Approximately 30 million steel containers and panel containers are in existence, filled and floating, or standing about empty in a port. Eight feet wide by 8.5 feet high, and either 20 or 40 feet long, the steel shipping container has been the globally standardized transportation module since 1956. Costs of shipping empty containers back to their origin are high, so oft times the containers sit unused in ports. If one lives near a port with abundant containers, then the energy required to transport the steel container to a local building site will be lower than an inland location, far from the port. But buyer beware, as that used container might have been sprayed with insecticides or fungicides inside, and coated with lead or heavy metal paints on the outside.