Among the many challenges to building, a difficult site poses one of the most daunting. For a social housing complex in Paris’s hilly 20th arrondissement, in the northeast part of the city—a rapidly transforming formerly working-class neighborhood—Bruther, a 2017 Record Vanguard firm, faced a particularly unusual spot. “It wasn’t obvious what to put there,” says Bruther cofounder Alexandre Theriot. The architects were confronted with a narrow, irregularly shaped lot that opened onto two streets—Rue Pelleport, a major road that runs through much of the precinct, and Rue des Pavillons, a winding street that descends to the west. Then there’s context. On one side of the tight site was an overwrought tower from the 1990s by Frédéric Borel, known in France for his deconstructivist architecture; on the other, a tall, nearly 400-foot-long housing block from the 1970s. A limited budget—just over $200 per square foot, typical for this type of project, where rents are often a fraction of market rate—left Bruther with a triple whammy. To build anything at all would be an achievement; that it turned out so well, an exceptional one.