continued

The 54,000-square-foot (5000-square-meter) museum has two levels. The ground level houses three galleries, offices, a boardroom, and a shop. The lower level houses a single gallery for light sensitive works, "back-of-house" functions, and an auditorium. The garden terraces downward to the auditorium, creating an open air theater.

Geometry of a Shading Device

Arup director Alistair Guthrie says designing the roof for the Nasher Gallery was a challenge for the entire team. "The project has been years in planning and this canopy is unique in its form and unique to this site."

The shading design was programmed on a computer, starting with a horizontal square with corners pointing north, south, east, and west. The engineers established an initial form based on a sine curve, determined by the building's latitude and longitude, passing through the east and west corners.

This form would block direct sunlight coming from south of the east-west axis. However in the summer, early or late in the day, when the sun is to the north of that axis, direct sunlight would not be blocked by that simple shade.

The Arup engineers next assumed the same form of shading on the north side as on the south side and then, simulating the sun's path, cut away the material that did not provide any shading. The lower half of the shade was formed by inverting the top half; this shades the opposite triangle of the original square.

The result of this geometric exercise was a single shell-like element of the roof, which was then repeated over half a million times. The roof was cast in aluminum directly from the original computer programming data. "A design first," according to Guthrie.

Below the matrix of shells is a thin skin of curved glass panels with a low-iron composition for maximum transparency. The effect of this roof construction is that direct solar radiation never penetrates to the building's interior, while maximum exposure to the sky provides ample north light, eliminating hard shadows on the sculptures in the galleries.

The Raymond and Patsy Nasher Collection encompasses more than 300 sculptures, including works by Calder, de Kooning, Giacometti, Picasso, and Rodin, as well as contemporary artists such as James Turrell, Tony Cragg, and Magdalena Abakanowicz.

Discuss this article in the Architecture Forum...

Nasher Sculpture Center in Dallas, Texas, designed by Renzo Piano Building Workshop. Photo: Timothy Hursley Each pavilion is enclosed by low-iron glass facades and roof which permit unobstructed views from the street, through the building, and across the length of the garden. Photo: Timothy Hursley Half a million shell forms make up the Nasher roof designed by Arup. Photographer: Michel Denancé Arup's computer program simulated the sun's movement and subtracted any material from the shell form that did not provide shade. Image: Arup Sun screen detail. Photographer: Michel Denancé Back of sun screen. Photographer: Michel Denancé Building section, Nasher Sculpture Center. Image: Renzo Piano Building Workshop Roof construction detail, Nasher Sculpture Center. Image: Renzo Piano Building Workshop   Click on thumbnail images to view full-size pictures.