HouseZero, a timber-framed building in Cambridge at Harvard University is under construction and will soon become a first-of-its-kind prototype for ultra-efficient retrofits. (Photo courtesy Harvard CGBC)

HouseZero, a timber-framed building in Cambridge at Harvard University is under construction and will soon become a first-of-its-kind prototype for ultra-efficient retrofits. (Photo courtesy Harvard CGBC)

HouseZero, a timber-framed building in Cambridge at Harvard University is under construction and will soon become a first-of-its-kind prototype for ultra-efficient retrofits. (Photo courtesy Harvard CGBC)