Tucked between the Convention Center and the Vine Street Expressway is a patch of Center City that time and development forgot. Its blocks are veined with cobbled alleys whose names have almost disappeared from the Philadelphia map: Watts, Florist, Clarion, Spring. In contrast to the snoozy monoculture that is the Convention Center, the little enclave is packed with humming workshops and rowhouses.

This is probably how much of downtown Philadelphia looked in the early 20th century, before the triumph of the car, before fragmented blocks were consolidated into neat, developer-friendly parcels. Despite way too many parking lots, the area between 11th and Broad remains as evocative of our city as old Istanbul or Beijing's surviving hutong neighborhoods are of those places.

But just as nature abhors a vacuum, so does real estate. As Center City has sloughed off its grit and filled up with tony high-rises and top-tier restaurants, developers have begun to turn their gaze to this forgotten pocket.

The latest project to emerge comes from a hotel developer and involves one of the area's newer buildings, the 1946 Warner Bros. film exchange building at 13th and Florist. In a neighborhood that includes many 19th-century houses and the historic red-brick Adelphi schoolhouse, built by Quakers in 1832 to educate black children, Warner Bros. stands out as a rare local example of streamlined moderne, a subset of the art deco style.

The tan-and-brown-brick exchange was designed by William Harold Lee, a prolific movie-theater designer and Furness protege, and it exhibits the style's classic traits, including a curvy entrance and glass-block details. Warner Bros. used it as a distribution center in the days when theater operators came in person to pick up film canisters and posters. Later, it had a second act in film history as the place where NFL Films was founded. The exchange is one of just a handful of  post-World War II buildings on Philadelphia's historic register.

Its charming facade is, no doubt, what attracted Baywood Hotels, which wants to top the two-story exchange with a nine-story tower, using the model that architect Norman Foster established with Manhattan's Hearst Tower. But because the hotel overbuild would be a major intervention, Baywood needed a sign-off from the Historic Commission.

That proved to be no problem. The commission voted July 11 to give the project conceptual approval over the objections of its architectural subcommittee. Normally diplomatic, the committee bluntly described the design as mediocre. Before giving the green light, the group wanted Baywood's architect, spg3, to rethink its whole approach and laid out suggestions for improving the design.

Spg3 did eventually implement several of the committee's ideas, producing a tower that is a not-so-subtle copy of the shaft of the PSFS building. The new version plays off the exchange's rounded corner, which calls to mind the shape of the PSFS podium.

It's a pretty weak concept given that this is 2014, not 1932, when the groundbreaking PSFS burst on the scene. With Foster's Hearst building, which also sits atop an art deco base, the tower at least has the advantage of being a dynamic, faceted, modern form. If Baywood and spg3 were half as ambitious, it would be a huge improvement.

Unlike PSFS's meticulously crafted brick, spg3's overbuild will most likely be constructed in budget-minded composite panels. Although the design could still be improved, so far it's not worthy of Lee's snappy art deco exchange or the eclectic neighborhood. The commission, which meets Aug. 8 to decide on final approval, still has a chance to demand more from Baywood.

Preservationists have been extremely critical of the project. Much of their concern has centered on whether it is appropriate to plop a tower on top of a historic building. The bigger sin, in my view, is the way design has been made an afterthought.

As Rich Thom, the architect who renovated the exchange several years ago into offices, points out, two outer walls and the entire interior will be removed to allow space for the tower. That makes this project more demolition than modification.

It's a big ask by Baywood. Yet the commission has demanded very little in return.

The commission is supposed to be the steward of Philadelphia's prized collection of historic architecture. But it increasingly sees its role as an arbiter of development proposals. Its first job should be to protect the public patrimony.

There are strong echoes here of the recent Boyd Theater case, in which the commission also allowed the developer to use the facade as a false front for a new building, the iPic movie theater. That building was also sold short.

The nine-story Baywood tower will dramatically transform how we experience the Warner Bros. exchange. It will also set the tone for the changes coming to the neighborhood.

It's no secret why Baywood wants to build in this still-sketchy location. Warner Bros. is just a block from the Convention Center. The area may look tattered today, but it's strategically placed between booming Center City, booming Chinatown, and the booming Loft District. Cleaned up, this pocket could emerge as a new neighborhood, an arts district, or a center for tech startups. A meaningful, original work of architecture would be a beacon for those creatives.

But that's only if the commission doesn't give away the city's treasures at fire-sale prices.

Note: This column has been modified to correct the number of post-World War II buildings on the city's historic register.

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