To Repair or Rebuild: Part I
Time has a way of treating seemingly similar buildings very differently. More than just the years of abuse from the elements and the course of daily use, the change in priorities and cultural trends of how we live and work ripples through the built environment, re-calibrating the value of buildings at any given time. The empty warehouse spaces of SoHo that seemed valueless in the 40?s and 50?s were viewed differently twenty years later when artists filled the open floor plates with studios and differently again when they were replaced with high end retailers at the turn of the century. The iconic landscape of commercial office towers in New York is going through a similar transition as demands for office space continue to evolve while a great deal of the building stock is not the gleaming, glass facets of One Bryant Park. Some office space, built in a specific time for a specific purpose, has fallen from grace in comparison to newer brethren.
The shift begs the question of what can be done with these towers, mostly built between 1958 and 1973, given that not only do they pale in comparison to other new office spaces (like the World Trade Center or the upcoming Hudson Yards) but are also energy hogs with their dated envelopes and mechanical systems constantly bleeding resources. Green consulting firm Terrapin Bright Green has just published their "Midcentury (un)Modern" report that levels a full environmental analysis of this particular breed of office tower as well as what is the best option for their future use.
The increasing focus on existing buildings is as timely as it is important. One of my favorite urban statistics is found in PlaNYC stating that 85% of the buildings that will be in New York City in 2030 are already here. Our goals cannot simply center around new, greener construction if we want to make a meaningful difference in energy use. At the same time, it is important to realize that not all existing buildings are created equal, varying in both their degree of inefficiency as well as opportunities for improvement.
The group of office towers highlighted in MidCentury (un)Modern distinguishes itself in a number of ways. Due to the height limits of the zoning at the time, building owners often made floor-to-floor heights as small as possible in order to take advantage of as much salable square footage as possible. The result is that it is not uncommon for these buildings to have ceiling heights of 7?-6? which cements them in the realm of what is known as "Class C" office space (Class "A" office space is the most desirable, fetching the highest rents). These first-generation curtain wall buildings are glazed with a single pane of glass, have nearly no insulation and leak air like a sieve. Their inefficiencies make them some of the biggest energy hogs in the city, especially given that their undesirable ceiling heights often leave them at occupancy levels less than 100%, only compounding the inefficiency of building performance. Terrapin found 107 buildings in Manhattan that fall into this profile.
The design task was to figure out what could be done with these buildings and they took a case study building that met all of the criteria: 675 Third Avenue. The office tower was built in 1966 and designed by Emory Roth & Associates and has roughly 280,000 square feet of space, built to an Floor Area Ratio (FAR) of 15. The team oversaw the creation of an energy model for the entire building to understand how and why it currently works.
How About an Upgrade?
When talking about sustainability and existing built environment there is something to said for reuse. Many would say (as I have said before) that the most sustainable option can be to retain existing building stocks and apply upgrades to increase its efficiency, thereby capitalizing on all of the latent or "embodied" energy embedded in the building. Terrapin diligently started here and looked at what could be done to make 675 more sustainable building. There is a standard bag of tricks that can be deployed on existing towers to improve their efficiency. They include re-glazing the building with a more efficient skin, insulate the column covers and spandrel panels, install a raised floor for heating and cooling (as was done in parts of the Empire State Building) and upgrade the mechanical systems.
Interestingly, the team found out that these buildings (along with 675 Third Avenue) do not lend themselves to the usual tactics. A double-glazed wall would make a big difference on the insulating value of this building, but as it turns out, the structural frame of the building could not carry the weight of two layers of glass. Further complicating the issue is the fact that the existing, single-glazed wall is only designed to a hurricane wind load of 30 pounds per square foot despite the fact that today we can see wind loads up to 70 pounds per square foot, raising a potential safety issue for a coastal environment where storms are growing in frequency and intensity. The raised floor system was out because ceiling heights were too low and the building skin was so leaky that you could never pressurize the floor to regulate temperature in the space above.
Not to be deterred, the team looked at the building's heating systems that operated on a Constant Volume Reheat system. When describing the technology Bill Browning said, "Think of trying to drive on the highway with the accelerator pushed to the floor and regulating your speed by applying the brake." Meanwhile the cooling load of the building is handled by chillers, driven by steam turbines–once very economical when steam was produced in excess in the city, but now extremely inefficient and very expensive.
New replacement technology could certainly lower the building's energy use, but the team found that the equipment is actually "entombed" in the basement of the building. The only way to get it out would be to demolish the two lower floors, cut up the equipment, remove it, bring in new equipment and then rebuild the floors. As cumbersome as it sounds it is possible to do, but the expense of the project would still leave you with Class C office space, making the payback in the realm of 43 years according to the team's estimates. Browning spoke of how "the real tragedy of these buildings is that they are not adaptable."
Replacing the Building?
Without question, a newer building built on the same site with today's technologies and best practices could outperform these antiquated sentinels of commerce. But knocking down what is already there to build a new building of the same size is a tough financial case to make to building owners. In some cases, the proposal is even more unattractive given that a number of the buildings sit in locations that have be down-zoned since their construction meaning they are "over built" and a new building would actually have to be smaller than what is already there.
For assets worth hundreds of millions of dollars, there needs to be a financial incentive to replace this genus of structure, but in New York there are a number of urban goals that are incentivized in order to help the built environment evolve. Examples would be square footage bonuses for things like Quality Housing (residential space that meets certain design criteria) or offsets for building affordable housing units targeting certain income brackets. Terrapin proposed a potential development bonus to owners of these buildings that would demolish them and rebuild as long as the new building met sustainability benchmarks (effectively the equivalent of achieving LEED Platinum and then some).
After some study, the team settled on an increase from the existing FAR of 15 to am FAR of 21.6–an increase of 44%. Sources were confident that a potential gain of square footage of that magnitude could entice owners to replace the building stock, but even then it still left the question of whether or not the process would leave a net-positive impact. As I recently wrote about, the difference between efficiency and using less is important. It is not enough for us to simply make a greater number of more efficient things that result in a net increase of energy use. As a culture we need to be using less. So now the team had arrived at the real challenge: Is it possible to make a building 44% bigger that still uses less energy than its historic predecessor?
Part II to follow.
Image Credits: Courtesy of Terrapin Bright Green