In 1896-1897, James Mason Crafts added a rear ell to 59 Marlborough, designed by architects Peabody and Stearns.
Plans for the remodeling are included in the Peabody and Stearns Collection in the Boston Public Library’s Arts Department (reference PS/MA.047). Included are three drawings of the addition, each showing changes in the design (for example, changing the windows from horizontal to arched architraves).
The drawings also include plans for a fifth story (penthouse) addition to be located in the center of the house between the front and rear chimneys; it appears this addition was not built.
These images are provided courtesy of the Boston Public Library. Included are all three iterations of the plans for the rear addition and the floor plan and section for the penthouse.
Plans for Rear Addition
Plans for Fifth Floor (Penthouse) Addition