Historic Boston Inc., a nonprofit real estate development and preservation organization, this week opened four new apartments in a historic H.H. Richardson-designed building that it has saved, rehabilitated and re-purposed in Boston’s Chinatown neighborhood.

The Hayden Building, located at 681 Washington St., at LaGrange Street, will feature retail on the ground floor. The four 930-square-foot apartments, on floors two through five, are in the process of being rented.

The Hayden Building, which was located at the heart of the Combat Zone adult entertainment district, was threatened with demolition when Historic Boston Inc. purchased it in 1993, with the help of the City of Boston and Mayor Menino. The organization secured the building and preserved it through years of inactivity, initiating a full-scale preservation and reactivation project about a year ago.

The full cost of the design and construction is $5.6 million.

The Hayden Building is architect H.H. Richardson’s only remaining commercial building in Boston.  The project manager for the Hayden reconstruction was Lisa Lewis. The general contractor was Marc Truant & Associates. The architect was CUBE design + research. The historic consultant was McCrostie Historic Advisors LLC.