Good Glazing Guidelines The design of a good glazing system incorporates experience and judgment and considers the glass type, in service loads, framing system, method of erection and associated tolerances. The glazing system should be designed to minimize loads on the glass created by building movement. To adequately retain glass in the framing system and prevent breakage caused by glass-to-metal contact or by mechanical and thermal stresses, architect’s specifications should include the following general glazing guidelines. Thermal Stress Considerations Glazing designs can help to prevent annealed glass breakage from excessive thermally induced stress. Heat-strengthened or fully tempered glass will adequately resist solar stress or HVAC-induced thermal stress and, therefore, heat-treated glass is exempt from the following thermal guidelines. Solar-induced stresses are caused by uneven absorption of solar radiation. Deep shadows from mullions or overhangs can reduce the solar heating in part of the glazing, while reflections at inside corners or off water or snow can increase the heating in other parts. Restrictions to natural convection such as tight-fitting closed blinds, suspended ceiling pockets in which rising hot air is trapped, or large signs fastened to the glass will interfere with uniform solar heating. Excessive thermal stress from louvers or venetian blinds can be prevented by following the dimension limits shown below or by adding lock stops to prevent the blades from being fully closed. Typically 30° off full closure is effective. HVAC ducts must not blow directly against the glass. Excessive stress can be created in both heating and cooling cycles by misdirected air vents. Pilkington Eclipse Advantage™ Reflective Low-E Glass products have varying amounts of solar absorption. Thermal stress calculations should be made for every project using these glasses with the calculator provided on our website at www.pilkington.com Pilkington Arctic Blue Eclipse Advantage TM and Pilkington EverGreen Eclipse Advantage TM Reflective Low-E Glasses have very high performance and will typically need heat treatment in most installations to prevent thermal stress breakage when installed in an I.G. unit. For additional information, please refer to Pilkington Technical Bulletin ATS-139: "Thermal Stress for Glazing Combinations". Cut-size annealed glass is supplied with clean- cut edges. These edges must not be allowed to contact any hard objects or be damaged in any way during construction or the glass strength which resists thermal stress will be reduced. 1 Insulating Glass 2” (50mm) Minimum Clearance 1 1/2 ” Minimum Clearance 1 1/2 ” 2” Louver Blind Drapery or Roller Shade Air Flow General Glazing Guidelines
Transcript
Good Glazing Guidelines
The design of a good glazing system incorporates experience and judgment and considers the glass type, in service loads, framing system, method of erection and associated tolerances. The glazing systemshould be designed to minimize loads on the glass created by building movement.
To adequately retain glass in the framing system and prevent breakage caused by glass-to-metal contact or by mechanical andthermal stresses, architect’s specificationsshould include the following general glazingguidelines.
Thermal StressConsiderations Glazing designs can help to prevent annealed
glass breakage from excessive thermallyinduced stress. Heat-strengthened or fully tempered glass will adequately resist solarstress or HVAC-induced thermal stress and,therefore, heat-treated glass is exempt from thefollowing thermal guidelines.
Solar-induced stresses are caused by unevenabsorption of solar radiation. Deep shadowsfrom mullions or overhangs can reduce thesolar heating in part of the glazing, whilereflections at inside corners or off water orsnow can increase the heating in other parts.
Restrictions to natural convection such as tight-fitting closed blinds, suspended ceilingpockets in which rising hot air is trapped, orlarge signs fastened to the glass will interferewith uniform solar heating.
Excessive thermal stress from louvers or venetian blinds can be prevented by followingthe dimension limits shown below or by addinglock stops to prevent the blades from beingfully closed. Typically 30° off full closure iseffective.
HVAC ducts must not blow directly against theglass. Excessive stress can be created in bothheating and cooling cycles by misdirected airvents.
Pilkington Eclipse Advantage™ ReflectiveLow-E Glass products have varying amountsof solar absorption. Thermal stress calculationsshould be made for every project using theseglasses with the calculator provided on ourwebsite at www.pilkington.com
Pilkington Arctic Blue Eclipse AdvantageTM
and Pilkington EverGreen EclipseAdvantageTM Reflective Low-E Glasses have
very high performance and will typically needheat treatment in most installations to prevent thermal stress breakage when installed in anI.G. unit. For additional information, pleaserefer to Pilkington Technical Bulletin ATS-139:"Thermal Stress for Glazing Combinations".
Cut-size annealed glass is supplied with clean-cut edges. These edges must not be allowed tocontact any hard objects or be damaged in anyway during construction or the glass strengthwhich resists thermal stress will be reduced.
1
InsulatingGlass
2” (50mm)MinimumClearance
1 1/2”MinimumClearance
11/2”
2”Louver Blind
Drapery orRoller Shade
Air Flow
General Glazing Guidelines
Framing System The framing system must structurally support the glass under static and dynamicloads and provide openings within specifiedlimits for squareness, corner offset and bow.These limits are:
Square . . . . . . . . 1/8” (3mm) difference in the lengths of the diagonals
Bow . . . . . . . . . . 1/16” (1.6mm) in any 4’ (1.22m) length of framing
Corner Offset . . 1/32” (.8mm) at each corner
General Glazing Guidelines
2
1/8” (3mm) MaximumDifference
in Length ofDiagonals
CornerOffset . . . . . . 1/32” (.8mm) at each corner
Square . . . 1/8” (3mm) difference in thelengths of the diagonals 1/32”
MaximumOffset
Bow
1/16” Limitin 4’ Span
General Glazing Guidelines
Framing SystemContinued
The deflection of glass framing membersunder design loads must not exceed either thelength of the span divided by 175 or ¾" (19mm). The deflection of horizontal membersdue to the weight of the glass should be limited to minimize bite variations and thermal stress at the glass edge. For heat-absorbing and reflective glasses, a limitof the lesser of either 1/8" (3 mm) or 25% ofthe design edge clearance of the glass orpanel below is recommended. Twisting of thesill member due to the dead load of the glassshould be limited to 1° between ends andcenter to minimize mechanical bendingstresses at the glass edge.
Anchors and Expansion Joints
Anchors and expansion joints should bedesigned so that loads are not applied to theglass framing due to the thermal or mechani-cal movement of the structure. For a sticksystem, there should be a vertical expansionjoint at every floor and preferably at a hori-zontal support member. Vertical expansionjoints should be at glass corners and neverplaced along an edge of insulating glass.
Horizontal expansion joints should be placedeither at each column line or within 30' (9.14 m) of each other, whichever is less.
3
3/4” OrLengthof Span
÷175,
WhicheverIs Less
Sill Member Twist
1°
Deflection of FramingUnder Load
Lengthof
Span
Maximum Deflection ofHorizontal Members
Glass
Glass
A = 1/8” or 25% of Design EdgeClearance. Whichever is Less
*Refer to ASTM C1036 for dimensional tolerance for cut-size glass.
RecommendedClearances and Bite
The glazing system should provide for mini-mum face clearances (A), edge clearances(B) and normal bite or cover (C) at the edgeof the glass as shown in the table below.Adequate bite is required to provide a properseal against infiltration of air and water.Excessive bite can increase thermal stressesat the glass edge, especially for reflective andheat-absorbing products, which could lead tobreakage of annealed glass. The table belowshows nominal bite recommendations whichshould be carefully adhered to in designingdetails and glazing systems
Inadequate edge clearance can result in glassdamage by glass-to-metal contact. The chartshows the minimum edge clearance necessary to accommodate glass cutting andnormal framing erection tolerances of ±1/16" (1.6 mm). When framing members orsurrounding material such as steel and concrete are used, construction tolerancesmay be difficult to control and therefore theedge clearance should be increased appropriately.
Proper face clearance should be provided bya continuous cushioning material with aShore A 65 ± 5 durometer hardness, such asneoprene or equivalent. Intermittent faceshims should not be used. The durometerrange of continuous shims may vary depending upon the intended purpose. Forexample, a high durometer neoprene may beused to apply adequate pressure to a pre-shimmed glazing tape. All glazing
materials must be resilient, nonhardeningcompounds, tapes or elastomeric gaskets thatwill retain an adequate face clearancethroughout the life of the project. When providing a watershed, the sealant or gasketshould be limited to a maximum height of1/16" (1.6 mm) beyond the sightline of theframing members to limit the thermal stresson the edge of the glass.throughout the life ofthe project. When providing a watershed, thesealant or gasket should be limited to a maximum height of 1/16” (1.6mm) beyondthe sightline of the framing members to limitthe thermal stress on the edge of the glass.
Annealed MonolithicGlass (Clear, Tinted and Coated)
Each lite of glass should be set on two set-ting blocks centered approximately at thebottom edge quarter points. When this isimpractical, the end of the setting block canbe moved within either 6" (152mm) or 1/8the width of the glass from the vertical edge,whichever distance is greater. Blocks shouldalways be an equal distance from the centerof the glass. Neoprene or EPDM settingblocks should have a Shore A durometerhardness of 85 ± 5.
In a metal glazing system, the length of eachsetting block should be 0.1" for each squarefoot (27 mm per square meter) of glass area,but not less than 4" (100 mm).
All setting blocks should be of sufficientheight to provide the minimum edge clear-ance for the type of glass being glazed andfor the nominal bite recommended. Settingblocks should be 1/16" (2 mm) less than fullchannel width or positively located in thechannel so they cannot be misaligned during
glazing. If setting block shims are required,they must be located under the setting blocksand have a durometer rating equal to orgreater than that of the setting blocks. Failureto properly design and locate setting blockscan cause point pressures, bending stress, orglass-to-metal contact resulting in glassbreakage or ponding of water, a primarycause of seal failure in insulating glass units.
Setting Blocks
Weep Systems –Monolithic andInsulating Glass
The glazing system must be designed so thatwater entering the glazing channel will beweeped out. Each window opening shouldhave a minimum of three weep holes 3/8"(10 mm) in diameter or equivalent. Theweep system should not be impaired byimproper placement of setting blocks orweep baffles; instead, a void should be leftbetween the edge of the glass and the glazing channel to avoid moisture beingtrapped. Failure to use a proper weep systemor the improper application of sealants canlead to glass breakage, delamination of laminated glass products, or seal failures ininsulating glass units.
General Glazing Guidelines
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Setting Blocks
Setting Block Setting Block
W/4 W/4(W)Width
Weep Systems
Weep to Outside
Glass should be centered in the opening vertically and horizontally. For glass in dryglazing systems, edge blocks should be usedin each vertical jamb to prevent lateral"walking." Glass movement can lead toglass-to-metal contact and breakage. Shore A65 ± 5 durometer hardness neoprene is preferred. Each edge block should be at least3" (76 mm) in length and may be placedanywhere along the jamb. A nominal 1/8" (3mm) clearance should be allowed betweenthe edge of the glass and the block to allowfor glass, metal and erection tolerances.
Glass should be handled and glazed carefullyto prevent edge damage. Care must be takennot to impact the glass edges on metal framing members or surrounding buildingmaterials during installation. Chips andimpacts at the glass edge can be initially hidden in the glazing channel and laterbecome break origins when the glass isexposed to normal thermal and mechanicalstresses.Undamaged, clean-cut, factory edgesor factory fabricated edges generally providethe strength needed for annealed glass products to withstand such stresses. Caremust be exercised in design to provide aglazing system which will minimize the possibility of edge damage during installation.
Finished products such as insulating glass,tempered glass, heat-strengthened glass andannealed glass ordered in cut sizes shouldnot be modified by further cutting, seaming
or grinding. Corner edge damage can alsooccur when glass is rotated on a hard surfaceprior to glazing. It is recommended that a"rolling block" be used by glaziers to rotatethe unit. The rolling block minimizes thechance of damage to the corner of the glassby distributing the glass weight along theedges rather than concentrating it at the corner.
General Glazing Guidelines
Edge Damage
Edge Blocks
7
1/8”
Rolling Block
3” Minimum PlusChannel Depth
Edge Blocks
Damage to GlassSurfaces
Glass is a durable product with weatheringproperties superior to those of most otherbuilding materials. The surface of glass may,however, become accidentally damaged during transport and installation. One causeof surface damage is sparks from welding.Glass near welding operations should be protected. Also, wind-blown objects and roofgravel can be blown into glass, thus causingsurface damage. This type of damage canlead to surface degradation and possiblebreakage. Other sources of glass surfacedamage are alkaline materials and oxidizingsteel. Run-down from these materials maybe deposited on the glass and stain the surface. Frequent cleaning of glass surfacesduring construction and after completionmay be necessary.
Glass must be properly stored to avoid wetting and drying cycles. A prolonged wetcondition can cause staining or etching ofthe glass surface. Glass in cases should bestored in dry, well ventilated areas. On a jobsite, the cases should be stored, elevated offthe floor, toward the building interior, andprotected from all moisture. Glass stored outof the case should always be stored withinterleaving or spacing between the individual lights of glass.
To prevent glass surface staining, the head ofall frames should incorporate a small projecting lip or recess to direct rain wateraway from the glazing below. When rainwater washes over upper building levels itpicks up dirt and other contaminants. In newconstruction, this water can become very alkaline from concrete floors or from precast concrete panels. Glass staining caneasily occur if run-down water is allowed todry on the glass and deposits are allowed toremain for an extended period of time.
Frequent washing of glass, especially duringconstruction is recommend to prevent staining.
For additional information, refer to TechnicalBulletins:ATS 104, Protecting Flat GlassSurfaces; Technical Bulletin ATS 144,Manual Washing of Clear and Tinted Glass;Technical Bulletin ATS 169 GlazingGuidelines for Pilkington Activ™ Self-Cleaning GlassATS 181, Washing PilkingtonEclipse AdvantageTM Reflective Low-EGlassATS 176, Handling, Inspecting,Fabricating & Glazing Pilkington EclipseAdvantage Reflective Low-E Glass.
When coated or reflective glass surfaces areexposed to high traffic areas care must betaken to avoid contacting the coated surfacewith abrasive materials or glass-to-metalcontact that can damage the coated glass surface.
Additional GlazingGuidelines forInsulating Glass
1. In dry glazing systems, compressive pressure on the glass edge should be a minimum of 4 pounds per linear inch (71.5 gper mm) of edge to assure an adequate seal.The pressure on the glass edge should notexceed 10 pounds per linear inch (180 g permm). Excessive pressure on the glass canincrease mechanical stresses and contributeto glass breakage.
2. Glazing materials must be resilient, non-hardening, nonbleeding compounds, tape orelastomeric gaskets. All materials should be
approved by the insulating glass manufacturer before they are applied.
3. Glazing compounds must not be thinnedwith chlorinated solvents (dry cleaning fluids) or benzene-related compounds suchas toluene.
4. When a heel or toe bead is necessary,compatibility between this material and theinsulating unit sealants is required.
The designer of structural silicone glazingsystems should be aware that not all glassproducts can be used in this type of systemdue to compatibility limitations of siliconesealants with certain insulating glass sealantsand some laminated glass interlayer materials. Consult the sealant manufacturerfor information concerning the compatibilityof glass and silicone for structural siliconeglazing. Also, the silicone manufacturer mustbe contacted for approval of neoprene,EPDM or silicone spacer formulations foroptimum joint configurations, for assurances
of silicone strength in the application, and for recommendations for proper adhesion toglass support members. The glazing contractor must design adequate joint dimensions for each application.
The designer must remember that structuralsilicone sealants may be incompatible withthe sealants used to manufacture certaintypes of insulating glass. Incorrectlydesigned or applied sealants will lead to premature failure of the insulating glass unitsand certain glass films.
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ContinuousSilicone Spacer(Shore A 60 ± 5)
Minimum1/4”
1/4”
1/4”
1/4”
Structural Silicone
Interior Metal Stop
Typical Monolithic Jamb or Head Detail
Note:Setting Blocks to BePreformed Silicone.
1/4”
1/4”
1/4”
1/4”
MinimumInterior
Metal Stop
Setting Block
ContinuousCompatibleSilicone Spacer(Shore A 60 ± 5)
Structural Silicone
Typical Monolithic Sill Detail
The information in this brochure is subjectto change. Consult your local Pilkingtonrepresentative for further information relevant to your particular product needs.
The information contained in this and otherPilkington publications is offered for yourassistance in the application of flat glassproducts, but DOES NOT CONSTITUTE A WARRANTY OF MERCHANTABILI-TY OR FITNESS FOR ANY PARTICU-LAR PURPOSE. Actual performancemight vary in particular applications. Youshould contact the Pilkington ArchitecturalTechnical Services Department concerningparticular product applications.
PILKINGTON MAKES NO WARRANTYOF MERCHANTABILITY, NO WARRANY THAT THE GLASS IS FITFOR ANY PARTICULAR PURPOSE ORUSE AND NO OTHER WARRANTY,EXPRESS OR IMPLIED.
Additional Information
www.pilkington.com
Arctic Blue Eclipse AdvantageTM, Eclipse AdvantageTM, Energy AdvantageTM Low-E Glass, EverGreen Eclipse AdvantageTM, Sun ManagementTM Glass System and First in GlassTM are trademarks of Pilkington.
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The information contained in this brochure issubject to change. Consult your localPilkington representative for any new information relevant to your specific productneeds.
The information contained in this publicationis offered for assistance in the application ofPilkington flat glass products, but IT DOESNOT CONSTITUTE A WARRANTY OFMERCHANTABILITY OR FITNESS FORANY PARTICULAR PURPOSE. Actualperformance may vary in particular applications.
