Artful addition: this new insertion balances sensitivity to history with a formal and civic boldness.

The extension to Higgins Hall at Pratt Institute in Brooklyn, the largest independent college of art and design in the US, is Steven Holl's first major institutional commission in his home territory of New York City. Higgins Hall, which houses Pratt's architecture programme, formerly consisted of three separate historic landmark buildings. However, when the central building was destroyed by fire in 1996, the two remaining were left isolated. Holl was appointed to stitch them together, a task that has been tackled by balancing the need for sensitivity to the historic buildings with the desire to create a new identity and a landmark on the street.

The difference in floor levels between the two historic buildings, which increases sequentially from a mere 12mm at ground level to 2m on the fourth floor roof, was the key factor in shaping the scheme. The new insertion pulls out existing floor levels from the north and south wings, and the fault line where they meet--which Holl calls the 'dissonant zone'--is reconciled by a ramp that creates an extended promenade traversing between the street front and garden back of the building. The ramp is capped by an asymmetrical gullwing skylight that juxtaposes different qualities of daylight from tall north- and low south-facing glazing. The new link provides public and social spaces including an entrance lobby that splits along the fissure to provide a ground level reception and gallery and a lower level lobby serving a new auditorium and classrooms. This entrance, together with design studios on upper floors, ensures that the new building is occupied and active around the clock.

In keeping with the character of the nineteenth-century brick buildings--which have been renovated by Rogers Marvel Architects--the material vocabulary of the new infill is robust. This provides the setting for Holl to pursue his interest in material experimentation, including handrails of rusted steel that are merely sealed and a handsome gallery door made of foamed aluminium, a product that is widely used for impact absorption in automobile bumpers. The building's structural frame, independent of the old loadbearing masonry walls, comprises six large precast concrete columns linked by beams. While the four corner columns are 'static,' the central column on each facade shifts and mutates to accommodate the cranked beams of different floor levels on either side of the fissure. Precast floor planks are simply finished with polished concrete topping, and voids in the planks are utilised as wiring conduits.

On upper levels, elegant linear aluminium uplighters, designed by the architects, illuminate the exposed concrete soffit, while in the auditorium, holes cut in the precast planks provide recessed lighting--bare bulbs without the usual metal housing. In contrast with this spartan character, galvanised ducts at the north and south ends of the new link are exuberant, dipping below the concrete beams to terminate in flamboyant three-throated grills adjacent to each column. The serene interior atmosphere is created largely by the design of the east and west facades, where structural glass channels filled with translucent white insulation provide diffuse daylight to the entrance lobby, gallery and studios. At the fault line, the thick translucent skin gives way to a patchwork of clear glazing, sometimes canted, in red oxide painted steel framing, which marks the dissonant zone of the ramp and allows generous views out. The clean repetitive character of the glass channels contrasts markedly with the historic buildings, which provide quirky 'as found' interior elevations to the north and south. This serendipitous character is very evident in the auditorium, where cast iron columns and remnants of field stone foundations combine with ad hoc openings in brickwork to create a striking contrast with the pared down discipline of the concrete insertion.

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The newly created H-block has a west-facing forecourt on St James Place. A sculpted ground of steps and ramps, partly formed of bricks salvaged from the fire, makes the transition from street to entrance, which is marked by a projecting glazed lobby that is an outgrowth of the clear fissure in the translucent facade. To the east, the basement auditorium roof creates a raised terrace that, accessible from the gallery, overlooks the rear gardens of terraced houses adjacent to the site.

Investing in the reconstruction of Higgins Hall is one piece of a larger initiative developed over the past 13 years by Thomas F. Schutte, President of Pratt, who has worked to improve the campus and use it as an engine to convincingly stimulate the regeneration of this area of Brooklyn. Because the architecture school is a block away from the Pratt campus, it must have an academic identity and work as part of the city. The building clearly fulfils both roles with its entrance forecourt providing a modest new public space where students meet and linger all hours.

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This modest infill project yields rich returns at many levels. The concept of the dissonant zone permeates the scheme, orchestrating plan, section and elevation as well as circulation, daylight and views. Through its direct expression of materials and details, the building enables the architecture school to play a didactic role for the students it houses. This quiet, spare insertion does not ape the old buildings but has its own distinct identity, creating an ensemble that provides welcome public and educational amenities and strengthens Pratt's presence in the city.