The Green Building Resource Guide gives steel framing its highest 5 icon rating. Its resource efficient because there is very little waste, and it won't rot or be consumed by termites. Steel studs are also available with thermal breaks that allow less heat loss than wood. Also, steel is nontoxic because it will not off-gas and contaminate indoor air quality. Since steel screws together, steel members can be unscrewed and reused when a structure is demolished providing a structure for another residence.
Steel structures have many environmental benefits and are considered very green.