The Skinny on Supertall

Tuesday, July 25, 2017

Ambition pushes us higher. The never-ending quest for generational advancement is no more evident than in the buildings indicative of an era. In recent years the number of supertall buildings has increased exponentially, and nowhere in the United States is this more evident than in New York City.

The Council on Tall Buildings and Urban Habitat (CTBUH) has set the height criteria for supertall as “a tall building over 984´ (300 m) in height.” As of July, CTBUH lists 123 total completed buildings that exceed this criterion. New York became home to the inaugural supertall when the Chrysler Building’s spire rose to 1046´ (319 m) back in 1930. The rise to #1 was short lived when the Empire State Building surpassed it 11 months later in 1931 when it topped-out at 1454´ (443.2 m) and held this reign for 40 years. Today, the architectural icon remains the fifth tallest building nationally and 28th tallest in the world, though a new crop of supertalls – many in Midtown Manhattan (The New New York Skyline) – will continue to push these historic towers further down the list. This next wave of supertalls is being facilitated by development practices which permit the transfer of air rights from nearby buildings not maximizing their full entitlement. In cities where the options to expand horizontally are limited, embracing the vertical expansion is on the rise.

As a participant in the construction of custom, high-performance facades, Enclos finds itself on a handful of recent and upcoming supertalls including 432 Park Avenue which was the 100th supertall constructed in the world when it became the tallest residential tower in the western hemisphere upon completion in late 2015. Other supertalls under construction with Enclos’ involvement include 30 Hudson Yards at 1268´ (386.6 m, 73 floors, 2019), 53W53 at 1050´ (320 m, 77 floors, 2018) and Comcast Technology Center at 1121´ (341.7 m, 59 floors, 2018).  53W53, as well as 220 Central Park South – though just shy of supertall status at 950´ (289.6 m, 66 floors, 2018) – will join 432 Park Ave in the high-end residential boom soaring over Central Park. In these residential structures, great value is placed on views, heightening the importance of the performance and aesthetics of the building facade.  Additionally, higher winds, congested sites, delivery of units into the city, all are reasons that point to the prefabricated unitized curtainwall.

When installing facades on supertall buildings, one of the initial main issues is the interface with primary structure. In projects that reach such great heights with a minimal footprint, the result is a very slender structure.  To achieve these forms, it is not uncommon to see the primary structure made of concrete, as is the case in 432 Park Ave, 53W53, and 220 Central Park South. Whether it be steel, concrete or composite primary structure, the relationship to the facade is very similar to other buildings. Where it does vary is when the structure implements a unique structural geometry like the diagrid system utilized in 53W53. This approach creates many unique anchorage conditions throughout the project, due to the diagrid and the many slopes to the facade, as well as many hard to reach locations during installation. To address these conditions, Enclos has developed project specific installation equipment to ensure safe and efficient field operations.  The intersections of the sloping faces on projects like 53W53 and 30 Hudson Yards amplify the number of unique unit geometries, require heightened coordination through engineering and manufacturing, and can result in oversized atypical units that may require unique installation measures.

Concrete diagrid structure on the 53W53 supertall results in many unique units and interfaces as a result of its many sloping faces.

Another critical aspect of on-site operations for a supertall building is that vertical mobility is paramount.  On project sites, a hoist is used to transport crew members and materials vertically throughout the building. It is common for facade contractors to use the hoist to lift bunks – crates or racks of several units – to their respective floors for uncrating and preparation for installation. This approach commonly uses installation equipment that is fairly mobile and is relocated up the building as it rises. Additionally, this approach of floor loading and setting does not require the use of a project’s tower crane, a high-demand piece of equipment that is as impressive as the structure it erects during construction.  The tower crane, or cranes for many mega projects, is a highly-sought after resource for many trades.  An early consideration for facade contractors is coordinating:

  • Is there access to the hoist for transporting curtainwall bunks?
  • Is the hoist dimensionally large enough to accommodate these bunks?
  • Is the hoist’s weight capacity adequate to handle the bunking plan?
  • Is a dedicated (for facade contractor only) oversized hoist required?

The last option, a hoist provided by and dedicated solely for the facade contractor, was the approach adopted for the 220 Central Park South enclosure where large unit dimensions and weights required something more than what existed in the contractor’s site logistics plan.  The limestone used in the stone-on-truss assembly of this project’s facade resulted in heavy units. Having a dedicated hoist helped avoid a dependency on the overall project’s tower crane which could have led to schedule delays, significant coordination with other trades, or the potential for setting during off hours such as night or weekend shifts when the tower crane is more readily available. On projects where a dedicated hoist was not possible, or over-sized units do not fit in the hoist, coordinating tower crane time during off hours during a night shift is a common approach to vertically transporting curtainwall units.

Delivery of over-sized trapezoidal units at 53W53 occurs during an evening shift amidst rush hour traffic. On-time delivery and efficient picks transfer curtainwall units directly from truck to its final position on the building.
Over-sized units that cannot be vertically transported are a special condition requiring use of the tower crane to install during an off-hours, evening shift. This condition shows the challenge of working around overhead protection several stories above while curtainwall units are installed around floor 20 on 53W53.

The construction of supertall structures is not a new challenge (see list below of supertalls completed by the Enclos lineage throughout the years), but it is increasingly more common in recent years. Here we have highlighted some of the considerations the facade contractor goes through that are likely more critical on supertall projects due to the limited site and floor footprint, as well as access to and throughout the site. Stay tuned in the coming months as we continue to provide updates on the ongoing efforts to elevate the building enclosure to new heights throughout the supertall landscape.

List of supertall projects completed, topped out, or under construction in the United States with Enclos involvement*

3. Willis Tower (442 m, 1450´, 108 floors, 1973), Chicago

6. 432 Park Ave (426 m, 1397´, 85 floors, 2015), New York

8. 30 Hudson Yards (386.6, 1268´, 73 floors, 2019), New York

12. Aon Center (346 m, 1136´, 83 floors, 1973), Chicago

13. John Hancock Center (344 m, 1128´, 100 floors, 1969), Chicago

14. Comcast Technology Center (341.7 m, 1121´, 59 floors, 2018), Philadelphia

19. 53W53 (320 m, 1050´, 77 floors, 2019), New York

29. JPMorgan Chase Tower (305 m, 1002´, 75 floors, 1982), Houston

* Domestic CTBUH rankings as of August 2020

List of completed supertall projects worldwide with Enclos involvement**

16 and 17. Petronas Towers (452 m, 1483´, 88 floors, 1998), Kuala Lumpur, Malaysia,  completed as Harmon Contract

21. Willis Tower (442 m, 1450´, 108 floors, 1973), Chicago, completed as Cupples

25. 432 Park Ave (426 m, 1397´, 85 floors, 2015), New York

36. 30 Hudson Yards (386.6, 1268´, 73 floors, 2019), New York

65. Aon Center (346 m, 1136´, 83 floors, 1973), Chicago

68. John Hancock Center (344 m, 1128´, 100 floors, 1969), Chicago, completed as Cupples

73. Comcast Technology Center (341.7 m, 1121´, 59 floors, 2018), Philadelphia

111. 53W53 (320 m, 1050´, 77 floors, 2019), New York

146. JPMorgan Chase Tower (305 m, 1002´, 75, 1982), Houston

** Worldwide CTBUH rankings as of August 2020