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| So many terms, so little time. A basic understanding of the terminology used in the window, door, and the general construction business will help you to better compare products and services offered by various companies and to make an informed purchasing decision.
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| A
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| AAMA | American Architectural Manufacturers Association |
| Air Infiltration | The amount of air that passes through between a window sash and frame or a door panel and frame. |
| Air Space | All high performance windows have at least two panes of glass sandwiched together, with an airspace in between. The size of the airspace and the type of gas that fills this space effects the overall window performance. A 1/2" to 3/4" space is considered optimal. |
| Apron | Inside flat trim member which is used under the stool at the bottom of the window. |
| Anti-Lift | Pop-out inserts added to the main frame which prevent the slider window from opening or being removed. A security device to discourage burglers. |
| Annealed Glass | The basic product produced in the float process. |
| Argon Gas | A colorless and harmless inert gas that is injected in the airspace of an insulating unit, to improve energy efficiency. |
| Astragal | The center member of a double door, which is attached to the fixed or inactive door panel. |
| Awning | A window that is hinged on the top to open like an awning.
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| B
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| Bay Window | A composite of three or more windows, usually made up of a large center unit and two flanking units at 30°, 45° or 90° angles to the wall.
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| Balances | Spring loaded single hung vent support system. |
| Bead | A continuous strip of glass stop. |
| Blocks | Rectangular, cured sections of neoprene used to position the glass product in the glazing channel of the frame. |
| Bow Window | A composite of four or more window units in a radial or bow formation.
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| Breather Tubes | A small metal tube that is placed into a insulated units spacer to equalize pressure differences. Breather tubes are larger than capillary tubes and can allow moisture to enter into the insulating unit. |
| Brick Mould | Outside casing around window to cover jambs and through which nails are driven to install the window. |
| Bulb Seal | A round, soft PVC weather strip used where a compression type seal is required (casement and awning windows). |
| Butyl | Polyisobutylene is a hot melt sealant used as the primary seal for dual seal systems on insulated glass units. |
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| C
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| Capillary Tubes | A small metal tube that is placed into a insulated units spacer to equalize pressure differences. Capillary tubes are used most frequently to equalize a unit that in shipping, will experience significant elevation changes. Unlike breather tubes, moisture cannot pass into the unit. |
| Casement | A window that is hinged on one side to open like a door.
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| Casing | Inside casing is a flat, decorative moulding which covers the inside edge of the jambs and the rough openings between the window unit and the wall. Outside casing (or Brick Mould) serves the same purpose, while it also is an installation device through which nails are driven to install the window unit into the wall. |
| CFM | The number of cubic feet of air leakage per minute per each lineal foot. |
| Check Rail | On a double-hung window, the bottom rail of the upper sash and the upper rail of the lower sash, where the lock is mounted. |
| Circlehead | A generic term referring to any of a variety of window units with one or more curved frame members, often used over another window or door opening.
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| Clerestory | A window near the top of an outside wall. |
| Cottage Double-Hung | A double-hung window in which the upper sash is shorter than the lower sash.
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| Condensation | Moisture that forms on a surface when it is colder than the dew point. |
| Conduction | Refers to heat flow through a solid material such as a window frame or glass. In the winter, the interior surface of a window is warmed by the home's heating system and that heat is conducted (or transferred) to the cooler outdoors. |
| Cripples | The short 2" x 4" members used to frame under the sill or above the header in a rough opening for a window in a frame wall. |
| Curb | A watertight wall or frame used to raise slope glazing above the surface of the roof as a preventive measure against water leakage from melting snow or rain run-off. |
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| D
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| Daylight Transmittance | The percentage of light that transmits through a window. The number ranges from 0 to 100%. Standard clear insulated glass (1/8" over 1/8") has a daylight transmission of 82%. |
| Deglaze | Removing the glass from the window frame. |
| Desiccants | Porous crystalline substances used to absorb moisture and solvent vapors from the airspace of insulating glass units. |
| Divided Lites | In traditional window construction, the separate panes of glass that make up the gridwork of a whole window. |
| Dormer | A space which protrudes from the roof, usually including one or more windows. |
| Double Glazing | Also called double-pane or twin-pane; window panes made up of two layers of glass with an insulating space in between. |
| Double Strength (DS) | Glass that is 1/8 inch in thickness. Also known as heat strengthened glass. |
| Double-Hung | A window with two movable up-and-down sashes for optimum ventilation.
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| Double Rafter | The doubling (side by side) of the roof members to reinforce an opening in the roof for a slope glazing installation. |
| Drip Cap | A moulding placed on the top of the head brickmould or casing of a window frame. |
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| E
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| Edge Deletion | This process removes the Low-E coating from the edge of the glass (following the sputter coating process) so that the insulating sealant can adhere to the glass surface. This also reduces the chance of corrosion when the coating is exposed to moisture. |
| Egress Code | A standard set by the United Building Council that requires entry and exit specifications in sleeping areas for emergency applications. |
| Emissivity | A measure of an object’s ability to emit long-wave infrared radiation or room temperature radiant heat energy. Emissivity varies from 0 (no emitted infrared) to 1 (100% emitted infrared). The lower the Emissivity, the lower the resultant U-value. |
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| F
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| Fenestration | An architectural term referring to the arrangement of windows in a wall. |
| Fin | The vinyl flange surrounding the perimeter frame of a vinyl window or patio doors. |
| Finger-Jointing | A means of joining individual pieces of wood together to form longer lengths. The ends of the pieces are machined to form a set of interlocking fingers, which are then coated with adhesive and meshed together under pressure. |
| Fixed Window (Lite) | A window or that part of a patio door that is permanently installed without movable sashes. Designated as the "0" panel in a slider diagram. |
| Flashing | A metal or plastic strip attached to the outside of the head or side jambs to provide a weather barrier, preventing leakage between the frame and the wall. |
| Float Glass | A fabrication process used to make flat glass by drawing molten glass across a tin bath. This type of glass is known as Annealed Glass. |
| Fogged Unit | Moisture found on the inside of an insulated unit caused by failure of the seal. |
| French Hinged Door | Hinged door(s) which have wider panel members around the glass. |
| French Sliding Door | A sliding door which has wider panel members around the glass, giving the appearance of a French hinged door. |
| Fusion-Welding | Strong, weathertight method of heat-joining the corners of sashes and frames. |
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| G
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| Gable Window | A window that usually follows the roof line with at least two non-90 degree angles.
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| Garden Window | A specialty window that forms a glass box recessed in a wall; contains a shelf suitable for cultivating house plants. |
| Geometric Windows | Windows that incorporate arcs or non-standard angles to make them a shape other than rectangular or square.
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| Gasket | A pliable, flexible continuous strip of material used to affect a watertight seal between sash and frame of roof windows much like the seal around a refrigerator door. |
| Glazing | The glass panes or lights in the sash of a window. Also the act of installing lights of glass in a window sash. |
| Glazing Bead | A plastic or wood strip applied to the window sash around the perimeter of the glass. |
| Glazing Compound | A pliable substance applied between the window sash and the lights of glass to seal against the elements and sometimes to adhere the glass to the sash. |
| Glazing Stop | The part of the sash or door panel which holds the glass in place. |
| Glider | A window with one or two sashes that slide sideways within a track.
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| Grids (or Grills) | Crosspieces applied to the interior of a window to replicate the look of muntins. See MUNTIN. |
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| H
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| Head | The main horizontal member forming the top of the window or door frame. |
| Head Board | A flat board cut to fit the contour of a bow or bay window and installed between the head jambs and the flat wall surface to finish off that area which would normally be ceiling. |
| Header | A heavy beam extended across the top of the rough opening to prevent the weight of wall or roof from resting on the window frame. |
| Heat Strengthened | The process of heat strengthening is similar to the tempering process. The glass is heated to near its softening point, then cooled faster than normal but not as rapidly as fully tempered glass. |
| Heel | Actual net window dimension. Most heel dimensions are 1/2" smaller than rough opening dimensions. |
| High Performance Windows | Windows that have U-factors of .40 or lower. |
| Hopper | A window with a top sash that swings inward. |
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| I
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| Infiltration | Air leakage, which can escape through cracks between the glass assembly and the window frame, resulting in heat loss. |
| Insulating Glass Unit (IG Unit) | More than one glass pane forming a sealed system of panes used to increase the thermal efficiency of a window. See Double-Glazing. |
| Integral Glazing | Insulating glass unit bonded to the sash to create a single unit and increase weather resistance. |
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| J
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| Jack Stud | Framing members, generally 2" x 4"s, which form the inside of the window or door rough opening. They run from the sole plate to the header, which is supported by them. |
| Jambs | The vertical sides of a window frame. |
| Jamb Liner | Metal or plastic covering the inside surface and head jambs of sliding windows. |
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| K
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| Keeper | The protruding, hook-shaped part of a casement window lock, which is mounted on the inside surface of the sash stile. |
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| L
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| Laminated Glass | This process bonds two pieces of glass permanently with a plastic interlayer of polyvinyl butyral through heat and pressure. Once bonded together, the sandwich behaves as a single piece. If broken, glass fragments adhere to the plastic interlayer rather than falling free and potentially causing injury. Laminated glass is considered a safety glass. |
| Lift | A handle or grip installed on the bottom rail of the lower sash of a double-hung window to make it easier to raise or lower the sash. |
| Light | (also spelled lite) Single piece of glass in either a window or door. |
| Light Shaft | An insulated shaft built to direct the light from a roof window or skylight through the attic to the room below. |
| Low-Conductance Spacer | A non-metallic material or system that separates the panes of glass in a double-pane window, reducing heat transfer and making the window warmer at the edges than traditional metal spacers; also reduces condensation. |
| Low-E Glass | A coating consisting of a very thin layer of metallic oxide or silver which is applied to the third surface of an insulating glass unit to block radiant heat transfer and ultra-violet rays. |
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| M
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| Monolithic Glass | Glazing construction consisting of one lite of glass or one lite of laminated glass rather than the two lites used to make an insulated unit. |
| Masonry Openings | The opening in a masonry wall to accept a window or door unit, the same as a rough opening in a frame wall. |
| Mortise | A slot or rectangular cavity cut into a piece of wood to receive another part. |
| Mortise and Tenon | A strong wood joint made by fitting together a mortise in one board and a matching projecting member (tenon) in the other. |
| Mullion | A separate joining piece that connects windows in a combination window. |
| Mullion Ccasing | An interior or exterior casing member to cover the mullion joint between single windows. |
| Muntin | A short bar used to separate glass in a sash into multiple lights. Also called a windowpane divider or a grille. |
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| N
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| Net Size | Actual window size. Also referred to as heel. |
| NFRC | National Fenestration Rating Council. |
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| O
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| O.A. | The thickness of an insulated unit of glass, including both pieces of glass and spacer bar. |
| Obscure Glass | A textured glass that provides a translucent or semi-opaque effect to provide privacy. |
| Operator | A metal arm and gear which allows for easy operation or closing of projecting windows. |
| Outer Frame Member | The exterior protruding portion of a window frame which has no exterior casing. |
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| P |
| PVC | Polyvinyl Chloride. |
| Palladian Window | A large, arch-top window flanked by smaller windows on each side.
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| Panel | Usually refers to the separate panel or panels in a door frame. |
| Passive Solar Collector | Any glazed area in the walls or roof of a building pointed to the south to take maximum advantage of the sun's heat without a mechanical (or active) method of storage or distribution of the heat. |
| Patio Door | A sliding door made of two large panes of glass set in sashes; one stationary, one operable. |
| Picture Frame Casing | The use of casing on all four sides of the interior of a window, replacing the stool and apron at the sill. Also know as full-bound casing. |
| Pitch | The pitch of a roof is the degree of the inclination upward from horizontal or flat. It may be expressed in degrees or as the ratio of the number of inches it rises in each 12 inches of horizontal span -- 4/12 means the roof rises four inches in every foot of horizontal span. |
| Picture Window | A window that is permanently fixed in one position to afford the least obstructed view of the outdoors. A picture window can also be referred to as a Fixed Window.
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| Pivot | A mode of operation for ventilating windows which generally means the sash pivots on a central axis and turns 90 or more degrees. |
| Profile | An individual extruded member of vinyl frame or sash. |
| Pyrolytic Coating | A coating applied to glass, with visually reflective or non-reflective properties. These coatings are sprayed on to the glass surface as it leaves the float process in a semi-plastic state. Also known as Hard Coat. |
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| Q
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| R |
| R-Value | Measures the insulation effectiveness of the window. The R-value equals one divided by the U-value. The higher the R-value, the better the insulating performance. |
| Radiation | This refers to the process of heat traveling via infrared or heat rays from a warm object to a cooler object. Radiant heat loss accounts for a large percentage of the heat loss in windows. Radiant heat gains occur when sunlight shines through a window and warms objects inside. |
| Rafter | Structural members of a roof that support the roof load and run from the ridge to the eaves (overhang). |
| Rails | The horizontal members of a window sash or door panel. |
| Relative Heat Gain | The total heat gain through the glass for a specific set of conditions. This value considers indoor/outdoor temperature differences and the effect of solar radiation. Expressed in Btu/hr/ft2. The lower the relative heat gain value, the lower the solar heat gain. |
| Rough Opening | The size of the opening for which the window is framed. The net or heel size of the window is usually 1/2" smaller than the rough opening. Same as nominal size. |
| Rough Sill | The horizontal rough framing member, usually two inches by four inches, which forms the bottom of the rough opening. It is toe-nailed into the jack studs and is supported by cripples. |
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| S
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| SASH | The operating part of a window. Also called a vent. |
| Sash Balance | A system of weights, cords and/or coiled springs which assist in raising double-hung sash and tend to keep the sash in any placed position by counterbalancing the weight of the sash. |
| Sash Cord | In double-hung windows, the rope or chain that attaches the sash to the counter balance. |
| Sash Lock | Generally, a cam-action type lock applied to the check rails of a sliding window or at the open edges of a projecting window to pull the check rails tightly together or to seal the sash tightly to the frame, both for security and weathertightness. |
| Seal | Insulating glass units are sealed at the edges to prevent moisture and dirt from contaminating the interior of the unit. The seal must be durable and usually consists of an aluminum space with an exterior sealant. |
| 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. |
| Setting Block | A plastic block used to support the insulating unit in the window frame. |
| Shading Coefficient | A ratio, which indicates the relative solar heat gain through a lite of glass or glazing system. A lower number means more shading and less solar heat gain. |
| Shims | Wood wedges (often wood shingles) used to secure the window or door unit in the rough or masonry opening in a square, level and plumb position during and after installation. |
| Side Lights | Tall, narrow, fixed or operating sash on either or both sides of a door to light an entryway or vestibule. |
| Single Strength (SS) | Glass that is 3/32 inch in thickness. |
| Sill | Horizontal member that forms the bottom of a window frame. |
Sill Course
(Soldier Course) | The row of brick, cement blocks or stones laid across the bottom of a masonry opening which lie under the outside edge of the window sill. |
| Simulated Divided Light | A method of constructing windows in which muntins are affixed to the inside and outside of a panel of insulating glass to simulate the look of true divided light. |
| Single Glazing | Use of single panes of glass in a window. Not as energy-efficient as double glazing. |
| Single-Hung | A window that slides open vertically.
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| Slider | A window that slides open horizontally.
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| Slope Glazing | Any glazed opening in a sloped roof or wall, such as a stationary skylight or fully operable roof window. |
Solar Heat Gain
Coefficient | Indicates the percentage of normal incident solar heat energy that makes its way through the glazing under standard summer conditions. This includes both directly transmitted and indirectly transferred heat from energy initially absorbed by the glazing. Lower values indicate less heat entering the building. |
| Sole Plate | The bottom horizontal member in a frame wall. Usually either single or double 2" x 4"s. It is nailed to the deck or rough floor and the studs are nailed into it. |
Sound Transmission
Class (STC) | The average value associated with a material’s effectiveness to reduce sound. The higher the value, the greater the reduction of sound. |
| Spacer | The material that separates the two lites of glass in an insulating unit. |
| Stile | The vertical side member of a window sash or door panel. |
| Stool | Inside horizontal trim member of a window sash or door panel. |
| Stop | A wood trim member nailed to the window frame to hold, position or separate window parts. The stop is often moulded into the jamb liners on sliding windows. |
| Stucco/Flush Fin | Fin option with the fin flush with the window face. This option is used most often in replacement window applications, with the fin serving as a frame around the window. |
| Stud | Vertical wood framing members which form a frame wall. In normal construction these are eight foot-long 2" x 4"s. |
Sputter Coating
(Magnetic Sputtered
Vacuum Deposition) | A thin metallic coating that is applied when molecular particles are vacuum deposited on the glass surface. This process occurs following glass production. Also known as Soft Coat. |
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| T
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| Tenon | A rectangular projection cut out of a piece of wood for insertion into a mortise. |
| Tempered Glass | Glass that is strengthened through the process of heating and then cooling the surfaces rapidly. This creates surface compression and tensile strength that causes glass to resist breakage, yet disintegrate into small pieces if a break occurs. Fully tempered glass must have a surface compression of 10,000 psi. This process produces glass four times more impact resistant than non tempered glass. |
| Transom | A smaller window above another window or door. A transom joint is also the horizontal joining area between two window units which are stacked one on top of the other.
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| Triple Glazing | A sash glazed with three lights of glass, enclosing two separate air spaces. |
| True Divided Light | A term which refers to windows in which multiple individual panes of glass or lights are assembled in the sash using muntins. |
| Twin Pane | Windows made up of two layers of glass with an insulating space in between. |
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| U
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| U-V Block | Measures the amount of damaging ultraviolet light that is blocked from being transmitted through the glass. |
| U-Value | Measures the heat loss or gain due to differences between indoor and outdoor air temperatures and is expressed in terms of BTU’s/hr/ft2. The U-Value (or Factor) equals one divided by the R-value. The lower the U-value the better the insulating performance. |
| Ultraviolet (UV) | Radiation having wave lengths just shorter than those of visible light. Ultraviolet rays represent 2/3 of the rays that cause fading. |
| Unison Lock | A casement locking system which secures the window at two locking points by operation of one handle. |
| Unit | Two or more pieces of glass separated by a hermetically sealed airspace, (hermetically meaning air tight) to form a construction that reduces heat transfer for improved thermal performance. |
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| V
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| Vapor Barrier | A watertight material used to prevent the passage of moisture into or through floors, walls and ceilings. |
| Vent | The sliding or projecting portion of the window. Also called the sash. |
| Venting Unit | A window or door unit that opens or operates. |
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| W
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| Warm Edge Spacer | State of the art three sided spacer bar replacing the traditional four sided aluminum spacer. Nickel plated steel is formed into a U-shape, eliminating the fourth side and increasing energy efficiency. One fully automated, continuous spacer is bent on three corners and riveted in the fourth, decreasing the possibility of unit failure due to old style plastic corner keys with aluminum spacers. |
| Weep Holes | Slots or holes in the frame sill to provide outside release of infiltrated water. |
| Windload | Force exerted on a surface by moving air. |
| Windowpane Divider | A short bar used to separate glass in a sash into multiple lights. Also called a muntin or a grille. |
| Wire Glass | Is produced by overlaying electrically welded, chemically treated, steel wire mesh over molten glass as it begins the controlled cooling process. The mesh is then overlaid with another ribbon of glass with the same thickness as the first. This sandwiches the wire between the two pieces of glass, which fuse together. |
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