Annealed Glass

Float glass (also called “flat” glass) that has not been heat-strengthened or tempered is “annealed glass.” Annealing float glass is the process of controlled cooling to prevent residual stress in the glass and is an inherent operation of the float glass manufacturing process. Annealed glass can be cut, machined, drilled, edged and polished.

the proportion of incident solar radiation absorbed by the glass, expressed as a fraction (see solar properties).

an alternative word for absorptance, expressed as a percentage.

Acid etching
a process whereby the polished surface of glass is etched by exposure to hydrofluoric acid to produce patterns, designs or obscuration.

Acoustic laminate
a laminated glass with special interlayers with better acoustic performance than ordinary laminated glass.

Acoustic performance
simply how much noise does a product stop. It is the properties of a glass or glazing product which describe its airborne sound insulation, as measured by the reduction or attenuation of sound, at specific pitches or frequencies, in decibels (dB), or by sound reduction indexes, such as the mean sound reduction index (Rm), the weighted sound reduction index (Rw) or the road traffic sound reduction index (Rtra).


A Frame
a rack or stillage that is A shaped in profile. It is normally used for transportation mainly for loose glass or for storage.

Air Mass 1
a particular definition of the solar spectrum. See also relative spectral distribution.

Air Mass 1.5
a particular definition of the solar spectrum. See also relative spectral distribution.

Air Mass 2
a particular definition of the solar spectrum. See also relative spectral distribution.

Air Gap / Air space
an alternative term for cavity in an insulating glass unit.

Annealed glass
another term for “ordinary” glass, most commonly used for float glass. Glass that immediately after it has solidified into the required form, while still at a high temperature, is slowly cooled in order to minimise the internal stresses in the glass. The resulting glass can be cut by scoring and snapping and worked. It is, in fact “ordinary” glass as taken from the production line and stored in stock plates. Annealed glass, when broken, gives large fragments with sharp edges and so is not usually classifiable as a safety glass.

Applied Bevel
a bevelled piece of glass that is stuck on to another piece of glass or insulating glass unit with a UV curing resin.

Applied Film
an organic (plastic) film stuck onto glass to give it additional properties, e.g. safety film.

Applied Leading
strips of lead adhered to both surfaces of a pane of glass to give the appearance of a leaded light.


Arrissed edge
an edge finish to the glass where the sharp corners of the edge have been removed.

a process of edge finishing where the sharp edges of a piece of glass are removed.

Aspect ratio
the ratio of the long edge of a pane to the short edge.

the reduction of either sound (see acoustic performance) or electromagnetic radiation (see electromagnetic shielding).

a large pressure vessel that Polyvinyl butyral PVB laminated glass is heated in, to bond the layers of glass and PVB together.


Backing paint: 
a form of opacifier, see also spandrel panels, or a protective coating applied to mirrors or any other glass.

a term commonly used for a barrier, protecting a drop, which comes up to about waist height.

structures designed to either guide the direction of pedestrian traffic or to provide a guarding to the edges of drops.

Base glass: 
a term used to describe the glass, which is subsequently processed, e.g. acid etching, sand blasting, or coated glass.

see glazing bead.

Bend glass: 
an alternative term for curved glass.

decorative process, of grinding a portion off the edge of the glass, to form a shallow angled face, which is subsequently polished.

Blast resistance: 
The ability of a particular type of glass to either withstand explosion pressure waves without breaking or to remain in position if broken.


Body Tinted Float: 
see tinted float.

Borosilicate glass:
Glass with increased amounts of Boron. This means that the glass melts at a higher temperature than conventional soda lime silicate glass.

a form of distortion of toughened glass or heat strengthened glass. Bow may vary depending on the glass type/thickness, size, aspect ratio and other factors. It is measured with the glass in the vertical plane and supported at quarter points. The maximum deviation from a straight edge is measured on the concave surface.

EN1063 classification for bullet resistant glass to withstand .22 Rifle

EN1063 classification for bullet resistant glass to withstand 9 mm Parabellum Handgun = G0

EN1063 classification for bullet resistant glass to withstand .357 Magnum Handgun = G1

EN1063 classification for bullet resistant glass to withstand .44 Magnum Handgun = G2

EN1063 classification for bullet resistant glass to withstand 5.56mm Rifle = R1

EN1063 classification for bullet resistant glass to withstand 7.62 mm Rifle = R2

Break Safely: 
see safe breakage.

Brewster’s Fringes: 
an effect like a rainbow visible under certain lighting conditions, produced in an insulating unit when the two panes of glass are almost exactly parallel to each other.

Brise soleil: 
a partial shading device, usually above a window on the exterior of the building.

stands for British Standard #. BS 6262 part 4 is a safety glazing standard. A full list of glass related British Standards appears at the back of this guide.

depending on context this could be:

  • a bubble of air trapped between interlayers in a laminated glass, or
  • a gas bubble that has become trapped within a piece of glass during manufacture.


Bullet Resistance: 
the ability of a particular type of glass to withstand armed attack using a particular type of weapon not just by stopping the bullets, but also in terms of the spall ejected from the opposite face by the impact. classification is explained in EN1063 standard see BR1 – BR6.

Butt joint: 
a joint between the edges of adjacent panes, which have no frame, but are filled with adhesive sealant, commonly silicone sealant.


Care and Handling

Glass is a very durable material, and if properly maintained, can provide many years of use. The following are several best practices for the care and handling of architectural glass.

  1. Preventing scratches and abrasion.

Scratches are possible, and some chemicals can damage glass. Glass is also susceptible to scratching from contact with other pieces of glass. For that reason, stored sheets of glass should always be separated by an air space or a piece of clean paper. When moving glass, don’t slide one pane over another; scratches and abrasions can result. Use rolling blocks as necessary.

  1. Preventing chemical damage.

It’s important to wash glass frequently, both to remove surface dirt and to prevent staining. If water in the air condenses on the glass surface, it can react with sodium in the glass to create a corrosive chemical called sodium hydroxide. If sodium hydroxide is left on the surface too long, the glass will be permanently damaged and may have to be replaced.

If you see sodium hydroxide forming, you can easily remove it with common cleaners, such as a 50-50 mix of alcohol with water, or a 50-50 mix of ammonia with water, followed quickly by a rinse with clean water. Dry with a soft cloth or a chamois and a cellulose sponge. Note also that installed glass is less prone to sodium hydroxide corrosion, because it’s naturally cleaned by rain.

  1. How to clean architectural glass.

You usually don’t need elaborate measures or chemicals. Cleaning can be as simple as using a water-saturated cloth. Pre-mixed glass cleaners are also acceptable, as long as you follow the printed instructions carefully, and dry the glass immediately with a soft, dry cloth. As mentioned earlier, a 50-50 alcohol/water mix or a 50-50 ammonia/water mix can be used. Just be sure to quickly rinse it off with clean water, and dry with a soft cloth or a chamois and a cellulose sponge.

  1. How to remove graffiti, marking pen, lipstick, paint, sealants or oily films.

Certain solvents can be used in moderate amounts, including isopropyl alcohol, acetone, toluene or mineral spirits. Follow up with a thorough water rinse, and wipe dry with a soft cloth. Used with extreme caution, steel wool is acceptable, but only in the finest grades (00 or 000) and saturated with one of the cleaning solutions listed above. For best results, always clean glass when it’s cool and shaded; not when it’s hot or in direct sunlight.

  1. Don’t use the following under any circumstances.
    • Avoid abrasive or highly alkaline cleaners. Never use petroleum products, such as gasoline, kerosene or lighter fluid.
    • Never use hydrofluoric or phosphoric acid, which will corrode the glass surface. If you’re not sure about a cleaning agent, test it on a small area first.
    • Abrasive brushes and razor blades will also damage the glass and must not be used.

Make sure glass is kept away from areas subject to overspray or run off of chemicals used to clean metal framing, brick or masonry.

And immediately remove any construction material, such as concrete, labels, tapes, paints or fireproofing.

Certifications and standards

National, Regional and Local Building Codes/Standards

The evolution of building construction has led to the development of codes and standards that mandate structurally sound, energy-efficient and environmentally conscious buildings. Many of these codes and standards apply directly to glazing components and should be thoroughly investigated prior to design finalization. A few of the applicable standards include:

  • EN 81 Safety rules for the construction and installation of lifts
  • EN 356 Glass in building – Security glazing – Testing and classification of resistance against manual attack
  • EN 410 Glass in building – Determination of luminous and solar characteristics of glazing
  • EN 572 Glass in building – Basic soda lime silicate glass products
  • EN 673 Glass in building – Determination of thermal transmittance (U-value) – calculation method
  • EN 674 Glass in building – Determination of thermal transmittance (U-value) – guarded hot plate method
  • EN 1063 Glass in building – Security glazing – testing and classification of resistance against bullet attack
  • EN 1096 Glass in building – Coated glass
  • EN 1279 Glass in building – Insulated glass units
  • EN 1363 Fire resistance tests
  • EN 1364 Fire resistance tests on non load bearing elements
  • EN 1522/1523 windows, doors, shutters and blinds – bullet resistance
  • EN 1627-1630 Burglar resistant construction products – Requirements and classification, test methods for the determination of resistance under static and dynamic loading and to manual burglary attempts
  • EN 1748 Glass in building – special basic products
  • EN 1863 Glass in building – heat strengthened soda lime silicate glass
  • EN 12150 Glass in building – thermally tempered soda lime silicate glass
  • EN 12207 windows and doors – air permeability – classification
  • EN 12208 windows and doors – water tightness – classification
  • EN 12412 thermal performance of windows, doors and shutters
  • EN 12488 Glass in building – Glazing requirements – Assembly rules
  • EN 12600 Glass in building – pendulum impact test
  • EN 12758 Glass in building – glazing and airborne sound insulation
  • EN 12898 Glass in building – determination of the emissivity
  • EN 13022 Glass in building – structural sealant glazing
  • EN 13123-1/2 windows, doors and shatters – explosion resistance
  • EN 13501 Fire classification of construction products and building elements
  • EN 13541 Glass in building – Security glazing – Testing and classification of resistance against explosion pressure
  • EN 14179 Glass in building – Heat-soaked thermally tempered soda lime silicate safety glass
  • EN 14449 Glass in building – Laminated glass and laminated safety glass
  • EN 15434 Glass in building – Product standard for structural and/or ultraviolet resistant sealant
  • EN 15651 joint sealants for non load bearing applications in buildings and on pedestrian paths
  • EN 20140 Acoustics – Measurement of sound insulation in buildings and of building elements
  • EN ISO 140-3 Acoustics – Measurement of sound insulation in buildings and of building elements Laboratory measurements of airborne sound insulation of building elements
  • EN ISO 717-1 Acoustics – Rating of sound insulation
  • EN ISO 1288-1…5 Glass in building – Bending strength of glass
  • EN ISO 9050 Glass in building – Determination of light transmittance, solar direct transmittance, total solar energy transmittance, ultraviolet transmittance and related glazing factors
  • EN ISO 10077 Thermal performance of windows, doors and shutters
  • EN ISO 12543 Glass in building – Laminated glass and laminated safety glass

Color Rendering Index (CRI)

The ability of transmitted daylight through the glazing to portray a variety of colors compared to those seen under daylight without the glazing. Scale is 1 – 100.

For instance, a low Ra value causes colors to appear washed out, while a high Ra causes colors to appear vibrant and natural.

In commercial glass, Ra indicates the effect the specific glass configuration has on the appearance of objects viewed through the glass.

Condensation Control

Condensation forms when the surface temperature of the insulating glass or frame drops below dew point, the temperature where the airborne moisture condenses.

For a double-IG unit, there are four surfaces, surface 1, 2, 3, 4, from exterior to interior. As long as the insulating glass (IG) unit is well sealed, condensation should not happen on surfaces 2 and 3.

Generally speaking, Low-E coatings can help reduce condensation on surface 4, or the interior surface because the insulation capability retards the flow of building heat through the glass and helps prevent the cooling of the interior glass below the dew point.


an overhead device to keep rain off can also is used to provide shading on southerly facing glazing.

an abbreviation for end cap.

a term used in glazing, depending on context it can mean:

  • a glazing compound that has been applied to protect another material, for example a silicone sealant that is applied to protect an intumescent compound from the weather
  • a metal glazing bead in a patent glazing system.

Cast-in-place (CIP): 
a type of interlayer used in the manufacture of laminated glass, by pouring a liquid resin between two panes of glass and curing it either chemically or by exposure to UV light.

the gap between the panes of an insulating glass unit also know as the airspace.

Class O: 
see reaction to fire.

Class A: 
see safety glass.

Class Ao: 
see safety glass.

Class B: 
see safety glass.

Class Bo: 
see safety glass.

Class C: 
see safety glass.

Class Co: 
see safety glass.

Clear float: 
untinted float glass (normal window glass) with  neutral appearance.

Coated glass: 
a base glass to which an inorganic coating has been applied, either a pyrolytic coating, usually applied on-line (i.e. during the manufacture of the float glass) or a sputtered coating applied off-line to stock sizes or cut sizes.

Cold radiation: 
a description of the apparent effect felt when sitting near to a cold window surface, e.g. single glazing in cold weather.

Coloured film: 
decorative applied film stuck on to the glass, usually in conjunction with applied leading to give the appearance of a leaded light.

see thermal comfort.

Comprehensive surface stress: 
see toughened glass.

the formation of water droplets on cold surfaces. Condensation is regularly seen on the room surfaces of single glazing, but its incidence is reduced by the use of insulating glass units and particularly those that contain Low E glass. (See also external condensation.)

one of the methods of heat transfer through glass or through the gas in the cavity of insulating glass units.

Conductive heat gain: 
the transfer of heat from outside the building to the inside when the external air temperature is hotter than the internal air temperature.

the ability of a glass or glazing product to prevent persons who accidentally fall against it from falling through.

one of the methods of heat transfer by the gas in the cavity of an insulating glass unit.

Critical locations: 
those areas of a building, e.g. doors, adjacent to doors, or low level glazing, where glazing is most vulnerable to accidental human impact and which may require the use of safety glass. These areas are defined in BS 6262 part 4:1992 Accident Human Impact.

Cross bar: 
a support for the lead cames in large traditional leaded lights.

a term used for broken glass. Cullet is often mixed with the other raw materials (see glass) and recycled in glass manufacturing because it takes 50% less energy to melt cullet.

Curtain Slider:
a type of delivery vehicle that has sliding curtains along the sides to protect the load from the weather.

Curtain walling: 
a glazing system in which the complete façade is glazed into frames attached to the building structure. The glazing may include both vision areas and spandrel panels.

Curved glass: 
glass, which has been heated past its softening point and formed into a curved shape, usually by draping the softened glass over or into a mould. The shaped glass is subsequently cooled slowly to form annealed glass or it may be rapidly chilled to form toughened glass.

Cut sizes: 
panes of glass cut to the final size for glazing.

Care and Handling

Glass is a very durable material, and if properly maintained, can provide many years of use. The following are several best practices for the care and handling of architectural glass.



a weighted measure of sound that is designed to stimulate that of our ears. The international standard for this measure is called the ‘A’ Weighting Curve. Measurements made with this facility are, therefore, termed ‘A’ weighted decibels or, more concisely, dBA, to discriminate from those made in plain dB, which do not depend directly on human reaction.

Decibel (dB): 
the scale used to measure or describe

  • Loudness of sound or
  • Sound insulation and sound reduction indexes (see acoustic performance), or
  • Attenuation of radar and radio waves (see electromagnetic shielding).

how much something moves out of true plane when a load is applied. Glass can bend when a load like snow or wind is applied. Deflections can be calculated in advance and the correct glass for the application specified.

a chemical drying agent that dries and helps remove any organic vapours from the air or gas trapped inside the cavity of an insulating glass unit. It is sometimes called a molecular sieve.

double glazing unit.

randomly scattering the incident light while still allowing transmission. Usually applied to the effects on light of acid etching, sand blasting and 3065 white tinted interlayers. (See also translucent.)

the length and width or other appropriate descriptions of the size of a pane of glass. The glass thickness is not usually referred to as a dimension of the glass.

Direct transmittance: 
the proportion of a solar radiation, which goes straight through the glass without being absorbed. (See also solar properties)

Distance pieces: 
sections of material used to space the pane of glass away from the upstand of the rebate in a frame, in order that an appropriate face clearance and an appropriate amount of sealant is present between the glass and the frame.

Double glazing: 
depending on context:

  • term often used for a replacement window,
  • is also used for secondary sash glazing,
  • and for insulating glass units.

Double glazing unit: 
an alternative name for insulating glass units comprising of two panes of glass.

Double window: 
a window containing two panes of glass in the same vision area, but which are glazed separately, not formed into an insulating glass unit. It is sometimes described as secondary sash glazing.

Drained and ventilated glazing: 
drained glazing where the rebates are deliberately ventilated so that external air circulates around the edge of the glass to assist in keeping the edges dry.

Drained glazing: 
a glazing system in which any lodged water is channelled out of the rebates.

Drying agent: 
another name for desiccant or molecular sieve.

Dual seal system: 
the edge seal of a high performance insulating glass unit, which comprises primary seals between the spacer bar and the panes of glass and a secondary seal between two panes outside the spacer bar.


Edge clearance:
the distance between the edge of the pane and the frame in which it is glazed. The clearance is required to allow for tolerances, avoid contact between the glass and it’s framing and, in the case of drained glazing, to give sufficient room for water to drain away.

Edge cover:
the amount of glass within the rebate, i.e. covered by glazing bead. This is required to ensure the pane is effectively secured (i.e. a mechanical requirement) and also to ensure the edge seal of an insulating glass unit is protected from the weather.

Edge seal:
the hermetic seal around the edge of an insulating glass unit, designed to limit the rate at which water vapour penetrates into the cavity. The better performing edge seals are usually dual seal systems.

Edge Work:
any extra work carried out to the edge of a piece of glass. This can be arrissed edge, a flat ground edge or a polished edge. It may be used to refer to bevelling the edge of the glass.

Effective U value:
sometimes called the energy balance value, a measure of the performance of glass as an energy saving wall construction when its ability to let in useful solar heat gains is combined with its capability for thermal insulation as described by the Ug value.

EN 357 classification for Insulation, fire resistant glass.

Electromagnetic radiation:
a technical expression for all the wavelengths of electrical or magnetic activity. The full spectrum from cosmic and gamma rays with very short wavelength, through X-rays, UV light (generally described as 280 to 380 nanometre (nm) wavelength), visible spectrum (generally described as 380 to 780) and infra-red, to radio waves with very long wavelength.

Electromagnetic shielding:
the use of a Faraday Cage to reduce or prevent the passage of the longer wavelengths of electromagnetic radiation, usually at the frequencies of radar and radio waves. The electromagnetic attenuation give by the Faraday Cage is measured in decibels.

the ability of a surface to absorb or emit electromagnetic radiation. In terms of glass, emissivity is only important with respect to long wavelength radiation (in the range 5000 to 5000 nm) produced as radiated heat by objects at around room temperature. Glass naturally has a high emissivity. However, when made into low emissivity (Low E Glass), the glass surface does not absorb the radiated heat, but reflects it back into the room, enhancing the Ug value of the glazing. Ecosense Essence is an example of Low Emissivity Glass.

European standard #.

a glassy material, which is melted into the surface of the base glass at high temperatures to form a ceramic coating.

End Cap:
wooden boxes held onto the ends of a pack of glass with metal banding. One of the standard methods of delivery for larger quantities of glass.

Energy Balance Value:
also known as the effective U value.

Environmental control:
a term used to describe a glass or glazing product which is used for particular effect on the environment inside a building. Often used as a euphemism for solar control it could also refer to sound insulation, thermal insulation, and the control of lighting levels or a combination of all of these.

EN 357 classification for partial insulation or reduced heat radiation, fire resistant glass.

External applications:
applications where glass or glazing products are used in positions exposed to natural weather.

External condensation:
condensation forming on the external face (surface 1) of glazing with very low Ug values. The effect requires particular combinations of high external humidity, average temperatures and exposure of the glass to clear night sky.


the face of a building, or the cladding covering it.

Façade element:
a part of the façade, such as a window or spandrel panel.

Face clearance:
the distance between the glass and the rebate upstand. This is usually filled with a gasket or sealant.

the glazing immediately above the door.

an alternative term for glass mullion.

Fin box:
the glazing system used at the ends of glass mullions to retain them.

Fire barrier:
an element of construction, such as a wall, partition or glazed screen, which gives an appropriate level of fire resistance.

Fire performance:
the length of time an element of construction, such as a wall, partition or glazed screen, continues to give fire resistance when tested under simulated fire conditions according to BS 476: Part 20.

Fire protection:
the action of a fire barrier in containing a fire.

Fire resistance:
the ability of an element of construction, such as a wall, partition or glazed screen, to maintain integrity and / or insulation when tested under simulated fire conditions according to BS 476: Part 20.

Fire resistant glass:
a glass that in an appropriate glazing system, allows the glazed screen door to achieve fire resistance for more than 30 minutes. The fire resistant glass may be a non-insulating glass, i.e. it satisfies only the integrity requirements of BS 476 for the time recorded during the test, or it may be fully insulating glass, i.e. it satisfies both the integrity and insulation requirements of BS 476 for the time recorded during the test.

Fired-on transfer:
an applied transfer containing ceramic material or enamel, which is melted into the glass surface at high temperature.

depending on the context this may mean either:

  • the method of retaining the glass in position on the building, or
  • the action of installing the glass (glazing it).


Flat ground edge:
a glass edge, which has been completely flattened by a grinding machine, after which the sharp corners are arrissed. The surface appearance is similar to sand blasting.

Flexible compound:
a type of glazing material or sealant, which remains permanently elastic, such as polysulphide or silicone sealant.

Float glass:
glass, which has been manufactured by floating the molten glass on a bed of molten tin until it sets, producing a product with surfaces which are flat and parallel. Sir Alistair Pilkington invented this process in the 1950’s. The first product became commercially available in 1959.

Flush glazing:
glazing which has no fixings or parts of the glazing system protruding beyond the outer surface (surface 1) of the glass.

specially adapted lorry for carrying Jumbo sheets of glass on a stillage.

pieces of broken glass.

a rack or frame for supporting or securing glass to. They are often found inside glass delivery vehicles or can be mounted outside the vehicle when they are known as a side frail.

supported by a frame along the full length of an edge. Typical descriptions of glazing systems would be 4 edge framed or 2 edge framed.

nor supported by a frame on any of the edges. The alternative to framing is by using bolted connections, which could be described as structural glass.

Framing system:
the type of material and the design of the frame supporting the glass. (See also glazing system).

Free path:
the distance, which a person can move directly towards a barrier. This is used as a measure of how much energy can be developed by accidental impact in order to determine the appropriate containment level for glass in the barrier.

Free standing glass protective barrier :
a balustrade in which the glass performs all the mechanical functions. There are no posts or balusters; the glass is cantilevered from the floor and has a continuous handrail mounted on the top edge.

the rate of vibration of a sound wave in Hz (Hertz), also know as the pitch, or the rate of vibration of electromagnetic radiation, particular radio waves, usually in MHz (Mega Hertz).

depending on the context can be:

  • a term used in float glass manufacturing for the raw materials fed into the furnace,
  • an alternative name for enamel,
  • sometimes also used to describe screen printed glass patterns.

glass that has had a screen printed glass pattern applied.


solid, preformed glazing materials used to separate glass from other parts of the fixing or frame.

Georgian Bar:
a grid of bars fixed inside an insulating glass unit in order to make it appear from a distance as though the insulating glass unit is composed of smaller panes. Bar are usually white though Gold and other colours are available.

excessive illumination or excessive contrast between lit and unlit areas, which causes difficulty with vision.

Glare reduction:
the ability to reduce glare problems, either by reducing the overall illumination or by diffusing direct light or a combination of both.

Glass is a liquid that has cooled to a rigid state without crystallising. It is sometimes described as a supercooled liquid, which it is not. A supercooled liquid is still a liquid at a temperature below that at which is would normally solidify. Glass is actually a solid with an amorphous random or non-crystalline structure. The use of the term supercooled liquid suggests the idea of flow, but in fact glass is too rigid to flow at normal temperatures however long a force is applied to it. Glass consists of a network of silicon-oxygen-silicon bonds. These are randomly modified by the presence of calcium and sodium. This arrangement is completely random as it would be a liquid, it is not orderly or regular like the molecules in a crystal of sugar or ice. Because of this random network glass is non-ductile (it cannot be beaten or worked like say copper) and it is this that sets it apart from most other materials. The raw materials we use to make glass are Sand (SiO2) 72.6%. The sand we use at St. Helens is dug from the Cheshire countryside near Sandbach. Soda Ash (Na2CO3) 13%, Limestone (CaCO3) 8.4%, Dolomite (MgCa(CO3)2) 4%, Salt Cake (Na2CO3) 1%. We like to mix as much clean cullet as we can with these raw materials because we use 50% less energy to melt cullet than we do raw materials.

Glass fin:
another name for a glass mullion.

Glass mullion:
a mullion support for glass panes made entirely from glass or from glass beams splice jointed with metal connectors. Usually fixed at a 900 angle as a brace and support. Also know as a fin.

depending on the context it is either:

  • the complete element of construction comprising the glass, the glazing materials and the fixing or frame, or
  • the glass or glass product itself, or
  • the act of installing the glass or glass product.

Glazing bead:
the common mechanism used to retain glass in a frame.

Glazing compound:
a glazing material, which is soft and pliable, such as putty or silicone sealant and can be used as a gap filler.

Glazing factors:
another term for radiometric properties, i.e. solar properties and optical properties.

Glazing materials:
the gaskets, glazing tapes, glazing compounds, bushes, sealants and other items required for the purpose of glazing a glass product.

Glazing platform:
the horizontal leg of the rebate in a frame, upon which the glass sits (on setting blocks) when it is glazed.

Glazing seal:
another term for glazing compound or sealant.

Glazing spacer:
a small separator placed between the glass and frame. See also location blocks and setting blocks.

Glazing system:
the frame and the design or method of fixing the glass into the frame.

Greenhouse effect:
the retaining of solar heat by glass, for two reasons. Firstly, the presence of the glass prevents the wind removing the heat rapidly. Secondly, the glass lets through the short wavelength radiation direct from the sun, but is opaque to the long wavelength radiation emitted by the warmed items inside the greenhouse, so the heat takes a lot longer to escape than it does to enter the greenhouse, resulting in the greenhouse getting warm inside. (See also effective U value).

Glass Minimum and Maximum Sizes

To determine the minimum and maximum sizes available for finished glass products, the glass processor must be consulted. Physical/mechanical capabilities and constraints of the fabricator will affect the final finished glass size availability.

Special considerations for oversized glass: IG and Heat Treatment

It’s important to understand that not all fabricators are equipped to process and / or heat-treat the sizes shown above. Minimum and maximum sizes are dictated by:

  • The size of glass available from the primary manufacturer
  • Any limitations in the fabricator’s equipment
  • The capabilities of the contract glazier
  • Availability of specialized shipping and handling equipment (particularly for oversize units)
  • Specific glass type: (silk-screened, heat-treated, laminated, etc.)

Glazing Guidelines

General Guidelines:

  • All architectural glass should be glazed in a way that ensures that it is free floating and non-load bearing. The glazing material must remain resilient.
  • To prevent premature failure of fabricated, opacified spandrel and laminated glass, an adequate weep system is necessary, or materials that totally repel the passage of water.
  • Adequate clearance must be provided for bow and warp of heat-strengthened and tempered glass, as specified in The related EU standards.


a term for loading or unloading glass from a vehicle by hand.

all the activities involved in transferring the glass from factory to the site and into position in the building ready for glazing.

a term for a coating, which is durable, i.e. resistant to abrasion. It is a term usually applied to pyrolitic coatings.

Heat soaked toughened glass:
toughened glass, which has been heated for a period of time (after the glass has been toughened), at moderately high temperatures to reduce the possibility of spontaneous fractures in service. Heat soaking is recommended where toughened glass is specified for use in roofs, structural glazing and some commercial contract applications.

All float glass contains some level of imperfection. One type of imperfection is nickel sulfide (NiS) inclusion. Most NiS inclusions are stable and cause no problems. There is, however, the potential for NiS inclusions that may cause spontaneous breakage in tempered glass without any load or thermal stress being applied.

Heat soaking is a process that may expose NiS inclusions in tempered glass. The process involves placing the tempered glass inside a chamber and raising the temperature to approximately 290ºC to accelerate nickel sulfide expansion. This causes glass containing nickel sulfide inclusions to break in the heat soak chamber, thus reducing the risk of potential field breakage.

The heat soaking process is not 100 percent effective, adds cost and carries the risk of reducing the compressive stress in tempered glass.

Heat-strengthened glass has a much lower potential incidence of spontaneous breakage than tempered glass. For applications where additional glass strength is required due to thermal stress, and safety glass is not mandated, it is recommended that heat-strengthened or laminated glass to reduce the potential for spontaneous breakage.

Nickel Sulfide (NiS) inclusions:

While extremely rare, nickel sulfide inclusions are another potential cause of breakage.

Nickel sulfide (NiS) inclusions can occur if during the manufacturing process there are nickel-rich contaminants present. These contaminants, such as stainless steel, can combine with sulphur to form nickel sulfide inclusions.

When glass is heat-treated to obtain fully tempered glass, nickel sulfide inclusions change size from what is known as a low-temperature (LT) structure to a high-temperature (HT), crystalline structure. When cooled quickly, the NiS particle is unable to change completely back to its original form (LT).

Over a certain period of time, NiS will slowly convert to its (LT) form but with an increase in volume of about 2 – 4 percent. That increase in size can cause breakage. Float glass manufacturers work extremely hard to avoid any nickel-based contaminants in the batch mix. Instances of NiS inclusions are very unusual.

Design professionals can reduce the risk of breakage due to inclusions by specifying heat-strengthened glass, heat-soaking for fully tempered glass, or laminated glass.

Heat strengthened Glass:
glass which has been heated past its softening point and chilled rapidly to increase its strength and make it thermally safe, but which breaks like annealed glass. Heat-strengthened (HS) glass has been subjected to a heating and cooling cycle and is generally twice as strong as annealed glass of the same thickness and configuration.

  • HS glass has greater resistance to thermal loads than annealed glass and, when broken, the fragments are typically larger than those of fully tempered glass.
  • Heat-Strengthened glass is not a safety glass product as defined by the various code organizations.
  • HS glass is intended for general glazing, where additional strength is desired to withstand wind load and thermal stress.
  • HS glass does not require the strength of fully tempered glass and is intended for applications that do not specifically require a safety glass product.
  • HS glass cannot be cut or drilled after heat-strengthening and any alterations, such as edge grinding, sand blasting or acid etching, can cause premature failure.

When heat-treated glass is necessary, it is recommended to use heat-strengthened glass for applications that do not specifically require a safety glass product. The requirements on heat-strengthened glass and the properties are defined in the EN 1863.

Heat transfer coefficient:
a measure of the rate at which heat can cross a boundary or surface (whether it is by conduction, convection or radiation). The heat transfer coefficients at surface I and surface 4 of an insulating glass unit, as well as the heat transfer coefficient across the cavity, are required to calculate the Ug value of the insulating glass unit.

Hermetically Seal:
an edge seal, which is designed to prevent gas passing. The edge seal of an insulating glass unit is a hermetic seal to minimise the rate at which water vapour can penetrate into the cavity.

a lorry with its own crane, which is used, for delivering stillages or end caps to customers who don’t have a crane.

Hot box:
a devise, which is used to measure the Ug value of insulating glass units or the overall U value of windows, including the frame.

Horizontally Toughened Glass:
glass, which has been toughened in the horizontal position supported on rollers.

Although the glass is kept moving during the process, when it is soft it tends to sag between the rollers. The final product shows traces of this sagging as a phenomenon called roller wave, which may manifest itself as a regular distortion of images reflected in the glass surface.

Hydrofluoric Acid:
This is the acid used in acid etching. It is the only acid that will attack glass and has to be stored in special plastic containers. It is also extremely hazardous to human beings.


Insulating Glass unit. Insulating glass (also referred to as insulated glass) refers to two or more lites of glass sealed around the edges with a gas space between, to form a single unit.

Commonly referred to as an “IG unit,” insulating glass is the most effective way to reduce air-to-air heat transfer through the glazing. When used in conjunction with low-E and / or reflective glass coatings, IG units become an effective means to conserve energy and comply with building codes.

Impact performance:
the impact resistance of a safety glass when tested according to BS 6206.

Impact resistance:
the classification according to BS 6206.

Impact resistant:
a euphemism for being a safety glass.

Impact safety:
an alternative term to impact resistance.

Inclined glazing:
glazing which is either horizontal or sloping up to 750 from the horizontal. Glazing within 150 of vertical is defined as vertical glazing.

an alternative word for non-combustible.

Infill panel:
depending on the context, this could mean:

  • an alternative term for spandrel panel, or
  • a panel underneath the handrail in a barrier.

Inner glass:
see inner pane.

Inner leaf:
see inner pane.

Inner pane:
the pane on the room side of an insulating glass unit or double window.

depending on the context this is either:

  • the act of glazing, or
  • the finished glazing.

Insulated panel:
a spandrel panel with insulation in the form of organic foam or mineral wool attached to the rear face to lower the U value.

Insulating glass unit (or I.G.U.):
Commonly known as a double glazing unit (D.G.U.) a construction consisting of two or more panes of glass spaced apart with spacer bars to form a cavity between the panes. An edge seal is applied around each cavity to form a hermetic seal, minimising the ingress of the moisture into the cavity. A desiccant is incorporated in the spacer bar to dry up any residual moisture. Insulating glass units are assessed in their effectiveness at resisting moisture penetration by BS 5713. The air in the cavity can be replaced by another gas to give the unit specific thermal insulation or sound insulation properties. An insulating unit does NOT normally have any fire resistance properties unless it incorporates at least one pane of fire resistant glass and is glazed into an appropriate fire tested system.

depending on the context, this may mean either:

  • the material applied to the back of spandrel panels to increase the thermal insulation of the panels, or
  • an alternative word for thermal insulation, or
  • the length of time that a construction can give fire resistance in relation to the passage of heat, as defined in BS 476: Part 20.

depending on the context, this may mean:

  • the ability of the glass to hold together after fracture, or
  • the length of time that a construction can give fire resistance in relation to the passage of flames and smoke as defined in BS 476: Part 20.

the material used to separate and bond the plies of glass in laminated glass. The interlayer can be polyvinylbutyral, cast-in-place or intumescent.

Internal applications:
applications where the glass or glazing products are not exposed to natural weather.

Interstitial condensation:
literally means condensation occurring in narrow gaps, cracks or crevices. It is usually found where condensation occurs inside porous structures such as walls.

capable of expanding. In terms of glass and glazing, intumescent means specifically that the material expands with heat.

Intumescent interlayer:
an interlayer which intumesces in fire conditions, not only holding the laminated glass together, but also creating an effective barrier to smoke, flames and heat.

ISO range:
the part of electromagnetic radiation, which is UV light according to the ISO definition (between 280 and 380 nm).


the glass which is bigger thaan the normal glass size is considered as jumbo size. Any size which is more than 3660mm in length or 2440mm in width is considered as jumbo size.


K value:
In some parts of the world, thermal transmittance is referred to as the K value. The units of K value are usually W/m2K, although it is sometimes quoted in kcal/hrm2°C. The latter unit is slightly larger, which may make K values appear smaller. To convert from kcal/hrm2°C to W/m2K, multiply by 1.163.


Laminated glass:
laminated glass is produced by combining layers of glass with plastic (PVB) or resin (CIP) interlayers to form sandwiches of material with specific design properties. Two or more lites (pieces) of glass permanently bonded together with one or more plastic interlayers (PVB) using heat and pressure.

The glass and interlayers can be a variety of colors and thicknesses designed to meet building code standards and requirements as necessary.

Laminated glass can be broken, but the fragments will tend to adhere to the plastic layer and remain largely intact, reducing the risk of injury.

Laminated glass is considered “safety glass” and meets the requirements of the various code organizations that set standards for safety.

Heat-strengthened and tempered glass can be incorporated into laminated glass units to further strengthen the impact resistance.

Hurricane resistance, the need for bomb blast protection, sound attenuation and ballistic or forced-entry security concerns are all primary uses for laminated glass.

Laminated toughened glass:
laminated glass made with all the panes in toughened glass. This is often specified for overhead and structural glazing applications.

Leaded glass:
an alternative name for leaded lights.

Leaded light:
glazing which is formed either:

  • in the traditional manner by using lead cames to fix small panes of glass, or
  • by sticking applied leading on to the surface of a single pane.


terminology used in float glass manufacturing. The annealing Lehr is the cooling area on a float line. Glass leaves the float tank and passes for several hundred yards down the Lehr where it is cooled in a carefully controlled way to prevent stresses being set up in the glass. See also annealed glass.

Lehr end size. Sheets of glass that are the width of the annealing lehr. Normally 3210 mm by another dimension.

Light reflectance:
the proportion of the visible spectrum, which is reflected by the glass, expressed as a fraction. (See optical properties).

Light reflection:
an alternative term for light reflectance, expressed as a percentage.

Light reflection can be described as low (< 15%) medium (15-25%) or high (> 25%).

Light shelf:
a reflective device (possibly a partial mirror), placed in a position near the upper edge of a window, which redirects light from the sun and sky onto the ceiling or towards the back of the room, in order to improve the natural illumination within the room.

Light transmittance:
the proportion of the visible spectrum, which is transmitted by the glass, expressed as a fraction. (See optical properties).

Light transmission:
an alternative term for light transmittance, expressed as a percentage. Light transmission can be described as low (<25%), medium (25-50%), or high (>50%).

Lighting conditions:
the level of illumination, specifically the illumination on the public side and the private side in relation to one-way vision effects.

Linseed oil putty:
the traditional glazing compound for single glazed timber windows. Linseed oil putty is NOT suitable for insulating glass units or laminated glass.

Location blocks:
small separators placed between the frame and the edge of the glass to maintain the edge clearance between the glass and the frame. The separators are called location blocks when positioned on the vertical and top edges of the pane. At the bottom edge their equivalents are setting blocks. Location blocks are not required in every instance, but are commonly used in opening windows, where there may be a tendency for the glass to move in the frame.

Long wavelength energy:
an alternative term for long wavelength radiation.

Long wavelength radiation:
that part of the electromagnetic spectrum (i.e. from 5000 to 50000 nm wavelength), which is produced by objects at around room temperatures. Glass is opaque to this radiation so short wave radiation from the sun is trapped by the glass, giving the green house effect. It is possible to design coatings which are transparent to visible light, but which are highly reflective, i.e. have a low emissivity, to long wavelength radiation.

Low emissivity glass:
simply a glass that keeps more heat in the building than ordinary glass. Glass is coated with a special metallic coating. To be a Low emissivity glass it has to have an emissivity less than 0.2 in the long wavelength radiation part of electromagnetic radiation. Uncoated glass has an emissivity of around 0.9. by comparison. The purpose of Low E glass is to reduce the radiation component of heat transfer across the cavity of an insulating glass unit. Since radiation is a significant component of the heat transfer across a cavity, insulating glass units incorporating Low E glass have much improved thermal insulation properties when compared to units without Low E glass (30% better insulation). Building Regulations across Europe are being tightened to make the use of Low E glass mandatory.

Low level glazing:
glazing which is wholly or partly within the critical location up to 800 mm from finished floor level.


Moire Patterns

An optical phenomenon that may appear as a wavy, rippled or circular pattern under certain lighting conditions. Moiré patterns may be created when one semitransparent object with a repetitive pattern is placed over another and the two are not aligned.

The moiré patterns are not imperfections in the glass or silk-screen pattern – they are a pattern in the image formed by the human eye. This may occur when silk-screen patterns of lines or dots are closely spaced and a secondary pattern is created by the shadow of the ceramic frit on another surface of an insulating glass unit, for instance, when a spandrel panel is installed behind silk-screened glass.

Another potential moiré pattern may be the result of light transmitted through the glass portion not covered with ceramic frit.

Monolithic Glass

Glazing construction of Monolithic Glass consists of a single sheet of glass formed using the float glass manufacturing process. Monolithic glass is often modified for increased strength, improved insulating capability, and safety glazing requirements.

Magnetron sputtering:
a technical term to describe the process used in off-line coating. This involves passing the glass into a vacuum chamber. Argon gas is then introduced and electrical currents are then passed into a series of special coating beams in the roof of the chamber. The current causes small amounts of metal oxides to “sputter” onto the glass below and form a thin uniform coating.

making panes of glass, whose presence may not be immediately obvious, easily visible by the application of permanent patterns, logos or other markings, in order that persons should not walk into them without noticing.

having a permanent inscription indicating the performance of the product and other information. The most common marks are those related to safety glass classification, fire performance and to insulating glass unit performance.

the permanent inscription marked on the glass.

Mean sound reduction index (Rm):
the average of 16 sound insulation values over the frequency range 100-3150 Hz (see acoustic properties).

Metal casement putty:
the traditional glazing compound for single glazed steel windows. Metal casement putty is NOT suitable for insulating units or laminated glass.

a glass, which is highly reflective and opaque. Silvering followed by an application of backing paint form the commonest type of mirror.

Molecular sieve:
another name for desiccant.

a vertical dividing bar between panes of glass in a window or a door.

containing more than two plies of glass in the laminate.

a term applied to fire resistant glazing which has been tested with more than one pane of glass in the assembly. It does NOT indicate double windows or insulating glass units.

Multiple glazing unit:
an alternative term for insulating glass unit comprising two or more panes.


Negative Image:
a term used in sand blasting and acid etching. It refers to the area of glass that has been eroded by the sand or acid.

Newton’s rings:
a fault occasionally found in insulating glass units caused by exceeding the maximum recommended size. If a large insulating glass unit is made with a narrow cavity it is possible that the two panes of glass can deflect and touch, causing a cold bridge. This can lead to a ring of condensation forming at this point.

Nickel sulphide inclusion:
small impurities in the glass that can cause spontaneous fracture of toughened glass some time after toughening.

Noise attenuation:
an alternative term for sound insulation.

Non-insulating glass:
a fire resistant glass which gives integrity for at least 30 minutes, when glazed in a suitable screen, but which does not give insulation for 30 minutes.

Non-loadbearing element:
an element of construction, which plays no part in supporting the building structure or part of the structure. Glazing is very rarely used in a structural capacity.


the range of sound frequencies over which the frequency is doubled, e.g. 200 to 400 Hz.

One-way vision:
an optical effect resulting from the relative luminance of transmitted and reflected light, which allows vision through a window from only one side. Typically a 7:
1 lighting ratio is required for this effect to work properly. This phenomenon is often used for discrete observation in security situations.

made opaque by the application of a backing paint or other backing material, a term related closely to spandrel panels.

Optical properties:
the light transmittance and light reflectance of glass products.

Optical quality:
the presence or absence of visual distortion or small blemishes in the glass.

Overall U value (U factor):
the U value of a window, i.e. the combination of glass and frame. It is a measure of the heat gain or loss through glass due to the difference between indoor and outdoor air temperatures. It is also referred to as the overall coefficient of heat transfer. A lower U-value indicates better insulating properties. The units are W/(m²K).

Overhead glazing:
sloping glazing or horizontal glazing, usually in roofs.


a bulk quantity of glass, around 1-1.5 tonnes in weight often used to describe an end cap. The number of sheets in a pack will depend upon the thickness and size of the glass. 55 sheets for 4 mm SSS, 35 Sheets for 6.4 mm Laminated SSS. LES sizes are also sold in packs but typically 20-30 sheets depending on thickness.

a packaging method for transporting and storing glass. See also rack and stillage.

a piece of glass.

Polished All Round. All the edges of a piece of glass are polished for decorative effect.

Parry Moon range:
the part of electromagnetic radiation, which is UV light according to the Parry Moon definition (between 300 and 400 nm). This is a stricter definition of UV light than the ISO range. In order to meet Parry Moon it is necessary to use products from the laminated glass range.

Patent glazing:
a system of drained glazing which is formed from lightweight framing sections incorporating a built-in gutter in the rebate, commonly used for roof glazing.

Patterned glass:
glass manufactured by passing between two rollers (hence it used to be called rolled glass), one of which rollers forms an impression or pattern into the glass.

literally producing electricity from light. Sometimes also called solar panels. These are special panels designed to convert light into electricity. A solar powered calculator has a photovoltaic panel, the ‘A’ Weighting Curve.

a small defect where part of a coating, enamel or backing paint is missing. Acceptable standards are defined in relevant Product Data Sheets.

the frequency of a sound.

Polarised light:
light waves which are vibrating in a specific orientation, either after passing through a polarising filter, or after being reflected from a surface or from the sky.

Polished Edge:
the edge of a piece of glass that has been first flat ground and is then polished to a high lustre. If all of the edges are polished it may be described as P.A.R. (Polished all round).

Polyvinylbutyral (PVB):
a type of interlayer used in the manufacture of laminated glass, by placing a sheet of the material between two panes of glass and curing under heat and pressure. This is the interlayer used in most laminated glass. In its unprocessed form PVB is opaque. It becomes tr4ansparent in the autoclave due to heat and pressure used, driving moisture from the interlayer.

Positive Image:
a term used in sand blasting and acid etching. It refers to the area of glass that has not been eroded by the sand or acid.

a term used by window manufacturers to describe bar lengths of P.V.C. window section.

an abbreviation for photovoltaic.

applied at high temperature. In relation to glass, this term describes coatings applied on-line when the ribbon of float glass is around 500 to 600°C.


The part of a toughening line where glass is cooled rapidly, usually by blowing high pressure cold air at the hot glass. This is done to set up surface stresses in the glass. See toughened glass.


Quench Marks

Also called strain pattern or anisotropies refers to a specific geometric pattern of iridescence or darkish shadows that may appear under certain lighting conditions, particularly in the presence of polarized light (also called “quench marks”).

The phenomenon are caused by the localized stresses imparted by the rapid air cooling of the heat-treating operation. The quenching process takes place by rapidly cooling the glass with a series of air nozzles arranged in rows. Glass positioned directly in line with a nozzle is induced to develop a slightly greater level of compression than glass positioned between nozzles. These compression differences result in small variations in the density of the processed glass.

Normally, the density variations will have no aesthetic consequences. Occasionally, though, under certain lighting conditions, lines or spots of localized brightness or darkness, known as quench patterns, are observed. Quench patterns are dependent upon the glass thickness, heat treatment equipment and processing conditions, lighting conditions during observation, angle of observation, and other factors. Quench patterns are not considered production or fabrication imperfections according to industry standards.


Relative Heat Gain

The total heat gain through glass for a specific set of conditions.

This value considers indoor/outdoor air temperature differences and the effect of solar radiation. The units are Btu/hr.ft². RHG = [(89°F – 75°F)(Summer U-value) + (200 Btu/hr.ft²)(Shading Coefficient)].


A measure of the resistance of the glazing to heat flow. It is determined by dividing the U-value into 1, (R-value = 1/U-value).

A higher R-value indicates better insulating properties of the glazing. R-Value is not typically used as a measurement for glazing products and is referenced here to help understand U-value.



depending on the context it could mean:

  • one of the methods of heat transfer across the cavity of an insulating glass unit, or
  • electromagnetic radiation;
  • one of the forms in which heat from a fire gets through non-insulating glass.


Radiometric properties:
the combined sets of optical properties and solar properties of a glass product.

the part of a frame, which holds the glass.

a packaging method for transporting and storing glass. See also pallet and stillage.

Reaction to fire:
the way in which a material or product behaves in a fire situation. There are four major classifications used to define the behaviour. Radiative combustion relates to whether fire can pass through a material when used as a roof covering subject to heat from an adjacent fire. Glass generally (1) obtains the highest rating, described as AA or Ext. AA. Materials are also classified by surface spread of flame, the ability or otherwise of a fire to spread along its surface. Glass generally (1) obtains the highest rating.  Materials are also assessed for being non-combustible, i.e. that they do not burn, and for their fire propagation, i.e. whether they contribute to a fire.

Glass is non-combustible, except for laminated glass, which generally (1) achieves the highest rating for fire propagation. Materials, which are non-combustible, or achieve the highest rating for fire propagation, are designated Class 0 according to Building Regulations.

Note (1) Cast-in-place laminated glass has not been tested.

Rebate depth:
the depth of the rebate in a frame, being the sum of the edge clearance and the edge cover of the glass.

Rectangular leading:
a style of applied leading.

Reduced heat radiation:
EN 357 classification EW for partial insulation fire resistant glass.

the proportion of incident light or solar radiation reflected by the glass, expressed as a fraction. (See optical properties and solar properties).

an alternative word for reflectance, expressed as a percentage.

Reflective glass:
glass with a coating which reflects light or short wavelength infra-red radiation.

The brand name for an on-line coated, mirror, which we no longer manufacture.

the distortion of the path of light as it passes through a glass/air interface.

Relative spectral distribution:
a specific description of the solar spectrum used to determine the radiometric properties of glass.

mean sound reduction index. See also Technical Bulletin “Glass and Noise Control”.

the ability of a pane of glass to resist breakage (under accidental human impact).

Rolled glass:
an old name for patterned glass.

Roller wave:
This is a visual distortion encountered in horizontally toughened glass. When glass is heated to a high temperature it becomes soft and it can sag between the toughening plant rollers this is called roller wave distortion. This can give a very slight waviness to things viewed through the glass, which varies with glass thickness and the pitch of rollers.

traffic sound reduction index. See also Technical Bulletin “Glass and Noise Control”.

R value:
Heat losses are sometimes quantified in terms of thermal resistance, abbreviated to R value. This is the reciprocal of the U value. R value = 1/U value, m2K/W (or ft2hr°F/Btu) this means that a glass with a U Value of 1.9 would have an R value of 0.53 (1÷1.9 = 0.53).

weighted sound reduction index. See also Technical Bulletin “Glass and Noise Control”.


Selectivity (Light-to-Solar Gain)

The ratio of the visible light transmittance to the total solar energy transmission (g-value) S = Tvis/g

A higher selectivity means sunlight entering the room is more efficient for daylighting, especially for summer conditions where more light is desired with less solar gain. This ratio is the measurement used to determine whether the glazing is “spectrally selective.”

Shading Coefficient

The non-dimensional value aids calculation of the cooling load of a building and is also known as b factor. It describes the ratio of the g value of a particular glazing to a 3 mm float glass with a g value of 87 %.

Pursuant to EN 410 (2011): b= gEN 410 / 0.87

Silicone Structural Glazing

A structural glazing façade is designed as an aluminium-adapter-framework glued together with a special insulating glass unit using structural glazing silicones. This aluminium-glass-system is suspended into a conventional curtain wall construction. From the exterior side only glass and – depending on the system – weather sealant are visible.

Main features:

  • Joining technique appropriate for the material involved
  • No microstructural change of parts (e.g. as per welding)
  • Load transferring function
  • No local stress peaks by planar transfer of forces trough planar adhesive area
  • Ageing stability of silicone (adhesion, UV resistance, temp. resistance)
  • Safety at extreme mechanical loads (earth quakes, tropical cyclones, explosions, etc.)

A typical structural glazing junction consists of

  • Structural bonding providing a static effective connection
  • Insulating glass edge seal adapted on wind and dead loads and with density function
  • Weather seal

The structural silicones provide a high sheer and Young’s modulus for compensation or transferring

  • Dynamic loads (wind suction, wind pressure, traffic loads)
  • Static loads (dead and snow loads)
  • Differences in the thermal dilatations of involved materials such as glass and aluminum

Safe breakage:
either cracking without producing large openings or separate large sharp edged pieces (i.e. in a manner similar to laminated glass), or cracking into many small fragments (i.e. in a manner similar to toughened glass). Safe breakage is precisely defined in BS 6206. Depending on the context, this may be either:

  • the ability of glass to reduce the possibility of piercing and cutting injuries when subjected to accidental human impact, or
  • the reduction of hazard from breakage of glass in overhead glazing, or
  • fire protection.

Safety backing:
an alternative term for safety film usually used in connection with mirrors.

Safety film:
a plastics film adhered to one surface of the glass with the intention of holding it together after fracture, so that the glass can be classified as a safety glass.

Safety glass:
a glass or glazing product, which conforms to BS 6206, which classifies the product as giving no break or safe breakage when the glass is tested. The glass is classified as Class C, Class B, or Class A (or Class Co, Class Bo or Class Ao, if the test is from one side only of an asymmetric product) according to the drop height achieved in the test.

Safety rating:
the classification achieved for a safety glass to BS 6206.

Sag bending:
technique for bending glass. Glass is heated over a mould till it becomes soft and sags into the shape of the mould. It is then allowed to cool slowly for annealed glass or can be cooled rapidly to make toughened glass. See also curved glass.

Sand blasting:
a process whereby the polished surface of glass is etched by exposure to high-pressure air blown sand or grit. The process is done primarily for decorative effect.

Screen printed glass:
glass which has been given a specific decorative surface finish of either ceramic ink (a type of enamel) which is subsequently fired onto the glass, or epoxy based ink. This product can be used for decorative effect or as a means of glare reduction or solar control.

a glazing compound, which sets after application into a rubbery consistency.

Sealed unit/s:
another name for insulating glass units.

Secondary glazing:
see secondary sash glazing.

Secondary processing:
subsequent processing of glass after initial manufacture, e.g. manufacture into laminated glass, toughened glass, insulating glass units or decorative processing.

Secondary sash glazing:
a double window.

Secondary seal:
see dual seal system.

depending on the context this means either:

  • the ability of glass to withstand manual attack or armed attack, or
  • blast resistance, or
  • electromagnetic shielding, or
  • one-way vision.


Security glass:
a glass, which assists in giving security.

Security glazing:
a glazing system including security glass, which assists in giving security.

a small bubble trapped within a piece of glass.

Setting blocks:
small packers, usually of hardwood, hard rubber or plastics, placed under the bottom edge of the glass to support it off the glazing platform and allow clearance for drainage and ventilation.

Shading coefficients:
the total shading coefficient is a measure of the total amount of heat passing through the glazing (known as the total solar heat transmittance) compared with that through a single clear glass. Glass lets heat through in two ways; a proportion of the short wavelength radiation is transmitted straight through, while some is absorbed by the glass and re-radiated as long wavelength radiation.

The total shading coefficient is split into two parts relating to the proportions of the total solar heat transmittance, which are:

  • the short wavelength – the short wave shading coefficient, and
  • the long wavelength – the long wave shading coefficient.

Short wavelength radiation:
that part of electromagnetic radiation (i.e. from 280 to 2500 nm wavelength), which is radiated by the sun. The main components of glass are transparent to the majority of this short wave radiation.

Silica gel:
a chemical often used as a desiccant or molecular sieve.

Silicone sealant:
a type of glazing compound made from silicone material which is gunned into position and cures into an elastic solid. The product is more resistant to UV light and so is used in roof glazing and structural glazing situations where the sealant could be degraded due to exposure to UV light.

depositing silver on glass to form a mirror. The layer of silver is then protected by a copper backing, which is then protected by a lead based backing paint.

Single glazed:
fitted with only one pane of glass, neither an insulating glass unit nor a double window.

Single sealed:
usually used to describe an insulating glass unit that only has one seal.
Soda lime silicate glass:
ordinary window glass, including float glass, patterned glass and wired glass and any products made of these.

Solar Control:
the effectiveness of glass is limiting solar heat gain. Solar control can be described in terms of the total shading coefficient of the glass, as being low (shading coefficient > 50%), medium (35% < shading coefficient < = 50%), or high (shading coefficient < = 35%).

Solar direct transmittance:
the proportion of incidence solar radiation, which passes straight through the glass, expressed as a fraction. (See solar properties).

Solar energy:
an alternative term for solar radiation. Radiant energy from the sun having a wavelength range of 300 to 2500 nm, which includes UV (300 to 380 nm), visible light (380 to 780 nm) and near infrared energy (780 nm to 2500 nm).

  • % Reflectance Out = percentage of incident solar energy directly reflected from the glass back outdoors
  • % Absorbance = percentage of incident solar energy absorbed into the glass
  • % Transmittance = percentage of incident solar energy directly transmitted through the glass

The sum of percent reflectance out + absorbance out + transmittance = 100%. This is commonly referred to as the RAT equation.

An additional consideration is emission, or emissivity. This refers to the irradiation of absorbed energy that can be emitted toward both the exterior and interior of the building.

Emissivity is controlled through the use of low-emissivity, or low-E coatings.

Solar gain factors:
numbers related to and derived from shading coefficients, which also describe the ability of the glazing to reduce solar heat gain.

Solar heat gain:
the amount of heat from the sun, which passes through the glass into a building.

Solar Heat Gain Coefficient

The percent of solar energy incident on the glass that is transferred indoors both directly and indirectly through the glass.

The direct gain portion equals the solar energy transmittance, while the indirect is the fraction of solar incident on the glass that is absorbed and re-radiated or convective indoors.

Solar Panels:
These fall into two main types, Photovoltaic which convert sunlight to electricity and panels designed to use the sun’s solar radiant heat properties to warm water.

Solar properties:
these properties of glass related to solar radiation, i.e. reflectance, absorptance, solar direct transmittance, total solar heat transmittance, shading coefficients and solar gain factors. The term is also used occasionally to include emissivities and optical properties.

Solar radiation:
the heat, light and UV light emitted by the sun as received at the surface of the earth.

Solar spectrum:
the electromagnetic radiation emitted by the sun and its variation with the wavelength of the radiation. The solar spectrum effectively has a range of wavelengths from 280 to 2500 nm, with the largest proportion present as visible light.


As low-E coatings have become better at reducing air-to-air heat transfer, spacer technology has become the focus of incremental thermal improvements.

Typical commercial spacers are composed of formed aluminum filled with desiccant to absorb any residual moisture inside the IG unit, thus reducing potential condensation. While aluminum is a structurally strong material, the aluminum-to-glass contact point is a very efficient thermal conductor and can increase the potential for temperature differential between the center of glass and the edge of glass, which can lead to condensation and reduces the unit’s overall U-value.

  1. Spacers for Glazing – Spacers for glazing are small blocks of neoprene or other compatible materials, placed on each side of the glass product to provide glass centering, maintain uniform width of sealant bead and prevent excessive sealant distortion.
  2. Spacers for Insulating Units – The spacer in insulating glass units is at the perimeter and keeps the two lites of glass separated at a specific gap width. The spacer material can be aluminum, stainless steel, silicone foam, etc.
  3. Warm-Edge Spacers – This technology is another option for improving thermal properties, reducing condensation and reducing U-values in IG units. There are a number of warm-edge spacer designs available, all of which thermally break the metal-to-glass contact point to some degree, while offering varying levels of structural integrity that may or may not be suitable for commercial applications. Warm-edge spacers can significantly reduce heat conduction when compared to conventional metal spacers.

Small blocks of neoprene or other compatible materials, placed on each side of the glass product to provide glass centering, maintain uniform width of sealant bead and prevent excessive sealant distortion.


Spacer bar/s:
the preformed section, usually aluminium or steel, which spaces apart the panes of an insulating glass unit in order to form the cavity. The spacer bar also usually acts as a container for the desiccant in the insulating unit. They are available in a variety of widths usually acts as a container for the desiccant in the insulating unit. They are available in a variety of widths usually 6, 12, 16 and 20 mm. They are also available in a variety of colours, silver, black, white, bronze and gold.

the pieces of glass ejected from one face of a pane of glass when it is impacted from the opposite face. This term is commonly used in connection with bullet resistance, where a requirement fro reduced spall may be part of the classification system.

Spandrel panel/s:
a glass panel, commonly used in a curtain wall, which is made of an enamelled glass or an opacified glass in order to hide parts of a building structure, such as the edge of floor slabs.  The area of glass panels that conceals structural building components such as columns, floors, HVAC systems, electrical wiring, plumbing, etc.

Spandrel glass is typically located between vision glass on each floor of a building.

Curtain wall and structurally glazed designs often require the use of spandrel glass to achieve a designer’s vision of the finished project.

Spandrel glass applications can be complementary or contrasting color(s) with respect to the vision glass.

Spandrel glass should be heat-treated to avoid thermal stress breakage..

When high light-transmitting or low-reflecting vision glass is specified, achieving an exact spandrel match can be difficult. Daylight conditions can have a dramatic effect on the perception of vision to spandrel appearance. For instance, a clear, bright sunny day produces highly reflective viewing conditions and may provide a good vision to spandrel glass match. A gray, cloudy day may allow more visual transmission from the exterior and produce more contrast between the vision and spandrel glass.

Spectrally Selective Glazing

Spectrally Selective Glazing is high-performance glazing that admits as much daylight as possible, while preventing transmission of as much solar heat as possible.

By controlling solar heat gains in summer, preventing loss of interior heat in winter, and allowing occupants to reduce electric lighting use by making maximum use of daylight, spectrally selective glazing significantly reduces building energy consumption. Glazing’s with a selectivity factor greater than 1.25 can be considered as a “Spectrally Selective Glazing.” The calculation of spectrally selective glazing follows the formula described in the “Selectivity” definition.

Sputter Low-E Glass

Glass with low-E coating applied through an off-line fabrication process.Glass is put into a vacuum chamber, where ionized gas bombards the surface of a series of metal cathodes with ions. Atoms of the desired metal are vaporized and then deposited in layers to form a thin film on the surface of the glass.

Spectral distribution:
the proportion of different wavelengths of a spectrum.

the wavelengths contained within a particular type of electromagnetic radiation, such as the solar spectrum.

Speech hole/s:
holes drilled or sand blasted into a cashier screen to allow cashier and public to hear each other.

Spontaneous breakage:
an alternative term for spontaneous fracture.

Spontaneous fracture:
the breakage of glass for no immediately obvious reason. The term is more often associated with fracture of toughened glass than any other type, because the mode of fracture of toughened glass tends to disguise the cause. See also nickel sulphide inclusion.

Stained glass:
depending on the context, this may mean:

  • a traditional leaded light made with glass of different colours to form a picture or decorative pattern, or
  • a pane of glass with coloured applied film and applied leading which looks like a traditional leaded light,
  • a piece of glass of the type used in the leaded light.


Strain Pattern

Also called quench marks refers to a specific geometric pattern of iridescence or darkish shadows that may appear under certain lighting conditions, particularly in the presence of polarized light.

The phenomenon are caused by the localized stresses imparted by the rapid air cooling of the heat-treating operation. Strain pattern is characteristic of heat-treated glass and is not considered an imperfection.



Steady state:
under constant conditions. This is usually associated with environmental properties. Since the environment (temperature, wind and sun) is in a constant state of flux, this makes calculations of the glass performance very difficult. The solar properties and Ug value of the glass are therefore calculated with a steady state set of conditions.

Stepped unit:
an insulating glass unit with one pane larger than the other. The unit may be stepped on only one edge (often used on the bottom edge of roof glazing) or it may be stepped on more than one edge.

a packaging method for transporting and sorting glass. See also rack and pallet.

Stock plate:
an alternative term for stock sizes.

Stock sizes:
the glass as manufactured and stored ready for cutting down to cut sizes.

a foreign body in the surface of a piece of glass.

Stress pattern:
the effect seen on toughened glass when it is viewed under polarized light or through a polarizing filter, which shows a patterning of spots or bars due to slight non-uniformity of the surface compressive stress in the glass.

Structural glass:
glass used in a manner where it may be supporting other building components (e.g. glass mullions) or where it performs a semi-structural role (e.g. free standing glass protective barriers). The term may also be used for glass fixed using bolted connections (frameless glazing), even if it performs no structural function.

Surface 1:
the surface of the glass exposed to the weather.

Surface 2:
the room side surface of single glazing, or the cavity surface of the outer glass in an insulating glass unit.

Surface 3:
the cavity surface of the inner glass in an insulating glass unit.

Surface 4:
the room side surface of double-glazing.

Surface comprehensive stress:
see toughened glass.

Surface resistances:
the inverse of the heat transfer coefficients at a surface.

Surface spread of flame:
see reaction to fire.


Tempered glass:
another name for toughened glass. Fully tempered glass is approximately four times stronger than annealed glass of the same thickness and configuration.

When broken, it will break into many relatively small fragments, which are less likely to cause serious injury. The typical process to produce tempered glass involves heating the glass to over 600 °C, then rapidly cooling to lock the glass surfaces in a state of compression and the core in a state of tension.

Tempered glass is referred to as “safety glass,” because it meets the requirements of the various code organizations. This type of glass is intended for general glazing, and safety glazing such as sliding doors, storm doors, building entrances, bath and shower enclosures, interior partitions, and other uses requiring superior strength and safety properties.

Tempered glass cannot be cut or drilled after tempering, and any alterations, such as edge grinding, sand blasting or acid etching, can cause premature failure.

The requirements on tempered glass and the properties are defined in the EN 12150.

an exact size physical model of the shape of the glass to be manufactured.

Textured glass:
depending on context this can either be:

  • a patterned glass or
  • a designer glass

Thermal break:
a gap or a portion of low thermal conductivity in a metal frame, separating the inner and outer parts of the frame, designed to increase the thermal insulation of the frame.

Thermal Breakage

Thermal breakage can be influenced by a number of factors. A critical factor to consider in the early stages of glass selection is whether or not the glass will be shaded. When glass is partially shaded by building overhangs or extensions, it becomes cooler at the edges, and stress in the glass may occur, which can result in thermal breakage.

In areas where thermal breakage may be of concern, a thermal breakage analysis must be completed to determine if heat-treating (heat-strengthening or tempering) may be needed.

Heat-treating may also be necessary due to high wind loads or safety glass code requirements. The degree to which the central area of the glass becomes hot is largely dependent on the solar absorption of the glass, which varies among different types of glass. Some additional factors that may influence thermal breakage are listed below:

  • Glass framing that is in direct contact with concrete or other materials that may contribute to the cooling of the glass edge
  • Excessive coverage of the glass edge by the frame
  • Heat-absorbing films attached to the glass after installation
  • The use of internal shading devices such as curtains, drapes or venetian blinds – If shading devices are used, they must be placed away from the glass to allow for a free flow of air at the glass surface
  • The airflow from room cooling or heating vents must be directed away from the glass
  • Buildings not heated during the construction phase may experience an increase in thermal breakage
  • Generally speaking, the greater the glass edge area, the greater the risk of thermal breakage

The potential risk can be estimated by a computer-aided thermal stress analysis.

Thermal comfort:
the physical feeling of comfort in relation to the absence of cold radiation and down draughts from window surfaces of insulating glass units with low Ug value.

Thermal fracture:
a phenomenon where glass is broken by the heat of the sun. See thermal stress and thermal safety.

Thermal insulation:
the ability to restrict the flow of heat. The lower the Ug value, the better the insulation.

Thermal properties:
depending on the context this could mean either:

  • the Ugvalue, or
  • the solar properties, or
  • both of the above

Thermal safety:
the determination of whether annealed glass is thermally safe, given that it has good quality edges. If a glass is not thermally safe it is necessary to use toughened glass instead.

Thermal Stress:
stress developed in glass due to difference in temperature across its surface. In buildings, this is commonly related to glass exposed to the sun, where the central part is heated, but the edges, in the frame, remain relatively cool. Too high a temperature difference can result in thermal fracture of the glass.

Thermal transmittance:
an alternative term for Ug value.

Thermally safe:
has a risk of thermal fracture sufficiently low to be acceptable.

a range of sound frequencies that is 1/3 of an octaveband. (Note that this is not a numerical 1/3. For example, the octaveband from 200 to 400 Hz is split at 250 and 320 Hz.) See Technical Bulletin “Glass and Noise Control”.

Thirdoctaveband centre frequency:
the frequency commonly used by sound engineers to ascribe the average loudness or sound insulation over that thirdoctaveband.

Tight size:
the size of the opening in frame into which glass is to be glazed. The glass should be smaller than the tight size, to allow a suitable edge clearance.

Time/temperature curve:
the prescribed temperature rise in a fire test furnace as a function of the duration of the BS 476 test.

Tinted float:
float glass that has small amounts of metal oxides added during the melting process to colour it and give it solar control properties. Sometimes called body-tinted float. Colored glass which reduces both visual and radiant transmittances.

Tinted glass almost always requires heat-treatment to reduce potential thermal stress and breakage and tends to reradiate the absorbed heat.

Tinted interlayer:
a coloured interlayer in laminated glass, which is tinted to give the glass solar control properties. The tints for PVB laminated glass are described by 4-figure code; the first two digits refer to the colour, the second pair, the amount of light transmission through the vinyl (the light transmission will fall the amount will depend on thickness of glass). The code numbers for the tinted interlayers produced by our sites as at 11/00 are listed below. As there are different vinyl manufacturers it is recommended that glass be supplied from one source to ensure tint matching.

It is possible to tint the resin used in cast-in-place laminated. However this is extremely susceptible to colour inconsistencies from sheet to sheet and batch to batch. The cast-in-place method is not recommended where any consistency of colour is required

Total solar energy transmittance:
an alternative term for total solar heat transmittance.

Total solar heat transmittance:
the proportion of incident solar radiation transmitted by the glass, including both the solar direct transmittance and a portion of the absorbed radiation which is re-radiated, expressed as a fraction. (See solar properties).

Total transmittance:
an alternative term for total solar heat transmittance.

Toughened glass:
glass which has been heated past its softening point and chilled rapidly to build in a surface compressive stress which gives it greatly increased strength and makes it break into small fragments if broken.

Traffic noise reduction index (Rtra):
is derived by taking into account a typical spectrum of road traffic noise (see acoustic properties). Also Technical Bulletin “Glass and Noise Control”.

letting light through, but obscuring clear vision.

an alternative word for transmittance, expressed as a percentage.

the proportion of incident light or solar radiation transmitted by the glass, expressed as a fraction. (See optical properties and solar properties).

a horizontal bar across an opening. Often used to refer to a window that is attached to the bar. Derived from Latin “transtrum” meaning a crossbar.

allowing through vision.

Triple glazing:
an alternative name for insulating glass units comprising three panes of glass.


Ultraviolet transmittance:
the proportion of incident UV radiation transmitted by the glass, expressed as a fraction.

an abbreviation of insulating glass unit.

U value:
a measure of the rate of heat loss through the wall of a building material. Also described as thermal transmittance. U values depend on several different variable factors, such as wind speed and temperature, so they are usually quoted in relation to a specific set of steady state environmental conditions.

Ug value:
a measure of the rate of heat loss through the glass.

UV curing resin:
a resin that has to be exposed to UV light in order to cure. This sort of resin is used in the manufacture of cast-in-place laminated and for sticking decorative features such as applied bevels to glass.

UV filter interlayer:
an interlayer in a laminated glass, which blocks the majority of the UV radiation.

UV Filter Layer:
an alternative term for UV filter interlayer.

UV light:
an alternative term for UV radiation.

UV protection:
an alternative term for UV reduction.

UV radiation:
the part of the electromagnetic spectrum with a slightly shorter wavelength than visible light, within the UV range, known as ultraviolet light or UV light.

UV range:
the wavelengths of the electromagnetic spectrum usually described as being UV radiation. There are two common descriptions, the ISO range (280-380 nanometers nm) and the Parry Moon range (from 300-400 nanometers nm).

UV reduction:
the proportion of UV radiation, which is blocked by the glass.

UV transmission:
an alternative expression for UV transmittance, expressed as a percentage.

UV transmittance:
the proportion of incident UV radiation transmitted by the glass, expressed as a fraction.




Vandal resistance:
the ability to resist damage, as opposed to the ability to resist penetration. We do not have an “unbreakable glass”.

Vent hole:
usually a round hole cut into an insulating glass unit for a fan or ventilator.

Vertical glazing:
glazing which is either true vertical or within 15 degrees of true vertical.

Visible Light spectrum:
that part of the electromagnetic spectrum, which is visible to the human eye, i.e. at wavelengths between 380 and 780 nm. Radiant energy in the wavelength range of 380 nm to 780 nm with Ill. D65 and CIE 2° observer.

  • % Transmittance = (%Tvis) percentage of incident visible light directly transmitted through the glass
  • % Reflectance Indoors = percentage of incident visible light directly reflected from the glass back indoors
  • % Reflectance Outdoors = percentage of incident visible light directly reflected from the glass back outdoors

Vision area:
depending on the context, either:

  • an oval with axis equal to the height and width of the pane, or
  • the parts of a building façade or curtain wall which are intended for the passage of light.

Vision panel:
depending on context, either:

  • a term used to distinguish a part of curtain walling as being distinct from the spandrel panel, or
  • a small pane of glass in a door to alow people to look through without necessarily opening the door.

Visual distortion:
the warping of images when seen through the glass, due to the surfaces of the glass being not exactly flat and parallel. The term also sometimes applied to reflected images.

Visual quality:
an alternative term for optical quality.


a characteristic of electromagnetic radiation, by which it can be described. Usually used to discriminate between different types of electromagnetic radiation, such as visible, UV and infrared (heat). Energy generated by radiated heat sources such as electric coil heaters or natural gas-powered, forced-air furnaces. Also, any object that can absorb heat and radiate it is producing long-wave, infrared energy.

NOTE: When short-wave energy from the sun is absorbed and radiated by glazing, it is converted to long-wave energy.

the area density of a pane glass, expressed in kg/m2. Glass weighs 2.5 kgs/m2 per mm of thickness (i.e. 4 mm = 10 kgs/m2, 6 mm = 15 kgs/m2, 10 mm = 25 kgs/m2).

Weighted sound reduction index (Rw):
incorporates a correction for the ear’s response and has been derived in accordance with BS 5821:
1984 (see acoustic properties).

Wind resistance:
the ability of the glass to withstand wind loads.

Wired glass:
generic name which covers polished wired glass and wired cast glass.

Wet Glazing

Glazing is a transparent part of a wall, usually made of glass or plastic (acrylic or polycarbonate). Common types of glazing that are used in architectural applications include clear and tinted float glass , tempered glass , and laminated glass as well as a variety of coated glasses, all of which can be glazed singly or as double, or even triple, glazed units.

Wet Glazing is a method of securing glass in a frame by use of glazing compound or sealants.

Wind Load

How can wind damage architectural glass? The key to prevention comes early in the design stage.

Wind load is the result of wind creating pressure and suction that the glass must resist. The wind load on a specific building depends on that building’s height, shape, relationship to surrounding buildings and terrain, along with local wind speeds and the duration of gusts.

Center deflection is a major consideration in wind load and should be addressed in the early phases of design. Excessive center deflection can result in edge pull out, distortion of reflected images and possible contact between glass and interior components, such as room dividers and window blinds.

Insulating Glass

The effects of wind on insulating glass units are, in many cases, complex and require a computer-assisted wind load analysis to adequately consider some of the variables. Design professionals must take into account the following variables:

  • Air space expansion and contraction caused by the effects of changing temperatures, barometric pressure, altitude and differences in weathering in the #1 and #2 surfaces
  • Asymmetrical loading, i.e., lites of varying thickness
  • Condition of edges (free, bonded or fixed)
  • Variation in sight line or air space width
  • Thermal stress

These variables must be considered carefully because they can dramatically alter the data taken from a standard wind load chart.

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