There’s a lot that lawmakers left out of the just passed $6.5 billion housing bond bill, such as a local-option transfer fee. But it did include a provision allowing so-called accessory dwelling units (ADUs) to be built as a right in single-family zones. … Abundant Housing Massachusetts is rightly praising passage of the ADU provision, noting it could lead to construction of thousands of apartment-like units attached to single-family homes in Massachusetts.