The HouseZero project at Harvard retrofitted a pre-war home on campus, creating a model of energy efficiency. (Photo by Michael Grimm, Courtesy Harvard Center for Green Buildings and Cities)

The HouseZero project at Harvard retrofitted a pre-war home on campus, creating a model of energy efficiency. (Photo by Michael Grimm, Courtesy Harvard Center for Green Buildings and Cities)

The HouseZero project at Harvard retrofitted a pre-war home on campus, creating a model of energy efficiency. (Photo by Michael Grimm, Courtesy Harvard Center for Green Buildings and Cities)