Responding to pressure from Philadelphia's leading preservation advocates, the state historical commission has instructed the Pennsylvania Convention Center Authority that it must preserve two small, historic office buildings north of City Hall and incorporate them into the expanded center's new Broad Street facade.

The ruling by the Historical and Museum Commission was spelled out Thursday in a letter to the state Department of General Services (DGS), which is overseeing the Convention Center's Broad Street expansion. In effect, one state agency is now pitted against another, and it is not clear whether the Convention Center Authority will abide by the commission's instructions.

That ambiguity did not stop the head of Philadelphia's Preservation Alliance, John Gallery, from hailing the letter as a victory yesterday.

"I was very pleased by it because I felt the historical commission was really listening to our expressions of concern," Gallery said.

In September, the historical commission was set to sign off on the demolitions when the alliance and the Design Advocacy Group launched a high-profile campaign to save the two buildings between Arch and Cherry Streets, once the headquarters of Philadelphia Life Insurance Co.

The preservationists argued that the conjoined structures are crucial to Philadelphia's history because they help frame City Hall and explain the city's 20th-century commercial development. Also, the addition to the original neoclassical insurance company building was designed in 1962 by Romaldo Giurgola, an important Philadelphia School architect, and is considered a small Modernist masterpiece.

Although several individual historic buildings stood in the path of the $700 million Convention Center expansion, it was agreed that these Broad Street structures were the most worthy of preservation because they were the only ones that were part of an intact block.

In 2004, the Convention Center Authority struck a deal: It pledged to save three of the four buildings on the 100 block of North Broad in exchange for permission to raze the other historic buildings in the two-block expansion zone. (The third building, a vacant 20-story tower, is not affected by the construction project.)

According to the agreement signed by the authority, the Broad Street buildings were to be woven into the expanded center's main facade. All the architectural renderings for the project feature the pair in the design.

But this fall, the Convention Center Authority abruptly announced that the structures had decayed beyond repair and could not be included in the project.

With DGS, the authority asked the state historical commission for permission to demolish them, saying it had no other option.

Although the historical commission was initially sympathetic, on Dec. 7 it asked for an independent engineering assessment of the buildings' condition.

Thursday's letter from commission director Barbara Franco rejects the claim that the buildings are unsound. She quotes the Convention Center's own architects as saying the pair can be saved and renovated.

Franco concludes her letter by saying DGS should "avoid further delays" and construct the Convention Center according to the design, with the two buildings forming a part of the facade.

Contacted yesterday, a spokeswoman for the authority, Jane Crawford, declined to comment, saying, "The letter speaks for itself."

The Convention Center is now wrapping up a massive demolition effort to clear the way for its addition. All that remains in the area is the 100 block of North Broad Street, the lavishly decorated Race Street firehouse, and two city blocks worth of rubble.

Read Inga Saffron's columns about the Convention Center

expansion at

com/ingasaffron

Contact architecture critic Inga Saffron at 215-854-2213 or isaffron@phillynews.com.