In place of the dome and courtyard, Blatstein has planned a four-story, 47-foot-high addition, with a roofline matching that of the mansion's original property - 1914 Rittenhouse.
The original mansion was erected in 1859 with three stories, capped by a one-story mansard roof with dormer windows. Its facade will remain unchanged.
The mansion's back entrance on Manning consists of a single-story structure and garage with a double-width door adjacent to a servants' entrance. Blatstein plans a two-story structure on the western end, with bedrooms atop two oversize garage entrances. On the eastern side, an addition will rise three stories above Manning Street.
Architectural plans are available to the public on the CCRA website ( http://www.centercityresidents.org) under CCRA Publications. Click on the link "What's New in the Neighborhood" to view the plans.
Blatstein will raze the dome at 1916 Rittenhouse, which was added by former owner Henry McIlhenny in 1957.
Blatstein declined to say how much the project would cost, but said his timeline was to complete the renovation within a year and a half. Neighbors did not ask for huge changes in the plans, he said.
"I'm coming in to be the best neighbor I can and keep them aware of any changes in construction," Blatstein said. "It's a jewel, and my wife and I feel lucky."
McIlhenny was well-known as an art collector and as chairman of the board of the Philadelphia Museum of Art. He was also, according to the artist Andy Warhol, "the only person in Philadelphia with glamour."
The mansion has, in the past, been a stop on the annual Center City Residents Association house tour.
"It's wonderful when people rehab a building that is historic but neglected," added Federico.
This year's tour is Oct. 19.