The south side of Walnut between 21st and 22nd Streets is a classic, 19th-century, Rittenhouse Square ensemble. While each four-story townhouse is slightly different in design, it's clear they all belong to the same regiment. The windows skip along at the same height, flowing from one house to the next. The top floors all feature sloping mansard roofs. The elegant streetscape, which includes a pair of houses designed by Frank Furness, is bracketed at the corners by slim high-rises.

But over the last year, an interloper has appeared among this well-mannered group, sowing discord. Poking out from a pleasant street wall of warm limestone and chocolaty brownstone is a slick, mini-skyscraper faced in flat glass panels. The modern structure looks as if it had made an emergency landing on the roof of the old townhouses. At the west end of Chancellor Street, a dull-gray wall looms like a medieval rampart over the tiny, 19th-century carriage houses.

The mini-skyscraper is, in fact, an overbuild, a kind of vertical addition that is becoming an increasingly common feature in Philadelphia's skyline. The glass structure sprawls across three properties, which have been combined to form a nine-story, nine-unit luxury condo tower. The building now tops out at 127 feet, more than double the height of the four-story townhouses. But the height of the condo project isn't the problem. The design is.

The view of the overbuild at 2110 Walnut is especially unsightly when viewed from the west.
Inga Saffron
The view of the overbuild at 2110 Walnut is especially unsightly when viewed from the west.

Architects love to use glass when they're making additions to historic buildings. They claim that the material is so ethereal that it appears to melt into the sky. Don't believe it. This glass addition, designed by Cecil Baker + Partners for developer Tim Shaaban, is solid proof that glass is just as visible and imposing as any other building material.

Rather than pretending the vertical addition wouldn't be seen, it would have made more sense to unify the project's three main parts. That probably would have meant using real limestone to match the facade of the Furness townhouse that forms the base of the new tower.

Instead, the developer and architects treat each section of the overbuild with a different material and different architectural style. The result is an architectural Frankenstein that looks as if it had been pieced together from a collection of disparate body parts.

The new condo tower at 2110 Walnut uses a different material and a different architectural style for each of its three main parts.
HEATHER KHALIFA / Staff Photographer
The new condo tower at 2110 Walnut uses a different material and a different architectural style for each of its three main parts.

To be fair, some of the worst aspects of the design spring from the developer's efforts to appease a group of self-centered and irrational neighbors.

Shaaban had originally planned to locate the curb cut for the condo's garage on the Chancellor Street alley. But it turned out that the narrow lane is a private street, and the property owners vetoed the idea. As a result, Shaaban moved the garage entrance to Walnut Street. Not only is Walnut one of Center City's premier streets, it is a major route for pedestrians walking to the universities and motorists heading to I-76. The last thing Center City needs right now is more congestion from drivers crossing the Walnut Street sidewalk to enter the garage.

The Chancellor Street neighbors made a technically complicated project even more complicated. The nine-story condo tower (which is being called 2110 Walnut) was created by combining three properties: the Furness townhouse, a new modern townhouse and a Chancellor Street carriage house. That new townhouse was built on a small, vacant lot, which had been used for private parking since the '60s.

Because Chancellor Street is privately owned, property owners had the power to veto a developer’s plan to locate the condo tower’s garage entrance on the alley. As a result, the entrance is now on Walnut Street. The photo shows the building’s east facade.
HEATHER KHALIFA / Staff Photographer
Because Chancellor Street is privately owned, property owners had the power to veto a developer’s plan to locate the condo tower’s garage entrance on the alley. As a result, the entrance is now on Walnut Street. The photo shows the building’s east facade.

The parking lot's existence is the reason that Shaaban was able to get city's approval for a garage entrance on Walnut Street. In the view of the Zoning Board, once a curb cut has been approved, it exists for eternity, no matter how disruptive it might be to the public good.

Eric Leighton, who led the architectural team, said he designed the new townhouse as a modern riff on the Furness house, which dates from 1868. But the white fiber cement panels, which were used to mimic Furness' dusky limestone, fool nobody. Even the glass on the overbuild is flat and lifeless. Most shocking is the required fire wall on Chancellor Street, which will be a blight on the neighborhood for decades.

In an effort to create more real estate in the highly desirable Rittenhouse Square neighborhood, a developer fused townhouses and added five more stories. But the creation of the new nine-story tower yielded a rampart-like wall that looms over the tiny carriage houses on the west end of Chancellor Street.
Inga Saffron
In an effort to create more real estate in the highly desirable Rittenhouse Square neighborhood, a developer fused townhouses and added five more stories. But the creation of the new nine-story tower yielded a rampart-like wall that looms over the tiny carriage houses on the west end of Chancellor Street.

Of course, you can find much worse designs going up all around the city. What makes 2110 Walnut so disappointing is that it represents what is supposed to be the leading edge of Philadelphia architecture. The condos have been selling for $1,100 a square foot — essentially New York prices — and the penthouse went for $6 million.

The bland and awkward design is especially discouraging because it sets the tone for future developer overbuilds. Even though Philadelphia is a big sprawling city (142 square miles, to be exact) and still has a huge inventory of vacant lots (over 40,000 at last count), developers continue focus their efforts on the same handful of neighborhoods.

Tim Shaaban’s company also put an overbuild on the historic Philadelphia Blueprint building at Eighth and Chestnut.
Inga Saffron
Tim Shaaban’s company also put an overbuild on the historic Philadelphia Blueprint building at Eighth and Chestnut.

Their range narrows even more when they are building high-priced condos. It's rare to find a developer willing to stray beyond the confines of Rittenhouse Square or Society Hill. Yet those two neighborhoods have practically run out of vacant land.

Because both are also historic districts, developers can't simply tear down an older building to make room for a bigger, fancier one. They can, however, get permission to modify them. One way to do that is with an overbuild, which effectively creates new real estate out of thin air.

Shaaban's companies, Astoban Investments and Urban Space Developments, now specialize in such overbuilds. They scour Center City for undersized buildings in high-density zoning districts. Last year they put a three-story condo addition on the Philadelphia Blueprint building at Eighth and Chestnut. Shaaban is now constructing a four-story overbuild on a nondescript building at 22nd and Chestnut, across from the Greenfield Elementary School. Meanwhile, another developer has jumped on the bandwagon and is raising the roof on a modest four-story building at 23rd and Walnut.

Stuart G. Rosenberg Architects is designing an overbuild for the four-story building at 23rd and Walnut.
SgRA Architecture
Stuart G. Rosenberg Architects is designing an overbuild for the four-story building at 23rd and Walnut.

Although developers see overbuilds as a means to extract value from older buildings in desirable areas, the additions can also have a public benefit. Like facadectomies — a variation in which only the front of the building is preserved — overbuilds can offset the cost of renovating historic structures. Even though the Furness house in Shaaban's project was previously occupied by apartments, its handsome limestone facade had been ignored for decades, probably because the rental income didn't justify major investment.

But just because overbuilds are a preservation tool doesn't excuse what happened at 2110 Walnut. Blank walls, curb cuts, and bland design are far too steep a price to pay for preserving Philadelphia's valuable architectural heritage.

Walnut Street is a major corridor for pedestrians heading to the university district and motorists accessing I-76.
HEATHER KHALIFA / Staff Photographer
Walnut Street is a major corridor for pedestrians heading to the university district and motorists accessing I-76.