Work is moving along on the downtown outlet of Plan B Burger Bar, a chain with five restaurants in Connecticut and one in Massachusetts, that plans to open its seventh in the former Post Office building at 1262 Post Road this autumn.

Most of the original brick structure, and a later addition, has been demolished, although the structure's facade will be incorporated into the multi-tenant commercial structure that will take its place. Plan B will be the building's anchor tenant.

The owner, 1262 Post Road Holdings LLC, an affiliate of Wilton real estate investment firm Westport Capital Partners, bought the building a year ago from the U.S. Postal Service for $4.3 million last year with plans to expand the 11,130-square-foot building for retail use.

The Postal Service moved its downtown office to a smaller storefront at 1300 Post Road, part of a nationwide downsizing plan.

1262 Post Road Holdings decided to adapt the structure for multiple-tenant use when a single occupant could not be found to take the space, Steve Grathwohl, an asset manager with Burr Street Equities hired by 1262 Post Road Holdings, told the Fairfield Citizen.

Plan B will occupy 4,600 square feet of space in the front of the building facing the street, while another three or four tenants are being sought to lease the rear area of the structure, he said.

Grathwohl said the facade of the original 3,600-square-foot post office, built in 1936 and expanded in the 1950s, will be preserved as part of the plan. A historic mural that was located in the post office lobby has been moved and now hangs in the second floor conference room at Sullivan-Independence Hall.

The Fairfield burger outlet, which will have about 85 workers and serve alcohol, will have about 140 seats in its dining room and another 20 to 24 seats on a planned patio.

Plan B Burger Bar was founded in 2006, and there are currently other outlets in Stamford, Milford, Glastonbury, Simsbury and Springfield, Mass., with plans to open two more sites in Washington, D.C., and Alexandria, Va.