Russell Byers Charter School intends to borrow millions for renovations to its building near 19th and Arch Streets, suggesting that a third Comcast tower, which many have speculated might rise on the block, won't be materializing any time soon.

Plans call for spending $4.75 million to convert the basement level into classrooms and to build a new entry structure on its Cherry Street side, among other improvements meant to accommodate the middle-school grades Russell Byers will begin hosting next year, head of school Jesse Bean said in an interview.

Much of the land on the block — bounded by 19th and 20th Streets, between Arch and Cherry — has been acquired by Liberty Property Trust in collaboration with Comcast Corp. The Malvern-based developer previously built Comcast's nearby headquarters tower at 1701 John F. Kennedy Blvd., across the street from where it is completing work on the 60-story Comcast Technology Center.

Though Liberty and Comcast have never commented on their plans for the assembled properties, they have seemed a likely site for additional space to be built for the expanding broadcast and technology giant.

But the 18,600-square-foot Byers School parcel — one of two mid-block properties not owned by Liberty — presumably isn't part of those plans, at least not yet.

Negotiations between Liberty and the charter school over the property's sale "have stalled indefinitely," the school said in a December presentation posted on its website.

"We're not in a hurry to dispose of or move from our property," Bean told the Inquirer.

Medical publisher F.A. Davis Co. also retains its property, to the immediate west of the Byers School.

Liberty's regional director, John Gattuso, said that he was aware of the school's expansion plans, and that his company endorses them.

"The Byers School is proceeding with the renovation of their building because they need to accommodate a larger enrollment in the coming school year," Gattuso said. "It's totally independent of any potential plans or timing for the development of the site."

On April 4, the Philadelphia Authority for Industrial Development approved $11.5 million in tax-exempt financing for the school to complete the renovations and to refinance some existing debt, according to minutes from the meeting.

In addition to the new classrooms and Cherry Street facade, improvements at the school will include work on an open-air courtyard, renovations to allow natural light into the building's lower stories, and upgrades to its parking lot, Bean said.

"We like our location here," he said, citing the surrounding museums and other cultural attractions. "We are making accommodations that would allow us to stay here indefinitely."