The environmental movement that has taken hold in the last half-century includes the objective of reducing the adverse impacts buildings have on the natural environment. In the United States, this has manifested itself in changes in the design and construction of buildings. Modern buildings-those built recently-perform better with respect to some, but not all, environmental criteria than older buildings. The most prominent characteristic is the efficiency of energy use for heating, cooling, and appliances.

Even when the combination of building codes and voluntary standards work effectively to promote the construction of new green homes, they cannot provide a solution with respect to the overall performance of our housing stock. This article reviews different definitions, standards and options for making existing housing more green.