Earthships – Another Recycling Frontier

Earthships are earth-sheltered autonomous buildings made of tires rammed with earth, which are usually arranged in “U” or horseshoe shaped modules. Each tire is rammed full of earth manually using a sledge hammer. Windows on the sunny side admit light and heat. The open end of the “U” shaped structure faces South in the northern hemisphere, and North in the southern hemisphere, so that the house will catch maximum sunlight in the colder months. An Earthship is designed to interface with its environment wherever possible and create its own utilities.

Internal, non-load-bearing walls are often made of a “honey comb” of recycled cans separated by concrete. The walls are then usually thickly plastered, using the pull-tabs on the cans as a lath to hold the adobe and stucco. This is known as a tin can wall. The roof of an Earthship is heavily insulated.

The Earthship, as it exists today, began to take shape in the 1970s. Mike Reynolds, founder of Earthship Biotecture, a company that specializes in designing and building Earthships, wanted to create a home that would do three things. First, it would be sustainable. It would use material indigenous to the entire planet as well as reuse materials wherever possible. Second, his homes would generate their own utilities and be independent from the “grid” so they would be less susceptible to natural disasters and free from the electrical and water grids that Reynolds considered ugly. Finally, it would be available. He wanted to create a home that the average person with no specialized construction skills would be able to create.

Eventually, his vision took the form of the common U-shaped earth-rammed tire home seen today. However, as a concept, the Earthship is not limited to earth-rammed tires. Any dense material with a potential for thermal mass, such as concrete, adobe, or stone can be used to create an Earthship. However, the earth-rammed tire version of the Earthship is now the most common for several reasons, and is usually the only structure referred to as “Earthship”.

Unlike other materials, rammed-earth tires are more accessible to the average person. Scrap tires are indigenous to all parts of the world and easy to come by; there are an estimated 2 billion tires throughout the United States. According to the Scrap Tire Management Council, as many as 253 million scrap tires are generated each year in the United States and of those 253 million tires only 53% are reclaimed by the scrap tire market. In addition to the availability of scrap tires, the method by which they are produced, the ramming of the earth, is simple and affordable.

The earth rammed tires of an Earthship are usually assembled by teams of two people working together as part of a larger construction team. One member of the two person team shovels dirt, which usually comes from the building site, placing it into the tire one scoop at a time. The second member, who stands on the tire, uses a sledge hammer to pack the dirt in. The second person moves in a circle around the tire to keep the dirt even and avoid warping the tire. All tires in an Earthship are made in place because, when properly made, they weigh as much as 300 pounds and can be very difficult to relocate.

Additional benefits of the rammed earth tire are its great load-bearing capacity and its resistance to fire.

A fully rammed tire, which is about 2 feet 8 inches wide, is massive enough to surpass conventional requirements for structural load distribution to the earth. Because the tire is so dense, it does not burn when exposed to fire. In 1996 after a fire swept through many conventional homes in New Mexico, an Earthship discovered in the aftermath was relatively unharmed. Only the south-facing wall and the roof had burned away, compared to the total destruction of the conventional homes. After testing the walls of an Earthship in Ridgway, Colorado, engineer Tom Griepentrog said, “It is my opinion that the construction method is equivalent to or better than the general quality, strength, effectiveness, fire resistance, durability and safety that is required by the uniform building code.”

Currently, Earthships are in use in almost every state in the United States, as well as many countries in Europe. The use of insulation on the outside of tire walls, which was not common in early designs, is improving the viability of Earthships in every climate without compromising their durability. In the year 2000, Mike Reynolds, in partnership with Daren Howarth, launched Earthship Biotecture Europe, an organization that aims to explore and evolve the concept of the Earthship within a European context. Two more directors were appointed to Earthship Biotecture Europe in July 2006 – Kevan Trott and Kirsten Jacobsen

Potential advantages

• Having an earth-bermed home with windows facing the sun is a good idea in any climate where heating is required.
• Collecting rainwater that falls on the roof reduces the runoff impact of the building and may reduce water and even sewer service fees.
• Having a combination of photovoltaic cells and wind generation is a prudent way to provide electricity in many situations.
• Using curved modules as horizontal arches to resist earth loads is a sound structural design.
• On-site processing of runoff water, grey water and black water using plant beds reduces the environmental impact of the building.
• Rubber tires make a wind and puncture resistant wall. They may be safe from outgassing when plastered semi airtight.
• Rubber tires are usually free and it may be possible to be paid to take them.

Potential disadvantages

• The sloped glazing may be hard to keep watertight and in warm climates allows excessive solar gain in summer. In colder climates, the glazing itself, which has far poorer insulating properties than any other component, will obviously be the major conduit of heat loss in winter. New designs call for vertical windows with an overhang.
• Uninsulated ground-coupled thermal mass presents a large potential for heat loss, especially in climates with a heating season. This varies to a degree with soil type and moisture content.
• Rubber tire walls tend to lack structural stiffness and may require perpendicular stiffening ribs.
• The novel design may diminish resale value or make buyers more difficult to find.
• The intimate ground contact inherent in this approach may increase hazards due to soil gases including Radon, and those due to water intrusion.
• Packing or ramming dirt into the inside of tires is a very labor intensive process.
• Many Earthship builders are drawn to this system by its apparently low environmental impact. However, this is only valid if the design is highly thermally efficient. Earthship designs may require substantial thermal analysis and redesign to be adapted to non-Southwest USA climates.
• Free or cheap tires would not be available in a society which managed its resources sustainably — they would have an economic value. The most sustainable material is presumably stone.
• Earthships built with concrete, sand bags or adobe, and with better solar and heat control, perform better.

Article courtsey of Wikipedia