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Facade Retroits: The Dilemma of the Highly Glazed High-Rise

Facade

MIC PATTERSON, LEED AP [BD+C] Director of Strategic Development, Enclos Advanced Technology Studio – Enclos PhD Candidate, University of Southern California, School of Architecture

JEFFREY C. VAGLIO, PE, LEED AP [BD+C] Design Engineer, Enclos Advanced Technology Studio – EnclosPhD Candidate, University of Southern California, School of Architecture

ABSTRACT

The post-war building boom in the mid-twentieth century produced the irst crop of glass curtain walled ofice towers. This trend has continued through the decades, growing to include highly glazed residential towers in the urban environment. This building type represents a problematic component of the existing building stock. Many of these high-rise towers are now thirty to forty years old or more. Moreover, the curtain wall technology of the time would be regarded as signiicantly substandard today. Improving energy consumption in the existing building stock will require the retroitting of many, if not most, of these facades. While many buildings are currently undergoing energy retroits, the scope of the renovation often stops short of the façade because of the relatively high cost and the potential disruption to ongoing building operations. Even when the façade is included in a energy retroit program, the options for approaching the façade element are often unclear. This paper will examine the dilemma presented by the façade retroit, and explore the complex issues related to this component of a building renovation.

1 INTRODUCTION

The statistics are well known: buildings consume more energy than any other commercial sector, including transportation, accounting for nearly 49% of all energy use and 77% of all electricity, while responsible for 47% of greenhouse gas emissions. Meeting the aggressive goals for energy reduction established by such initiatives as the White House Agenda and the 2030 Challenge will require energy retroits to the existing building stock on a widespread scale. The building stock is comprised of a wide variety of building types, many of which present very particular problems with respect to retroit. None are more challenging, however, than those presented by the tall building façade.

The statistics are often repeated:

Buildings consume more energy than any other sector.
76% of building energy comes from fossil fuels.
Building energy use is growing faster than any other sector.
The building sector produces 47% of all green house gases.

Tall buildings are virtually synonymous with highly glazed curtain wall façade systems, especially those constructed from the mid-twentieth century onward. Many of these buildings were constructed during post-war boom times in the 1960s and 1970s, and are approaching 40 years of age and older. Insulated glass warranties are typically 5 to 10 years, with the products having a life expectancy of

20 to 30 years. Similar durability can be expected from many of the sealants and gasket materials used to provide the weather seal. Nor was this emergent curtain wall technology particularly robust to begin with: problems with water penetration and air iniltration were common, thermal performance was often miserable resulting variously in condensation, unwanted heat transfer, and general discomfort to building occupants. Meanwhile, there have been many developments in curtain wall technology over the past 3 decades involving progressive design technique, high performance materials, and advanced fabrication processes.

These factors combine to create a real opportunity in the retroit of tall buildings. Retroit is, quite simply, the application of new technology to existing systems. Yet there remain many uncertainties, and more questions than answers. Façade retroit, or re-clad, is expensive; does it make economic sense? What are the programmatic options with a façade retroit? Is glass a blessing or a curse in the building façade? What are best (and sustainable) practices in undertaking a façade retroit; what means-and-methods and project delivery options are available? This paper attempts to provide a framework for these issues suitable to furthering a comprehensive dialog that may yield answers to these and other questions regarding the façade retroit of tall curtain wall buildings.

2 STRUCTURE + SKIN: EMERGENCE OF THE GLASS SKYSCRAPER

Several technologies and a dominant architectural movement combined to make possible the high- rise building tower that now so dominates our urban centers. The separation of skin and structure as individual building components evolved through the 19th century in the design and construction of the great iron and glass conservatory structures built throughout Northern Europe and England. By the turn of the 19th century, William Jenny had developed structural steel framing systems, Willis Carrier was poised to contribute the air conditioner, and elevator technology as pioneered by Elisha Otis was well established. The masonry practices of the day, however, remained in use in the construction of walls, even as those walls were no longer load bearing and building heights were climbing ever higher. Windows slowly grew larger in turn of the century Chicago architecture, but they were still framed by heavy masonry walls.

The vision, in this case, had preceded the technology. Paul Scheerbart’s 1914 novel, The Gray Cloth, predicts contemporary glass architecture with stunning detail and accuracy, right down to the double-skin facade. Mies van der Rohe beautifully conceived of and expressed the lightweight, highly transparent glass façade in such work as the Friedrichstraße Skyscraper in 1921, a competition entry, followed by a study for the Glass Skyscraper in 1922. Both projects went unbuilt but were widely published, and the inluence they had on the modernist vision and what was to come in architecture some few decades later is hard to over emphasize.

The irst of the glass skyscrapers to foreshadow the dramatic upcoming changes to urban skylines included 860-880 Lakeshore Drive (Mies van der Rohe, Chicago, 1949), Lever House (Skidmore Owings and Merrill, New York City, 1951), and the Seagram Building (Mies van der Rohe, New York City, 1957). These façade designs were sophisticated and exceptionally innovative. Skyscraper construction inally boomed in the 1960s, driven by a real estate industry that recognized a way to maximize leasable area in a ixed building footprint by using the new façade technology, and fueled by material advances that included a plentiful supply of inexpensive and high quality lat glass, and an abundance of aluminum to feed the extrusion process for framing components. The modern curtain wall industry was thus born, and remains the dominant technology for cladding tall buildings.

Figure 1: The Lever House by SOM, 1951, and the Seagram Building by Mies van der Rohe, 1954, across the street from each other in New York City, are iconic examples of the building type discussed here. The Lever House has already required a remedial retroit completed nearly a decade ago. (Lever House photo by Shankbone)

2.1 Underperforming Facades

However, the quality and performance of this new exterior wall technology was problematic, resulting in a proliferation of what Michael Wigginton (1996) refers to as high-rise "heat sinks." The technology was new and largely untested. Thermally broken framing components had not yet been developed, so the aluminum frames acted as thermal conductors between inside and out. The gasket and seal materials were inferior by today’s standards. Design practices were often dictated by the speculative developer intent upon minimizing initial construction costs and a quick turnaround of the building. Many of the buildings were only single-glazed, and the highly eficient low-e coatings had yet to be created. Insulated glass units (IGUs) did not come into widespread use in North America until after the oil crisis of 1972. Mirror coatings emerged early on as a means to mitigate the poor thermal performance of glass, but so reduced the visible light transmission that electrical lighting was required all day long despite sunny exterior conditions. The abysmal energy eficiency was enabled by cheap energy and the new air conditioning technology. The result is a building type with poorly designed and constructed facades to begin with that are deteriorating with age.

There are other issues, as well. In addition to being a poor thermal insulator, glass is an equally poor acoustical insulator. A signiicant threshold has been recently crossed, whereby the majority of the global population now lives in densely populated urban environments. In the early decades of tall buildings the applications were predominantly ofice towers and the urban centers cleared out in the early evening as people returned to homes in the suburbs. Recent decades, however, have seen the rise of many highly glazed residential towers within the urban context, where noise pollution is a signiicant and growing concern, albeit one not particularly well understood or easily dealt with. Nonetheless, today’s insulated, and particularly laminated, glass panel constructs possess signiicantly improved acoustical properties as compared to those often used in early curtain wall systems.

2.2 Curtain Wall Technology

It is necessary to have an understanding of basic curtain wall technology in order to assess the potential for façade retroit. The technology is simple enough in concept, with complexity found in the design, performance and delivery. While today’s curtain walls are little different in concept than the early applications of the 1960s, important differences have evolved over the past decades.

Stick and unitized are the predominant forms of curtain wall. Stick systems were the earliest, the name deriving from the long aluminum extrusions, called sticks, that were used to construct the wall system in place on the building façade. Typically, the long vertical mullions were irst installed on the glazing grid by attaching them at the loor slabs. Horizontal mullions were then installed between the vertical mullions. Gaskets and seals were installed as dictated by the system design, and inally, the inill panels were lifted into position, itted into the framed openings, then ixed and sealed in place.

Unitized systems developed as a prefabrication strategy, driven by the intent to minimize expensive site labor, and to improve quality as provided by manufacture under factory-controlled conditions as opposed to the adverse conditions often presented by the building site. The design necessitated the division of vertical and horizontal mullions into two pieces, a so-called split mullion, accommodating the provision of a frame around each unit. The origin of the term unitized is unclear. They are essentially prefabricated modular systems. The extruded aluminum framing members are irst fabricated (drilled, notched, cut to length), and then assembled into complete frames. The units are most often designed to span a single loor in height, with the width determined by the width of a single inill panel. Economics sometimes favor larger panels, however, and some systems have utilized units spanning two loors in height, or multiple inill units in width. Regardless, once the frames are assembled, gaskets and seals are itted and the inill panels are installed and glazed as required. Unit construction may include such add-on items as sunshades and photovoltaic panels. The assembled units are shipped to the site, lifted into position and attached to preinstalled anchors at the loor slabs. The adjoining split mullions are typically designed to interlock, such that installation must proceed with the sequential setting of neighboring units wrapping a loor level, typically starting at a lower level and progressing upward loor by loor. The weather seal between units is typically a dry gasket, and only minimal onsite caulking is required.

While curtain wall systems can incorporate virtually any panel material; metal panel constructs, natural stone, or tile, their use enabled the extensive use of glass in the building skin. In fact, curtain wall became synonymous with the glass skin of the 1960s high-rise, establishing glass as the dominant cladding material for this new building form.

Figure 2-3: Typical stack joint and vertical joint of unitized curtain wall system. Note the split mullions. The split mullion replaces the simpler single mullions used in stick type systems.

3 THE RETROFIT OPPORTUNITY

So the problem of the poor performing, aging glass curtain wall is now the opportunity to combine need with solutions in a facedil;ade retroit. Sustainable building practice will certainly recognize reuse of these aging buildings as superior to a strategy of deconstruction, recycling and rebuilding. Retroit supports a sustainable strategy of reuse. There is no question that many buildings of the type addressed here could beneit signiicantly from a façade retroit, and there is equally no doubt that recent material developments and technology can signiicantly improve their performance, and likely their appearance.

Curtain wall framing systems have improved somewhat; the mullions are often thermally broken, at least in colder climates, to prevent heat transfer through the mullion. However, much of the opportunity for performance improvements resulting from façade retroit yields from two sources: material advances in architectural glass, and increasing sophistication in façade design.

3.1 Thin Skins

Material advances in architectural glass can be characterized as "thin skin" developments. Most glass building skins are comprised of a single glass panel, whether it is single glazing, laminated and/or insulated. This puts the vast majority of building skin thickness at one inch or less. Even triple-glazed panels – IGUs with three glass plies and double cavity – are less than two inches in thickness.

Developments in architectural glass have been quite dynamic. Glazing materials keep improving. Architectural glass is a highly engineered material bearing little resemblance to the raw material

produced by the loat process. The value-added post processing of raw loat glass has come to dominate growth in the glass industry. Glass is variously heat-treated, laminated, coated, and built up into insulated panels. Thin-ilm coatings, for example, have signiicantly improved the thermal performance of glass in the building skin over the past 30 years. Ongoing improvements include interlayer materials for laminating glass, and cavity enhancements of IGUs as provided by aerogels and mechanical shading devices built into the cavity. Vacuum glass products are beginning to appear on the market with super insulation properties provided by very shallow, evacuated cavities, promising future multi-ply super-insulating vacuum glass units (VGUs) itting within the same thin- skin envelope.

Figure 4: The construction of a typical double-glazed insulated glass unit (IGU).

3.2 Deep Skins

In contrast to thin skins, deep skins are much more about the design of the building façade than simply about the material properties of the glass. Façade designers are becoming increasingly inventive with advanced façade designs in recognition of the combined effect of the building skin on both performance and appearance. The skin is no longer merely a membrane enclosing the building, measured in inches of depth, but a multi-layered construct comprised of both indoor and outdoor elements measured in feet. Some double-skin designs have even been developed that use the cavity space for public circulation. The Loyola Information Commons incorporates a vestibule entry space that is part of a double-skin cavity buffer. Consider a façade on a Morphosis building such as the San Francisco Federal Building, or the new Cooper Union in New York City; where exactly does the facade begin and end? Layers of material and function comprise the facade.

Façade Retroits: The Dilemma of the Highly Glazed High-Rise Facade

in response to internal, external and programmatic factors (solar exposure, natural ventilation, circulation, etc.), with the weather barrier but one among them. On either or both sides of the weather barrier may be found sensors and controllers, operable blinds and shades, ixed louvers and screens, and daylight redirecting devices such as light shelves.

The double-skin facade is a particular coniguration of deep skin in which a cavity is developed between two skins, separated by a depth that can range from inches to feet. The cavity affords opportunities for enhancing the thermal and acoustical performance of the wall, controlling glare, and providing natural ventilation. In fact, a double-skin strategy may provide an optimum solution for certain retroit applications, for reasons discussed later.

Figure 5: Working within the deep cavity of a multi-story double skin system, workers install the outboard skin. A grating system divides the cavity at each loor level to provide maintenance access without restricting airlow.

3.3 Smart Skins

Smart skins also represent emergent technology with potential application in façade retroit projects. Smart or intelligent skins are facades or façade materials that undergo an adaptive responsive to changing internal or external conditions. They may be comprised of smart materials, as with electrochromic glazing, or smart systems, such as dimmable lighting and operable shading systems that employ sensors and controllers to optimize daylighting effect, moderating glare and minimizing electricity consumption from artiicial lighting. The differentiating characteristic of smart systems is the dynamic response to environmental change. There is often an active integration among the façade components in a smart system, and with other building systems, through a building management system (BMS), which may involve such things as energy management, lighting control, natural ventilation, solar-tracking sunshades or rooftop photovoltaic arrays, or other building integrated photovoltaic (BIPV) devices.

Figure 6: Section rendering of a unitized double-skin system showing glass makeup and operable blinds located in the cavity between the two skins.

4 THE RETROFIT CHALLENGE

Façade retroits can be considered a subcategory of building energy retroits, a relatively new market phenomenon. There have, of course, been past instances of façade retroit, but these were largely isolated instances of remedial work: reitting facades that had suffered some kind of failure. In contrast, energy performance considerations are driving the current retroit dialog, and the whole-building energy retroit is the manifestation of that dialog. Many of these retroits focus on items with the quickest payback cycle: more eficient mechanical systems, for example, or lighting and lighting controls. Most of these programs stop short of including the façade, other than with perhaps an adhesive ilm application to the interior glass surfaces, a bandaid approach to the problem. The usual reasons for this are cost and the potential disruption to ongoing building operations. The relative cost of a façade retroit compared with other energy retroit program elements can be signiicantly higher, and challenging to justify in a simple payback equation.

In many cases this will prove a false economy, however. Payback and lifecycle costs incorporate basic assumptions about the cost of energy. These igures seldom include the true cost of non- renewable energy use, not accounting for the escalating cost of extraction and environment cleanup associated with post peak-oil production, or the cost of developing renewable energy sources to replace the dwindling supply of non-renewables. And what value should be placed on issues of national security as related to continued dependency on oil from increasingly politically volatile foreign sources?

The building energy retroit presents an opportunity to address the energy eficiency of a building holistically, in a manner to truly optimize energy consumption and greenhouse gas emissions. There is also an economic eficiency in addressing these issues in an integrated manner. If the façade is not retroitted as part of an energy retroit program, the opportunity to integrate the façade with the BMS will be missed, resulting in a larger mechanical system than might otherwise be required. Such a building may yet require a façade retroit in coming years as energy costs increase and regulations for energy consumption become stricter. The BMS and mechanical systems will then need additional evaluation and potential modiication to accommodate the new façade.

4.1 Sustainability Issues

If improperly implemented, upcoming façade retroits may create more problems than they solve. Sustainability issues, always complex, are perhaps even more so with retroit work.

The predominant materials in curtain walls are aluminum in the framing systems and glass as the inill material. The metals used in curtain wall systems, particularly the aluminum, are typically recycled into new products. Architectural glass, on the other hand, is not recycled: a fact surprising to many outside of the glass industry. It turns out that the product development of glass to compensate for its performance deiciencies in the building envelope has rendered the material unrecyclable. The value-added secondary processing of loat glass, including insulating, laminating, coating and fritting, all alter the raw loat material, making it unit for reintroduction into the loat process. The loat process is sensitive to contaminants, and while raw loat glass is theoretically recyclable simply by reintroducing it into the melt, this is not practiced by any of the major loat glass producers beyond recycling the cullet, the breakage that occurs within the plant during the manufacturing process.

The reality is that very little raw loat glass is used in buildings today, thus architectural glass is not recycled. It is occasionally down-cycled, ground up and used as asphalt ill or landscaping material, but there is no current recycling technology capable of eficiently processing loat glass products into a form that renders the material recyclable. So most of it it ends up in a landill. There are currently over 10,000 landills in the US. How many more will be required to accommodate all the Façade Retroits: The Dilemma of the Highly Glazed High-Rise Facade architectural glass that must be replaced in the existing building stock if energy eficiency goals are to be achieved? The complexity of the problem is evident in the example of the low-e coatings that have so dramatically and effectively improved the thermal performance of glass. The coatings are comprised of many layers of different heavy-metal oxides in combination to produce speciic performance and appearance (color, relectivity) attributes. Even if a process can be developed to effectively clean the glass of the coatings, another challenge remains in what to do with the metal-oxide soup resulting from the process. There are solutions to these problems, no doubt, but there are also costs associated with these solutions. Current costing models used in payback and lifecycle analysis do not account for the cost of recycling, a fundamental requirement for sustainable building practice.

Considerations of sustainability necessarily embrace a long-term timeframe. Another effect on the sustainability of glass in the building skin resulting from the value-added processing of glass is the durability of the resulting materials. Float glass can last for hundreds of years in the building envelope. Glass coatings can fail through oxidation and weathering, compromising performance and appearance, and considerably shortening the effective lifetime of the material. The same is true of laminating and insulating processes. Laminations can fail and discolor, and the seals of IGUs can fail allowing condensation to occur within the unit cavity. Manufacturer’s warranty for these products is typically in the range of 5 years, with superior product warranties running from 10 to 12 years. In fact, in the absence of fabrication defects or damage during installation or use, the materials will likely last well beyond the warranty period, but their lifespan is signiicantly less than raw loat material.

Figure 7: With over 10,000 landills in the United States, it is imperative that future building façade retroits maximize material reuse and recycling strategies.

5 FAÇADE RETROFIT PROCESS

Unfortunately, curtain wall systems, like many other products, are not designed with retroit in mind. Re-clad strategies are, partly for this reason and partly because few of this building type have actually been retroit, poorly articulated in the industry. Unitized systems can be particularly challenging for inill retroits. The glazing joints that essentially glue the glass to the framing units can be dificult to access, and separating the glass from the unit frame as part of an inill retroit can be a challenge. With façade replacement retroit strategies, unitized systems present challenges because of the way they typically interlock, unlike the older stick systems, preventing their ad hoc removal. They are most easily removed as they are installed, in a progressive, sequential fashion, peeling loor after loor of building skin, but limiting important lexibility in retroit installation strategy.

A façade retroit program must anticipate the deconstruction requirements of the existing façade, and the implementation of a new façade solution, most often in the context of a building that will remain operational throughout the process. It is this context of maintaining ongoing building operations throughout construction that most differentiates the retroit process from new building construction. The dominant consideration with such projects becomes the mitigation of disruptions resulting from the construction work that might negatively impact ongoing operations and the comfort and eficiency of the building occupants. To achieve this, it is critical that all aspects of the re-clad process, from design through fabrication, delivery, installation, and commissioning, be developed in the context of this overriding consideration. There are other differences as well. The makeup of the design and construction teams may vary considerably between retroit jobs, as well as varying considerably from conventional new construction practice. Many retroit jobs may not even include an architect or a façade consultant. If the scope of work is limited to the building façade, the building owner may contract directly with a specialty façade contractor, foregoing a construction manager or general contractor.

Figure 8: The Javits Convention Center in New York City is currently undergoing a façade retroit involving the removal and replacement of the entire façade system.

6 CONCLUSIONS

Façade retroit thus represents a unique process, signiicantly different from that of new construction, for which there is a tremendous looming need of some importance. It is critical that this retroit work be carried out eficiently and effectively. Yet this remains largely undeined territory. Everything from contracting strategies to system designs and means-and-methods considerations involve considerable ambiguity, and sustainability issues are problematic in the extreme. Following are the primary conclusions derived from this exercise.

The looming requirement for facade retroit should be regarded as a fundamental infrastructure problem; energy eficiency and carbon reduction goals cannot be achieved without addressing this problem.

Meeting the demand will be costly and complex, with a high potential for the process being wasteful.

There is urgent need for deining appropriate retroit strategies, evaluation criteria for their application, and the deinition of means and methods for the implementation of the various strategies, possibly taking the form of best-practice guidelines for the various stakeholders.

Design practices for new facades that anticipate and accommodate the eventual need for retroit could facilitate future retroit requirements. Façade systems should be designed to facilitate the retroitting of new materials and technology as developments occur.

Sustainable facade retroit practices must be developed; a focus on material reuse is imperative to avoid illing landills with discarded façade materials, particularly glass.

New architectural glass recycling (not down-cycling) technologies are needed.

Advanced facade solutions using raw loat glass should be pursued because of the uncompromised material life and the potential for easy recycling. Double-skin strategies may accommodate this in certain applications.

Costing models that factor in the environmental cost of damaging construction practices and the true cost of energy are badly needed to correct inaccurate perceptions of long payback periods for energy eficient technology.

Legislative measures regarding building energy and carbon performance will be required in the private commercial sector to achieve appropriate goals for energy use in existing buildings within this sector.