American Loft Building, Philadelphia, USA

From certain vantage points, the asymmetrical American Loft Building commands attention on the Philadelphia skyline. In this exercise in bold geometry, the residential structure consists of interlocking, L-shaped sections of black and grey that contrast in a striking way. The L shapes don't fit together neatly but rather culminate in a multilevel roof.

Rising 11 storeys and 119ft above North American Street, the 38-loft building towers over two and three-storey structures in Northern Liberties, a semi-industrial artsy neighbourhood rapidly attracting the hip and young.

But the building, by architect Winka Dubbeldam of New York City's Archi-Tectonics, looks most distinctive close to the ground, because the sloped base appears to hover in the air.

AMERICAN LOFT BUILDING DESIGN

This aspect came in response to a major design challenge. The zoning envelope mandated that the structure stand on concrete columns over an open parking area. With ground-level parking, passers-by would have glimpsed unattractive views of cars, rather than feeling any sense of connection to the building.

Dubbeldam therefore sloped the parking area; cars enter the space at street level, proceeding downhill until they're one storey below grade. As they go, they pass over a grassy carpet sprouting from porous pavers. Dubbeldam thought greenery would make the concrete look friendlier.

To provide vehicle clearance, the bottom of the building is sloped, using the same angle as in the parking lot. In the lobby, this slope translates into a ramp and steps.

Also for the sake of clearance, the bottom of the building curves up into a rounded edge over the vehicle entrance. An Alucobond exterior made this possible, as the insulated aluminium panels can bend. Once again, the curve translates into the interior; the living rooms of two split-level townhouses feature concave concrete walls with built-in benches.

Because of the irregular bottom plane, the building might appear as if it's listing, a sailboat heeling in light wind. But this is an illusion, because the structure rises straight to the sky.

From top to bottom, the building has a floating quality. For instance, in the parking area, the concrete columns are recessed and angled, making them less visible from the exterior. At the top of the building, a glazed curtainwall makes it look as if the uppermost story rests only on glass.

LOFT INTERIORS

Intent on avoiding the monotonous repetition typical of large buildings, Dubbeldam lent variety to the interior and exterior in a number of ways. First, she designed the open-plan lofts to be different from each other. There are two to six units on each floor, and some span floors. That made it challenging to find a space for the shafts extending through the building.

Irregularly positioned, the tall, thin one and two-light windows bring different amounts of light into each flat. They also make the grey façade resemble a punch card used in a voting machine or in a 1960s computer.

EXTERIOR DESIGN

Rather than being monolithic or monochromatic, the exterior features the interplay of light grey and jet black.

These hues, as well as multiple materials, exist on different planes. Grey aluminium (which reflects the shifting sky) appears to fit hand-in-glove with the deep black natural plaster. And yet they never meet. A curtain of glass hangs between them, both joining and separating the dominant parts of the facade.

Large cantilevered balconies with glass railings jut out from every unit, creating a sense of additional depth.