On Wednesday, November 5, ADD Inc hosted Preservation Mass.' Annual Fall Event at the architecture and design firm's new headquarters in Fort Point Channel. The event celebrated the 15th Anniversary Retrospective of the Most Endangered Historic Resources between 1993 and 2008.   Every November, Preservation Mass. hosts their fall event in an historic building that has been successfully rehabilitated. ADD Inc. historically preserved and renovated its new headquarters at 311 Summer St. this year. The firm is pursuing LEED Gold certification by the U.S. Green Building Council and when certified, 311 Summer St. will be one of very few LEED Gold commercial interiors in Boston.