Exactly one year ago, a piece of masonry began to peel away from the top of a six-story building at 16th and Walnut. Bricks rained down in a torrent, crashing through the ceiling of the adjacent Lululemon store and injuring three young women - one of them seriously - who had been shopping for workout clothes. Fortunately, everyone else managed to walk away, shaken but unscathed.

Though nowhere as terrible as the fatal tragedy at the Salvation Army store in 2013, the injuries and a subsequent lawsuit might have been expected to put the two properties into a real estate deep freeze. Instead, the owner saw opportunity in the newly vacant Lululemon lot, and today a handsome 14-story apartment tower is rising on the double site. The designers, DAS Architects, incorporated the six-story office building that caused the accident, using it as a base for the tower.

Even if the circumstances had been more ordinary, it would be rare for a project of this size and complexity to come together so quickly in Philadelphia. Negotiations with neighborhood groups and city commissions typically take months to conclude. But the building, called the Beacon, was intentionally designed to avoid such scrutiny.

The stealth tower is the latest offering from Pearl Properties, the Greta Garbo of Philadelphia developers. The company, which has amassed large holdings on Chestnut, Walnut, Sansom, and Broad, is notoriously sparing in its communications with civic groups. The Center City Residents Association was unaware of the tower until I sent it renderings gleaned from the architects' website. The company is even less forthcoming with journalists.

To avoid such time-consuming interactions with the public, Pearl has perfected the art of the "by right" project. The Beacon was able to fly under the radar because it conforms perfectly with the site's zoning, which means it didn't require a variance from the Zoning Board. Because 16th and Walnut sits just outside the Rittenhouse-Fitler Historic District, no Historical Commission review was necessary, either. A staffer at the Planning Commission signed off on the facade design.

Because the site has the city's densest zoning classification, CMX-5, Pearl could have actually built a much taller skyscraper without applying for a variance. But the developers knew a bigger building - anything greater than 100,000 square feet - would have triggered a hearing before the Civic Design Review board. By keeping the Beacon below that threshold, Pearl was able to avoid public hearings - and complete the design and start construction in under a year.

That kind of turnaround is almost unheard of in most American cities and suburbs. But that is actually how things are meant to work under the city's new zoning code. Still, it's too bad Pearl was not more communicative.

Zoning policy has been so tangled in Philadelphia for so long it's hard to get used to seeing a skyscraper (even a small one) rising unannounced on a busy downtown street. Though the main goal of Mayor Michael Nutter's reforms was to make by-right development the norm, that hasn't happened often because the city hasn't updated its zoning maps. The Beacon worked because the site was properly zoned.

With Philadelphia's housing boom showing no signs of letting up, it's likely other canny developers will go the by-right route. If only all the projects could be as well-designed as this one.

Pearl deserves props for preserving the corner building, which once housed Brown Bros. Harriman, a private investment bank. Although the office dates from 1927, it is not landmarked. Pearl was smart enough to realize the limestone building could serve as an elegant entrance to its apartment tower. Its original wood-paneled lobby will become a retail space for the athleisure brand Under Armour.

DAS, which designed the Sansom and the Granary for Pearl, has done a fine job of weaving the new tower around the old structure, without trying to imitate its '20s style. The six-story bank building will be topped with a glassy overbuild of roughly the same size - a lightweight counterpoint to the heavy masonry base. Marbled porcelain panels subtly recall the limestone tint of the former bank.

The availability of the Lululemon site made it possible for the architects to expand the tower on its east facade. DAS architect David A. Schultz has designed a slim, brick-clad structure he calls the "spine."

The 197-foot addition climbs up the side of the enlarged bank building, and caps it with a swank two-story penthouse. At the 16th Street corner, Schultz cut three terraces into the building. These setbacks not only help to slim the tower as it rises, they also help to call out each part of the addition.

It turns out Pearl's self-imposed limitations worked in the design's favor. Because the developer was keeping a low profile, it didn't overreach by attempting to build a monster tower, as the Southern Land Co. wants to do with its project on Rittenhouse Square. That's better for Walnut Street, which is already a busy place.

Unlike many developers, Pearl didn't try to shoehorn a garage onto the modest site; instead, it will offer tenants reserved spaces in a nearby garage. The developer also adhered to the zoning requirements for ground-floor retail. In other words, it followed the rules.

It should be said this isn't the first time Pearl has tried to build a skyscraper without having to submit to public hearings.

Its Boyd tower at 19th and Chestnut was intended as a by-right development. When the developers realized their initial plan would be twice as dense as the site allowed, and would require an extended zoning review, they quickly abandoned the design. They then proceeded to buy up several neighboring properties, including the historic Boyd Theater. By spreading the density over a larger footprint, they figured they could eliminate any need for a variance.

Their attempt to steamroller the project was thwarted, however, when neighbors used the Boyd's historic status to demand input on the project. Thanks to those negotiations, and the advice of architect Cecil Baker, the Boyd tower's design has been vastly improved. Pearl's bottom line also benefited: Now there is much more space for stores on the building's Sansom Street facade.

Throwing out the red tape certainly makes it easier to build in Philadelphia. But as the story of the Boyd tower shows, even by-right projects can benefit from a few more eyes.