE: Stile to which the hinges are applied, as distinguished from the lock stile.

HINGED DOOR: An exterior or interior door hung by attaching the hinges to the stile so that the door swings on a vertical axis; may be single (swinging thru 90 degrees) or double-acting (swinging thru 180 degrees); double-acting doors do not require a door stop; conventionally hinged.

HOPPER VENT: Inward-opening sash hinged at the bottom (an upside-down awning window). Many basement windows are this type.

HUNG WINDOW: Window with one or more hanging (counter balanced) sashes.

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INACTIVE DOOR: A door that does not contain a lock, but is bolted when closed, and to which a strike is fastened to receive the latch or bolt of an active door.

INFILTRATION: Leakage of outdoor air into a house, such as through cracks around sash or window frame.

INSTALLATION ACCESSORIES: Components supplied by the fenestration manufacturer that are specifically designed to mate or “trim out” the product with various surrounding constructions.

INSTALLATION FIN OR FLANGE: A vinyl or metal flange inserted into or an integral part of the side and head jambs of a window unit used for installing the window in an opening.

INSTALLATION HOLES: Holes in window or doorframes that are fabricated by the manufacturer to locate and accommodate installation fasteners.

INSULATING GLASS: Double- or triple glazing with an enclosed, dehydrated, and hermetically sealed air space between the panes; the space is commonly from 3/16″ to 3/4″.

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JACK STUD: A block or short stud nailed to the rough door or window studding to add strength and to provide a solid bearing for the lintel and nailing member for the finished door jamb or window frame.

JALOUSIE WINDOWS: A window composed of overlapping narrow glass, metal or wood louvers, operated by means of a crank handle for adjusting the louver angles; introduced in the 1950’s.

JAMB: A vertical member at the side of the window frame; also refers to the horizontal member at the top of the window frame, as in Head Jamb and Window Jamb.

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KEEPER: The part of a window lock, mounted on an opposing surface of the window, that the lock arm locks under or into to pull the sash into a locked position and fully releases it when opened.

KERF: A thin cutout in the frame to accommodate the weather-strip flange.

K FACTOR: The coefficient of thermal conductivity. The amount of heat that passes through a unit cube of material in a given time when difference in temperature of 2 faces is 1°F.

KING STUD: The full-length stud next to a door or window opening to which the trimmer and lintel are nailed.

KNOCKED-DOWN (K.D.): Not assembled; parts for a window (or door) frame pre-manufactured for assembly at a later date on the job-site.

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LAMINATED GLASS: Two or more sheets of glass bonded together with a plastic inner layer to produce a stronger, more break-resistant glass. May also have wire mesh or other reinforcing embedded in the glass sandwich for extra strength.

LATCH (Catch/Lock): A device which holds a window shut, such as the latch at the meeting of a double-hung window or one mounted on the stile of casement windows, often referred to as Lock.

LEXAN®: A trade name for a glazing material, which is extremely resistant to breakage. LEXAN® is a registered trademark of G.E.

LIFT RAIL: Handle for raising the lower sash in a double-hung or single-hung window.

LINTEL: A horizontal structural member (beam) that supports the load over an opening, such as that of a door or window. Also called a header.

LITE (light): A window; a pane of glass within a window. The number of lites in upper and lower sash designates double-hung windows, as in six-over-six. This is typically spelled “Lite” to differentiate from sun light or other sources of light that shine through a window.

LOCKBLOCK: A concealed block the same thickness as the door stile or core which is adjacent to the inside edge of the stile at the midpoint and into which a lock is fitted.

LOCK RAIL: Rail on a door located at the proper height to receive the lock and, for that purpose, usually made broader than the other rails. See Meeting Rail.

LOCK STILE: Stile of a door to which the lock is applied, as distinguished from the hinge stile.

LOUVERED WINDOW: A window having louvers or slats that fill all or part of the opening. See Jalousie Window.

LOW-E GLASS: Stands for Low-Emissivity. Glass that has been given a special micro-thin coating (usually silver & metal oxides) that blocks the passage of radiant heat through the glass for better energy efficiency without appreciably affecting the view through the glass (like tinting can do).

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MASONRY OPENING: The opening in a masonry wall to accept a window or door unit, the same as a rough opening in a frame wall.

MEETING RAIL (Lock Rail): One of the two horizontal members of a double-hung sash, which come together.

MEETING STILE: The vertical members in a pair of sash, as in a horizontal sliding window.

MITER: Moulding returned upon itself at right angles. In joinery, the ends of two pieces of wood that are cut at a 45° angle abutting upon one another so as to form a right angle.

MITER JOINT: Two members joined at an angle, commonly 45 degrees.

MODULAR SIZE: Callout size. “M.S.”.

MODULAR OPENING: Callout opening. “M.O.”.

MODULUS OF ELASTICITY: The ratio of stress to strain, being an indicator of a material’s bending resistance to a load.

MULLION: Vertical or horizontal divisions or joints between single windows in multiple units. Can be either decorative or functional (structural). Decorative only versions are also mull casings or covers.

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OBSCURE GLASS: A glass (frosted, etched, fluted, ground, etc.) for privacy, light diffusion, or decorative purposes.

OPERABLE WINDOW: Window, which can be opened for ventilation.

OPERATING PANEL: In a two – door or two – panel swing or sliding door, the panel that opens.

OPERATOR: Crank-operated device for opening and closing casement or Jalousie windows.

ORIEL WINDOW: A window projecting from the wall and carried on brackets, corbels or a cantilever. Similar in appearance to a Bay Window. The term is also applied to a style of window with a larger top sash than its bottom sash. It is the opposite of a cottage-style window.

OUTSIDE CASING: Trim or molding around a window or door on the exterior of the house. Casing usually refers to a flat board trim, typically, 3″ or 4″ in width.

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PAN / PANNING: Cosmetic covering, usually found on the exterior of the window or door to achieve aesthetic sight lines or to integrate the window or door system into the building surface or weatherproofing system. If panning is being used for weatherability, the panning is not considered cosmetic, but part of the window system.

PARTING BEAD: A vertical strip on each jamb that separates the sashes of a double-hung window.

PICTURE FRAME CASING: The use of trim casing on all four sides of the interior of a window, resembling a picture frame when installed.

PICTURE WINDOW: Large fixed windows; introduced in the 1940’s.

PIVOT PIN (Pivot Bar): Part mounted on or in the end of the sash that fits into balance shoe and from which the sash may be tilted or pivoted in.

PLATE GLASS: High quality, ground and polished glass sheet with thickness from 1/8 to 1-1/4 inches (3.2 mm to 31.8 mm).

PLEXIGLASS (Acrylic): A trade name for a clear, durable sheet plastic made of acrylic; used for safety glazing and for inside storm panels. Plexiglas is a registered trademark of Rohm & Haas.

POCKET SILL: A deep sill (frame) design that completely surrounds the bottom edge of the sash in the closed position.

PRIME SASH: The balanced or moving sash of a window unit.

PRIME WINDOW (PRIMARY WINDOW): The first window completely installed in a rough opening, which is designed to function as the sole fenestration product (contrasted with a storm window, which serves as a secondary window in conjunction with a primary window).

PROJECTED WINDOW: An awning type window that swings either inward or outward at the top or the bottom. The ‘PIB’ or ‘project in at bottom’ window can be cleaned from the inside.

PUSH BAR: Used on awning and other projecting sash windows for opening and closing instead of a crank (gear) operator.

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QUARTER ROUND WINDOW: Stationary or operating window with glass shaped as a quarter circle; it is often divided into separate panes by a removable grille, installed on the interior or grille between the glass.

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RABBET: A flat “cut” in the frame to reduce the thickness to form a stop for the door.

RADIATION: Energy released in the form of waves or particles, due to a change in temperature within a gas or vacuum. (Usage – ‘Short wave radiation’ refers to energy emitted from a high temperature source, such as the sun; ‘long wave radiation’ refers to energy emitted by low temperature sources, such as the human body.)

RAIL: Horizontal members of a window sash or door panel.

REVEAL: That part of the edge of a door or window jamb not covered by the casing.

ROOF WINDOW: Sloped application of fenestration product, which allows for in-reach operation and rotation of sash to facilitate the cleaning of exterior surfaces.

R-VALUE (Thermal Resistance): A measure of the resistance a unit of heat has in flowing through a given material or construction; a higher value indicates a better heat-insulating property. The R-value of an ordinary single-pane sash with a 15 mph wind on one side is about 0.9.

ROUGH OPENING: The opening left in a frame wall to receive a window or door unit. The jack studs on each side, which supports the header across the top, form it. Cripples support the rough sill at the bottom. The rough opening generally allows 1/2″ or more in each dimension in excess of the window or door unit dimension. Openings in brick walls are known as masonry openings.

ROUGH SILL: The horizontal rough framing member, usually a 2 x 4, which forms the bottom of the rough opening. It is toenailed into the jack studs and is supported by cripples.

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SAFETY GLASS: Annealed glass that undergoes further processing becomes a safety glass. The characteristic of safety glass is to reduce the possibility of severe injury upon accidental impact. There are two types of safety glass that meet the (CPSC-federal standard) 16 CFR 1201, Cat. II: Tempered and Laminated. Tempered glass, through a heat strengthening process, becomes four times stronger than annealed glass and when broken, separates into dice-like cubes approximately the thickness of the glass. Laminated glass is two lites of glass sandwiched together with an interlayer of polyvinyl butyral (PVB) under heat and pressure. Laminated glass when broken tends to remain intact.

SAFETY GLAZING AND USE Safety glazing is the use of safety glass and certain plastics in hazardous locations. The building codes require safety glazing in two broad types of hazardous locations. 1. Glazing subject to accidental human impact, such as in doors, sidelites (glazing next to doors), other glazing that extends to or near the floor or walking surface, and glazing in the walls and enclosures of bathing compartments. 2. Skylights or sloped glazing in walls and roofs greater than 15 degrees from the vertical. Laminated glass or certain plastics is required to reduce the possibility of any part of the glazing from vacating the glazed opening when broken. Note: See Chapter 24 of the Model Building Codes for specific requirements.

SASH: A single assembly of stiles and rails in which the lites of a window are set. The framework holding the glass in a window unit.

GLAZED SASH: A sash in which the glass has been installed.

OPEN SASH: A sash in which the glass has not been installed.

SASH AND FRAME: A window and its cased framing.

SASH BALANCE: A device for counter-balancing a sash of a double-hung or single-hung window to hold it in the up position. There are four basic types:

Spiral: A balance using a spirally wound spring;

Spring: A balance using a spring for counter-balancing; introduced in the 1980’s;

Coiled Tape (Pullman Balance, Overhead Balance): A coiled steel tape under spring tension for balancing the sash, located in the head jamb of the window frame.

Counterweigh: The most common type of balancing system in older homes, utilizing a weight held by a sash rope or chain over a pulley.

SASH CORD: In older windows, the rope used to connect the sash with its counter weight.

SASH CRACK: The opening between the operating sash and the frame of the window. Its thickness or measurement is equal to the difference between the inside window frame dimension and the outside sash width. Crack foot length is used in calculating total air infiltration on a window unit.

SASH LOCK: Generally, a cam-action type lock applied to the rails of a window or at the open edges of a projecting window to pull the rails tightly together or to seal the sash tightly to the frame, both for security and weather tightness.

SASH STOP: A molding that covers the joint between window sash and the jamb.

SEALANT: A compressible plastic material used to seal any opening or junction of two parts, such as between the glass and its sash, commonly made of silicone, butyl tape or polysulfide.

SEALED DOUBLE GLASS: Two panes separated by a sealed space.

SEAT BOARD: A flat board cut to fit the contour of a bow or bay window and installed between the sills and the flat wall surface, providing a seat or shelf space.

SHIMS: Wood wedges (often wood shingles) used to position the window or door unit in the rough or masonry opening in a square, level and plumb position during (and after) installation.

SHORE HARDNESS: Measure of firmness of a compound by means of a Durometer Hardness Gauge (A range of 20-25 is about the firmness of an art gum eraser. 90 is about the firmness of a rubber heel).

SIDE JAMB: The upright vertical member forming the sides of the frame of a window or door unit.

SIDE LITE (light): A fixed, often narrow, glass window next to a door opening (or window).

SILL: The horizontal member at the bottom of the window frame; a masonry sill or sub-sill can be below the sill of the window unit.

SILL ANGLE: An L-shaped installation accessory that may be employed at the sill of a replacement window to accommodate the slope of the existing sill construction.

SILL COURSE (SOLDIER COURSE): The row of bricks, cement blocks or stones laid across the bottom of a masonry opening which lie under the outside edges of the window sill.

SINGLE-HUNG WINDOW: A window that is similar to a double-hung window except that the top lite (light) is fixed (stationary).

SINGLE-STRENGTH GLASS: Glass with thickness between 0.085″ to 0.100″ (2.16 mm to 2.57 mm) or approximately 3/32″.

SOLE PLATE: The bottom horizontal member in a frame wall. Usually either single or doubled 2 X 4’s. It is nailed to the deck or rough floor and the studs are nailed to it.

SPLINE: For screening, a small strip of metal or flexible tubing or gasket material that fits into a groove in the screen frame to secure the screen cloth.

STACKED WINDOW UNITS: A vertical (combined) grouping of awning, hopper, casement or non-operating windows to form a large, multiple units.

STATIONARY SASH: A fixed sash; also referred to as a picture, studio, vista or view sash.

STILE: The upright or vertical outside members of a window (sash) or door panel, blind, screen or shutter.

STOOL: The inside horizontal trim member at the bottom of the window frame, which rests on the sill. The shelf-like part that projects into the room. This is a common inside trim method used on wood double hung windows, sometimes called the “inside sill”.

STOP: A trim member attached to the window frame to stop the sash of a projecting window when closed to prevent it from swinging through the opening. It also covers the perimeter crack between the sash and the window frame in double hung and sliding windows and prevents the sash from coming out of the frame. Stops used at the top or bottom of the balance channel prevent the sash in hung windows from hitting when opened.

STRIKE: Metal plate or box, mounted in the doorframe that is pierced or recessed to receive the bolt or latch when projected.

SURFACE HINGE: Hinge having both leaves surface applied as opposed to mortised in.

SWAGING: Slight offset of the hinge at the barrel, which permits the leaves to come closer together and improves the operation and appearance of the door.

SWEEP: Door bottom weather-strip mounted to the door slab on swinging doors.

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TEMPERED GLASS: Special heat-treated, high-strength safety glass which shatters into pebble-sized particles but not into long slivers, when broken.

THERMAL BARRIER: A strip of non-conducting material, such as wood, vinyl or foam rubber, which is used to separate the inside and outside surfaces of a metal window sash or frame, or a metal door or sill to stop the conduction of heat to the outside (which results in a cold inside surface). Vinyl windows, because of their thermal efficiency, do not require a thermal barrier.

THIN FLOAT GLASS: Referred to as single strength glass, which is typically used in, insulated glass units for small and medium sized windows.

THROUGH-WALL FLASHING: Flashing that extends completely underneath the sill or over the head of a window, and has an upturned leg on the interior side.

TILT PIN: A metal or hard plastic nail-like pin fastened to the sash to allow it to engage the balance shoe and from which the sash may tilt or pivot in. See Pivot Pin.

TOP ROLLER GUIDE: Hardware fastened to the top of a sliding door and which contains a roller, which glides in the door’s overhead track.

TRANSOM: Generally refers to an opening or stationary sash above a door or window which serves a similar purpose to a side lite. A transom joint is the horizontal joining area between two window units, which are stacked one on top of the other.

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U-VALUE: A value indicating the rate of heat flow through a building construction (combination of materials), expressed in units of ‘Btu/h per square foot of surface per degree F. difference between indoor and outdoor air temperature.’ This is numerically equal to the ‘inverse of the sum of R-values’ for the construction. See Heat Transfer Coefficient.

ULTRA-VIOLET: Type of radiation with wavelengths shorter than those of visible light and longer than those of X-rays. Causes sunburn, fading and breakdown of fabric, wood, furniture and other exposed surfaces.

UNITED INCHES: The sum in inches of the width and height of a window unit. Common “call size” for replacement windows.

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VENTING WINDOW: Operating window, such as a venting awning, etc. One that opens for ventilation.

VERTICAL SLIDING WINDOW: One or more sashes that move in a vertical direction.

V-GROOVE: A V-shaped groove cut into the surface of a glass pane for decorative purposes.

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WARM EDGE SPACER: Use of a non-conductive edge spacer in insulating glass units instead of the conventional metal (conductive) edge spacer. “Warm Edge” spacers may be made of butyl, silicone foam or other non-metallic materials and sealants.

WEEPHOLE: Small holes drilled along the bottom edge of storm sash, combination storm-screens, or windows with “pocket” sills to permit moisture condensation or wind-driven rain to drain away from the sill to the outdoors.

WINDOW HARDWARE: Various devices and mechanisms for the window including: catches, cords and chains, fasteners and locks, hinges and pivots, lifts and pulls, pulleys and sash weights, sash balances and stays.

WINDOW SCHEDULE: A listing of windows required in a given house, stating types, sizes, number of lites (lights), manufacturer, and any special needs, etc.

WINDOW / WALL ASSEMBLY: The building envelope and the fenestration products incorporated into it.

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