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The Technical Information gives you the accurate, detailed information you need to choose the right Solar Protection Glass, including:
- Types of glass
- Performance capabilities
- Glazing procedures
- Wind load and thermal stresses
- Proper handling and maintenance
It is important to be knowledgeable of which side of the glass is coated. Do not touch the glass surface to identify the coated side.Touching the coated surface with bare hands or with gloves is not a reliable method for detecting the coated surface. The functional layers are electrically conductive (except the Anti-reflective and Low Maintenance Glass coatings, SunGuard HD Silver 70 and SSG 52), so may be easily identified with a commercial coating detector or ohmmeter. Use these detectors within 12mm of the edges whenever possible to prevent damage to the coated surface. If you have more questions, however, please call us at +352 52 1111 to consult with a SunGuard Solar Protection Glass specialist, or click here to order a sample.
Glass is potentially very strong; however, in sheet form the strength is reduced by the presence of invisibly small defects, known as Griffith cracks, which cause stress concentrations allowing cracks to propagate. Strength may be reduced further by larger visible defects.
Most glass breakage is caused by one or more of the following conditions:
- Surface or edge damage
- Deep scratches or gouges
- Severe weld splatter
- Missile/windborne debris impact
- Glass to metal contact
- Wind/thermal loading
Generally, thermal loads on glass occur as a result of the glass being exposed to sunlight and/or interior heating. If the glass is heated nonuniformly, temperature gradients occur within the glass, creating tensile stresses. The amount of tensile stress is a function of the extent of temperature differences within the glass. Thermal breakage occurs when the tensile stresses exceed the glass edge strength.
Strategies to Avoid Architectural Glass Breakage
Go to the following sections in this Technical Library that deal with common problems relating to architectural glass breakage and the best ways to prevent them:
- Wind Load
- Improper care and handling (Glazing Guidelines)
- Improper care after installation (Care and Handling)
Reducing the Risk of Thermal Breakage
Glass is vulnerable to thermal breakage under several circumstances. One common example occurs when glass is partly shaded by building overhangs or extensions. In this situation, heat causes the center of the glass to expand, while the edges remain cool, which can result in stress and thermal breakage.
The other situation occurs when glass is installed before heat is turned on in the building. Here again, edges will remain cool in the frames, while the center of the glass may be heated by the sun. The resulting temperature difference between center and edge can cause breakage.
Generally speaking, the greater the area of the edge, the higher the risk of thermal breakage. But other factors can also come into play, both during construction and after the building is occupied.
- Putting the glass frame in direct contact with concrete or other materials that may increase cooling of the edge
- Excessive coverage of the edge by the frame
- Installing glass in an unheated building
- Attaching heat-absorbing films after the glass is installed
After the building is occupied:
- Curtains, shades or blinds that are placed too close to the glass. Heated or cooled air trapped too near the glass can cause thermal stress. Air must have sufficient space to circulate.
- Airflow from heating or cooling vents that is not directed away from the glass.
How can you reduce the risk of breakage?
Go to our Product Performance Comparison Tool for a quick guideline on thermal stress. Or ask your Guardian Architectural Sales Manager for a computer-modeled estimate of potential thermal stresses when you’re selecting glass for your project. Contact us at +352 52 1111.
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.
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.
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.
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 mix of 10 % ammonia with 90% tap 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.
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 mix of 10% ammonia with 90% tap water 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.
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.
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.
Protect your glass on the building site. 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.
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:
- ANSI Z 97.1 Glazing Materials Used in Buildings, Safety Performance Specifications and Methods of Test
- ASTM C 1036 Standard Specification for Flat Glass
- ASTM C 1048 Standard Specification for Heat-Treated Flat Glass–Kind HS, Kind FT Coated and Uncoated Glass
- ASTM C 1172 Standard Specification for Laminated Architectural Flat Glass
- ASTM C 1376 Standard Specification for Pyrolytic and Vacuum Deposition Coatings on Glass
- ASTM E 773 Standard Test Method for Accelerated Weathering of Sealed Insulating Glass Units
- ASTM E 774 Standard Specification for the Classification of the Durability of Sealed Insulating Glass Units
- ASTM E 1886 Test Method for Performance of Exterior Windows, Curtain Walls, Doors and Storm Shutters Impacted by Missile(s) and Exposed to Cyclic Pressure Differentials
- ASTM E 1996 Standard Specification for Performance of Exterior Windows, Curtain Walls, Doors and Storm Shutters Impacted by Windborne Debris in Hurricanes
- ASTM E 2188 Standard Test Method for Insulating Glass Unit Performance
- ASTM E 2190 Standard Specification for Insulating Glass Unit Performance and Evaluation
- ASTM F 1642 Standard Test Method for Glazing and Glazing Systems Subject to Airblast Loadings
- CPSC16CFR-1201 Safety Standard for Architectural Glazing Materials
The following images depict the most common glass configurations and identify the glass surfaces with numbers showing the glass surfaces counting from exterior to interior.
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.
To determine the minimum and maximum sizes available for finished glass products, the glass fabricator 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 Treament
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.)
- 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 ASTM Standard C-1048.
Guidelines For Conventional Glazing:
- Framing must be structurally sound, able to support the glass weight without any sagging, twisting or deformation that may impose a load on the glass. No framing member should deflect more than 1/175 of its span. Maximum deflection, under load, is 3/4”.
- Appropriate setting blocks, face gaskets, wedges and edge spacers must meet the current requirements of ASTM Specifications D-395 and C-864 for hardness, deformation, compression set and polymer content.
- Framing members must be free of any glazing obstructions that would result in glass damage.
- To reduce the risk of thermal breakage, a minimum framing extension is necessary. If thermal breakage is a potential concern, ask for a thermal stress analysis.
- If lateral glass movement is anticipated due to wind load, seismic load or other causes, anti-walk blocks should be used.
Guidelines For Silicone Structural Glazing:
- Remember that glass is not typically used as a structural member. The support framing must be of sufficient strength and dexterity to absorb all loads resulting from wind, thermal expansion or building movement.
- Back up mullions are recommended when glass is 1/4” thick or less, and in all instances where insulating glass is specified.
- Coatings that transmit higher amounts of light may show edge read-through. Insulating glass used in structural glazing must be silicone units.
- Opacified spandrel must have trim in the back of the opacifier to ensure glass-to-silicone adhesion.
- When structural silicone is used, its compatibility and adhesive characteristics must be confirmed in the early design stages.
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.
Guardian offers SunGuard coated glass products that can be safely heat soaked if it is determined the heat soaking process is necessary.
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, Guardian recommends heat-strengthened or laminated glass to reduce the potential for spontaneous breakage.
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 (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 must achieve residual surface compression between 3,500 and 7,500 PSI for 6 mm glass, according to ASTM C 1048. Please contact Guardian regarding thicker glass standards.
- 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, Guardian recommends the use of heat-strengthened glass for applications that do not specifically require a safety glass product.
Also referred to as insulated glass, insulating glass refers to two or more lites of glass sealed around the edges with an air 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.
The most common architectural insulating glass unit configuration is 1/4" glass / 1/2" air space / 1/4" glass.
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.
Moiré is 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 defects 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.
Glass is made by mixing metal oxide components together, such as sand (silica or silicon dioxide), soda ash and limestone. After being mixed in certain proportions, these components are heated and cooled in a controlled process to create the desired type of glass.
Float Glass Properties Reference
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.
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.
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.
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.
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 must be heat-treated to avoid thermal stress breakage.
Guardian has extensive experience with spandrel glass applications and can help architects and building owners achieve the desired appearance, while reducing the risk of 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.
Guardian recommends full-size, outdoor mock-ups be prepared and approved in order to confirm the most desirable spandrel option for a specific project.
Also called "quench marks"
Strain pattern 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 a defect.
Fully tempered glass is approximately four times stronger than annealed glass of the same thickness and configuration. Residual surface compression must be over 10,000 PSI for 6mm glass, according to ASTM C 1048. Please contact Guardian for thicker glass standards.
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 1,000 degrees F, then rapidly cooling to lock the glass surfaces in a state of compression and the core in a state of tension, as shown in the diagram.
Tempered glass is often 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.
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. Contact Guardian’s Science & Technology Center for assistance with thermal stress analysis.
Wind load is the result of wind creating pressure 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
- Load-sharing other than 50-50
- Condition of edges (free 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.
Guardian follows the current ASTM E 1300 "Standard Practice for Determining the Minimum Thickness and Type of Glass Required to Resist a Specified Load." This information represents in-service glass and supersedes the traditional straight-line graph as well as other wind load charts.
The ASTM wind load standard is applicable to projects built in the United States. Wind load standards for other countries may differ, and this difference must be addressed in the early stages of design.