|June 12, 2014|
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|CHICAGO – As did many cities throughout the Western world, in the post-World-War-II era, Chicago built hundreds of thousands of square meters of high-rise residential and commercial office buildings. In keeping with the Modernist principles in vogue at the time, most of these were built with single-glazed curtain wall exteriors, which afforded more space and better views. Today, the problems with this construction type are well known – low floor-to-floor heights, tight column spacing and highly inefficient mechanical systems, as well as even more pervasive structural issues.|
|CCHRB Panel (From Left to Right): Sara Beardsley, AS + GG; Pranav Seth, Gensler; Ken Walerius, Permasteelisa; Matthew Herman, Buro Happold; Jamie Ponce, C40 – Clinton Climate; Craig Burton, PositivEnergy Practice; and Ralph Muehleisen, Argonne National Laboratory; Images provided by Abbas Aminmansour, University of Illinois at Urbana-Champaign.|
|The tall building community has begun to address this issue through research such as the CTBUH Life Cycle Analysis research project, and initiatives such as the Chicago Central Area DeCarbonization Plan. A recent seminar of the Chicago Committee on High Rise Buildings (CCHRB), co-sponsored by CTBUH, “Existing High-Rise Buildings: Refurbish, Repurpose or Replace?” provided an update on this ongoing dialogue, as well as a sobering account of a real-life refurbishment.|
The Chicago building community will need to start addressing the issues of its mid-century building stock quite soon, if it is to meet the objectives of the Sustainable Chicago 2015 Action Agenda, which aims to reduce greenhouse gases by 25 percent below 1990 levels by 2020, and 80 percent by 2050. And of course, very little action can take place without good data. There are signs that this is happening.
A substantial portion of the “efficiency actions” that come from this agenda will involve retrofitting existing buildings, said Jamie Ponce, Chicago City Director, C40 Clinton Climate Initiative. Building owners representing 28 million square feet (2.6 million square meters) of floor space in downtown Chicago have already committed to reduce their energy use by 20 energy within five years, Ponce said.
|That could make a substantial difference, as 71 percent of greenhouse gases in the Chicago area are produced by buildings energy use, and the 3,500 buildings of 50,000 square feet (4,645 square meters) or greater make up only 1 percent of the city’s area, but use 20 percent of its energy. At the beginning of June, owners in the largest tier – 250,000 square feet (23,226 square meters) and above – were beginning to report their building specific energy performance measurements, which the city will share online.|
Sara Beardsley, a tall-building architect at Adrian Smith + Gordon Gill Architecture, and Craig Burton, director of the AS+GG energy-modeling offshoot Positive Energy Practice, shared some of their own findings and suggestions about what to do with that data. AS+GG joined with the City of Chicago to develop the DeCarbonization Plan, encompassing about 400 buildings representing the highest-intensity use in the city center.
|Speaker Sara Beardsley, Adrian Smith + Gordon Gill
||Speaker Jamie Ponce, C40 – Clinton Climate|
|The team studied some aggressive options, including a retrofit of the Willis Tower that went hand in hand with a developer’s plan to build a net-zero “off the grid” high-rise hotel in the same superblock.|
“Instead of taking the new-build hotel off the grid, which would have been very costly, we found that saving 10 percent of the energy used by the Willis Tower would offset the entire cost of building the hotel,” Beardsley said. “Re-cladding the Willis Tower alone would cover 20 percent of that 10 percent.” Even so, this would cost in excess of $250 million. Beardsley also found that the energy-bill savings from a re-cladding of the Dirksen Federal Building would never recoup the 20 to $40 million such an operation would cost.
||Burton added that energy savings are not often top-of-mind for building owners, particularly with commercial buildings, which are seen as short-term investments with three-to-five-year hold periods. In order to make a convincing argument to owners, an energy-savings plan would have to have a three-year payback period, he said.|
As an alternative, Beardsley and Burton suggested that combining energy and envelope overhauls with repurposing older office buildings with dated floor plates to residential and educational use, thus reducing carbon-intensive commutes between offices, homes and schools that would now be much more tightly concentrated. This would go much further toward carbon-reduction targets than re-cladding and maintaining office use, as offices use four times as much energy per unit of area as residences do, they said.
|Speaker Craig Burton, PositivEnergy Practice|
|Going the Distance|
The practical considerations of a re-cladding are nevertheless important, and a presentation by Ken Walerius, Structural Engineering Manager at Permasteelisa North America, made clear why some owners find re-cladding a daunting proposition. Walerius was part of a team involved in the re-cladding of 475 Park Avenue South in New York, a 35-story concrete office building constructed in 1969. Pelli Clarke Pelli designed a retrofit plan for the building in 2008, and Permasteelisa became involved in 2009, converting the façade from a system of punched windows and brick piers to a steel-and-glass curtain wall system. The prior system had a U-value of 1.1, and was replaced by a system with a U-value of 0.42, attributable mainly to the changeover from monolithic ¼-inch (6 mm) glass to 1-inch (25 mm)-thick thermal panes.
| Conditions were not optimal for a construction project – there was limited space for construction lay-down areas and the re-cladding had to take place while the building was fully occupied. The quality of original drawings was poor, and the steel-sleeve embeds for the original curtain wall had rotationally deflected too far to support a new system, forcing the team to drill into the concrete columns using adhesive anchors. However, installers were able to use the old embeds as clamps for a vertical lift track to ease the units into place.
Additionally, a laser scan by the team revealed that the building was leaning, with some of its columns having shortened by as much as 25 mm. The line of the new façade, as designed, would be up to 4.93 inches (125 mm) out of skew with the vertical plane of the structure, and up to more than 3 inches (76 mm) out into the airspace of a neighboring building. The overall building was 4.5 inches (114 mm) shorter than drawn, and three “typical” floors decreased in height by 1½ inches (38 mm).
|Speaker Matthew Herman, Buro Happold|
|“We had to make some adjustments,” Walerius said. “We went with longer slots on our brackets, and some were notched to get additional lateral adjustment. And on those three floors, we literally made shorter curtain wall units to accommodate that. We had 2,800 anchors on this project and we individually designed almost all of them.”|
The new façade was installed on the exterior of the building with the old windows still in place during the day, which meant many occupant requests to stop work in certain locations and at certain times. At night, a second team removed the old windows and installed flashing to complete the seal from the interior to the new windows.
|These adjustments slowed the installation process for the 8-foot 3-inch-by-10-foot-6-inch (2.5 by 3.2 meter) units, which would normally run at 30 to 50 units per day, to 10 units per day. The project was also put on hold for a year by the owner.|
“It started in 2009, and we still aren’t finished,” Walerius said. “It’s what I call the ‘stress, tension and fatigue’ factor. And we don’t know yet if we’re going to hit the building when we get to the top.”