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July 2007July 2007 Vol. 49 No. 4

Also:Watching Paint DryWatching Paint Dry

Sound Acoustics for Multi-family ProjectsSound Acoustics for Multi-family ProjectsWater Infiltration WoesWater Infiltration Woes

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Silkscreening Glass

C O N F E R E N C E2007 WRAP-UP

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From ancient art to current construction, serigraphy (a.k.a. silkscreen printing) has been an ever-evolving process. Although estimates of its use date back as early as the 15th

century, the technique was fi rst patented in the early 1900s in England. Throughout history, various materials and methods have been explored, but the basic silkscreen printing process has remained consistent.

To make a silkscreen print on anything from fabric to paper to glass, the method is basically the same—a mesh fabric is stretched over a frame. (While silk is the traditional fabric used, a synthetic material such as nylon is typically chosen for today’s applications.) Portions of the fabric screen are masked off to create a stencil, and the screen is placed on top of the material to be printed. Paint or ink is then pushed across the screen with a squeegee, and

paint fl ows through the screen in the unmasked areas to form the desired image or pattern.

The process of silkscreen printing for use on glass façades has been available for more than two decades and follows the same basic process. The paint used is ceramic-based and once applied, must be fired to the glass. Similar to pottery in a kiln, firing the ceramic frit paint to glass is done by running the painted glass through a heat-treating furnace at approximately 593 C (1100 F).1 Once the firing is complete, the ceramic paint is essentially part of the glass. Additionally, with the increased knowledge of the toxic nature of lead, many manufacturers now offer lead-free paint.

There are many benefi ts of incorporating a silkscreen

By Alissa Schmidt, CSI, AIA Allied

Silkscreen GlassSilkscreen Glass Energy performance and esthetics Energy performance and esthetics

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Cover Story

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Silkscreen Glass Energy performance and esthetics

pattern with glass. Designers seeking improved solar performance, energy savings, reduced glare, and artistic expression often add silkscreen patterns to the glazing of building façades.

Solar control—performanceThe traditional method of solar control for glazing typically involves incorporating an insulating unit with a low-emissivity (low-e) or refl ective coating. A coating can reduce heat gain by approximately 50 percent over a similar unit without a coating. With sustainable design becoming a priority, building codes are gradually being modifi ed worldwide. The reduction provided by a coating is signifi cant, and in some instances, the glazing may require a higher level of performance than traditional methods alone can provide. Adding a silkscreen pattern can help achieve the next level of performance by blocking more heat than a traditional coated insulating glass (IG) unit.

For example, the city of Seattle, Wash., requires a maximum solar heat gain coeffi cient (SHGC) of 0.40.2 While some traditional low-e coated IG units can achieve this performance, many more options are available once a silkscreen pattern is added. For example, a 25-mm (1 in.) IG unit with a clear low-e coating has an SHGC of 0.54 and does not meet Seattle’s requirement of 0.40. Adding a white silkscreen pattern with 50 percent coverage increases performance to an SHGC of 0.37, therefore, meeting the requirement.

Not only does this increased performance assist in meeting codes, it can also help qualify a project for the Canada Green Building Council’s (CaGBC’s) Leadership in Energy and Environmental Design (LEED) rating system. For instance, under the Energy and Atmosphere Category (EA), points can be obtained for reducing design energy cost compared to the energy cost of the Model National Energy Code for Buildings (MNECB) or for the American Society of Heating, Refrigerating, and Air-conditioning Engineers/Illuminating Engineering Society of North America (ASHRAE/IESNA) 90.1-1999, Energy Standard for Buildings Except Low-rise Residential Buildings. Energy performance above the prerequisite standard reduces the environmental impact associated with excessive energy use. Under this category, one to 10 points are available, depending on how far the standard is exceeded.

Customizing solar control Although a silkscreen pattern of 50 percent coverage in a white ceramic frit improves performance, there are several additional ways to customize the level of solar control to meet project requirements. One way to adjust the solar control is to determine the pattern’s optimal placement. The highest performance is achieved through putting both the low-e coating and silkscreen on the second surface of the insulating unit.3 When the coating and silkscreen pattern are on the same surface, the pattern is applied fi rst, followed by the coating. While it is possible to place the pattern on the third surface, this blocks less heat, decreasing the unit’s performance.

In addition to placing the silkscreen pattern on the second

surface, performance can be customized by adjusting the percentage of glass covered by the pattern. To achieve the desired esthetic and solar performance, a lower percentage of coverage may be used with a higher performing low-e coating, a higher percentage of coverage with a lower performing low-e coating, or a balance of the two.

The colour of ceramic frit can also affect solar performance. A medium grey frit, for example, may block more heat than the traditional white frit. Using the medium grey frit would require a lower percentage of coverage than a white one to achieve the same level of performance (Figure 1).

Glare reductionArchitects and designers frequently specify glass with a very clear, transparent appearance. While this look can be attractive from the exterior, it can cause glare concerns for occupants. Glare is any type of light interfering with visual perception. It can be direct (e.g. the sun or a light bulb) or refl ected from surfaces (e.g. desks or computer screens). Windows and exterior glazing can be used to reduce glare. Although the best way to determine the potential for glare is through project-specifi c simulation and modeling, a guideline of 50 percent or more visible light transmittance (VLT) increases the potential for glare. Depending on the VLT of a proposed makeup, silkscreening can generally reduce both transmittance and glare. Since the project may be driven by esthetics, the percentage of silkscreen coverage can be customized to meet the proper balance of that goal, as well as provide solar control and glare control. Generally, the greater the density of the silkscreen pattern, the greater the potential for glare control.

Esthetic options aboundEnergy performance is just one of the benefi ts of using silk- screen glass. Once it is determined a silkscreen pattern is

Esthetics and energy efficiency led to the use of silkscreened images at the Minneapolis Central Library. Up to 50 different screens were used to create images on the fi ve-storey building’s 4600 insulating glass panels.

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advantageous for a specifi c project, there are many visual options to be explored, such as patterns and colour options.

The basicsMost manufacturers of silkscreened glazing typically have standard designs, such as a dot or line pattern. These tend to provide even coverage over the entire piece of glass. Typically, standard colours such as white, black, and various shades of grey are available. In addition to standard opaque colours, translucent ceramic frits can simulate the appearance of sandblasted or acid-etched glass.

A graduated silkscreen pattern is an alternate option to the standard patterns. It starts with a high percentage (sometimes 100 percent) of coverage and graduates to a lesser degree, in some cases fading down to zero.

Beyond the basics—artistic expressionUsing customized patterns, unique colours, tinted glass, and coatings opens the door for endless design options, and a silkscreen pattern can quickly turn a building façade into a work of art.

Although the majority of manufacturers have standard paint colours, most also

offer the ability to customize and match hues. This can be especially benefi cial when complementing glass to other building façade materials, such as stone or metal. Colour matching also provides the opportunity to change a frit shade throughout the façade even if the pattern remains consistent.

The design options are even more numerous when designing a custom silkscreen pattern. Like creating a stencil, each area of the artwork must be either designated as a printed area or a non-printed area, which is commonly referred to as black and white artwork. The only design boundaries are related to the process itself.

Typically, each element of the artwork (e.g. dots) must be at least 1.6 mm (1/16 in.) and spaces between the multiple elements at least 0.7 mm (1/32 in.). Anything less leaves a very small area in the screen for the paint to pass through. This creates the potential for the design to either not print completely where the dots are, or fi lling in where the spaces are supposed to be.

Is it worth the price?While silkscreening may add initial up-front costs to the glazing, it can improve solar performance and by doing so, reduces a building’s energy consump-tion, thus saving operating costs throughout the structure’s life.

For example, consider a building with 457.2 m2 (1500 sf) of 25-mm (1-in.) clear insulating glass. If a 60 percent white silkscreen pattern is added to the 25-mm IG unit, the initial cost is approximately 35 percent higher. The time it would take to pay back the initial investment, however, is only four to 12 years.4 Installing a low-e coating and dropping the coverage to 40 percent further improves performance and reduces payback time to three to seven years, even though the up-front cost to incorporate a coating is added (Figure 2).

It is important to note a silkscreen pattern will not decrease in effi ciency over time. Other building products, such as interior blinds or window fi lms, may prove to save money after the initial investment and, thus, have similar payback timeframes. The difference with a silkscreen pattern is it requires neither

Silkscreen is achieved by applying a ceramic-based paint to glass, which is then fi red at approximately 593 C (1100 F). When complete, the ceramic is part of the glass.

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maintenance nor replacement.The savings and payback timeframes

discussed assume all other aspects of the building remain as they would have been without a silkscreen pattern. For some applications, the addition of a silkscreen pattern can change other building decisions.

For example, with improved glazing performance, it may be possible to reduce the size of the HVAC system. This would lower initial costs and the money saved could be used toward the initial investment in a silkscreen pattern. Not only can a smaller HVAC system save money, but it is also typically the preferred esthetic.

Money is often spent to hide HVAC equipment located outside a building. A

smaller system would obviously require less screening or fencing necessary to disguise the unit, reducing a portion of the budget. If applied toward a silkscreen pattern, both budget reductions would even further reduce the length of payback time.

If the energy savings and related equipment reductions are not enough, there may be innovative ways to fi nd money in the budget for a silkscreen pattern. Could it serve a dual purpose? For example, if one of the items budgeted for the project is building signage, it may be possible to take that portion of the budget and incorporate signage and logos into the glass façade. Another area to consider is interior shading devices. If the glass

façade is composed of two vision units (i.e. a lower portion and an upper transom), it may be possible to silkscreen the transom, thus saving money on the blinds. This could also increase occupancy comfort by reducing the amount of dust accumulating on the blinds, as well as lowering the amount of maintenance and cleaning necessary.

Moiré patternWhen a silkscreen pattern is applied to glass, there is a potential to see a moiré pattern—an optical phenomenon of waves, ripples, or circles. Just as the glass on a building appears different under sunny versus cloudy conditions, the moiré pattern may appear or disappear under changing conditions. It is not a defect in the glass or silkscreen pattern, but rather an image formed by the eye.

This moiré is produced when two regularly spaced patterns—one in front of the other—are slightly offset, creating interference. In architectural applications, this may occur on a glass façade when silkscreen patterns are used on the second and third surface of an insulating unit, or when a second surface pattern creates a shadow on the third surface.

Special consideration must be given to the selection of colours, patterns, and application of these products. Although there may be cases where moiré is part of the design intent, it is undesirable in most cases. While it may not be possible to identify those cases where it will occur, the following glass treatments are generally more prone to exhibiting a moiré:• patterns with closely spaced lines,

dots, or holes;• a silkscreen pattern on the second and

third surface of insulating glass;• insulating spandrel glass with a

silkscreen pattern on the second surface and a full coverage frit on the fourth surface; or

• aluminum panels installed behind glass with a silkscreen pattern.

Viewing a full-size mock-up is recommended to better evaluate lighting conditions at different times of day and under varying temperature conditions. The best location to view the mock-up is at the project site in the conditions

The Toronto Medical Discoveries Tower design team specifi ed a white ceramic frit on the number two surface of its insulated glass units, and a full coverage grey opacifi er on the number four surface. The elements created a shallow, shadow box effect.

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likely anticipated once the project is complete. Surrounding buildings, landscaping, or anything else that could affect the pattern’s appearance should always be as closely represented as possible for mock-up viewing.

Innovation and advancesCreative design can sometimes produce unexpected results and adding a silkscreen pattern to glass is no exception. In a project worked on by this author, a spandrel area was specifi ed to include a silkscreen pattern on the IG unit’s second surface and a full coverage ceramic frit on the fourth surface. The intent was to brighten the

spandrel so it more closely resembled the vision area and could help create a continuous façade. The pattern consisted of 19.05-mm (0.75-in.) lines alternating with 12.7-mm (0.5-in.) spaces. Unrelated to this decision, an interior design selection was made to install horizontal blinds in the vision areas. On completion, it was discovered the horizontal lines in the spandrel areas emulated the horizontal silkscreen pattern. The blinds, balanced with the silkscreen pattern, helped achieve the desired continuous look between the vision and spandrel areas.

A developing area for silkscreened glass relates to bird safety. Due to glazing’s refl ective nature, birds do not always see the glass façade. As a result, in cities like Toronto, thousands of birds are killed each year. To help alleviate the number of birds being killed, some cities, including Toronto, have created ‘lights-out’ strategies for both interior and exterior lighting. The goal is to reduce refl ection from the glass surface, as well as see-through glass applications often associated with atriums.

Although not as effective as other strategies currently being researched, silkscreen patterns have been used as a way to change the refl ection on the glass as well as reduce the see-through, creating a visual marker for birds. When using a silkscreen pattern for bird safety, the pattern should only be used in combination with non-refl ective glass.5 As further research is conducted and technology progresses, silkscreening may become a more viable solution.

ConclusionBuildings consume a large amount of energy. As awareness and energy prices continue to increase, the implementation of more stringent energy codes is being seen in more and more jurisdictions. Many designers are faced with the challenge of designing to conserve energy while still providing a creative, unique building. It can be a diffi cult task to fi nd products fulfi lling both these needs, especially for the building façade. Glass with a silkscreen pattern can be used to increase energy effi ciency, as well as to provide endless design opportunities. ✍

Notes1 Glass is heat-treated in a furnace to increase its strength to

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Creating Depth with Silkscreening

Situated on the corner of College and Elizabeth Streets

in downtown Toronto, the new 15-storey Toronto

Medical Discoveries Tower at the Medical and Related

Sciences (MaRS) Centre needed to hold its own in an

architecturally diverse city. (See photo on the cover).

To visually enhance the expansive curtain wall, the

architects accented the glazing system with a controlled

series of silkscreen patterns. Applied in a unique

confi guration, the patterns transform the exterior, giving it

added visual interest and depth.

“We manipulated the glass spandrels above and below

the vision panels to make the curtain wall appear to be

composed of predominantly vision glass,” said senior

designer Domenic Virdo at Toronto-based Adamson

Associates Architects, the group responsible for the

building’s design.

“By using a combination of a custom white ceramic frit on

the number two surface and full coverage grey frit on the

number four surface of the insulated glass unit, we were able

to create a shallow, shadow box effect. As light shines through

the frit pattern, a shadow is cast onto the opacifi ed glass

surface giving the cladding a sense of depth.” ✍

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either heat-strengthened or fully tempered levels per ASTM C 1048, Standard Specifi cation for Heat-Treated Flat Glass—Kind HS, Kind FT-Coated, and Uncoated Glass. Whenever a silkscreen pattern is applied, the glass is heat-treated as part of the process.2 This is based on the 2004 Washington State Energy Code plus Seattle Amendments. See Table 13-1 Building Envelope Requirements for Climate Zone 1. For more, visit www.seattle.gov/DPD/Codes/Energy_Code/Nonresidential/Chapter_13/default.asp.3 The surfaces are counted starting with the exterior as surface ‘number one’ working inward, counting each side.

Each ply of glass has two surfaces; an insulating unit has four.4 This is based on the assumptions each building consists of four façades and each façade has an equal square footage of glass. Payback for Washington, D.C., New York City, and San Diego, Calif., is calculated based on November 2006 energy prices for each city as published by the Energy Information Administration, Offi cial Energy Statistics from the U.S. government. Vancouver and Toronto payback is calculated based on electricity pricing of $0.09 per kWh and natural gas pricing of $0.65 per Therm.5 See City of Toronto Green Development

Standard (March 2007), Bird-friendly Development Guidelines, at www.toronto.ca/lightsout/guidelines.htm.Alissa Schmidt, CSI, AIA Allied, is an architectural design associate with Viracon, an architectural glass fabricator. She assists design/construction professionals with selecting practical solutions that meet project-specifi c performance and esthetic needs. In addition, Schmidt is a member of the Construction Specifi cations Institute’s (CSI’s) Minneapolis-St. Paul Chapter’s Education Committee. She holds a bachelor of science in interior design/construction management from Minnesota State University in Mankato.

Contents of Construction Canada are copyrighted and are reproduced by FosteReprints with consent of Kenilworth Publishing Inc.

The publisher and Construction Specifi cations Canada shall not be liable for any of the views expressed by the authors,

nor shall these opinions necessarily refl ect those of the publisher and Construction Specifi cations Canada.

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