The 46 Blackstone Street renovation unified three 19th-century masonry buildings into an environmentally sustainable workplace for Harvard University Operations Services (UOS). A glazed 100'-long lightslot joins the buildings, and a three-story skylit stairway allows light deep into the building. Over 90% of occupants now enjoy daylight, fresh air and views from operable windows. Blackstone was Harvard's first LEED Platinum-certified building, and a model for environmental design on campus. At the time of completion, it was the highest-scoring LEED renovation in the nation, and the oldest building to earn Platinum certification. Energy-saving features include an innovative insulation system at the historic brick walls, a geothermal cooling system, and a heat recovery wheel. Energy-efficient, low-VOC equipment and materials were used throughout (including daylight sensors, occupant sensors, and an energy-efficient elevator). A landscaped courtyard, sculpted from earth excavated during construction, requires no irrigation; a bio-retention pond treats storm water runoff.