Is it possible for humans to live on this planet and not leave any footprints while at the same time saving on heating costs? It may sound a bit exaggerated, but that seems to be the unfulfilled wish behind much of today's environmentally friendly architecture. The problem is that even if these homes are passive and are energy-efficient, it takes a lot of energy to build them. The production of the materials, transport and construction are all energy-intensive and also offset the environmental gains made by these buildings. The numbers are even worse if one first tears down a building in order to erect a new one.