Repositioning of One Post Office Square in Boston’s Financial District will add 250,000 square feet of leasable space while improving the 40-year-old tower’s energy efficiency and modernizing tenant and common areas. Image courtesy of Gensler

A Boston law firm’s 358 attorneys and staff will relocate from the waterfront to the updated One Post Office Square tower.

Goulston & Storrs leased 100,000 square feet in the Financial District tower, which is being updated with a new glass exterior and amenities including outdoor terraces. The offices will replace a similarly-sized space at 400 Atlantic Ave., where Goulston & Storrs leases the entire building, the Boston Globe reported.

Goulston & Storrs will join another major law firm, Sullivan & Worcester, which remained and relocated within the tower during the renovation project which began in 2019.

Office vacancies in Boston’s central business district hit 11.3 percent in the fourth quarter, according to research by brokerage Newmark.

Tenants in the market for class A office space in Boston have abundant options amid a surge in construction of projects planned before the pandemic, including MP Boston’s Winthrop Center and Hines’ South Station tower.

International Place, which is losing tenant Eaton Vance to One Post Office Square, recently announced a $100 million capital improvement program including new common-area and outdoor amenities.

The firm has 188 Boston-based attorneys, Managing Partner William Dillon said.

“Now more than ever, the physical office destination that employers are inviting their employees to, matters. Post Office Square allows us to invite our employees to one of the most modern, flexible, efficient, environmentally conscious, and convenient locations in the heart of Boston’s CBD with top-notch amenities,” Dillon said in an email.