September 25, 2020

Tammany Hall’s New High-Tech Glass Dome Honors New York’s Original People

An articulated dome of glass and steel now rises from the historic Tammany Hall, honoring the building’s namesake on the northeast corner of Union Square in Manhattan. The new iconic rooftop addition is the visible top of a new 6-story building rising from within the restored century-old street walls of the individual NYC landmark. The undulating, turtle shell-like dome honors the source of Tammany Hall’s name, the legendary native American Lenape Chief Tamanend. Known for supporting peaceful coexistence with 17th century European settlers, Tamanend inspired both pre-and post-revolutionary political clubs to listen to all voices while they debated what a new republic could be.  Dozens of populist Tammany Societies dotted the young United States, but only New York’s Tammany Hall survived into the 20th Century. By then, the name Tammany had become synonymous with corruption and greed; this was an ignominy we felt in need of an overdue correction. In order to refocus public awareness on Tammany Hall’s namesake, we went back to its roots.  We took inspiration from the image of a great turtle rising from the sea, Chief Tamanend’s clan symbol and a scene from the Lenape creation story, to give this Neo-Georgian building the grand dome many Georgian and Neo-Georgian buildings originally had, or now like Tammany Hall, acquired over time.  Along the way, we consulted the Lenape Center to ensure an appropriate use of cultural symbolism.

Tammany Hall, New York NY, Architect: BKSK
Tammany Hall, New York NY, Architect: BKSK

Juxtaposing a classically proportioned yet contemporary glass and steel form above Tammany Hall’s Neo-Georgian masonry allows the dome to compliment the landmark building below yet provide a showcase for the technology of our time. To create a parametric mesh evoking an amphibious shell breaking through the surface of water, we used various cross-discipline computer modeling and image rendering software used in automotive, industrial, architectural, and video game design including Rhino 3D, Vray, Maya, and 3ds Max. We then brought our mathematical representation of the curving 3-dimensional form to life by deploying a self-supporting free form grid structural system, a system well suited to undulate effortlessly and enclose a great volume of space. Collaborating with our structural engineers at Thornton Thomasetti, we produced an early construction document package that was bid on by 10 European fabricators familiar with free form grid shells.  Ultimately, a design-assist award was given to Josef Gartner, a division of Permasteelisa.  Working with us, the engineering team optimized the dome’s geometry to achieve the most efficient use of repeated glass sizes and steel shapes.

To maximize flexibility of tenable uses under a glass dome, the specification of the right glass became crucial to address occupants’ needs for a low-glare and thermally comfortable environment. We were also concerned with mitigating sunlight reflecting off the convex form onto neighboring buildings, all while maintaining the imagery of a rising shell shedding water. With those issues in mind, we hit the road.  Of the many local and foreign glass roofs we visited, the most informative were Norman Foster’s ground breaking covered courtyard of the British Museum, completed in 2000, and his 2007 encore covering the courtyard of the Smithsonian Portrait Gallery in Washington DC, as well as Helmut Jahn’s freestanding glass egg-shaped Mansueto Library emerging from the grounds of the University of Chicago completed in 2011.

Coincidentally, the Mansueto Library’s form and use closely resembled our intentions to create a glass domed workspace. We noted how the fritted glass of Mansueto’s dome performs exceptionally well and was virtually invisible, creating a very low glare environment with the illusion of clear glass. We were inspired to use a similar strategy but quickly learned through sample and mockup iterations, the affect achieved at Mansueto is due to the height of the fritted glass above the occupants; the higher the better. We learned when frit is closer to one’s eyes, direct sunlight can be perceived between fritted patches, reaching occupant’s eyes, rendering even very closely place frit useless.  We moved on to study combinations of frit, film, and tinted glass to eventually choose two insulated glass unit assemblies using a combination of clear and tinted St. Gobain glass.  The slightly clearer of the two assemblies encloses the lower areas of the dome where Tammany’s small hipped roof once stood.  Terra cotta sunshades protect portions of this lower tier in the same inclined plane as slate tiles once sat. Strategic placement of projecting painted stainless steel fins on the exterior of the upper dome offer articulation to the shell and also provide rain and snow control.

The domed vertical enlargement encloses an additional 30,000 sf of rentable square feet over 3 floors on the top of the historic building with dynamic views of Union Square and beyond.  The dome is comprised of over 2,000 2”x 6” steel tube purlins with customized node intersections and varying wall thickness depending on location.  The glass is from Eckelt, a member of the Saint Gobain group. The glass product is a structurally glazed insulated glass unit comprised of a clear PLANICLEAR float glass panel with a high performance sputter coat solar coating on surface 2, an air space, and 2 layers of laminated glass; a tinted St. Gobain Parsol Grey panel, and a clear glass panel facing the interior. The solar coating on surface 2 is SGG Cool-Lite Xtreme, an extremely high selectivity solar control with advanced thermal insulation properties for commercial glazing; it is applied by cathodic sputtering under vacuum conditions. The coating creates a low solar factor to reduce air-conditioning load and has a U-value of 1.0W/m2K, encouraging energy savings and improved thermal insulation. Neither too green nor too blue in appearance, COOL-LITE XTREME allows the insulated glass units at Tammany Hall’s dome to retain a neutral appearance.