The Macallen Building is a 150-unit condominium which will play a major role in the urban revitalization of South Boston. Occupying a transitional site that mediates between highway off-ramps, an old residential fabric, and an industrial zone, the building negotiates different scales and urban configurations at each elevation. The massing and materials of the building respond at each face to changing urban context. A staggered truss structural system makes possible a sloping green roof and a variety of apartment layouts with high ceilings, flexible plans and wall-to-wall windows.