september 2005 vol 55 | num 9 glass · september 2005 vol 55 | num 9 ... resistance to ultraviolet...

September 2005Vol 55 | Num 9

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Glass Magazine

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e 55Num

ber 9Septem

ber 2005 Protect valuable museum

collections • Guide to fire-rated glass • Expand your business—cut stone

• Protect valuable collections

• Guide to fire-rated glass

• Dining out atGlassBuild America

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Contents68 Selecting glazing for museums74 Protecting collections from ultraviolet radiation78 Another way of looking at light damage82 Five world-class institutions

Museum glazing

Nasher Sculpture Garden2001 Flora St. Dallas, Texas 75201www.nashersculpturecenter.org

Cost: $70 million

Architects: Renzo Piano BuildingWorkshop, Genoa, Italy; Beck Architecture, Dallas

General contractor: The Beck Group,Dallas

Design engineer: Arup Associates,London

Contract glazier: Haley-Greer, Dallas

Photos by Brian Stacy, Arup, New York City

66 Glass Magazine® • September 2005



Museum glazing

Museumsthis approach gives good control over UV and lightlevels, the quality of light can be compromised. As aresult, more museum and gallery curators adopt nat-ural daylighting solutions that display, for instance,an artwork’s colors in the lighting environmentexperienced by the artist when creating the artwork.

It is now possible to simulate accurate daylight-ing performance with computer software. Suchanalyses must take into account more than just asun-path study indicating shadows and direct sunpatches but must include transmission and diffu-sion through glazing and also reflected light offinternal surfaces. Once an initial daylighting studyhas been carried out, the location and size of win-dows and skylights, location of sunshades—fixed oroperable—and types of glass can be determined.

The total amount of light entering a galleryspace, called total lux hours, is a governing criterionfor a curatorial space. This approach to light controlallows short direct sun patches or hot spots to occur,provided that lower light levels exist at other times.A hot spot can have 1,000 times the intensity ofbackground light, thereby creating a major advan-tage to a full-time diffuse light solution.

Architects for the High Museum of Art inAtlanta adopted an indirect light solution with aseries of 3-foot diameter north-sloping skylightsbeing shielded by ‘bishops’ hat’ sunshades (see story,p. 84). The Wexner Center in Columbus, Ohio,allowed hot spots within the gallery but not on anydisplay walls. Diffusing and dark glass was selectedto minimize the effects of the hot spots.

How to choose glazingA color rendering index provides an average mea-sure across the visible light spectrum of the differ-ence in changes between the color bands. Coloredglass, including normal clear glass, and coloredcoatings reduce the CRI. Neutral colors may reducethe total amount of light passing through but donot adversely affect the CRI. Low-iron glass pro-vides the best CRI and now widely selected for usein art galleries. From a CRI perspective, low-emis-sivity coatings required for enhanced thermal per-formance become an unhelpful burden but anessential component of the glazing. The dark butneutrally tinted glass adopted for the Wexnergallery for solar control—and to match the originalglass patterns—did reduce the CRI slightly, butwith the use of low-iron glass for a sizeable percent-age of the walls and skylight, a good quality of lightwas still achieved with good solar control.

Resistance to ultraviolet light is naturally providedby the polyvinyl butryal interlayers in laminated glassand regularly sold as such. This natural resistanceremains true for a limited bandwidth of UV radia-

tion. For curatorial environments, a broader bandUV resistance will typically be required.

Designing for heat lossAt the macro level, the thermal performance of anyglazing system must be sufficient to maintain inter-nal gallery temperatures where artifacts and artworkwill be displayed. At the micro level, condensationformation on internal surfaces must be predictedand ideally avoided for temperatures down to thelow external design temperature.

For a cold condition design, “simple rectangu-lar” museum and gallery space conditions can bepredicted by conventional mechanical design soft-ware. For more complicated spaces, computationalfluid dynamics analyses predict air flow and tem-peratures. Such CFD analyses provide much more

demand the best

useums and art galleries present challenges to glaz-ing designs, given the tight environmental condi-tions that must be met. Consideration must begiven to many parameters, often conflicting, includ-ing the quality and quantity of light, ultraviolet resis-tance, aesthetics, thermal performance, condensa-tion resistance, strength, security performance,safety and cost. For a best-practice curatorial envi-ronment, temperature and humidity must be con-

when antiquities, priceless collections, venerable art, fussy curatorsand deep pockets come into play.

By Neil McClelland and Brian Stacy

tained within a tight band of 70 degrees Fahrenheitand 50 percent relative humidity year-round. Arti-facts and artwork must also be protected from UVand visible solar radiation at the same time as beingdisplayed in “natural” light.

Designing for light controlA simple approach to lighting control is to omitglazing entirely and use only artificial light. While

mJack S. Blanton Museum of Art, Austin, Texas

High Museum of Art, Atlanta

Photo by Brian Stacy , Arup, New Y ork City

Photo by Matt Franks, Arup, New

York City

McClelland is associate façade engineer and Stacy lighting designer with Arup in New York City.

Glass Magazine® • September 2005 69

The warmer the air, the more moisture it can hold.Relative humidity, expressed as a percentage, mea-sures the actual amount of airborne moisture, calledvapor pressure, against the absolute amount ofmoisture the air can hold at a given temperature.The dew point temperature is reached when relativehumidity reaches 100 percent. For a fixed vaporpressure, the relative humidity rises as the temper-ature falls. For a typical art galley environment of70 F and 50 percent relative humidity, the dewpoint temperature is 50.5 F. That is, if any surfacetemperature falls below 50.5 F, then condensationwill occur. As a comparison, in a typical officeenvironment of 70 F and 30 percent relativehumidity, the dew point temperature is 37.2 F—much easier to design for.

Selecting an appropriate external design temper-ature is not straightforward. Engineers plan typicalmechanical designs based upon the American Soci-ety of Heating, Refrigerating and Air ConditionEngineers’ ASHRAE Heating Dry Bulb 99.6 per-cent temperature. This is a statistical value and thetemperature will fall below this measure about 35hours per year, on average. For a museum or artgallery, this tolerance may not be acceptable and alower design temperature may be necessary, thoughthis should be measured against the added cost ofdesigning for a worst-case temperature.

Given the above, designing for condensationresistance gets down to micro-level design. We rec-ommend carrying out solid thermal modeling tocheck the full internal surface profiles for areas withtemperatures below the dew point.

Explore the following options to improve per-formance:• Low-e coatings. They provide approximately 50

percent better thermal performance thanuncoated glass. Note the adverse effect that low-ecoats may have upon CRI.

• Triple glazing. It provides approximately 50 per-cent better thermal performance than doubleglazing.

• Argon-filled insulating glass. It provides approx-imately 15 percent better thermal performancethan unfilled triple glazing.

• Warm-edge technology. Insulating glass spacerssuch as stainless steel spacers have better perfor-mance than traditional aluminum spacers; anumber of proprietary spacers, based upon poly-mers, perform even better.

• Thermally broken framing. Performancebecomes a function of thermal break depth, so ashallow thermal break does not perform as wellas a deep spacer. Consider structural glazing as apoor man’s thermal break.Active solutions to condensation control may

typically be adopted in tandem with passive glazingdesigns. Active solutions include local heating ofthe glazing and framing through ducted air, fin tubeor panel radiators or electric trace heating.

In some instances, condensation may be allowedto form and be controlled through an appropriatelydesigned drainage system. Typically, invisible glaz-ing at a slope greater than 20 degrees off horizon-tal—to prevent condensation dripping—is the onlycase where condensation formation would be con-sidered.

Thermal tests of framing to predict condensationperformance is possible following the AmericanArchitectural Manufacturers Association’s AAMA1503-98 test method. This method, based uponstandard sample sizes and test conditions, deter-mines the condensation-resistance factor for frameand glass. CRF is a useful preliminary guide forframe and glazing selection, as it fairly rates relativeperformance between systems. However, it is notpossible to derive direct condensation performanceon all frame surfaces from the CRF, as it is basedupon average temperature readingsin a number of locations; so, makedirect calculation as described.

Nonstandard testing of actualsample sizes, shapes and environ-mental conditions should not beundertaken by the unwary if reliableresults are required. For the HighMuseum and Wexner Center, forinstance, we conducted two full-scale mock-up tests using actualhumidified internal air to visually inspect wherecondensation formed, in addition to relying uponthermocouple readings, to prove the design assump-tions and verify the analyses. Close work with theresearchers at the testing labs is required to run thetests in a reliable manner and to collect reliable data.

Other design issuesWhen designing for strength and deflection, muse-ums or galleries do not have specific requirements.In designing for security, however, many museumsand galleries rely on full-time guards monitoringclosed-circuit television and movement alarms astheir principal means of defense against theft. Lam-inated glass is almost universally used for UV pro-tection, so there is at least some resistance to inci-dental instances of accidental glass breakage,break-ins and over-pressure.

High Museum, AtlantaMany of these lessons can be seen in recent con-struction of the a main gallery for the Renzo PianoBuilding Workshop-designed expansion of the

information than required for glazing design. Theycan greatly assist with the mechanical design of aspace and allow an optimal design for duct loca-tions and input air temperatures and velocities.Related to glazing, a CFD analysis also helps deter-mine the need for fin tube or trace heating at mid-height locations on tall glass walls.

Mechanical and glazing combosEngineers working on the High Museum, theWexner Center and the Cleveland Museum of Artextension all relied heavily upon CFD analyses tofine-tune the interaction of mechanical systems andglazing design.

In designing for macro-level performance, ineither simple or CFD mechanical analyses, it isimportant to use the overall system U-value, notjust the center-of-glass U-value. Frame effectsreduce thermal performance because of direct ther-mal conduction paths from inside to outsidethrough glass spacers, glazing seals and gaskets andframing. To optimize overall system thermal perfor-

mance, frame and glass-edge performance shouldbe matched to glazing performance. For example,there is little point in using a thermally brokenframing system if single glazing will be used. Like-wise, using a thermally unbroken frame or one witha very shallow thermal break with triple glazingbecomes a waste of time.

As glazing tilts off the vertical, as with skylightapplications, thermal performance decreases, up to40 percent in some instances. This happens becausea “short circuit” of the vertical air flow within aninsulating glass unit can occur, creating a shorter airpath between warm and cold inner and outer glasssurfaces. This proves the case for all applications butbecomes more critical for museums and galleriesdue to more demanding internal conditions andthe unacceptability of dripping condensate.

Designing for condensation controlCondensation forms when the surface temperatureof glass or framing falls below the dew point, thetemperature where airborne moisture condenses.

Museum glazing

Jack S. Blanton Museum of Art, Austin, Texas

Photo by Brian Stacy, Arup, New York City

Wexner Center, Columbus, Ohio

Photos by Neil McClelland, Arup, New

York City

70 Glass Magazine® • September 2005 Glass Magazine® • September 2005 71

High Museum. More than1,000 3-inch-diameterskylights accent the upper galleries. These consistof a sloped glass layer 2 feet above the main roofline with a 5-foot-deep shaped tube below inte-grated into the ceiling and Bishop’s-hat sunshadeson page 69. Piano’s arrangement was carefully ana-lyzed from a lighting perspective to prevent anydirect sunlight from entering the gallery spacesbelow. Low-iron glass was selected to minimizereduction in CRI. A low-e coating was used forincreased thermal performance with a consequentbut acceptable reduction in CRI. The complicatedair space within the tube directly below the glazingwas analyzed using CFD to predict actual air tem-peratures directly below the glass to be used in acondensation risk assessment. A mock-up of a sky-light, including the tube below, was tested with acustom test box and procedure using actual humid-ified air to verify the design assumptions.

The Wexner Center, Columbus OhioEisenman/Trott Architects’ Wexner gallery hasrecently undergone refurbishment that includedreplacing existing skylights and glazed walls. CFDmodeling of the interlinked galleries was carried outto predict the air flows and temperature profiles.This analysis provided a realistic design air tempera-ture to be used in the condensation analysis andenabled the omission of fin-tube heaters at mid-height levels on the glazed wall. Triple glazing with

stainless steel spacers, argon gas and a low-e coatingwas used to minimize U-value. This was glazed intoa thermally broken standard framing system. Alarge scale mock-up consisting of a 20-foot verticalsection of wall and a 12-foot section of skylight wasthermally tested, including full humidity control,to verify the design. From a lighting perspective, afull daylighting study was carried out on the galleryspaces to determine that hot spots did not occur ondisplay walls and to establish lighting levels. A com-bination of body-tinted glass and opacifying andtranslucent interlayers was used to match the exist-ing glass nomenclature and to provide the requiredlighting control.

Cleveland Museum of ArtThe expansion to the Cleveland Museum of Art byRafael Vinoly is in the design stage. It includes anumber of cladding elements designed with con-densation resistance in mind. A structural glassconnector joins the existing gallery to the expan-sion. This was carefully analyzed using CFD todetermine the maximum temperature of inlet airto provide the maximum amount of warmingwhile still keeping the space comfortable and estab-lishing that the local conditions within the connec-tor did not extent into the gallery spaces by morethan a small distance. Rather than using trace heat-ing to control humidity formation, the glazingdetails were adapted locally to allow warmth to

penetrate into the body of a fewcritical details. For example: Themain new galleries have largeglass walls. These were designedas cavity walls to meet the aes-thetic requirement for framelessglazing with good condensationperformance, so dryer andwarmer air then allowed in agallery space can be used. Themain atrium space includes apotential major thermal bridgeat the main roof support, how-ever, three-dimensional solidthermal modeling demonstratedthat this was not a problem area.In addition, back-of-house cura-torial spaces have “conventional”triple glazed and thermally bro-ken framed windows.

These museum projects andcountless others prove fascinat-ing to work on for every con-struction professional and pro-vide visitors with lasting symbolsof the fenestration arts. g

Photo by Brian Stacy , Arup, New Y ork City

Jack S. BlantonMuseum of Art

www.blantonmuseum.org/ Congress Ave. &

MLK Jr. Blvd. Austin, Texas

Opening: February 2006

Architect: KallmannMcKinnell & WoodArchitects, Boston

General contractor:SkanskaUSA,

Parsippany, N.J.

Lighting design: ArupAssociates, London

Contract glazier:Win-Con Enterprises,New Braunfels, Texas

Advertisementp. 73



SunlightTo understand the options and benefits of UV pro-tection, you must understand the science of sunlight.

Radiation from the sun contains ultraviolet, vis-ible and infrared light. Shown on the graph at left,these three spectrums get defined by their wave-lengths and measured in nanometers. One nano-meter equals one-billionth of a meter.

Visible light runs from 400-to-800 nanometersin wavelength. Any distortion of this spectrum willdiminish or alter the appearance of a curator’sexhibit. Outside of that range, curators want toblock as much solar radiation as possible.

Scientists define ultraviolet radiation as light inwavelengths of 295-to-380 nanometers. Invisible, itcan be blocked completely without any detectabledifference in lighting.

Ultraviolet light accounts for approximately50 percent of fading damage. Although Young spe-cializes in physical repairs and removing discol-oration from artwork, there is no cure for UV dam-age. “Fading cannot be reversed,” she says. “Inks,paints, pastels—once they’ve faded, that’s it.”

An advanced UV glass coating that virtually elim-inates UV radiation with minimal effect on the visi-ble light spectrum becomes a most effective weaponagainst fading. The use of UV glass, in combinationwith humidity and temperature controls, offers pow-erful protection from fading. Architects, specifiers,curators, glass-shop owners and contract glaziershave three ways to employ UV glass in museums orgalleries: frames, windows and light fixtures.

unning a museum is no day at the beach, but theexperiences do have one thing in common: theneed for advanced protection from ultraviolet rays.

Ultraviolet light constitutes the most damagingform of solar radiation. It damages more than justskin; it steals color from paints, paper, fabric andeven plastic. As any curator or conservator can tellyou, fading is cumulative and permanent.

“We spend a lot of time talking about UVdamage,” says paper conservator Christine Youngof Nashville, a consultant for museums, librariesand universities. “It is common. Most incidents ofcolor fading are the result of UV light.”

The life and health of museum exhibits andworks of art depend on protection from sunlight.With 27 years in art conservation, Young has seenUV technology improve considerably during hercareer. Today, a range of solutions exists, and theycome with a variety of price tags.

Museum glazing

The author is market segment director in charge of marketanalysis and strategic planning for Guardian Industries Corp. inAuburn Hills, Mich., [email protected], 734/654-4243.

FramesFramed artwork might be considered the easiest toprotect because the glass lies immediately in front ofa protected item. No light touches the piece with-out first passing through the UV-blocking glass.

“To me, archival framing must include UVglass or it is not archival,” says Jim Parrie, owner ofMillennial Technologies & Consulting Interna-tional of Covington, La. “If we protect the frameditem from acid burn and adhesives but not UVlight, then we have not done our jobs as framers.”

Parrie notes that low-quality printing materialshave become more abundant, especially amongupcoming artists who may not be able to affordpremium materials. “We can restore many piecesof art when they have been damaged by acid due toimproper framing. But when a piece fades due toUV light, it is gone forever.”

Standard glass effectively blocks UV radiationbelow 310 nanometers in wavelength. This leaves awide band, 310-to-380 nanometers, unblocked. Tohelp museum and gallery owners as well as artists andphotographers eliminate this problem, GuardianIndustries Corp. of Auburn Hills, Mich., developed ahigh-performance UV-blocking coating for theframing industry containing organic and inorganicmaterials and called Inspiration UV glass. Otherglass manufacturers have competing products.

The UV-blocking technology in framed art-work is not just effective for displays, it preventssun damage anywhere, including during storage ortransport. “You can see damage after a single day inthe sun,” points out Amie Geremia, registrar of theFrist Center for the Visual Arts in Nashville.

WindowsTwo common methods enhance the UV-blockingperformance of window glass. The first involvesuse of polymer films by physically applying theUV-blocking material to the glass surface followingwindow fabrication. The advantage is that thistechnology can be applied to existing windows.

The Frist Center, like most major art museums,does not have any windows in display areas. “Theonly windows we have near exhibition areas are inthe clerestory overlooking the lobby, and thosewindows are UV-filtered,” Geremia says.

The UV coating on the Frist Center windowswas applied to existing windows during a 1999renovation when the building was first trans-formed into a museum. The use of aftermarketwindow film can be an effective method of block-ing UV radiation when window replacement is notan option, or in building designs such as the FristCenter where windows sit near the ceiling and donot provide light for viewing the artwork.

However, smaller museums, such as historichomes that have been renovated into art galleries,tend to have windows closer to exhibit spaces. Inthese environments, aftermarket films may havedistinct disadvantages, such as a slight discol-oration, reflectivity problems, wrinkles, bubblesand peeling. Also, aftermarket films may voidmanufacturers’ warranties on the windows.

Guardian and other manufacturers offer glasssurface coatings for advanced UV protection. Thesecoatings cannot wrinkle or peel, do not create anydistortion and can be cleaned with most commonglass cleansers. Plus, coatings such as ClimaGuardSPF are scratch-resistant and can be resized withstandard glass-cutting tools. However, the coatingmust be applied during glass fabrication, not on site.

Light fixturesIndoor light from artificial sources contains thesame three spectrums as sunlight: ultraviolet, visi-ble and infrared. However, artificial light remainsfar less intense than solar radiation. Fading causedby sunlight can also be caused by artificial light,especially fluorescent lights, but to a much smallerdegree. UV coatings designed to minimize damagefrom sunlight also will prevent damage from artifi-cial sources.

Artwork behind a frame with UV glass is, ofcourse, largely protected from artificial light. Youcan provide additional protection with UV-block-ing light covers, now available in glass or Plexiglass.

What causes fading?Although generally defined as a simple loss ofcolor, “fading” actually comprises a complex chem-ical reaction that allows sunlight to break apart thebonds in organic molecules.

Different materials can handle different levels ofUV light before they break down. For example,

Advanced technology blocks damage from ultraviolet light

By Tim Singel

r

Sun’s energy spectrum

The sun’s energy in watts per square meter

Wavelength in nanometers300 400 500 600 700 800 900 1000

2.5

2.0

1.5

1.0

.5

0

Ultraviolet Visible Infrared

Source: Guardian Industries

Corp., Auburn Hills, Mich.

Transmission of ultraviolet light

Wavelength300 350 400 450 500

100

90

80

70

60

50

40

30

20

10

0

Perc

enta

ge

Uncoated glass

Ultraviolet glass

Fight

ethanol, used in paints, paint thinners and finishes,tends to breakdown if exposed to UV light below 311nanometers in wavelength. The plastics componentmethyl chloride has a threshold of 340 nanometers,and the paint component ethyl chloride breaks downrapidly in UV light less than 353 nanometers. Asthese materials break down, color rapidly disappears.

The most advancedUV coating technologyon the market today canblock 99 percent of UVlight below 380 nanome-ters in wavelength. Com-pared to traditional glassand as shown on thegraph on p. 75, UV glassvirtually eliminates mostof the ultraviolet energy

that would otherwise devastate artwork.To demonstrate how effective UV glass can be

in real-world applications, Guardian researcherstested a framed photograph printed on high-qual-ity, brand-name paper, subjecting it to the equiva-lent of 10 years of perpendicular 365-nanometerUV radiation. As shown above, the right side of thephotograph was protected by UV glass while theleft side was under ordinary glass. The unprotectedhalf lost its intense red pigments and faded to paleyellow. The other half remains vibrant.

Infrared lightYou may ask yourself, “What about infrared light?”

Infrared light, more than 800 nanometers inwavelength, would be responsible for approxi-mately 25 percent of fading if museum and gallerydisplays were left unprotected. Fortunately, theheat, or infrared, resistance of glass has long been ofinterest to glass manufacturers who want to mini-mize heat loss and excessive heat gain through win-

dows. Low-emissivity coatings have become com-monplace and effective at significantly reducing theamount of infrared light penetrating a window.Combining a low-emissivity coating with advancedUV-blocking coating achieves maximum protec-tion from all wavelengths of invisible light.

The future of UV protectionUV glass is rapidly becoming commonplace in con-sumer products. In the coming months, UV-block-ing windows will hit the marketplace for home-owners and builders who have become increasinglyconcerned about the harmful effects of UV light.

Nearly all windows sold today contain a double-pane insulating glass unit and more than half includea low-e coating. Combining a UV-blocking coatingwith a low-e coating will reduce UV penetrationfrom the current standard of 56.9 percent for a stan-dard clear glass window to less than 1 percent. Inother words, almost all ultraviolet radiation will beblocked from entering the building at the source, thewindow. This is important for museums and galleriesbecause it will protect more than just artwork.

Carpeting, fabrics and furniture are all suscepti-ble to the chemical breakdown caused by ultravioletlight. Museums curators will see the same advan-tages that homeowners demand: better protectionfor all vulnerable colors.

“Homeowners want to protect their invest-ments, whether it’s artwork or furniture,” Parriesays. “If consumers understand the value of UVprotection and are willing to pay for it, then amuseum definitely should.”

Testing is currently underway to determine thehealth benefits of UV-blocking windows. As thequality and availability of UV glass continues togrow, the marketplace for this technology is des-tined to spread from museums to homes to busi-nesses and beyond. g

Ultraviolet glassvirtually eliminates mostof the ultraviolet energy

that would otherwisedevastate artwork.

Accelerated testing — 10-year simulation

Clear glass Guardian UV glass


Advertisementp. 77

Fading: a growing concernSeveral factors explain why people voice more con-cern about fading of interior components.

Supported by the outstanding energy-efficiencylevels of today’s low-emissivity glasses, currentarchitectural designs favor a large number of win-dows with clearer glass than ever before. Consumersalso drive this trend, with their demand for large,open interior spaces flooded with natural light.

While this trend has brought more light intobuildings, another trend has, at the same time,made interior fabrics and finishes more fragile: theemergence of environmentally friendly materials.

Driven by pollution laws, fabric dyes, woodstains, paints and other coatings found in modernbuildings have been formulated to have a morebenign environmental impact, but may be less sta-

n choosing the most appropriate glass for commer-cial and residential projects, more architects look atthe issue of fading, specifically with regard to fab-rics, finishes, carpeting and artwork that willoccupy the interior of their finished buildings.

In assessing the potential fading risks associatedwith the glass they specify, most architects look at asingle measure on the performance data sheet:ultraviolet light transmittance. While useful, thismeasure fails to present a comprehensive view ofsolar-radiation risks, because light outside the ultra-violet range also causes significant fading.

Members of the construction industry slowlydiscover that a lesser-known measure—damage-weighted transmittance—may be a far more reli-able indicator of potential fading because it consid-ers UV light and visible light.

Museum glazing

The author is technical manager at AFG Industries Inc. in Toronto, [email protected], 905/669-1930

ble than their predecessor materials, typically, sol-vent-based. Today’s water-based products have anumber of obvious environmental benefits, butsome are more susceptible to fading over time,which is a primary drawback.

In addition, because of ozone depletion, higherlevels of UV light now reach the surface of the earth.This has the effect of increasing the rate of fading.

These three trends—more natural light trans-mittance, more fragile interior components and ahigher concentration of UV light—have resulted ina greater awareness of fading issues among archi-tects and those who ultimately occupy buildings.

A limited measure of potential fadingSince UV light represents only a small fraction ofthe total radiation from the sun—3 percent—thismeasure is extremely limited. In fact, fading of inte-rior components can also be caused by light in thevisible spectrum, accounting for a much greaterportion—47 percent—of total solar radiation. Theremaining 50 percent of solar radiation comes from

the infrared spectrum and is associated with heatgain, not fading.

Since UV light constitutes only one of severalcomponents that cause fading and is not weighted,assessing a glass based only on its UV transmittancelevel does not provide a true indication of its abilityto protect against fading.

The 2003 edition of the Glass Association ofNorth America’s Laminated Glazing ReferenceManual recognizes that UV light transmittance isan insufficient measure, and advises architects tolook beyond the UV spectrum:

Because of its high energy level, ultravioletradiation—radiation below 380 nanome-ters wave length—is a very significantcontributor to material deterioration andcolor fading. However, damage can alsobe caused by visible light … [and thosespecifying glass should] account for dam-age in the visible spectrum, as well as thatcaused by UV. —The manual is availableat www. glasswebsite.com.

A little-known measure, damage-weighted transmittance, emerges as a way to assess fading risks

By Per Werthwein

i

Architectural designs favor large numbers of windowswith clearer glass—hence, more risk of fading

Ultraviolet light transmit. Damage-weighted transmit.300-380 nanometers 300-700 nanometers

Glass type light range light range

6 millimeters clear monolithic 0.62 0.806 millimeters plus 6 millimeters clear insulating glass unit 0.46 0.696 millimeters clear laminated, 0.76 millimeters polyvinyl butyral Less than 0.01 0.626 millimeters clear laminated. plus 6 millimeters clear, IG unit Less than 0.01 0.556 millimeters green 0.30 0.636 millimeters green plus 6 millimeters clear 0.24 0.556 millimeters clear low-e on second surface,* plus 6 millimeters clear 0.31 0.536 millimeters clear low-e on second surface,* plus 6 millimeters clear laminated Less than 0.01 0.44

Fading potential: Two different views

*AFG’s Comfort Ti-AC 36 low-e coating. Values determined using Window 5.2 software Tdw-ISO function used to calculate damage-weighted transmittance.Source: AFG Industries Inc., Kingsport, Tenn.

Shedding light on

and fading


Advertisementp. 79


interior fading. However, when damage-weightedtransmittance is used to compare glass choices, itbecomes evident that low-e and tinted glasses can bejust as effective in preventing fading as laminatedproducts when considering the full 300-to-700nanometer light range.

In fact, the combination of a high-performancelow-e coating with laminated interior lites results inan excellent damage-weighted transmittance of0.44, and is an attractive glass type for many applica-tions. This glass choice will protect against fadingand reduce infrared energy to a low level to mini-mize solar heat gain, while still allowing high levelsof natural light into a building’s interior.

Best measures lead to best glass choicesWhatever the specific concerns associated with anarchitectural project—and whether they centeron energy efficiency, appearance, fading or all ofthese issues—architects must work with the bestand most comprehensive performance measuresavailable.

While several trends—an increasing number ofwindows, less stable fabric dyes and interior finishes,and higher levels of UV light—have made fading agrowing concern, the glass industry has respondedwith technologies that protect against fading whilemaximizing other performance elements.

Low-e and tinted glasses often make outstandingchoices for protecting against fading, while alsooffering excellent year-round energy efficiency, yetthese options may be overlooked if only the UVtransmittance level is considered.

Working with damage-weighted transmittance,in order to provide a look at the overall solar-radia-tion protection provided by a given glass configura-tion, architects can make informed choices that willprotect fabrics, furniture and other interior designelements while meeting the spectrum of their clients’performance needs. g

Despite its limitations, UV light transmittancehas been the traditional way of assessing the risk ofdamage to interior components. But that slowlychanges, as members of the architectural industrydiscover a readily available and more realistic assess-ment tool.

Damage-weighted transmittanceTo account for the fading damage that can resultfrom radiation in both the UV range and the muchlarger visible spectrum, German researcher JurgenKrochmann has created a measure called damage-weighted transmittance.

Krochmann’s original measure, Tdw-K, coversthe UV and visible parts of the spectrum from 300nanometers to 500 nanometers. However, a moreaccurate assessment of damage-weighted transmit-tance can be calculated using Tdw-ISO, a functionrecommended by the Commission Internationalede L’Eclairage in Austria. Tdw-ISO covers the solarspectrum from 300 nanometers to 700 nanometers.

While not yet standard information on glass-performance data sheets, the damage-weightedtransmittance rating for a given glass product can berequested from the manufacturer or easily calcu-lated using Window 5.2 thermal-analysis software,provided free of charge by Lawrence BerkeleyNational Laboratory, www.lbl.gov. Window 5.2allows users to calculate damage-weighted transmit-tance using both Tdw-K and Tdw-ISO functions.Tdw-ISO is generally considered to have greatervalidity, because it covers the visible range all theway to 700 nanometers.

The difference in fading potential can be dra-matic when one compares the traditional UVtransmittance measure to the more comprehen-sive damage-weighted transmittance measure (seetable on p. 78).

Based on UV light transmittance alone, a lami-nated glass may seem the best choice to minimize

Advertisementp. 80

Advertisementp. 81


Advertisementp. 82

and skylights to illuminate and bring life to art withnatural light and add magic to interiors. The play ofnatural light through glass makes for dramatic insidesand establishes continuity with the outside.

Different kinds of glass are being used in museumconstruction: insulating, laminated, low-emissivity,soundproof and self-cleaning. The following pagesfeature five recently built and renowned museumsthat use glass in their construction. g

useums house antiques, treasures and heritage. Theyconserve history and tell the story of who we are. Peo-ple visit museums to view exhibits, preferably well lit.Curators and visitors, however, express dramaticallyopposing views of what kind of light best illuminatesexhibits in a museum. The trend runs toward naturallight from large expanses of glass. Nearly every cur-rent museum renovation, expansion and new con-struction feature glass façades, curtain walls, panels

m

Museum glazing

The play of glass in the preservation of art, history

5of treasure

Nancy M. Davis, Katy Devlin, Jenni Chase and publicist Heather West of Minneapolis contributed to these profiles. Managing EditorSahely Mukerji coordinated and edited the museum section.


storehouses

Advertisementp. 83

he High Museum of Art will more than double itssize with the completion of a $130 million expan-sion and renovation.

The High’s current home opened in 1983 andwas designed by architect Richard Meier of NewYork City. To accommodate the museum’s rapidlygrowing collection and increased visitation,renowned Italian architect Renzo Piano conceptu-alized “a village for the arts” with four new buildingssurrounding a central, open-air plaza. When com-pleted, the structures will house a main pavilion, aspecial collections building, an administrative office

building, restaurant and dining areas, ampleexhibit halls, and a parking garage.

Building on Meier’s appreciationfor natural light, Piano relied heavily

on direct and filtered light to illu-minate “the magic about themuseum.” Bringing to life thissunlit icon of architecture andart, specialty glazing contrac-tor Harmon Inc.’s projectteam in Lithia Springs, Ga.,worked with Atlanta’s gen-eral contractor joint ventureSkanska-Russell and archi-tectural firm Lord, Aeck &

Sargent Inc., also of Atlanta. Greeting the museum’s

guests, 4,200 square feet of Pilk-ington Planar canopy crowns the

main pavilion’s primary entry. Forthis and the other buildings’ street-level

entrances, Harmon’s team installed threeall-glass revolving doors and 46 leaves of all-glass

doors. For inter-building access, four glass-enclosedpedestrian bridges connect the main pavilion to themuseum’s original building and the special collec-tions building.

tOnce inside, expansive, light-filled interiors wel-

come visitors to the pavilion’s lobby. The museum’sstaff also enjoys comfortable, naturally lit, windowviews from their desks and meeting rooms in theoffice building. Catering to these amenities, Har-mon provided approximately 29,000 square feet ofcurtain wall featuring PPG Starfire glass enhancedwith Viracon’s low-emissivity insulating and lami-nated products.

Perhaps the most intriguing architectural aspectsof the High’s exterior are its light scoops and rain-screen aluminum panel system cladding themuseum’s exhibit halls. Although nearly hiddenfrom view, the light scoops dot the roof with 1,000small skylights shrouded with metal hoods to dif-fuse the direct sunlight into the galleries below.

While most of theses scoops are of uniform size,60 required custom fabrication. Along with ensur-ing the proper angle for capturing the natural light,glaziers seamlessly blended these scoops into thebuilding’s aluminum panel system running its four-story height. “These panels are an essential elementthat complement the glass and glazing systems,while delivering on our customer’s vision for thissignature space,” says Tim Ryals, Harmon projectmanager. g

High Museum of Art1280 Peachtree St., Atlanta, Ga. 30309, www.high.org

Cost: $130 million

Architect: Renzo Piano, Italy; Lord, Aeck & Sargent Inc.,Atlanta

General contractor: Skanska-Russell, a joint venture,Atlanta

Glazing contractor: Harmon Inc., Lithia Springs, Ga.

Museum glazing

Culture around an open-air plaza

By Heather West

village squareHigh-brow

High Museum, AtlantaPhotos by Jim Roof, Atlanta



n designing the National Museum of Art in Osaka,Architect Cesar Pelli used space-age technology toturn earthbound underground caves into etherealspaces. Located on the island of Nakano betweenthe Tosabori and Dojima rivers, the 13,500-square-foot museum that opened in November 2004serves as the entrance to a site that planners see as afuture cultural district. They required Pelli buildentirely underground, yet sought a distinctivesculptural form and image. The New Haven,Conn., architect designed a concrete-clad vaultthree levels below grade and topped it with “freesculptural use of glass and steel elements in thelobby, creating a landmark that stands against thesky with greater impact than its size would allow,”according to a press release from the architect.

“The glass enclosure of the Museum’s lobby islike a crystal bubble rising to surface,” Pelli said in an

e-mail. “At night, it is a glowing beacon anchoringthe new arts district; during the day, its trans-

parency funnels the light caught by the sil-very threads of the stainless steel forms tobathe the three floors of the museum withnatural light. One soon forgets that oneis underground and becomes absorbedin the dynamics of people moving inthree dimensions and attracted to theart being exhibited.”

Titanium-coated stainless steel tubesprovide support for the glass and rise to

two vertical peaks 170 feet and 112 feetabove grade. Earthquake-zone require-

ments call for the steel sculpture to sway inall directions. Furthermore, many of the steel

tubes penetrate the skylight through water-tight seals on plates with bellows. The bellows

allow the steel tubes to move 4-to-6 inches in anydirection without breaking glass or causing leaks.

Titanium film coatings on the steel tubes preventcorrosion and dust. The glass in the skylight also has

a titanium coating and a 50 percent ceramic frit pat-tern for shading.

The curtain-wall system was adapted from astandard skylight system based on design parame-ters developed by the architect. Portions of the sky-light sit under a 100-year flood plain, so the insulat-ing glass units were laminated and tempered toresist enormous potential lateral loads.

High-performance gaskets and seals also guardagainst leaks and temperature changes. Standardmullions join heavy-duty aluminum stick-typemembers painted a special color to complement thestainless sculptural members. Custom-designedtrusses form a cage for the skylight system. Slidingpanels allow the vertical tubes that penetrate theskylight to move independent of the skylight.

“The light that filters into the building interior,crisscrossed by the many shadows of the steel tubes,has a silvery, diffused quality,” the Pelli’s publicistwrites. “On rainy days, water streams across theroof like a river current.”

Engineers on the project were Mitsubishi Jisho,Tokyo; the glazing manufacturer and fabricator,Nippon Sheet Glass Co., Japan; and the curtain-wall manufacturer was Fujisash Co., Japan. g

Museum glazing

Steel tubes penetrate skylights

By Nancy M. Davis

pillarsPelli’s sculptural

iNational Museum of Art4-2-55 Nakanoshima, kita-ku, Osaka City, Japanwww.nmao.go.ja

Cost: $133 million

Architects: Cesar Pelli & Associates, New Haven,Conn.; architect of record, Cesar Pelli & AssociatesTokyo

General contractors: Zenitaka Corp., Konoike Con-struction Co. and Ohmoto Gumi Co. of Japan, a jointventure

Glass installer: Sheet Glass Techno, Japan

National Museumof Art, Osaka

Photo by Turan Duda, Durham, N.C.

Photo by N. Kurozumi



orkers from InterClad of Plymouth, Minn., system-atically installed 2,000-pound lites of glass into themassive expansion of Minneapolis’ Walker ArtCenter, facing challenges from limited workingspace and constant traffic along the city’s busy Hen-nepin Avenue.

With lites up to 16 feet tall and 6 feet wide forthe custom curtain wall, the contract glazier Inter-Clad of Plymouth, Minn., had to look overseas tofind a fabricator capable of handling the order, says

Curtis Meade, InterClad senior project manager.“Handing even one piece of glass that

weighs almost a ton takes extra time,manpower and care [compared to

average installations],” Meadesays. “In some areas, we had

to use a 120-ton crane toreach out far enough to setthe glass.”

The $67.5 millionaddition doubles thesize of interior space tototal 260,000 squarefeet. The extensive glaz-ing and lightly crum-pled aluminum cladding

of the expansion contrastthe dark brick and win-

dowless nature of the origi-nal building. The design

essentially turned the old build-ing “inside out,” says John Cook,

project manager for architect and engi-neering firm Hammel, Green and Abra-

hamson Inc. of Minneapolis. “The building isabout transparency and light and bright materials.Of course, one of those materials is glass.”

This transparency of the structure is achievedin Swiss architects Herzog & de Meuron’s designpartially through large lites featured in a 150-footdouble-glass wall along Hennepin. The wall fea-tures 1-inch laminated glass on the inside, a heatedarea of 3 feet and 3⁄8-inch plate glass on the outside.

“The double wall serves thermal purposes as wellas aesthetic,” Cook says. “It’s all flush glazed insideand out, burying the structural columns.”

The design combined the supports for the glaz-ing and the building, so the structure that supportsthe building also supports the glass.

The exterior wall includes a spandrel area that isacid-etched at the top, fading to clear glazing at thebottom and lit from the outside creating a “lightwall,” Cook says. The etched frosted area also serves asa projection screen for signs announcing Walkerevents and creates effects under the lighting at night.A ultraviolet coating produces a slight tint to the glass.

“The glazing really does stand out,” Meade says.“It appears different every time you view it: differ-ent if it’s cloudy, sunny, day or night.”

Adjacent to the double wall, the cube sectionexpands over the center’s entrance and features sec-tions of polygon-shaped windows. g

w

Museum glazing

Large glass lites in Walker expansion challenge installers, transform center

By Katy Devlin

Sizematters

Walker Art Center1750 Hennepin Ave., Minneapolis, Minn. 55403www.walkerart.org

Cost: $67.5 million

Architects: Herzog & de Meuron, Basel, Switzerland;Hammel, Green and Abrahamson Inc., Minneapolis

General contractor: M.A. Mortenson Co., Minneapolis

Glazing contractor: InterClad, Plymouth, Minn.

Walker Art Center,Minneapolis

Photos by John Devlin, Richfield, Minn.

stone façade wouldn’t shine. Copper might gleamand shimmer, but wouldn’t look alive enough forthe designers of Shaw Center for the Arts, WarrenSchwartz and Christopher Ingersoll from Schwartz/Silver Architects. They needed to achieve the“biggest bang” with the façade, using a material that“was luminous in the daytime and glowed atnight,” Schwartz says. “That would reflect natureand the live things going on.”

The answer: an outer layer of hundreds of multi-length and width cast-glass channels and an inner

layer of corrugated aluminum.“Baton Rouge is right on the Missis-sippi, Schwartz says. “We saw glass act-

ing in a way as a metaphor for theriver itself, flowing, shimmering

and luminous.” The glass pieces range in

size from 7-to-9 inches wideto 7-to-22 feet long. Placedin a staggered pattern, thepieces create the feel ofmoving water on the façadeof the $37.5-mi l l ion,125,000-square-foot centerthat opened in March.

Shaw will serve as home totwo institutions, the Louisiana

State University Museum of Artand the Manship Performing Arts

Center. Many see its construction asa sign of the revitalization for the city

characterized in recent years more by aban-doned buildings than art complexes.

Shaw encourages this renewal in part throughinnovative structural design elements, such as the40-foot cantilever that appears to float over theadjacent Auto Hotel, and also through its lantern-

like appearance, Ingersoll says. At night, when litfrom eight exterior locations, the channel glass andaluminum exterior appears to cast a glow on thesurrounding city.

However, the motivations behind the channelglass go beyond aesthetics. The channels, spaced 2inches apart, sit 6 inches in front of the aluminumsiding and act as a rain screen, says Michael Tryon,general manager of Bendheim Wall Systems of Pas-saic, N.J., Shaw’s channel-glass provider.

“That glass will keep the heavy rains and winds,even from hurricanes, off the structural wall,”Tryon says. A mock-up of the glazing system wastested against 110-mile-per-hour wind pressures toensure strength.

The channel glass is 9⁄32-inch annealed, except forthe bottom 12 feet that are tempered to meet safetycodes. In the upper levels, the 2.4-inch flanges faceoutward, adding texture to the design.

Despite its glazed shell, the building containsfew view windows. “We were basically making thebuilding watertight, Ingersoll says. “To protect theart, we created a solid box inside a translucent box.”

The clear-glass atrium entrance represents theonly area of notable transparency in the building,and features 3⁄16-inch insulating glass from Viraconof Owatonna, Minn. The atrium glazing has a fritpattern on west-facing areas to reduce heat gain,Ingersoll says.

Shaw’s ability to spur revitalization throughoutBaton Rouge is apparent, Ingersoll says. “[Shaw] isnot just being received well by the architecturalcommunity, but by the people in the city,” he says.“It has been a dramatic change in the downtownand has already generated hundreds of millions ofdollars in planning and construction. It bringsattention to a place that normally doesn’t get muchattention.” g

Museum glazing

Innovative center revitalizes Baton Rouge

By Katy Devlin

changeChanneling

a

Shaw Center for the Arts100 Lafayette St., Baton Rouge, La. 70801, www.shawcenter.org

Cost: $37.5 million

Architects: Schwartz/Silver Architects, Boston; Eskew + Dumez + Ripple,New Orleans; and Jerry M. Campbell Associates, Baton Rouge, La.

General contractor: The Lemoine Co., Lafayette, La.

Glazing contractor: BHN Corp., Memphis

Channel glass supplier: Bendheim Wall Systems, Passaic, N.J.

Shaw Center for the Arts,Baton Rouge, La.

Photo by Timothy Hursley, Little Rock, Ark.

Photo by James McCown, Boston


Advertisementp. 91


Advertisementp. 93

ehind modern glass façades, visitors to the Museumof the Earth in Ithaca, N.Y., travel millions of yearsback in time as they move through displays featur-ing more than 650 specimens from one of theUnited States’ largest fossil collections. Opened inSeptember 2003, the museum is run by the Paleon-tological Research Institution—an organizationdedicated to increasing and disseminating knowl-edge about the history and evolution of the earthand its life—and occupies an 18,000-square-footaddition to the existing PRI complex on Ithaca’s

West Hill. It is organized into two parallel and inter-connected buildings containing three

“worlds” corresponding to differentperiods in the earth’s history. Both

buildings make extensive use ofPilkington glass in their exte-

rior façades, incorporatinga total of approximately6,000 square feet.

An aluminum cur-tain wall contains in-sulating glass unitswith Pilkington Activself-cleaning glass onthe exterior and Pilk-ington Energy Advan-

tage low-emissivity glasson the interior.

“The decision to installself-cleaning glass came

because the cost was less thanother options,” says Jillian Timm,

development assistant for PRI andthe Museum of the Earth. The fact that

Activ glass is low maintenance added to itsappeal, says Matt Miner, former project managerfor Cortland Glass, the glazing contractor. “Thedesign of the building features an overhanging roof

in some areas, so not all of the glass is exposed to theelements as it could be,” he explains. “But themuseum’s designers still believed that using Pilking-ton Activ glass would greatly reduce maintenanceeven in those areas because all it needs is an occa-sional light hosing to keep it clean.” This character-istic was put to the test during installation of the IGunits. “One day after our guys left, another contrac-tor drilling a well was still at work,” Miner recalls.“When we returned the next day, there was thickdirt from the drilling over about 20 percent of theglass. After allowing the dirt to dry, we hosed downthe glass, and it came clean.”

Pilkington Activ glass “literally keeps itselfclean,” according to literature from the UnitedKingdom-based company. A photocatalytic exte-rior surface uses the sun’s ultraviolet light to gradu-ally break down, loosen and dissolve dirt and soil. Alight rinse from a hose or rain shower then rinsesaway the loose dirt. “Thus far, we have been veryhappy with our decision [to use the Activ prod-uct],” says Timm. “Our expectations on the projecthave been fulfilled.” g

Museum glazing

Latest glass technology surrounds ancient artifacts

By Jenni Chase

futureBack to the

b Museum of the Earth1259 Trumansburg Road, Ithaca, N.Y. 14850www.priweb.org/museumoftheearth

Cost: $10.5 million

Cost of glazing: 240,808

Architect: Weiss/Manfredi Architects, New York City

General contractor: Cortland Glass Co., Cortland, N.Y.

Glass fabricator: Floral Glass, Hauppauge, N.Y., nowOldcastle Glass Santa Monica, Calif.

Glass supplier: Pilkington North America, Toledo

Photos by Paul Warchol

Museum of the EarthIthaca, N.Y.


september 2005 vol 55 | num 9 glass · september 2005 vol 55 | num 9 ... resistance to ultraviolet...

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