The development of wood architecture in early North America grew from New England where the earliest buildings were frame structures in the English tradition rather than log buildings. A regional approach to buildings using timber is being driven by concerns for sustainability and green construction. The Bullitt Center, designed to be one of the world's most energy-efficient buildings, epitomizes this ethic. It is the first urban mid-rise commercial building designed to meet the living building challenge (LBC)-a green building certification system that requires net-zero energy use, net-zero water use, on-site waste management, naturally daylit spaces and natural ventilation for all the occupants. The technology in the building creates a central nervous system in which interior spaces adapt to changing environmental conditions throughout the day. Nevertheless many multi-story urban heavy timber and brick buildings from the late 1800s and early 1900s still stand, demonstrating the durability, safety, and adaptability of these structures over time.