We want you to make an informed choice. Below you’ll find an alphabetical list which we hope will help answer some of your questions about the terms and technology of commercial glass repair and replacement.



A type of thermoplastic, sometimes used for glazing. Good weather resistance, shatter resistance and visual clarity.

Air Infiltration

The amount of air leaking in and out of a building through cracks in walls, windows and doors.

Air Pockets

Bubbles of air that form within a compound used to adhere/affix glass.

Annealed Glass

Standard float glass (see below).

Aluminosilicate Glass

Aluminosilicate glass contains 20% aluminum oxide, and often includes small amounts of calcium oxide, magnesium oxide and boric oxide. It is able to withstand very high temperatures.

Awning Window

Similar to a casement (see below) except the sash (see below) 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.


Sealant or compound in a joint, a molding, or a stop (see below) used to hold glass or panels in position.

Bed Or Bedding

The bead of a compound applied between a lite (plate) of glass or a panel and the sash or frame. Usually the first bead of compound to be applied when setting glass or panes.


Amount of overlap between the top of a stop (see below) and the inserted edge of a panel or lite of glass.


A piece of lead, neoprene or other suitable material used to position the glass in the frame.


To shim (see below), level and plumb windows/doors in required position.

Borosilicate Glass

Borosilicate glass has a low alkali content, good chemical durability and thermal shock resistance. It is suitable for use in chemical processing plants, laboratory equipment, various high intensity lighting applications and, in the home, as oven ware. It is well-known under the trade name Pyrex™.

Bow Window

A window with three or more units of equal width, which can be fixed, operable or mixed in any combination.


British Thermal Unit


A synthetic rubber used as a sealant and architectural glazing tape.


Applying a compound or sealant to the flat surface of glass before placing it into position.


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


The blocking of exterior air or moisture leaks by filling cracks around doors, windows, or anywhere else with a putty-like compound.

Cavity Wall

When an outer wall is fastened to an inner wall separated by an air space.


A unit for air flow referring to cubic feet per minute.


Wire spring devices to hold glass in rabbetted (see below) sash without stops.


The ability of two or more materials to exist in close and permanent association for an indefinite period with no adverse effect of one on the other.


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


Heat transfer by the movement of fluid or air.

Convex Bead

Bead of compound with convex exposed surface.


Condensation Resistance Factor

Curtain Wall

An exterior building wall which carries no roof or floor loads, made entirely or mostly of metal, or a combination of metal, glass and other surfacing materials supported by a metal framework.


A porous transparent substance that absorbs moisture from within sealed air space or an insulating glass unit.

Double Glazing

Two sheets of glass, separated by an air space. Double glazing improves insulation against heat transfer and/or sound transmission.

Double-Hung Window

A window consisting of two sashes of glass operating in the same rectangular frame. Both the upper and lower halves can be slid up and down. There is usually use a counter balance mechanism to hold the sash in place.

Dry Glazing

A method of securing glass in a frame without the use of a compound.


Ability to take up a certain degree of expansion and contraction.


Ethylene Propylene Diene Monomer – A weather-protection compound with good resistance to ultra-violet radiation.


A thermoplastic resin.

Exterior Glazed

Glass set from the exterior of the building.

Exterior Stop

The removable molding that holds the panel in place on the exterior side.


Exterior perimeter of the roof just below the roof-line, perpendicular to the overhang.

Fixed Window

A window which is stationary, also known as a picture window.

Float Glass

High optical quality glass with parallel surfaces that retain the fire-finished brilliance of the finest sheet glass without polishing and grinding. Float is replacing plate glass.


A warp on the inside surface of a sealed insulating glass unit. Caused by extremes of temperatures.


A pre-formed shape of rubber or rubber-like composition used to fill and seal joints or openings.


The work of installing glass in a frame.

Glazing Bead

A molding or stop around the inside of a frame to hold the glass in place.

Glazing Compound

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

Head or Header

Upper horizontal component of the master frame of a window, patio door or entrance way.

Heat Gain

The transfer of heat from outside to inside.

Heat Loss

The transfer of heat from inside to outside.

Heat-Strengthened Glass

Glass which is reheated to just below melting point and then cooled. A compressed surface is formed which increases its strength.

Hermetically Sealed Unit

An insulated glass unit made up of two lites (panes) of glass which are separated by an aluminum spacer tube. The unit is completely sealed, creating a moisture-free, clean, dead-air space.


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

Horizontal Slider

A window in which the moveable panel slides horizontally.

Insulating Glass

Insulating glass comprises two or more transparent glazing layers, separated by dead air spaces to reduce the heat conduction. Insulating glass units are standard for modern commercial glass applications and a requirement for most new construction.

Interior Glazed

Glass set from the interior of the building.

Jalousie Window

A window of horizontally mounted, louvered glass panels that abut tightly when closed and extend outward when cranked open.


The two vertical members of the perimeter of the sash (see below).


A device into which a latch hooks for security.


A cut, notch, or groove in a material.

Laminated Glass

Two or more sheets with an inner layer of transparent plastic to which the glass adheres if broken. Used for overhead, safety glazing, and sound reduction.

Lead Glass

Lead glass has a high refractive index. Its relatively soft surface makes it easy to decorate by grinding, cutting and engraving. Glass with very high lead oxide content may be used as radiation shielding because it absorbs gamma rays and other forms of harmful radiation.


Another term for a pane of window glass.


A window in which slats are so placed to block rain, sunlight or vision.

Low-E Glass

Glass with a low-emission coating that reduces heat loss in winter and heat gain in summer.


A connector bridging two or more windows or patio doors together.

Outside Casing

Wooden exterior framing of the window.

Patterned Glass

Textured glass for ambient lighting and architectural detailing.

Photochromic Glass

Some types of optical glass become dark when exposed to ultraviolet or short-wave infra-red radiation. When removed from exposure, they revert to their original state.

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 that offers 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 (see above).

Prime Window

A window installed during initial construction, serving as an integral part of the structure.


Pounds per square foot.


A two-sided L-shaped recess in sash or frame to accommodate lites or panels.


The portion of a window which includes the glass and the framing sections directly attached to it.

Security Glass/Glazing

Security glass has multiple layers of glass, and in some cases acrylics, in order to achieve maximum impact resistance from explosions, ballistic assaults and forced entry.

Shading Coefficient

The shading coefficient is the ratio of solar energy that passes through a piece of glass relative to piece of 1/8″ clear glass. A lower number indicates improved solar control.


Strain put on a compound between two surfaces when there is slippage.

Sheet Glass

A transparent, flat glass whose surface has a characteristic waviness replaced by float glass (see above).


Small blocks of composition such as neoprene, etc., placed under the bottom edge of a lite or panel to prevent it from settling down onto the bottom of the frame and distorting the sealant.

Silica Glass

Silica glass is glass whose primary constituent is sand. A temperature of above 1500ºC is necessary for the melting process, making the transparent variety (often known as fused quartz or quartz glass) is expensive and difficult to produce. It is hard, with limited expansion capability, and is used as UV optical glass.

Single Glazing

The use of single thickness of glass in a window or door (as opposed to sealed insulated 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 panes of glass. Whatever the type, the windows slide horizontally in the frame.

Soda-Lime Glass

The most common type of commercial glass, the chemical and physical properties of soda-lime glass transmits light very well and has been used since the time of the Ancient Romans. One of the main disadvantages of soda-lime is high thermal expansion. The higher the soda content of a glass, the poorer its resistance to sudden changes of temperature.

Solar Heat Gain Coefficient

Solar heat gain coefficient refers to the solar gain through glass relative to the current solar radiation.


Small blocks of composition, wood, rubber, etc., placed on each side of glass panels to center them in the channel of the frame.

Spandrel Glass

Heat-strengthened float glass (see above) with a colored ceramic coating on the surface. It has double the strength of annealed glass. It is available in a wide array of colors.


The upright vertical edges of a door, window or screen.


Either the stationary lip at the back of a rabbet (see above), or the removable molding at the front of the rabbet, which helps hold the glass panel in place.

Storm Windows

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

Tempered Glass

When shattered it breaks into small, rounded pieces of glass, rather than sharp, irregular pieces. It is approximately 4 times stronger than standard annealed glass, and is used as safety glazing in patio doors, entrance doors, side lites (see above), and other hazardous locations

Tilt Window

A single or double hung window whose operable sash (see above) can be tilted into the room, for easier washing.

Tinted Glass

A colored mineral admixture is incorporated in the glass. Tinting offers sun protection and better temperature control.

Trombe Wall

Glass covered concrete wall that collects and stores heat passively. Heat radiates back into the outdoors or into internal air or heating.


Uniform Building Code


Term normally used to refer to one single lite (see above) of insulating glass.


The measurement used in determining the ability of different structural components (such as windows) to conduct heat. U-values can tell you how well your windows will hold in your heated or cooled air. The lower the number, the better.

Vinyl Glazing

Glass is held in place in vinyl channels.

Water Glass

The primary ingredient in commercial glasses, like all glasses, is sand, which can be fused to produce glass at a temperature of about 1700ºC. Adding other chemicals to sand can considerably reduce the temperature for fusion to occur. Sodium carbonate, or soda ash, will help reduce the temperature of fusion to about 800ºC, but the resulting composition is water soluble, It is known as water glass. In order to give the glass stability, other chemicals are needed.


A small opening in a wall or window member through which water may drain to the building exterior.

Wet Glazing

A method of sealing glass in a frame by using a knife or gun-applied glazing compound or sealant.

Window Wall

A metal curtain wall (see above) in which windows are the most prominent element. Also refers to the smallest fixed lites (see above) used with wall systems.

Wire Glass

Wire mesh is embedded within the glass so it won’t shatter when broken and remains in the opening longer in the case of a fire. Frequently used in skylights, overhead glazing, and locations where a fire-rated glass is required.

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