Awning Window: This style of window swings out from the bottom and away from a building, just like an awning.

Argon Gas: This odorless, colorless gas is inserted between panes of glass for insulation and also increases a window's energy efficiency by reducing conductive heat transfer.


Bay Window: Windows that project out from the wall and extend to the ground. An Angle Bay Window refers to the angle departure from the plane of the wall.

Bottom Rail: The bottom horizontal member of a window sash.

Bow Window: (Compass Window or Radial Bay Window): A rounded bay window that projects from the wall in the shape of an arc; commonly consisting of five sash.

Boxed Mullion: A hollow mullion between two double-hung windows to hold the sash weight.


Casement: A window sash which swings open on side hinges; in swinging are French in origin while out swinging are from England.

Casement Window: A window with one or more casements.

Caulking: A mastic compound for filling joints and sealing cracks to prevent leakage of water and air; commonly made of silicone- bituminous-acrylic or rubber-based materials.

Clerestory: (Clearstory or High-Light Window): A window in the upper part of a lofty room that admits light to the center of the room.

Coated Glass: A window glass with an outside surface provided with a mirror reflective surface; the shading coefficient ranges from 20% to 45%.

Combination Window Unit: (Combination Storm Sash and Screen): A window assembly containing a half screen and two glass storm panel; in frame, exposing the screen panel.

Condensation: The deposit of water vapor from the air on any cold surface whose temperature is below the dew point, such as a window glass or frame that is exposed to cold outdoor air. Convection See Natural Convection and Forced Convection. A heat transfer process resulting from the circulation or movement of fluids, such as air.

Crack Perimeter: The total length of the crack around a sash through which outdoor air could leak into the room. In a double-hung window, the total crackage is 3 times the width plus 2 times the height of the sash.


Degree-Day: A measure of heating demand, based on the difference between the mean daily outdoor temperature and 65° F. Cumulative totals for the month or heating season are used by engineers for estimating heating energy requirements.

Design Heat Loss: The calculated values, expressed in units of Btu per hour (abbreviated Btuh), for the heat transmitted from a warm interior to a cold outdoor condition, under some prescribed extreme weather conditions. The values are useful for selecting heating equipment and for estimating seasonal energy requirements. Infiltration heat loss is a part of the design heat loss.

Desiccant: A drying agent, such as silica gel, used by some manufacturers between the panes of insulating glass to prevent fogging between the panes.

Dew Point Temperature: The temperature of the air at which the water vapor in the air starts to condense in the form of liquid or as frost.

Double-Hung Window: Window with two vertically moving sashes, each closing a different part of the window.

Double Windows: (Double Glazing): Two windows, such as a regular window plus a storm sash; also an insulating window with air space between panes.

Drip Cap: A horizontal molding to divert water from the top casing so that the water drips beyond the outside of the frame.


Emergency Exit Window: (Egress Window) Fire escape window; large enough for a person to climb out; each bedroom should be provided with exit windows.

Emissivity: The relative ability of a surface to radiate heat.

Extension Jamb: (Jamb Lining or Jamb Extender) A board used to increase the depth of the jambs of a window frame to fit a wall of any given thickness.


Fanlight: (Sunburst Light or Fan Window or Circle-Top Transom) A half-circle window over a door or window, with radiating bars.

Finish Casing: (Finish Trim) Interior trim boards around a window unit.

Fire-Escape Window: (Emergency Exit Window) Window which opens onto fire escape; window designed for emergency exit.

Fixed Light: (Fixed Sash) Window which is non-operative (does not open).

Flashing: Sheet metal provided for drainage of water and to prevent water penetration into building.

Frame: The outer components of a window or door unit, consisting of a head jamb, side jambs, blind stops and window sills, as applies.


Glass: An elastic transparent material composed of silica (sand), soda (sodium carbonate), and lime (calcium carbonate) with small quantities of aluminum, boric, or magnesia oxides.

Glazing: The installation of glass in a window opening; also the fenestration or windows.

Glazing Bead: (Glass Stop or Wood Stop or Sill Bead): A removable trim that holds the glass in place.

Glazing Channel: A groove cut into the sash for the mounting of glass.


Head: The top or upper member of any element or structure; in windows, it refers to the top of the frame, as in Round Head Window.

Head Jamb: (Head) All of the horizontal members at the top of the window frame.

Heat-Absorbing Glass: (Tinted Glass) - Window glass containing chemicals (with gray, bronze, or blue-green tint) which absorb light and heat radiation, and reduce glare and brightness. Shading coefficient of this glass varies from about 50% to 70%.

Heat Transfer Coefficient: (U-value) - A value indicating the rate of heat flow through a building construction, expressed in units of 'Btuh 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 H-values' for the construction.

Hinge: A movable joint enabling a window to swing open.

Horizontal Sliding Window: (Horizontal Slider) Windows which slide horizontally.

Hung Window: Window with one or more hanging sashes.


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

Infiltration Heat Loss: The heat loss, expressed in units of Btu per hour (Btuh), resulting from leakage of outdoor air into a structure and the escape of indoor air. The loss depends upon the indoor and outdoor temperatures, the crack perimeter, and the rate of air leakage per foot of crack.

Insect Screen: (Window Screen) - Woven mesh of metal, plastic, or fiberglass stretched over a window opening to permit air to pass through, but not insects.

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 ¾.

Insulated Window: A window with multiple glazing that provides one or more air spaces between layers of glazing.

Interior Glazes: Glazing installed from inside of building.


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.

Jamb Depth: Width of the window frame from inside to outside.


Knocked-Down: Not assembled; parts for a window frame pre-manufactured for assembly at a later date on the job site.


Laminating: Method of bonding two or more layers of glass together using heat and pressure, with inner layers of transparent plastic. This process provides one of the best avenues to blocking ultraviolet rays.

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

Lite: (Light) - A window; a pane of glass within a window. Double-hung windows are designated by the number of lights in upper and lower sash, as in six-over-six.

Lock Stile: The vertical member (stile) of a casement sash which closes against the surrounding frame.

Low Emissive Coating (Low-e): Coating for glass surfaces which reflect radiant heat energy rather than allowing that energy to radiate through the glass surface. The lower the emissive of the glass the lower the heat transfer coefficient.

Low E Glass: Windows that have been coated with a transparent, metallic layer to the glass surface, reducing its emissivity or ability to radiate heat.


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

Millwork: Window sash and other wood products made in a wood-working plant.

Miter Joint: Two members joined at an angle, commonly 45 degrees.

Mold: (Molding) A relatively narrow strip of wood used to conceal a joint or to emphasize ornamentation of a structure.

Mullion: Vertical member between window units.

Muntin: (Sash Bar) - (Window Bar) - (Glazing Bar) - a secondary framing member (horizontal, vertical, or slanted) to hold the window panes in the sash. This term is often confused with Mullion.

Multi-Life Sash: A sash divided into many lites.


Natural Convection: A heat transfer process involving motion in a fluid (such as air) caused by difference in density of the fluid and the action of gravity This is an important pail of heat transfer from the glass surface to room air.

Nailing Fin (Flange): A strip of sheet material either integral or fastened to a unit's frame, creating a flange. This is a common method to install new construction windows and doors.

Notching: A rectangular cut across the grain of the wood member at the end of the board.


Obscure Glass: (Vision proof Glass) - Any textured glass (frosted, etched, fluted, ground, etc.) used for privacy, light diffusion, or decorative effects.

Operator: Crank-operated device for opening and closing casement or jalousie windows.

Outside Glazing: Glazing installed from the outside.


Pane: A sheet of glass for glazing a window. After installation, the pane is referred to as a 'light' (lite) or 'window light.'

Patterned Glass: One or both surfaces of glass with a rolled design; used for privacy and light diffusion.

Picture Window: Large fixed windows; introduced in the 1940's.

Prime Sash: The balanced or moving sash of a window unit.

Projected Window: An awning type window that swings either inwards or outwards at the top or the bottom. The 'PIB' or 'project in at bottom' window can be cleaned from the inside.

PVC: (Polyvinylchloride) - An extruded or molded plastic material used for window framing and as a thermal barrier for aluminum windows.


No words in this glossary that begins with letter Q.


Radiation: The transmission of energy through space without heating the air between, as in Solar Radiation.

Rail: (Head Rail) - (Top Rail) - (Bottom Rail) -(Meeting Rail) - Horizontal member of a window sash.

Reflective Glass: Window glass coated to reflect radiation striking the surface of the glass.

R-Value: (Thermal Resistance) A measure of resistance to heat flow of a 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.


Safety Glass: A strengthened or reinforced glass that is less subject to breakage or splintering, such as glass for storm doors and some windows.

Sash: (Window Sash) - Framework of stiles and rails in which the lights of a window are set.

Sash Balance: A device for counter-balancing a sash of a double-hung window to hold it in the up position.

Sash Stop: A molding that covers the joint between window sash and the jamb.

Screen: Wire Cloth - A close-mesh woven screening material of metal, plastic, or fiberglass for a window screen, to block the entry of insects but permit light, air, and vision through the screen.

Sealed Double Glass: Two panes separated by a sealed space.

Shatter-Proof Glass: (Laminated Glass) - Two sheets of glass with a transparent plastic sheet sandwiched between to form a pane resistant to shattering.

Side Light: (Margin Light) - A fixed often narrow glass window next to a door opening (or window).

Single-Hung Window: A window that is similar to a double-hung window except that the top sash is stationary.

Sliding Sash: (Sliding Windows) - A window which moves horizontally in grooves or tracks.

Sling Psychomotor: A measuring instrument with two thermometers(dry-bulb and wet-bulb) used for determining the dew point and relative humidity of air; its relation to windows is ascertaining the point at which moisture will condense on the inside surface of the glass.

Sound-Insulating Glass: Sound-Resistive Glass -Double glass fixed on resilient mountings and separated so as to reduce sound transmission.

Spacer: The linear object that separates and maintains the space between the glass surfaces of insulating glass.

Stained Glass Window: A window with a painted scene or pattern that has been fired into the glass. Windows with plain colored glass set in lead are also called stained glass.

Stop: (Bead, Side Stop, Window Stop, Parting Stop) - The molding on the inside of the window frame against which the window sash closes, or in the case of a double-hung window, the sash slides against the stop.

Storm Sash: (Storm Window) - An extra window on the outside to protect an existing window, but mainly to increase the thermal resistance of the window.


Tempered Glass: Special heat-treated, high-strength safety glass which shatters into pebble-sized particles but not into slivers.

Thermal Resistance: (R-value) - A property of a substance or construction which retards the flow of heat; one measure of this property is R-value.

Transom: (Transom Bar) - A horizontal member separating a door from a window panel above the door, or separating one window above another.

Transom Light: (Transom Window) - The window sash located above a door.

Triple Glazing: Three panes of glass with two air spaces between, commonly consisting of an insulating glass with a separate storm sash. Also available as an Insulating Window in a single frame.


Ultra-violet Radiation: Extremely short wave length invisible radiation, which is a component of solar radiation, and merges into the visible spectrum; attributed as a source of skin sunburn and color fading of draperies and carpeting.

U-value: A value indicating the rate of heat flow through a building construction, expressed in units of 'Btuh 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 H-values' for the construction.


Vapor Barrier: (Vapor Retarder) - A membrane or coating which resists passage of water vapor from a region of high vapor pressure to low pressure, more accurately called a Vapor Retarder.

Vertical Sliding Window: One or more sashes that move in a vertical direction.

Visible Spectrum: That portion of the total radiation that is visible to the human eye and which lies between the ultra-violet and the infra-red portions of the electromagnetic spectrum. The colors associated with the visible spectrum range from violet, indigo, blue, green, yellow, orange, through red.


Weather-strip: 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.

Weather tight: Sealed to prevent entry of air and precipitation into the structure.

Weep hole: Small holes drilled along the bottom edge of storm sash or combination storm-screens to permit moisture condensation or wind-driven rain to drain away from the sill to the outdoors.

Window: A glazed opening in an external wall; an entire unit consisting of a frame, sash and glazing, and any operable elements.

Window Frame: The fixed frame of a window, which holds the sash or casement as well as hardware.

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 Unit: A complete window with sash and frame.

Wind Pressure: The pressure produced by stopping the wind velocity; the main cause of air infiltration.


No words exist in glossary starting with X or Y or Z.