Pretty curves all in a row

Philadelphia is such a relentlessly right-angled city, a place so completely devoted to its colonial grid, that it's not surprising that some architectural dissidents would insist on flaunting their curves. The PSFS tower, now the Loews Hotel, is the city's best-known nonconformist, but plenty of modest rowhouses also break out of the box with similar hip-jutting moves.

Take the intersection of Fourth and Poplar Streets in Northern Liberties. For more than a century, a charming pair of well-rounded corner houses have gazed at each other across the narrow breach of Poplar Street.

The talented architects at QB3 were so taken with the pair that they decided to make it a threesome. They've just completed a voluptuous newcomer on the northeast corner that they call the Split Level House. That's a pretty modest name for the most innovative take on the traditional rowhouse that Philadelphia has seen in years.

The house is a gorgeous piece of construction, lovingly assembled brick-by-brick by South Philadelphia artisan Luigi DeLaureta and overseen by QB3's Tim Peters. But what makes it important architecture is the compare-and-contrast dialogue that QB3 set up with the neighbors. Their modern design abides by all the rowhouse rules of Philadelphia, even as it cleverly remixes them for the 21st century.

So, the house's curves are faced in brick, just like its 19th-century companions, but the architects used a rich charcoal variety flecked with oranges and browns to update the mood. QB3's house comes to the sidewalk and embraces the world with ground-floor windows, as all good rowhouses should.

Those windows, however, cut through the house's core like a seismic fault, opening up dramatic views into, out of, and through the structure. The bold, three-sided opening confounds our expectation of how a Philadelphia rowhouse is supposed to engage the street: There's too much glass to condemn the house as a fortress, yet its swaths of brick are too extensive to think of it as a transparent building. We're simultaneously invited in and held at bay by the arrangement of solids and voids.

QB3's marriage of traditional urban values and boundary-pushing architecture works so well that you have to wonder why similar fusions didn't emerge during the city's decade-long housing boom. After all, the enduring attraction of the rowhouse form is that it is infinitely malleable. And yet, too many designers were content to slap a metal bay window on a conventional box and call it modern.