Last Updated: Jul 10, 2021
In 1987, a man named Phillip Clark filed a patent with the idea of transforming a few used shipping containers into a habitable building. While the concept was received with a few laughs, today, thousands of shipping container homes worldwide. From shopping malls in New Zealand to even a Starbucks coffee house made from upcycled shipping containers, this type of architecture is quickly gaining wide approval and popularity.
Shipping container architecture is usually labeled as a green, sustainable, or eco-friendly form of building. It focuses on recycling or upcycling used shipping containers that would otherwise be nothing more than a discarded pile of steel taking up space in some ports worldwide. Also, by recycling these steel structures, there is less demand for brick, wood, and other building materials. This subsequently lowers the total embodied energy cost associated with a home. So if you're thinking of getting a 'new' container, think again - more on that in a bit.
While using recycled materials is a fundamental aspect of sustainable architecture, several aspects are related to shipping container homes that need to be revisited. From toxic chemicals in the original flooring of most shipping containers to an enormous amount of mined steel that makes up your home's structure to inadequate insulation capacity, shipping container homes, like any architecture, need to be planned accordingly to achieve their maximum potential sustainability.
Transforming an abandoned shipping container into a livable home is undoubtedly a useful and meaningful example of recycling. However, as one engineer has shown, you can melt down two forty-foot shipping containers to form over 2,000 eight-foot steel studs. A typical home of similar size would only use around 144 of those studs. While this analysis doesn’t consider the energy needed to melt down the container into studs or the energetic cost of the alternative material that would eventually make up the walls of that steel-studded home, the fact remains: a shipping container home does contain much more steel than necessary.
Many people are worried about the container's condition and opt for one-trip containers because they are usually in optimum condition without any dents or issues with rusting. The problem, of course, is that it is hard to advertise these containers as “recycled” since they have not completed a lifetime of work in the globalized trade industry. Using one-trip containers for your home structure essentially means that you are incorporating an enormous amount of mined steel (an unrenewable resource) that could ideally be used to ship cargo around the world. Opting for shipping containers that have completed their useful life aboard cargo ships and are sitting unused in a port or parking lot is a much more sustainable way to recycle materials into your house design.
Shipping containers are designed to endure a life at sea. Since most cargo ships have issues with rodents that live as stowaways aboard the ship, the wooden flooring in shipping containers is usually heavily treated with pesticides to deter these unwanted guests. Steel walls and roofs of shipping containers usually contain paints incorporating heavy metals such as phosphorus and chromate. These chemicals help protect the steel from the steady spray of saltwater, which can corrode the steel containers.
One recent study showed that when shipping containers arrive in a harbor, up to 20% of these containers contain volatile toxic substances that are substantially higher than the established exposure limit values and that these volatile, off-gassing chemicals can lead to serious health risks for dock workers, customs inspectors, and others. The types of gasses accumulating inside these airtight containers also depend on what is being shipped. However, it is common for dangerous chemicals such as formaldehyde, styrene, benzene, or toluene.
When transforming a shipping container into a livable home, one of the first tasks should be ripping out the pesticide-laced flooring and taking measures to cover or encapsulate the toxic paints. Trying to remove the toxic paint will most likely lead to more off-gassing and dangerous dust that poses serious health risks when inhaled. Instead, using a non-toxic sealing primer will help encapsulate the chemicals and block the off-gassing of hazardous, volatile organic compounds.
Suppose you have chosen a “retired” and well-used shipping container and done the work to remove the potentially dangerous, toxic chemicals. In that case, you can still do a few things to maximize the sustainability of your home. Steel conducts heat efficiently, meaning that your shipping container home will need to be more heavily insulated than a traditional stick-built or brick home in most climates. If your shipping container home isn’t well-insulated (including the floor and the roof), the energetic cost to maintain the home comfortable will be high.
While most contractors who specialize in shipping container construction use spray foam insulation because it adheres well to the containers' irregular shape, almost all spray insulation is made from polyurethane, leading to health problems, asthma, lung problems, and respiratory irregularities. These sprays often also have a high Global Warming Potential.
One natural way to insulate a shipping container home is through straw bales to the home's exterior. Straw bale construction has existed for centuries and is a great way to reuse the leftover products of grain agriculture that are sometimes burned or left to rot. Straw bales are some of the best building materials for insulation, with R-values up to R-35. To add straw bales to the exterior of your home, you will need to build a small stem wall to keep the straw bales free from ground moisture, which could cause rotting and mold issues. You need to plaster the straw bales with cement and lime stucco to further protect the bales from accumulating moisture.
Shipping container homes will also need some roof and roof insulation. Adding a green or living roof is one way to kill two birds with one stone. The steel roofing of a shipping container offers a perfect “substrate” to build a living roof. You will most likely need to add some steel stud reinforcements to the roof, but the steel itself will offer an impermeable layer or at least a roofing layer that is more waterproof than the traditional 2x4s and plywood.
On top of the reinforced steel roof, you will need to add a small layer of rigid insulation slightly pitched to help in water runoff. A waterproof membrane such as a pond liner then covers the insulation. On top of the pond liner is placed a growing medium encased by steel bars to keep the soil on your roof from sliding off during heavy rain.
Once your growing medium is in place, you can plant flowers, turf, or other types of plants (even vegetables) on top of your home. The thick growing medium is not only beautiful but also offers a thick layer of insulation to keep your shipping container home warm.
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.