In the heart of Cambridge, Massachusetts, a hop, skip and jump away from Harvard University, presiding over the restored Joan Lorentz Park, the Cambridge Public Library now stands with a new image of modern grace. Attached to the existing library designed in 1887 by Van Brunt & Howe, the new work of metal and glass offers us a model for sustainable, public projects. Designed by William Rawn Associates, the building is not only a case study of integrating sustainability into a house of knowledge, but moreover, the product of diligent research by a team that is interested in sharing that knowledge and progress with the profession at large.
The base of the project fundamentally begins with sustainability by utilizing and adding to an existing structure. Despite the numerous ways we accumulate to make our new construction more ecologically responsible, building reuse can still trump even the greenest of new construction. As PlaNYC (New York’s sustainability plan under the Bloomberg Administration) points out, 80% of the buildings that will be on Manhattan in 2030 are already there. A meaningful, reduction in resource and energy use in nearly any municipality has to include existing buildings.
Upon seeing the project for the first time, I was immediately impressed with the clean, organized appearance of the addition. The face of the building that greets most of its visitors manages to combine open, inviting views with energy efficiency by employing a two-floor, double-skin glass wall spanning the entirety of the façade. A double-skin wall is comprised of two wall surfaces, commonly glass, with an air space between that serves as a buffer to significantly increase the wall’s insulating value. There are many examples of double-skin walls in a variety of projects, but when it comes to optimum performance the devil is in the details.
The designers point out that this is the first American example holding all of the ingredients of a European Double-Skin wall system. (Once again, those Europeans are ahead of the curve when it comes to sustainable standards) According to the firm, achieving such a designation requires three distinct characteristics:
- A 3-foot deep airspace providing adequate insulating depth and maintenance access
- Multi-Story Thermal Flue to induce natural stack effects to pull air through the space efficiently
- Moveable 1-foot deep sunshades that collect the sun’s heat inside the wall cavity and protect against glare
Only when all of these components are used together does the wall function at its peak level of efficiency and likewise cost effectiveness. The system works by studying the sun enough to decipher how to take what is helpful and shed what is unwanted. Like all of nature’s own systems, this installation is not static, but a series of components that has to respond to not only the sun angle but the time of year. Subtle changes can allow the efficient tempering of the space beyond by working to make it warmer or trying to keep it cool.
On the exterior, a pair of glass visors hanging perpendicular to the wall block a portion of the sun’s rays to allow the glass below them to be clear and provide views to out to the park. Each glass wall behind them is comprised of insulating glass units (IGUs) that have two layers of glass and an air space between them meaning that the system has a total of 4 layers of glass and three air spaces ( ½”, 3’, ½”). Each air space is a thermal break that forces heat to radiate from one surface to the other rather than being directly conducted through a solid composition. In the space between the two glass surfaces are 1-foot wide aluminum louvers that can pivot to catch the changing sun angles and keep the heat that they accumulate in the wall cavity instead of the library space beyond.
Once the column of air is defined, it can be manipulated by drawing more air in from a trough at the base or exhausting air out at the top allowing it to change the temperature of the air in response to climate conditions. In the winter, when the building wants more heat, the warmth of the sun is trapped the wall cavity with no air taken in and none exhausted to provide a warm buffer to the interior space. When spring brings more temperate weather, air can be drawn into the stack and then directly into the reading spaces to naturally cool the interior. Lastly, in the summer the sun is caught by the louvers while air is drawn in from the base. The warming of the air causes it to rise and draw it out the top. A “living, breathing” system.
A winter diagram of the wall system, trapping warm air and using it as an insulating buffer
One could ask how I know all of this. Admittedly, though familiar with their construction and how they operate, I am not an expert in double-skin walls. Part of the reason is that William Rawn Associates took the information and research that they gathered during their project and created a case-study document recording their efforts. This tome of double-skinned know-how lives on their firm’s website for all to download… free of charge. In all my time as architect and student of design, I have yet to come across such an occurrence.
So why are the best double-skin walls built in Europe? First of all, the deficiencies of hybrid systems that do not utilize all of the European components are partly to blame for their lack of popularity in the U.S. Two walls of glass only 8” apart has less space to act as an air barrier and insulates the interior space less, but still essentially costs the same as two-walls. (Similar to the western wall of the Riverhouse in Battery Park City, designed by Polshek.) The lack of a sun-blocking device inside the cavity means a lot of that sunlight can permeate through and actually heat the space. In an environment that is almost always cold, this could be fine but a temperate or warm climate would find this unfavorable. Having a wall that is not able to both intake and exhaust air dilutes the responsiveness of the installation and how effective it can be in a variety of seasons. On the other hand, it is cheaper to leave some of these components out.
Another reason is the size of buildings, particularly the floorplates, of buildings built on either side of the Atlantic. In America, we like it “big”. Buildings in cities like New York have floorplates that can be rather deep, spanning an entire New York City block. European buildings have a tendency to be smaller–not only shorter, but more compact. With a smaller floor plate that is not as deep, a greater percentage of the square footage is up against the exterior wall rendering the insulating value of that wall that much more important. Conversely, with a deeper floorplate more of the space is insulated by interior space and removed from the walls of the building. This can mean that it is sometimes more worthwhile per square foot for buildings smaller than American towers.
It seems all too fitting that the design of such an endeavor was a library: a storehouse or archive of ideas and events and part of a system that is the epitome of distributing knowledge through our culture. The process of designing a building that addresses the needs of the present while respecting the wisdom of the past is a lesson that (some) architects take upon themselves each time a new project arises. The perspective and insight gained by the toils of crafting a building become a valuable commodity, building on what is arguably the most valuable asset of a firm: their knowledge base. After all, there is a reason why Santiago Calatrava designs so many bridges, or HOK designs so many stadiums. Experiential knowledge gives these firms an edge.
In this case, William Rawn Associates sacrificed a bit of that edge in deference to furthering architecture as a whole. By not only taking the time to create a document of their research and lessons learned, but giving it away online to any wondering minds, the firm is increasing the chances that more buildings can incorporate this technology into the American built environment, which helps everyone in the end.
Just because discussions about this building have centered around the double-skin system does not mean that it is all the project has to offer. For those that do not walk to the site, parking lies underground, beneath 33,000 square feet of intensive green roof with a soil depth of 4 feet. All that pavement is kept from the sun’s rays and the heat islands that result from open exposure. The project has a stormwater retention tank with a capacity of 350,000 gallons (that is larger than the volume of water storage at One Bryant Park) and collects stormwater for a 3-square mile section of the city.
When it comes to buildings, it is also not just about what gets built, but what does not get built. The projects boasts a net post-consumer, recycled material content of 20% while the firm reports that 95% of the construction waste was diverted from landfills. Naturally (no pun intended) the designers hit all of the easy bases as well with low-flow fixtures, energy efficient lighting and low-VOC paints and adhesives.
I often talk about a definition of sustainability as not being a technological fix to supplement a wasteful lifestyle, but instead a lifestyle itself, revolving around actions that determine how we live. While it is true that I wrote here about a number of impressive, technological feats that were integrated into the Cambridge Public Library, perhaps unsurprisingly I find the sharing of knowledge and experience to be the most sustainable thing about the project. Even if the project had looked horrible (which it clearly doesn’t) this alone could have made it a success. My compliments and thanks to WRA.
Photo Credit: All Images from William Rawn Associates