An eco-home is a house built or changed so that it harms the living world as little as possible and uses as little energy as possible. Thick walls that keep warm air in, windows that catch winter sun, solar panels, tanks for rain, careful use of water — those are the usual ideas. In some places there is an official label for this kind of building. It is a fairly new compound, used in housing talk and green-design writing. It is not just a house with plants on the balcony. Eco- is the same short piece as in eco-friendly.