Glossary of Terms


That property of a coating or sealant which measures its ability to stick or bond to the surface to which it is applied.

Air Infiltration

The measure of air movement through the weather seals of a window.

Air pockets

Bubbles of air formed within a compound or between two adjacent beads of compound applied successively in a joint.

Awning Window

Similar to a casement except the sash is hinged at the top and always projects out.

Bay Window

An arrangement of three or more individual window units, attached in such a way as to project from the building at various angles. In a three unit bay, the center section is normally fixed with the end panels operable as single hung or casements.


A sealant or compound after application in a joint, irrespective of the method of application, such as caulking bead, glazing bead, etc. Also a molding or stop used to hold glass or panels in position.

Bed or Bedding

The bead of a compound applied between a lite of glass or a panel and the permanent stop or sight bar of the sash or frame, and usually the first bead of compound to be applied when setting glass or panes.


To shim, level and plumb windows in required position.


A single unit of glass, generally longer vertically than horizontally, that can either be opened to the outside (most common) or inside, via crank mechanism.


The 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.


When water vapor, which is present in all but the driest air, comes in contact with a surface that is below what is called the "dew point temperature," the vapor becomes liquid and is called condensation. An example is as follows: condensation forms on a glass of ice water since the surface of the glass is down to the dew point temperature of the inside air.


Process of heat transfer through a material from a warm surface to a cool surface.


Heat transfer by the movement of fluid or air.


Illumination of indoor spaces by natural light.


A unit for expressing the relative intensity of sounds on a scale from zero for average least perceptible sound to about 130 for the average pain level.

Dew Point

The 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.

Double Glazing

In 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.

Dry Glazing

A method of securing glass in a frame by use of a dry, preformed resilient gasket, without the use of a compound.


Pliability, ability to take up expansion and contraction; opposite of brittleness.


The ability of a material to radiate energy.


A flexible usually thermosetting resin made by copolymerization of an epoxide with another compound having two hydroxyl groups and used chiefly in coatings and adhesives.

Fading Factor

The 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.


A flat, usually horizontal member of a building having the form of a flat board; a flat piece used as a molding, a horizontal piece (of board) covering the joint between the top of a wall and projecting eaves.

Float Glass

Glass which has its bottom surfaces formed by floating on molten metal, the top surface being gravity formed, producing a high optical quality of glass with parallel surfaces and, without polishing and grinding, the fire-finished brilliance of the finest sheet glass. Float is replacing plate glass.

Fixed Window

1. A window which is stationary, also known as a picture window. 2. The part of a sliding window or door which is non-moveable, also known as inactive.


A preformed shape of rubber or rubber-like composition used to fill and seal joints or openings either along with or in conjunction with a supplemental application of a sealant.


The sealing of the joints around lites of glass or panel set in a U-shaped channel employing removable or fixed stops.

Glazing Bead

A soft dough-like material used for filling and sealing the space between a pane of glass and its surrounding frame.

Glazing Compound

A soft dough-like material used for filling and sealing the space between a pane of glass and its surrounding frame.

Heat Gain

The 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 Loss

The transfer of heat from inside to outside by means of conduction, convection, and radiation through all surfaces of the house.


Similar to casement window except the sash is hinged at the bottom.

Horizontal Slider

A window where the moveable panel slides horizontally.


Relating to, or having a strong affinity for water; water ‘sheets’ on this surface, does not bead.

Insulating Glass

Insulating glass refers to two (or more) lites 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 when two lites of glass are used.


In sash, the two vertical members of the perimeter of the sash.


Another term for a pane of glass used in a window. Spelled "lite" in the industry to avoid confusion with light as in "visible light".


A slatted opening for ventilation in which the slats are so placed to exclude rain, sunlight or vision.


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.


The tabular tip of a caulking gun through which the compound is extruded.

Outside Casing

Exterior framing of the window. 1. A pre-assembled section of wall, including framing (if any), window area, and solid area. 2. A solid filler or facing material, either of one piece or an assembly, or use with a surrounding frame.


The quality of permitting passage of water vapor through openings without causing rupture or displacement.


Relating to the acceleration of a chemical reaction by radiant energy (as light) acting either directly or by exciting a substance that in turn catalyzes the main reaction.

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.

Plate Glass

Polished 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.

Prime Window

A window that is installed during the initial construction and services as an integral part of the structure. Not to be confused with storm windows which serve as a secondary weathering device.


A special coating designed to enhance the adhesion of sealant systems to certain surfaces or a final organic coating to a surface.


Sealing of a porous surface so that compound will not stain, lose elasticity, and shrink excessively, etc., because of loss of oils or vehicle into the surface.


The process of a chemical change brought about by the action of heat.


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.


The portion of a window which includes the glass and the framing sections which are directly attached to the glass. Not to be confused with the master frame into which the sash sections are fitted.

Sash & Door

Manufacturer of doors and windows (complete units). There are 3 basic sash types: wood, aluminum and vinyl.


Compound used to fill and seal a joint, or seal an insulating glass unit around its edge; as contrasted to a sealer which is a liquid used to seal a porous surface.

Shading Coefficient (SC)

The measure of the heat gain through glass from solar radiation. Specifically, the shading coefficient is the ratio between the solar heat gain for a particular type of glass and that of 3mm clear glass. The lower the number, the better the shading performance.

Single Glazing

The use of single lite of glass in a window or door (as opposed to sealed insulating glass which offers far superior insulating characteristics).

Single Hung

Similar in appearance to the double-hung window, the single-hung window features a stationary top and a movable bottom half.


A slider window may have one or two movable sash members. Whatever the type, the windows slide horizontally in the frame.

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.


A second set of windows installed on the outside or inside of the prime windows to provide additional insulation.

Summer Day U-Value

The calculation of U-Value using Summer Daytime environmental conditions of a hot outside temperature and direct sunlight.

Tilt Window

A single or double hung window whose operable sash can be tilted into the room for interior washability.

Tinted Glass

A mineral admixture is incorporated in the glass, resulting in a degree of tinting. Any tinting reduces both visual and radiant transmittance.


The fraction of radiant energy that, having entered a layer of absorbing matter, reaches its farther boundary.

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.


A 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.


Polyvinyl chloride material that can be both rigid and flexible, used in glazing channels, weather stripping and/or frame materials of both windows and doors.

Volatile organic compounds (VOCs)

Are emitted as gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects. Concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors. VOCs are emitted by a wide array of products numbering in the thousands. Examples include: paints and lacquers, paint strippers, cleaning supplies, pesticides, building materials and furnishings, office equipment such as copiers and printers, correction fluids and carbonless copy paper, graphics and craft materials including glues and adhesives, permanent markers, and photographic solutions.

Winter Night U-Value

The calculation of U-Value using Winter Nighttime environmental conditions of a cold outside temperature and no sunlight.

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