Developers aim to start work on One Post Office Square’s facade

Developers hope to start work later this year to replace the precast concrete exterior of One Post Office Square with a glass facade as part of a $250 million office tower and garage modernization project.

Renovations for the 41-story tower would include a minor expansion, revitalized retail and office amenities including an expanded gym and juice bar, a new pedestrian entrance, and the creation of a new mid-level “porch” and penthouse “Lantern” club, according to a detailed project filing with the Boston Planning & Development Agency.

A six-story, 371-space, open-air parking garage on Oliver Street would be replaced with an automated parking garage system with up to 300 parking spaces and ground-floor retail topped with 13 levels of office space that will connect to One Post Office Square.

Hub investment firm Anchor Line Partners and Chicago’s Jones Lang LaSalle hired San Francisco architecture firm Gensler to rework the Financial District tower that overlooks Norman B. Leventhal Park and is connected to The Langham, Boston hotel.

The 1980 building is “no longer at the top of the leasing market,” according to project documents.

“It’s a once-in-a-lifetime opportunity to take an A-plus location with a building just shy of 40 years old and to reposition it for the needs of tenants for the 21st century,” Anchor Line cofounder Andrew Maher said. “The building doesn’t have the same attributes of new construction today.”

In total, the entire development would increase from about 853,300 square feet to 1.1 million square feet. The project also calls for a new glass pavilion with three stories of retail and dining space.

One Post Office Square currently has an approximately 95 percent occupancy rate, according to Maher. But Putnam Investments — which occupies more than 30 percent of the building, from the 18th floor down — is moving to Boston Properties’ 100 Federal St. building in the fourth quarter.

Maher said no new tenants have been lined up for Putnam’s space or the new retail space.

ARTIST'S RENDERING BY GENSLER SHINY AND NEW: Developers for One Post Office Square will begin renovating the building’s exterior this year, converting it from concrete to glass.