Mayor Kenney is calling on the developer of a planned 16-story condo tower on Jewelers Row "to go above and beyond what the law requires" in preserving the buildings at the proposed construction site.

In a statement Wednesday, Kenney said that he has urged Horsham-based Toll Bros. to keep intact the second- and third-floor facades of those five buildings in its development plans and to follow recommendations offered by the city's design-review board, even though they are nonbinding.

The mayor's efforts come as moves led by preservationists to thwart Toll's  plan for 80 luxury condo units in the venerable Sansom Street shopping enclave have failed to gain traction.

"I share the frustration of the Philadelphians who have called out in recent weeks for historical protection of Jewelers Row," Kenney said. "Regrettably, we have reviewed the current law at length, and the developer has proceeded in accordance with city code."

But he said Toll Bros. representatives have given "their word that they are committed to maintaining Jewelers Row as a historic, cultural gem for future generations of Philadelphians to enjoy."

Paul Steinke, executive director of the Preservation Alliance for Greater Philadelphia, said the mayor's involvement in the preservation effort was welcome.

"We're pleased he's taking a strong leadership role," Steinke said. "It's pretty clear there's strong public support for preservation in this instance."

Tim Spreitzer, a spokesman for Toll's City Living division, which is developing the project, said the company had no comment on Kenney's remarks Wednesday.

The mayor's preservation request covers only the buildings' second- and third-floor facades because the ground-level frontages have already been significantly altered, city planning and development director Anne Fadullon said.

Kenney is seeking voluntary commitments from Toll in the absence of any legally binding protections for the Jewelers Row buildings, which are not listed in the city's Register of Historic Places.

The project's permitting process also will eventually land it before the city's Civic Design Review board, which may urge the developer to keep the street's historic character intact. But that panel's recommendations are also nonbinding.

Opponents of the proposed tower recently lost a challenge to its zoning but continue to seek the plan's derailment through the nomination of three of the affected properties to the city Register of Historic Places.

In most cases, developers seeking to demolish or alter properties on the register must prove to Philadelphia's Historical Commission that preserving them represents a special hardship.

The outcry over Toll's proposal has city officials focused on new protections for historic buildings citywide, with legislation to be introduced in the coming weeks to better fund the city Historical Commission, Fadullon said Wednesday.

The Kenney administration wants to boost the commission's budget by about $500,000 to nearly double the size of its six-member staff so it can work to identify properties and historic districts for nomination to the register, she said.

"Moving forward, there is no question that we have to increase resources to protect Philadelphia's historic buildings," Kenney said in the Wednesday statement.