You've probably seen them stacked high to the sky at city ports, left empty after traveling around the world carrying furniture, appliances and other household goods.
But the next time you see a shipping container, it might be far from the waterfront and serving a purpose for which it was never intended: housing.
Originally developed as an artistic experiment, shipping container homes are moving into the mainstream, as architects and builders recognize the economic and environmental benefits of working with the giant Lego-like steel boxes.
"It's not just a bunch of mad scientists tinkering in a garage making these buildings," said Peter DeMaria, principal architect of DeMaria Design Associates, a Manhattan Beach, Calif.-based firm that has designed several container-based suburban homes. "It's people who understand the economics and understand the environmental benefits."
Each year, millions of shipping containers arrive on American shores. Because it's so expensive for empty containers to make a return trip across the ocean, DeMaria estimates that up to half never make it back. Some industry experts say the number of containers available for reuse hovers around 100,000, but can reach 700,000.
In addition to the several modern homes DeMaria's firm has already completed in southern California, it will launch a new line of shipping container homes in the coming weeks.
In the last year, he said, 25,000 people have inquired about these Logical Homes through the company's Web site. Each day, he said, about 10 others approach the firm by telephone or e-mail.
Although architects and builders have been experimenting with shipping container homes for the last few years, questions about structural integrity and legality have continued to nag.
But, DeMaria said, a home he designed for a family in Redondo Beach, Calif., last year changed the landscape for his company and others in the field.
Its completion demonstrated that a container-based building could conform to local building codes, he said, and proved that "it isn't going to fall down, rust away. The technical, functional issues have been put to bed."
Adam Kalkin, a New Jersey-based artist and architect, was one of the first people to experiment with shipping container homes more than 10 years ago.
Now, he has about 12 container-based homes under his belt, in addition to a new crop of prefabricated Quik Homes. But, when he started, building homes from the steel shells -- 40 feet by 9.5 feet by 8 feet -- was more performance art than practical enterprise.
"For me, it was an intriguing idea. I like their very sculpture in nature. [They're] beaten up. They've had this history," he said. "God knows where they've gone, what they've done and what they've seen."
"I loved the idea that you've taken something that has been all around the world and you localize it," he said.
When Kalkin first started, builders were so reluctant to join his experiments in construction that he had to take hammer to nail himself and recruit his friends.
But now, he said, two forces are contributing to the growing acceptance of container-based homes: a slumping economy and increasing environmental awareness.
Founded two years ago, SG Blocks (for Safe Green blocks) is one of the companies at the front of the field working to source and convert shipping containers for construction.
"We take instruments of trade -- cargo containers -- and turn them into instruments of construction," David Cross, the company's business development director, told ABCNews.com.
Through a partnership with ConGlobal Industries, a leading retailer of shipping containers, SG Blocks has access to a network of 17 depots in North America that house used containers.
But sourcing containers close to their destination sites, the company can significantly cut down on energy costs.
At these depots, metal workers torch, weld and remove rust to transform the battered steel boxes into large building trusses, he said.
Depending on the container's condition, one container costs between $1,500 to $4,500 and needs about 100 hours of labor to prepare it for construction, Cross said.
In the last year, the company has converted about 100 containers for a handful of projects, including a two-story office building for the U.S. Army in Fort Bragg, N.C. Designed by the St. Louis, Mo.-based architecture firm the Lawrence Group, the building was made from 12 shipping containers converted by SG Blocks.
In the next two years, the company expects to convert 5,000 containers for 50 to 80 residential, commercial and mixed-use projects across North America.
"Builders and developers are looking for a leg up. Everyone is really wanting to be green," said Bruce Russell, managing director for SG Blocks.
Noting that the process of converting the containers into construction blocks consumes far less energy than the process of totally melting the whole container down, he said, "we have the greenest building structural system that there is."
Attracted by the company's sustainable approach to construction, developers, architects and builders have had an overwhelmingly positive response, Russell said.
Right now, the company is working on a 220-unit dormitory for Lubbock Christian University in Lubbock, Texas, and a senior housing development in Oceanside, Calif. SLS Partnership, Inc., a Lubbock, Texas-based architecture firm, designed the dormitory and the Lawrence Group designed the housing development.
Because the containers were designed to brave the elements at sea, they're perfect for hurricane- and tornado-prone parts of the country. They're also best suited for multiunit buildings.
"The higher we go, the more cost advantageous it is," said SG Blocks' Russell.
Fifteen containers can be installed with one crane in one day, which means that months can be shaved off construction time.
"This is far faster than conventional construction," said Dan Rosenthal, a principal with the Lawrence Group. "There are significant savings associated with that."
The larger the project, the more apparent the savings, he said. But, in general, an SG-based project is at least competitive with, if not 15 percent cheaper than a conventional project.
John K. McIlwain, a housing expert at the nonprofit Urban Land Institute who saw an SG Blocks-Lawrence Group home at a recent conference, said he was impressed by both the economic and the environmental benefits of the innovation.
"They strike me as a very practical solution to lowering the cost of construction," he said. "While costs of many materials are coming down, it's still going to go back again."
Given the state of the economy, finding ways to reduce housing costs is very important, he said.
"It's not the answer, but it's one of the ways we can provide attractive decent housing to people at a lower cost of production."