With 46 stories and a height of 182 m (597 ft), Foster’s skyscraper, his first in the United States, is rather modest in size with respect to the other high-rise buildings of Manhattan, but what it lacks in scale it makes up for in personality. The polyhedron glazed blocks that make up the upper part of the building achieve a perfect continuity of tone with the pronounced linear trajectories and shapes of the original base. The result is a perfect match between disparate styles, with the allegorical figures, moldings and spires giving way to a volumetric yet seemingly weightless upper section that floats upon a sandstone bed. The project created an exciting interplay between the historic base and the new tower while maintaining the integrity of both buildings. The new tower that emerges from the historical 1920s building is set back with respect to the three main façades below. A Clerestory, rows of vertical glass panes skirting the perimeters of the old building, and a horizontal Skylight connect the historical base to the new tower and form a transparent interface for the natural light that illuminates the atrium inside.
182 m / 597 ft
46 stories tall
Working with Lord Foster, the Hearst Corporation settled upon an innovative ‘diagrid’ system (a portmanteau word combining ‘diagonal’ and ‘grid’) consisting of a series of four-story triangles that are such a characteristic feature of the façade and distinguish the building from other more conventionally framed structures. In addition to giving the tower a bold architectural and spatially efficient and flexible. The triangularity of the modules maximizes the resilience and minimizes the weight of the structure. Thanks to the intrinsic properties of the triangle, a geometric shape that is capable of withstanding structural forces without buckling under pressure, the size and therefore also the weight of the construction materials can be reduced to a minimum. Each triangle acts as a reinforcing brace for the next as they proceed up the structure. The inclined axial strength afforded by the diagonal pattern resists the pressures of lateral loads and shear stresses better than a traditional frame in which the loads have to be absorbed through the compression of vertical columns.
It has always been critical to engage with the industry, to penetrate the manufacturing process, to appreciate the working of the factories, to engage with those fabricating the structural elements and to understand the materials used. With the Permasteelisa Group we have enjoyed a very creative relationship that goes back a very long time and will, I predict, continue far into the future.
Lord Norman Foster, Foster + Partners
Design & engineering, manufacturing and installation of different curtain walling and cladding types special in sizes and characteristics for an overall area of 26,400 sqm (284,200 sq ft).
Flat and 'birdsmouth' façades: resilience and deformability
Two purpose-built and specially designed engineering solutions define the main façade, both of which were adopted to facilitate the construction process and, especially, the logistics of installation. The two solutions, which are combined to form the particular diagrid shell of the building, are known as the ‘Tower Vertical Façade’ and the ‘Birdsmouth Façade’. The first façade, which begins from the tenth story, comprises the principal planar face of the building and includes the various other hybrid shapes that the configuration demands. The second façade, on the other hand, is to be found on the external edges of the building and is made up of a succession of sections that incline inwards from below and outwards from above rather like the lower and upper beaks of a gaping bird’s mouth, and give the sides of the building its notable diamond effect.
Of the 3,200 units used on the shell of the tower, 625 are unique in their size and shape. From the inside, they provide floor-to-ceiling glass panes that flood the offices and the atrium area with natural light. Some 95% of the interior office space is illuminated by natural light, and 80% of it offers spectacular views of the city. As the interface between the two façades is geometrically complex, the two façade types were developed to allow the systems to be installed almost independently from one another.
The units on the principal flat-surfaced façade are 4.1 m (13.5 ft) high and 1.5 m (5 ft) wide. Each consists of an aluminum façade framing system with double glazed unit (DGU) vision panels and stainless steel diagrid elements. The glazing, developed and engineered to withstand any extraordinary events and whatever load stresses and energy waves they cause, is made up of laminated glass panels covered by a special low-emissive coating that makes the most of the natural light while also protecting the inside of the building from excessive solar radiation. The units are completely prefabricated. The panes they contain are made from safety glass, and are fixed to their aluminum frames with perimeter joints. The window mullion is formed by two superimposed panels, and reinforced with the insertion of a thicker section of frame. The top and bottom transoms are secured to the floor by aluminum and stainless steel brackets. The spandrels, depending on their position, are made up of the DGUs or, where they correspond to the rail of the supporting frame, by the steel-clad cover panels enclosing the beams of the structural frame. The open-ended joints are specially designed to allow water that has infiltrated the cavities to escape. Further, an internal insulated panel, which is composed of metal sheets and a rock wool slab duly sealed with silicone against the panel periphery aluminum frame, guarantees air-tightness and vapor barrier continuity. The air chamber between the external cladding elements and insulating slab is ventilated, which minimizes the amount of moisture that can form. A system of weep and drainage holes, protected by gaskets, completes the construction. The entire façade system is designed to absorb loads and dissipate them through the various elements that make up the skin of the building, through the mullions and transoms, the glass curtain wall, the brackets and all the other elements that make up each unit.
The Birdsmouth sections, like those of the flat façade, are prefabricated but differ from the former in that the units making up the vision area are independent of the spandrel panels. The system comprises a continuous horizontal spandrel panel, whose length is determined by extrusion and transport limitations, that spans the width of the Birdsmouth opening. The spandrel unit is fixed at each mullion with brackets attached at the slab and underside beam levels. Upon the completion of each spandrel, the vision panels were locked into the spandrel sill and rotated into position. The distinctive inward and outward slope of the Birdsmouth sections meant that each unit is larger than any to be found on the flat façade. Some of them are as much as 4.6 m (15 ft) high and 3.7 m (12 ft) wide, and 36 of them constitute some of the largest single units to be found anywhere on the building. The incorporation of these independent areas into the overall system of design is what gives the Hearst Tower its highly distinctive and impressive look. The dimension of these unit components, spandrels and visions were elaborated also to facilitate their factory construction and on-site installation.
About half way up the tower, the continuity of the façade is interrupted by mechanical plantroom louvers, with a full-height single weathered unitized louver panel system that is fully integrated into the curtain wall.
Where the base of the older building meets the new glass tower are two fully fenestrated walls through which daylight can penetrate into the lobby, where it diffuses into an interesting play of shadows and light. The Clerestory Façade is the vertical section at the bottom of the new tower. Stretching from the 7th to the 10th floors and slotted into the cast-stone blocks base, it consists of an aluminum framing system with DGU vision panels. The Skylight is a flat, transparent ceiling that runs horizontal to the base building on the 7th floor, and is composed of a glazed stick system made of glass, extruded aluminum elements, brackets and gaskets.
The tower’s structure is anchored to the interior atrium, which therefore offers an impressive view from below of the vertical ‘mega columns’ and angled ‘mega diagonals’ stretching out to the peripheral sections. The columns and diagonals, which are integral to the primary structure, are jacketed in stainless steel and, indeed, a set of brackets and steel framing system was attached to the mega columns in the lobby to allow the installation of the stainless steel cladding.
The first 'green' office building in New York City's history
A distinctive tower's diagrid external cladding
Exterior diamond-shaped pattern
Birdsmouth Façade giving the tower multifaceted aspect
3,200 customized, unitized façade glass units
625 unique in size and shape units
CTBUH ‘Best Tall Sustainable Building Award’ 2007 Winner
CTBUH ‘10 Year Award’ 2016 Winner
OWNER: Hearst Corporation
DEVELOPER: Tishman Speyer
DESIGN ARCHITECT: Foster + Partners
ARCHITECT OF RECORD: Adamson Associates Architects
CONTRACTOR: Turner Construction Company
Setting a high-rise tower on top of a pre-existing building was a considerable challenge that required the careful management and organization of the construction site. The installation of the Tower Vertical Façade was one of the most spectacular moments, panels were installed using a manually operated crane system device that is positioned at least two floors above the floor to be installed. The panel is launched horizontally from the floor, rotated vertically and then fixed to the crab system and then lowered into position. The stainless steel diagrid panels were installed from the outside of the building using a hanging scaffolding system.
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