SECTION 08 8000 – GLAZING
The prevention of water getting in the glazing system is critical and depends on various details inherent to the system. The framing system must be configured to allow for the promotion of drainage, and have internal as well as an external seal that is glass to frame seals, and frame perimeter seals and flashings. All water, whether in the form of rain, melting snow, or condensation cannot be excluded with the glazing sealants, so a long-lasting means of providing for this internal drainage is very important.
Glazing materials generally fall within two categories; wet and dry. Wet glazed systems are generally better than dry glazed systems in preventing water entry around the glass and into the glazing pocket. The timelines for replacement of dry gaskets and the cab bead of wet glazed systems are about the same. The pros and cons of these wet and dry glazing systems are as follows:
- Wet glazing has an improved resistance to water penetration.
- Wet glazing requires exterior access for installation, maintenance and glass removal.
- Wet grazing protects IGU edges and laminated glass from water and premature deterioration.
- Wet glazing is dependent on highly skilled workmanship for surface preparation and is affected by weather conditions.
- Wet glazing reduces glass movement.
- Wet glazing is more expensive than dry glazing.
- Dry glazing may be done from the interior.
- Dry glazing is not as watertight as wet glazing.
- Dry glazing is less dependent on workmanship and the effects of inclement weather.
- Dry glazing gaskets can shrink, creating water openings, and gaskets can roll into glazing pocket placing uneven stress on the glass and allowing the glass to move or “walk."
Compatibility of the glazing materials and the glass is essential for the long term performance of the installation. Reactions due to physical contact or close proximity of incompatible materials may occur. Volatile fumes from one material can adversely affect adjacent materials within the closed confines of the glazing pocket. Fillers, plasticizers, oils or other elements or compounds may leech out of sealants, gaskets, spacer shims, jamb blocks or setting blocks and possibly have a negative effect on the sealants, adhesives or coatings of fabricated glazing products. Some of these materials or compounds can act on their own, while others react with moisture, heat, or other materials. It is extremely important to use compatible materials and sealant manufacturers generally conduct compatibility tests in their labs and provide these results.
Wet Glazing Method
There are three general types of wet glazing materials; pre-formed tape, curing and non-curing gunnable elastomeric sealants, and putty and glazing compounds. Lateral shims are normally used to center the glass within the opening with wet glazing materials and to hold the glass in position due to wind loads, building movement, or vibration.
Dry Glazing Method
Dry glazing, also known as compression gasket systems, utilizes extruded rubber gaskets as one or both of the glazing seals. Their performance is not affected by installation, weather, workmanship and compatibility issues as found with wet glazing systems.
Two gasket types are used; soft closed cell gaskets and firm dense gaskets. Materials used are generally neoprene, EPDM, or silicone rubber composition. A glazing system may use one type on both sides (dense and dense), or a combination of the two (soft and dense). Each gasket requires a means to prevent disengagement; they may use an integral dart, a locking nub, or an adhesive material to prevent release. Verify fit and tolerances with gasket and metal manufacturers when using gaskets having an integral dart or locking nub. The softer gasket may compress 25 to 40 percent and form a weathertight seal when the dense gasket is in place.
Wet/Dry Glazing Method
Wet/dry glazing is simply a combination of wet and dry glazing used on each side of the glass. Cap beads may be applied at the exterior perimeter of the glazing to make the glazing watertight/weathertight. The cap bead may be a component of the original installation or a post-installation corrective maintenance solution.
Butt-Joint Glazing Method
Butt-joint glazing involves the installation of glass that provides a wide horizontal viewing area without vertical framing members. It uses a conventional captured approach to support the head and sill of glazing panel, using metal or wood retaining members and wet, dry, or wet/dry sealants. The difference occurs at the vertical edges of the glass where these edges are spaced slightly apart and sealed with a silicone sealant. This vertical sealant joint is not considered structural and only serves as a weather stop.
The design of an acceptable butt-joint glazing installation requires attention to detail at every stage. Since the glass is only supported on two edges, usually the top and bottom, design load charts provided for four-edge supported systems do not apply. Substantially greater glass deflection and stress under design load is expected for two-edge supported glass than four-edge supported glass. Typically, 3/8 inch (9.5 mm) thick glass is recommended. Thicker glass will reduce deflection, but heat-treating the glass will not. The characteristic warp of heat-treated glass will make it more difficult to achieve the aligned vertical silicone sealed joint. These vertical glass edges should be ground with a slight arris along the outside and inside corners and polished.
The use of insulating glass for butt-joint glazing is not recommended. As the glass deflects, the sealants are under extreme shear loads along the unsupported edge between the glass and the spacer. Glass-clad polycarbonates as well as plastic laminates are also not suitable for butt-joint glazing due to the expansion and contraction rates of these materials.
Pressure Glazed Systems
Pressure glazed systems apply pressure or compression to achieve weather-tightness. This pressure is typically applied using mechanical means, but a dry or wet/dry system may also be considered pressure glazed due to the dense wedge gasket exerting pressure through the glass to compress the weather seal and making the glazing resistant to water penetration.
The exterior weather seals are typically neoprene, EPDM, or other synthetic rubbers. Excessive or inadequate torque on the pressure plate bolts may cause damaging stress on the glass edge or result in possible air and water leakage. A continuous isolation joint is often used to assist in the control of compression on the glass and to control the weeping of water to the outside along the horizontal rails.
Proper installation and sealing of the system joint plugs is necessary to provide for watertight construction.
Structural Silicone Glazing
Structural silicone glazing (SSG) is not to be confused with butt-joint glazing. Structural silicone glazing provides support of the glass along the edges.
SSG provides a structural silicone sealant to attach one or more edges of the glass to a metal framing support. These systems are typically described based on the number of sides of the glass are being supported in this manner.
A two-sided system typically has the opposite two edges of the glass structurally sealed to the faming mullions and these may be either vertical or horizontal. The remaining two edges of the glass will be retained conventionally. From the exterior, a two-sided system does appear like butt-joint glazing, but a framing member is at the interior side supporting the glass. Two-sided systems may be designed to be either shop or field glazed.
A four-sided system has the four edges of the glass structurally sealed to the framing mullions, both vertically and horizontally. Four-sided systems should be designed to be shop glazed. The glass is adhered to the framing mullions in the shop with structural silicone sealant. This assembly is then transported to the project site and erected as a unit. The weather seal is then applied to finish this work.
Shop glazing typically provides better results because of the uniform, controlled working conditions, improved quality assurance aspects, and the ability to use a fast-curing two-part silicone sealant. Certain local building codes require the use of shop glazing for four-sided SSG applications.
Acrylic Foam Tape Structural Glazing
Acrylic foam tapes are relatively new for use in structural glazing applications. These types provide an acrylic adhesive throughout the entire tape construction including the frame core. Acrylic foam tapes act as the primary bonding agent of the glass to the metal frame for curtain wall or commercial window system application.
The same basic guidelines of SSG should also be followed for use of acrylic foam structural glazing tape for a glazing application. This includes the following;
- a design review of the glazing systems and project details.
- adhesion testing.
- proper surface preparation.
- training and a quality assurance program.
Only acrylic foam tapes that are designed, tested and manufactured for structural glazing should be considered for curtain wall and commercial window application. These tapes should only be used for factory or shop glazed projects.
Primary Glass Products
Tinted or Heat-Absorbing Glass is created by simply adding various colorants to the clear batch of glass to produce a desired color. VLT varies from 14 to 85 percent depending on color and thickness of glass. Density of color is a function of thickness; as the glass thickness increases, the VLT will decrease.
Tinting lessens the solar transmittance of glass and increases the solar heat absorption. Due to this heat build-up and subsequent thermal stresses, heat-treating is sometimes required for tinted glass; heat-strengthened or tempered.
Due to design and aesthetic reasons, and for color matching requirements, the actual color of tinted or heat-absorbing glass is a major consideration. The glass should be viewed as installed for color comparison. Colors may vary among the various manufacturers and from run to run of glass. There is no published color standard. Consult with manufacturer for glass color information.
Rolled Glass is produced by passing molten glass from a furnace through a series of rollers for the desired thickness and pattern. This rolled glass process is used to create wired glass, figured or patterned glass and art/opalescent/cathedral glass.
Wired Glass is created by adding a welded wire mesh into the molten glass during the rolling process. It may be further processed by grinding and polishing both surfaces, providing “polished wired glass”.
Wired glass cannot be heat-treated. To enhance the safety glazing purposes it can be laminated. Use the proper type of interlayer material to fit the application. Comply with the local building code requirements for the use of wired glass in fire-rated openings. There are limitations on the duration, maximum area and dimension, and percentage of wall area permitted.
Figured or Patterned Glass is created when one or more of the rollers in the rolled glass process have a pattern etched in it. This glass is typically available in 1/8 inch (3.2 mm) and 3/16 inch (4.8 mm) thickness. Colors are extremely limited. This type of glass may also be called decorative glass or obscure glass due to the pattern of the rollers reproduced on the glass surfaces diffuses the details of objects viewed through the glass. This glass type generally does not provide privacy. Heat-strengthened pattern glass should be used with caution due to the variations in glass thickness.
Art/Opalescent/Cathedral Glass types are also created by the rolled glass process and typically only in small batch-type operations. These sheets of glass have variegated colors and no two sheets will match for hue. Maximum sheet thickness is 1/8 inch (3.2 mm) with a variance from sheet to sheet. This art glass should be glazed in the same manner as tinted/heat-absorbing glass, and should not be heat-strengthened.
Fabricated Glass Products
Heat-Treated Glass Annealed float glass products may be subjected to specific heat-treating processes to provide increased resistance to thermal and mechanical stresses and to achieve specific break patterns for safety glazing applications. Generally this process involves the use of glass cut to the desired size, transported through a furnace and uniformly heated to approximately 1,150 degrees F (621 degrees C). Upon leaving the furnace, the glass is rapidly cooled (quenched) by blowing air uniformly onto both surfaces at the same time. This cooling process creates a state of high compression in the two glass surfaces and a state of compensating tension in the central core.
The two compression zones are at the surface and each approximately 20 percent of the glass thickness and the tension zone is the center 60 percent of the glass thickness. The color, clarity, chemical composition and light transmission characteristics of heat-treated glass remain unchanged. In addition to the hardness, specific gravity, expansion coefficient, softening point, thermal conductivity, solar transmittance and stiffness also remain unchanged. The glass does obtain improved flexural and tensile strength and improved resistance to thermal stresses and thermal shock. Heat-treated glass, under uniform loading, is stronger than matching annealed glass, and it does not reduce the deflection of the glass for any given load.
There are two types of heat-treated glass; heat-strengthened glass and fully tempered glass, defined by the amount of residual surface compression or edge compression.
The predominant method for producing heat-treated glass uses a heat-treating furnace, and a horizontal roller hearth that transports glass on horizontal rollers through the heating and quenching processes. This method eliminated the potential for tong marks when using vertical furnaces that use tongs to hold glass in vertical position as it is transported through the heating and quenching process. These methods both provide some degree of bow and warp in the glass that is an inherent characteristic of all heat-treated glass. Industry fabrication requirements, product tolerances and testing procedures for heat-treated glass are defined in ASTM C1048 and the latest version only covers the horizontal based system.
Heat-Strengthened Glass (Kind HS) Heat-Strengthened - Kind HS of heat-treated glass is produced with surface and edge compression levels less than fully tempered glass, in compliance with ASTM C1048. These lower levels still provide a product that is typically twice as strong as annealed glass of the same thickness, size and type. The size and shape of the break pattern of heat-strengthened glass varies based on the surface and edge compression levels achieved in the heat-treating process. Heat-strengthened glass with low compression levels will fracture into large fragments, similar to annealed glass breakage. As the compression levels increase, the size of the broken glass fragments will decrease in size. Heat-strengthening of glass thicker than 1/4 inch (6.35 mm) may be difficult, consult with manufacturer for availability.
ASTM C1048 requires that heat-strengthened glass has a surface compression level between 3,500 and 7,500 psi (24 to 52 MPa). Kind HS glass has a relatively large break pattern, and the glass pieces typically remain engaged in the glazing pocket, decreasing the probability of fall out. Heat-strengthened glass does not comply with safety glazing requirements of ANSI Z97.1 or the federal safety standard CPSC 16 CFR 1201.
Fully Tempered Glass (Kind FT) Fully Tempered - Kind FT of heat-treated glass is required in ASTM Cl048 to have either a minimum surface compression of 10,000 psi (69 MPa) or an edge compression of not less than 9,700 psi (67 MPa) or meet ANSI Z97.1 or CPSC 16 CFR 1201. Fully tempered glass is typically four times stronger than annealed glass and twice as strong as heat-strengthened glass of the same thickness, size and type.
Kind FT glass immediately shatters into relatively small pieces when broken by impact thereby greatly reducing the likelihood of serious cutting or piercing injuries when compared to ordinary annealed glass. Safety glazing materials may qualify with ANSI Z97.1 and CPSC 16 CFR 1201 when the 10 largest particles taken from a broken Kind FT lite weighs no more than the equivalent weight of 10 sq. inches (64 cm²) of the original specimen when tested in accordance with these standards. Kind FT glass that meets ASTM C1048 does not necessarily qualify as a safety glazing material.
*Refer to the Glazing Industry Code Committee (GICC) as an additional resource for information on current safety glazing requirements on their website: www.glazingcodes.org.
North American fabricators typically offer fully tempered glass in thicknesses ranging from 1/8 inch to 3/4 inch (3.2 mm to 19 mm). Safety glazing materials, such as fully tempered glass, are required by various standards and local building codes to be permanently labeled with an etched, sand blasted, ceramic-fired or laser logo identifying the fabricator, the glass type and the standard it complies with, such as ANSI Z97.1 or CPSC 16 CFR 1201.
Design professionals should be aware of the numerous considerations relevant to the selecting and specifying of heat-treated glass products. Consult with your project architectural glass fabricators to confirm the ability of the specified glass construction to meet the design parameters.
*Refer to the Glass Association of North America (GANA) for Glass Information Bulletins (GIB), Manuals, Test Methods/Standards and videos for additional information on their website, www.glasswebsite.com.
Laminated Glass typically consists of at least two sheets of glazing material bonded together with various types of interlayer material such as the following:
- plasticized polyvinyl butyral (PVB) between glass sheets bonded by heat and pressure.
- aliphatic urethane between glass and polycarbonate sheets bonded by heat and pressure.
- liquid resin between glass sheets bonded by exposure to UV light, heat, or chemicals.
- ionomer or ionoplast rigid sheet between glass sheets bonded by heat and pressure.
- aliphatic urethane between polycarbonate or acrylic sheets bonded by heat and pressure.
- polyvinyl butyral (PVB) between glass sheets and polyester polyethylene terephthalate (PET) film bonded by heat and pressure.
Numerous types of glazing materials can be incorporated into the laminated units, such as;
- annealed float glass.
- heat-strengthened glass.
- fully tempered glass.
- wired glass.
- tinted glass.
- patterned glass.
- spandrel glass.
- coated glass.
- one-way and two-way mirrors.
With the integration of these materials there are a variety of performance benefits in architectural, security and other specialty applications. The key benefit is the ability of the interlayer to support and hold the broken glass and/or plastic sheet when cracked. This provides additional protection against fall-out and penetration of the opening. Overhead glazing is required by most building codes to use laminated glass in monolithic lites or as the lower lite in insulating glass units. Additional applications include safety, security, detection, seismic-resistant, blast-resistant, bullet-resistant, burglary-resistant, hurricane/cyclic wind-resistant and sound reduction applications.
Additional specialty applications of laminated glass include aquariums, animal enclosures, glass stairs, floors and sports stadiums.
Plastic interlayers in a variety of thicknesses are used for the following applications:
- safety glazing – 0.015 inch (0.38 mm) or 0.03 inch (0.76 mm) thick.
- sloped overhead glazing – 0.03 inch (0.76 mm) or 0.06 inch (1.5 mm) thick.
- sound control – 0.03 inch (0.76 mm) 0.06 inch (1.5 mm) thick.
- windborne-debris/impact-resistant and security glazing – 0.06 inch (1.5 mm) or 0.09 inch (2.29 mm) thick may also be reinforced with PET film for additional strength.
- heat strengthened or fully tempered glass - recommended greater than 0.060 inch (1.5 mm) thick to compensate for small voids or mismatches in glass lites produced by the heat-treating process.
The quality standards for laminated glass are provided in ASTM C1172. Safety glazing that uses laminated glass shall comply with ANSI Z97.1 and CPSC 16 CFR 1201 requirements.
Proper sealant selection is critical for laminated glass used for glazing. Incompatible sealants can create progressive and unacceptable edge delamination or cloudiness within the laminated lite. Contact the laminated glass manufacturer for assistance in the proper selection of sealant to be specified.
Insulating Glass Units (IGU) can be used to limit heat gain or loss through two or more glass lites that are sealed together enclosing a hermetically sealed air space. The lites are separated by a spacer located around the entire perimeter. This spacer typically contains a moisture-absorbent material call a desiccant that helps to keep the air space free of moisture to prevent fogging or condensation within the unit. The entire perimeter of the IGU is sealed by a single or dual seal. A single seal consists of polysulfide, polyurethane or hot-melt butyral. A dual seal consists of a primary seal of polyisobutylene and a secondary seal of silicone, polysulfide or polyurethane, hot-melt butyral or warm applied reactive sealant. The corners of the metallic spaces may be square-cut and joined together using a metal, plastic or nylon corner key that may be miter-cut and brazed, welded or soldered, or bent.
Warm-edge technology type spacers have seen increased usage recently as they will improve the overall window thermal transmittance or U-Value. These warm-edge spacer materials include extruded butyral, foam rubber based, formed plastics and metal strip based products. Many of these spacers include a desiccant component. When these warm-edge type spacers are specified, it may be advantageous to insert the performance properties for the glass edges and the center of the glass into the section text.
IGU thermal performance is enhanced by using solar-control (tinted glass) substrates and coated glass (low-emissivity [Low-E] or solar-control/reflective), coated polyester suspended films, and insulating gasses such as argon, krypton or xenon. Sulfur hexafluoride gas may also be used where reduced sound levels are necessary.
The Insulating Glass Certification Council (IGCC) provides a certification program for insulating glass units and they have created a product key that designated IGU generic construction. The Certified Products Directory product key includes sealant construction components and materials, desiccant, thermal break, generic integrated spacer systems, substitute fabrication techniques, vapor barrier, and gas content.
The typical thermal performance properties of glass being provided are winter nighttime U-Value, summer daytime U-Value, and solar heat gain coefficient (SHGC), each located at the center of glazing. SHGC is the ratio of solar energy passing through glazing and that passing through the unglazed opening. U-Value is the radiant energy that passes through the glass either by direct transmission or by absorption and re-radiation, conduction, or convection to the interior. SHGC is similar to shading coefficient, except the ratio for shading coefficient compares the glass to 1/8 inch (3 mm) thick clear glass in lieu of an unglazed opening. The essential performance properties are visible light transmittance (VLT) and visible light reflectance and other properties that may be necessary for design purposes.
Coated IGU should be specified by selecting performance characteristics that are based on the manufacturer’s data. These performance characteristics should be established in accordance with Lawrence Berkeley National Laboratory’s (LBNL) WINDOW 5.2/6.3 computer program, that was developed by the LBNL Windows and Daylighting Group with contract support by the Department of Commerce (DOC), and the National Fenestration Rating Council (NFRC) procedures as indicated in the section. Coordinate the glazing IGU performance criteria with the buildings’ mechanical system design. It is critical that these values for performance of the IGU be included in the section text.
Transporting IGU’s through or to high elevation areas typically requires breather tubes from the air space to allow the unit to adjust to these pressure changes. North American fabricators generally provide either capillary tubes or breather tubes that are to be sealed upon arrival at the project or that remain open after glazing. Consult with glazing fabricators for the capillary/breather tube project requirements. Insulating glass warranty may be void upon failure to properly handle this issue.
Sloped Glazing Systems consist of a conventional pressure glazed system and also two- and four-sided structural silicone glazing (SSG) systems. With the pressure glazed system there is increased water infiltration due to the damming of water flow caused by the purlin cap and corner intersections of sloping rafter caps. A two sided SSG system limits this impact to water flow. The four sided SSG systems eliminate this water flow impact to an even greater extent. Use of SSG purlins at a minimum slope of 15 degrees from horizontal is recommended for sloped glazing applications. It significantly reduces water infiltration, sediment accumulation and staining of the glass. For safety reasons, construction workers in addition to maintenance personnel must not be allowed to walk or apply any weight to sloping glass systems. Any work that needs to be done should always be accomplished from a secured temporary platform that does not come in contact with the glazing.
Fire-Rated Glazing Products The intent of fire-rated glazing materials is to compartmentalize fire and smoke in a building. This glazing is used in doors, walls, openings and fire resistant products, and may be used as a wall with an approved framing system to provide safe egress for people in the building. The fire rating is the established length of time a product can meet fire endurance testing in compliance with either fire-resistance or fire-protection standards. Fire-rated glazing materials have been tested to specific door, window, and wall performance standards and may not match the building codes. With that in mind, a fire rating should not be confused with approval for a particular application. The fire-resistance or fire-protection ratings mandated by most major building codes in the U.S. are based on the application requirements. These application requirements are dependent on the amount of time necessary to maintain the structural integrity of the building and the safe egress of its occupants.
Fire-rated glazing may be used to limit the fire from spreading from one room to another. These fire-rated glazing materials carry a label on the glass that includes the manufacturer, listed fire-rating and testing agency. There are numerous fire-rated products that meet the necessary fire-rated building code requirements, and these products are divided into fire-resistance or fire-protection categories.
Fire-Resistance-Rated Glazing These glazing products are intended to restrict the spread of flames and smoke, and limit the transfer of radiant heat for 60 to 120 minutes. This category includes intumescent multi-laminate and gel-filled units. Fire-resistance glazing products are listed by testing agencies as transparent walls and are not limited to the 25 percent glazed area restriction that applies to fire-protection glazing when used in a temperature rise framing system of equal rating to the glazing. Verify appropriate use of fire-resistance-rated glazing with local authorities having jurisdiction.
Intumescent Multi-Laminate Products use a quantity of annealed glass lites laminated using a special intumescent interlayer. The fire rating is determined by the number of interlayers and overall thickness. When exposed to the heat of a fire, the intumescent interlayers become opaque and expand to prevent the transmission of heat, smoke and flames.
Gel-Filled Units are similar to insulating glass units, but the air space is filled with a clear gel. The width of the cavity determines the fire rating. The gel crystallizes under fire conditions into an opaque heat absorbing char that prevents the transmission of heat, smoke and flames.
Fire-resistance-rated products must meet various performance standards when used in hazardous locations requiring safety glazing. In addition, these products can provide improved acoustical separation and are available for exterior use with energy saving characteristics available. They may also be provided with additional characteristics for bullet, blast, hurricane, attack-resistance and others. Contact local fire-rated glazing suppliers for details on these enhanced performance characteristics.
Fire-Resistance-Rating; the period of time a building element, component or assembly maintains the ability to confine a fire, continues to perform a given structural function, or both, as determined by the following tests; NFPA 251, ASTM E119, and UL 263.
Fire-Protection-Rated Glazing These glazing products include polished wired glass, ceramics, specialty tempered glass and specialty laminated or filmed glass; both non-wired and wired. The glass is typically between 1/4 inch (6.4 mm) and 5/8 inch (15.9 mm) thick. Fire ratings range from 20 to 180 minutes, depending on the product and application. Verify appropriate use of fire-protection-rated glazing with local authorities having jurisdiction.
Wired glass was the original fire-rated glass. Currently there are restrictions on the use of traditional wired glass in hazardous locations. Safety-rated filmed or laminated wired glass in compliance with standards is readily available. Verify appropriate use of wired glass with local authorities having jurisdiction.
Laminated non-wired glass uses two lites of annealed glass laminated with a protective interlayer. This product meets safety requirements and carries a 20 minute fire rating with 9 sq. ft. (0.84 sq. m) size limitations in door locations. Verify appropriate use of laminated non-wired glass with local authorities having jurisdiction.
Fire-protection-rated products can provide improved acoustical separation, energy performance or radiant heat transfer characteristics depending on the product selected. Contact local fire-rated glazing supplier for details on these enhanced performance characteristics.
Fire-Protection-Rating; the period of time that an opening protective assembly will maintain the ability to confine a fire as determined by the following tests – NFPA 252, NFPA 257, UL 9, UL 10C, ASTM E2010 and ASTM E2074.
Burglar-Resistant Glass provides a level of security against the “smash and grab” type of thefts, used to protect store merchandise or to protect residential glass doors and windows against intruders. Laminated glass is also used to protect against forced-entry with the capacity to resist repeated blows from hammers, bricks and other materials.
UL 972 is the testing method used for glass to establish the level of burglary resistance. This test subjects the glazing sample to at least five impacts from a 5 lb. steel ball 3-1/4 inch (82.5 mm) in diameter, dropped from different heights and shall not penetrate the laminate. The various tests include Multiple Impact, Outdoor Use, Indoor Use, and High Energy Impact.
Two layers of annealed glass with an interlayer of the appropriate thickness can typically comply with the UL 972 requirements.
Bullet-Resistant Glass The next level of burglary resistance is forced-entry or bullet resistance. This is a more stringent application, such as a secluded bank entrance or other high-risk facility with sustained attach by individuals with sophisticated weapons. There are many standards used in North America for testing the bullet-resistance of glass, the ASTM F1233 standard makes a distinction between the various types of weapons and ammunition. There are a dozen different classes/levels, including weapons such as a handgun, rifle, and shotgun. This test method has procedures for the evaluation of resistance against the following threats:
- Ballistic Impacts.
- Blunt Tool Impacts.
- Sharp Tool Impacts.
- Thermal Stress.
- Chemical Deterioration.
This method consists of the following classifications:
- Ballistic Class.
- Forced Entry Class.
- Ammunition Class.
The sequence of testing begins with ten blows from a ball-peen hammer and progresses thru more than forty attack sequences using blunt and sharp impact weapons in combination with thermal and chemical stress agents. These tests are conducted on monolithic and laminated security glazing ranging in thickness from 1/2 inch (12.7 mm) to 2 inch (51 mm).
Explosion-Resistant Glass To resist explosives, laminated glass products are produced to meet the requirements of the U.S. General Services Administration (GSA) or ASTM F1642. These test methods are designed to measure the performance criteria of glazing is subjected to air blast loads similar to those of an explosion.
When glass is exposed to a blast, broken shards of glass fly into the inhabited area and potentially cause personal injury or loss of life. These test methods establish the performance level of glazing in its ability to retain the broken shards of glass and restrain them from flying into the occupied area. These five (5) levels range from a “No Break” safety level to a “Low Protection” level where the glazing cracks and the window system fails catastrophically. Glass fragments enter the space and impact a rear panel located 9.8 ft (2.98 m) from the window at a height of 2 ft (0.61 m) above the floor.
The U.S. Department of Defense (DOD) Unified Facilities Criteria UFC 4-010-01 standards set minimum guideline for windows and doors resistance to explosives. This standard requires that 1/4 inch (6.4 mm) nominal thick laminated glass is used at a minimum. For insulating glass units the DOD design criteria requires the use of 1/4 inch (6.4 mm) laminated glass for the inboard lite as a minimum. The requirements for the laminated glass and PVB interlayers are based on the appropriate explosive weight and standoff distance as defined in ASTM F2248 and ASTM E1300.
Explosives, whether accidental or intentional, transmits blast energy in all directions, causing damage to the intended target as well as the surrounding structures. Within and outside these structures, glass fragments fly at high speed or fall from upper levels and become hazards to the occupants and people in the streets outside the effected structures. Based on the analysis of numerous bomb attacks, the majority of damage and injury may be attributed to architectural glass failure and shattering.
Hurricane Impact Resistance Glazing Along the coastline of the U.S., building codes require that in wind-blown debris areas, glazing in buildings be impact-resistant or protected with an impact-resistant covering in compliance with ASTM E1886, ASTM E1996, Florida Building Code TAS 201 and TAS 203, or AAMA 506. Wind-borne debris provisions of these building codes shall comply with ASTM F1996 for glazed openings located within 30 ft. (9.14 m) of grade. This large missile test simulates the effects of large wind-driven debris that can impact glazing during a hurricane, such as broken roof tiles, branches, patio furniture, etc. The small missile test is for testing of glazing located greater than 30 ft. (9.14 m) above grade, such as roof gravel and other small debris. These large missile and small missile tests each have Basic Protection and Enhanced Protection provisions.
The four (4) Wind Zones have a basic wind speed of (1) 110 to 120 mph, (2) 120 to 130 mph, (3) 130 to 140, and (4) greater than 140 mph.
In addition to meeting the large and small missile tests of the wind-borne debris requirements, fenestration systems must also pass load testing for static positive and negative cyclic pressure tests that simulate the extended force of the wind during a hurricane. There are 8 cyclic static air pressure loadings in this test, 4 positive and 4 negative. Window systems may be certified when three similar specimens pass the testing criteria.
Glass-Clad Polycarbonate Security Glazing
Glass-clad polycarbonate contains glass layers to the exterior and one or more polycarbonate layers on the inside. This product combines the performance benefits of heat, chemical and abrasion resistance of glass with the impact resistance of polycarbonate. This laminated layout may also be unbalanced having a polycarbonate layer exposed to the interior. Glass-clad polycarbonate glazing provides resistance to forced-entry and ballistics and is commonly used in prisons, detention centers, jails, psychiatric facilities and other settings where security is of primary concern.
Radiation Shielding Glazing
Radiation shielding glazing provides protection against gamma and x-rays by adding lead oxide to the glass. These transparent lites are well suited for use in viewing windows, radiation protection for doctors, nurses and health care personnel. Glazing options such as laminated glass, tempered glass. or components of an insulation glass unit are available.
Anti-reflective glazing is produced by the application of a pyrolytic coating (hard coat) to the glass surface. This surface coating can reduce interior and exterior light reflection to less than 2 percent. As a result, views from both inside and out are clear, un-obscured and virtually reflection free. This glazing system can be applied to monolithic laminated glass, and insulating glass units.
Sound Control Glazing
Materials naturally provide a greater degree of sound control against high frequencies than low frequencies. Single-pane or monolithic glass will provide additional sound control as the thickness is increased to some extent.
Laminated glass provides additional sound control. The typical interlayer of polyvinyl butyral (PVB) is stiff given its main function is to increase security of the opening. By using a suppler acoustic PVB interlayer, the STC performance is improved by 1 dB regardless of the glass thickness while providing the same security properties as standard PVB interlayer. For 1/4 inch (6.4 mm) laminated glass with acoustic PVB interlayer the STC is approximately 35 dB and improves to 40 dB for 1/2 inch (12.7 mm) laminated glass.
Insulating glass or double glazing improves sound control when laminated glass is used. Performance levels of symmetrical double glazing are often lower than those of monolithic glass with the same total glass thickness. The key is using dissymmetrically thick glass in the double glazing along with a substantial air space. Additional sound control can be achieved by using laminated glass with conventional or acoustic PVB in place of one of the two monolithic glasses. Position laminated glazing with PVB on the interior side to ensure safety in the event of breakage.
Given the expanding thickness of the double glazing and the impact of increasing the width of the glazing pocket, this type of glazing is not widely used in practice for sound control.
Bent glass is often used to make the transition from sloped to vertical glazing. Due to this, it may also use structural silicon glazing. Handling of bent glass requires installers to exercise a higher level of care than when working with typical flat glass. Given that the center of gravity shifts when the glass is bent, it typically requires additional manpower to carry or set in place bent glass compared to flat glass of the same size and thickness. Slings or power vacuum cups of appropriate size to maintain a tight seal on the glass should be used to handle large bent lites.
Tolerances of bent glass mandate extra care and planning. A curved section of wall may consist of numerous bent lites and bent aluminum framing supports. An accumulation of tolerances can cause a slight misfit that can create a pressure point on the glass and ultimately breakage of the glass. The typical tolerance observed in bent architectural glass along with the curved framing system is an 1/8 inch (3.2 mm) for each radius.
Due to this accumulation of tolerances in bent glass and the curved support framing special considerations are required in the selection of glazing stops and gasket materials. In order to provide for the attachment of the glass stop without placing stress on the glass, the glazing pocket must be of appropriate width. Stresses accumulate; starting with a pressure point created by glazing, then adding thermal, wind or snow loads later on can eventually lead to breakage. The use of intermittent spacers, backer rod and wet seals is recommended to minimize the stress placed on a glass at glazing stops. Provide a nominal 3/8 inch (9.5 mm) or greater face clearance for both interior and exterior sides to allow for tolerances of the glass and framing.
It is very important to provide for flexibility in the glazing system to avoid creating added stresses on the glass, due to the tolerance differences. These differences require early recognition of the problems prior to proceeding with glazing, and are essential to prevent glass breakage later on. Good supervision by people with experience in this type of glass work is essential at the beginning of each installation.
Plastic Sheet Glazing
Plastic sheets have a much greater change in dimensions due to thermal expansion and contraction that most other construction materials. Glass will expand 0.060 inch (1.5 mm) over a 10 foot (3 m) length with 100 degrees F (55.5 degrees C) temperature change.
An acrylic will expand 0.504 inch (12.8 mm) and polycarbonate will expand 0.43 inch (10.9 mm) under the same conditions. Since plastic sheet has a relatively high rate of water vapor transmission it is also not recommended for use as lites in insulating glass units.
Most acrylic and polycarbonate sheets are classed as safety glazing materials. Confirm with manufacturer their compliance with ANSI Z97.1 and the state and local building codes. These plastic materials do not apply with CPSC 16 CFR 1201, since this federal standard only applies to glass.
Given the glazing characteristics of plastic sheets is quite different from glass, it is important to be conscious of the expansion and contraction, adhesion and compatibility with glazing materials, preparation of the glazing pocket and deflection.
Plastic films can be used over existing or new glass panes for added environmental control. There is a wide variety of films available that offer a range of color tint, quality of light or luminous transmission control, shading coefficient, and exterior light reflectance. The substrates include optical grade polyester (PET), polyethylene napthalate (PEN) and polycarbonate (PC).
Putty or Glazing Compounds
Putty or glazing compounds are not used to glaze laminated or insulating glass. They lack service effectiveness in medium-to-large lite glazing. The oil and solvent content they have is incompatible with neoprene, butyls, polysulfide, silicones, EPDM and acrylics.
The glazing must never come in direct contact with the frame or any other hard material. The use of suitable setting and location blocks will prevent this when installed in compliance with edge clearance requirements. There are three types of blocks. Setting blocks transfer the vertical load of the glazing to the frame work at specific locations so as to protect the squaring of the frame and limit deformation of the supporting bar. With the exception of U-profiles gaskets, setting blocks must be used. Location blocks allow the glazing to be positioned and held correctly within the glazing pocket to maintain a square frame. Distance blocks allow the end glazing to be positioned and held in place correctly in relation to centering the glass within the glazing pocket. This ensures that the joint between the glass and frame remains constant. For sloped glazing, the distance blocks will carry a portion of the glazing weight.
Setting blocks consist of synthetic materials such as polypropylene or polyamide, and silicone. The Shore A durometer hardness is typically in the range of 70 to 95. Setting blocks made of EPDM or neoprene is not recommended as there could be some deformation.
Spacer shims center the glass within the glazing pocket, between the front and back stops. They can be either intermittent or continuous and provide a consistent gap between the glass and the sash or frame. Shim hardness range varies, typically 40 to 60 Shore A hardness durometer is recommended. Consult with glass manufacturer for project specific requirements.
Preformed tape consists of an elastomeric material extended into a ribbon with a width and thickness applicable to the glazing requirements. The tape has long term resilience as well as excellent adhesion to glass, metal or wood substrates when continuous pressure is being applied. Tape with an integral continuous shim is recommended. Elastic hybrid tapes, without an integral shim, are also available. These are not to be confused with the more typical, non-elastic tapes without an integral shim.
Gunnable Elastomeric Sealants
Gunnable elastomeric sealants are either curing or non-curing types. Curing sealants become a semi-rigid piece of synthetic rubber while the non-curing sealant remains soft and tacky.
Curing-type gunnable sealants consist of materials such as polysulfide, silicones, urethanes, acrylics and other synthetic polymers. They are used as a gunned-in-place glazing sealant or cap bead. Surfaces must be clean and dry, and primed, if necessary, in accordance with manufacturer’s instructions.
Non-curing type gunnable sealants are typically used as a metal-to-metal joint sealant in non-exposed locations. There are skinning and non-skinning types. The surface of the non-skinning type remains tacky and collects dirt becoming unsightly if used in an exposed location.
Editing of Glazing Section 08 8000 is designed to start in PART 2 - PRODUCTS, progress to PART 3 - EXECUTION, and finish up with PART 1 - GENERAL. The various types of glazing specified comprise the main articles in PART 2. When a particular type of glazing is activated for use in the project, the appropriate glass type listed under SECTION INCLUDES article in PART 1 will be activated. Related articles and optional text in PART 1 and PART 3 will be activated as well.
When a particular article or paragraph is chosen that contains a reference standard in PART 2 and PART 3 the corresponding standard cited under REFERENCE STANDARDS article in PART 1 is activated. If the Consolidated List of Citations option is active, cross sectional links (not visible in the links window) will activate the reference standard in Section 01 4219 – Reference Standards as well.
When a particular article or paragraph is chosen that cites another section in PART 2 and PART 3, the corresponding Section cited under RELATED REQUIREMENTS article in PART 1 is activated.
Certain Sections cited under RELATED REQUIREMENTS article in PART 1 are not cited in either PART 2 or PART 3 but are listed under RELATED REQUIREMENTS because they include items that might be expected to be found within this Section or include action items important for the completion of the work that are not specified in an obvious location (e.g. isn't obvious from the section title).
Optional text and choices under PART 2 include a fill-in option to accommodate any updates that listed manufacturers may offer but are not shown in the listed choice of options. Default options for choices are based upon what would be reasonable for the application. The content of PART 2, including the choices, has been structured to accommodate the listed manufacturers.