JLL’s Boston office is about to get a pricey facelift.

Developers hope to start work in 2018 on a $250M upgrade on the concrete facade at One Post Office Square. The modernization project would reclad the 41-story building with glass and expand it from 853K SF to 1.1M SF, the Boston Herald reports. A midlevel “porch” and penthouse club would be added, and the building’s parking garage would be replaced with an automatic parking system.

JLL and investment firm Anchor Line Partners hired architecture firm Gensler to design the building’s renovation. Putnam Investments is vacating 300K SF in the building for One Federal Street, and a Boston Planning & Development Agency filing for the project notes One Post Office Square is “no longer at the top of the leasing market.”

“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 co-founder Andrew Maher told the Herald. “The building doesn’t have the same attributes of new construction today.”