An Earthship refers to a passive solar home made of natural and recycled materials. Designed and marketed by Earthship Biotecture of Taos, NM, the homes are primarily constructed to work autonomous and are generally made of earth-filled tires, utilising thermal mass construction to naturally regulate indoor temperature. They also usually have their own special natural ventilation system. Earthships are a type of off-grid home, which minimizes their reliance on public utilities and fossil fuels.
Earthships are built to utilize the available local resources, especially energy from the sun. For example, windows on the sunny side admit light and heat, and the buildings are often horseshoe-shaped to maximize southern (or northern in the southern hemisphere) sunlight and warmth in the colder months. Likewise, the thick, dense outer walls provide effective insulation against summer heat.
Internal, non-load-bearing walls are often made of a "honey comb" of recycled cans joined by concrete and are referred to as tin can walls. These walls are usually thickly plastered with adobe or stucco.
The roof of an Earthship is heavily insulated - often with earth or adobe - for added energy efficiency.
Eventually, Reynolds' vision took the form of the common U-shaped earth-filled tire homes seen today. As a concept, the Earthship was not limited to tires - any dense material with a potential for thermal mass, such as concrete, adobe, or stone could theoretically be used to create an Earthship. However, the earth-rammed tire version of the Earthship is now the most common design, 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 ubiquitous around 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 converted into usable "bricks", 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 full of soil, 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
In 2004, the very first Earthship in the UK was opened at Kinghorn Loch in Fife, Scotland. It was built by volunteers of the SCI charity. In 2005, the first earthship in England was established in Stanmer Park, Brighton.
Earthships are designed to catch and use water from the local environment without bringing in water from a centralized source. Water used in an Earthship is harvested from rain or snow. As water collects on the roof it is channeled through a silt catching device and into a cistern. The cisterns are positioned so they gravity feed a WOM (water organization module), that filters out bacteria and makes it suitable for drinking. The WOM consists of filters and a DC-pump that are screwed unto a panel. Water is then pushed into a conventional pressure tank to create common household water pressure. Water collected in this fashion is used for any household activities except flushing toilets the conventional way. Rather, flushing toilets can be done as a last step (after the water has been used for other purposes).
Treating and reusing greywater
Greywater, water that has been used and is unsuitable for drinking, is used within the Earthship for a multitude of purposes once it is reclaimed. First, before the greywater can be reused, it is channeled through a grease and partical filter/digester and into a 30”-60" deep rubber lined botanical cell, a miniature living machine, within the Earthship. This filter with imbedded plants can potentially also be used to produce food (by using a fruit tree, ...). Oxygenation, filtration, transpiration and bacteria encounter all take place within the cell and help to cleanse the water (Reynolds 2000). Within the botanical cell filtration is achieved by passing the water through a mixture of gravel and plant roots. Because of the nature of plants, oxygen is added to the water as it filters while nitrogen is removed. Water taken up through the plants and transpired at their tops helps to humidify the air. In the cell, bacteria will naturally grow and help to cleanse the water.
Water from the low end of the botanical cell is then directed through a peat moss filter and collected in a reservoir or well. This reclaimed water is then passed once more through a grey water board(see earthship.net) and used to flush conventional toilets.
Often, any greywater that is made at earthships, is not polluted enough to justify treatment (its "pollution" being usually just soap, which is often not environmentally damaging). At earthships, the use of plants placed at outlets of fixtures is then practiced to regain the nutrients lost (from the soaps, ...) and water from the greywater. Usually, a single plant is placed directly in front of the pipe, but mini drain fields are also sometimes used. The pipe is made large enough (5,08cm) so that the formation of underground gas (from the greywater) is avoided. This is done with kitchen, bathroom sinks and even showers, washing and dishwashing machines. The plants are usually placed indoors with the sinks and outdoors with the washing/dishwashing machines and shower (to avoid indoor "floods"). Also, with the latter, larger drain fields are used instead of a mere placing before a outlet.
Treating and reusing black water
Black water, water that has been used in a toilet, was usually not created within many earthships as the use of conventional toilets was discouraged. Instead, in the early days composting toilets were advocated, which use no water at all. However, with the new greywater treatment system design (used in Nautilus, Helios, ...) created by Michael Reynolds, flush toilets have now found a place in the earthship and the general water system has been redesigned according to the new "6-step process". Now, when the newly included flush-toilets are used, blackwater is not reused within the Earthship. Instead, blackwater is sent to a solar-enhanced septic tank with leech field and planter cells (the whole being often referred to as the “incubator”). The solar enhanced septic tank is a regular septic tank which is solar heated and glazed with a south-facing window. The incubator stores the sun's heat in its concrete mass, and is insulated, to help the anaerobic process. Water from the incubator is channeled out to an exterior leech field and then to landscaping "planter cells" (spaces surrounded by concrete in which plants have been put). The cells are similar to the botanical cell used in greywater treatment and are usually placed just before and under the windows of the earthship.
In cases where it is not possible to use flush-toilets operating on water, dry solar toilets are now advocated, instead of regular composting toilets. If this is the case, obviously no black water is formed and the use of a incubator is thus (usually) not necessairy. Instead, regular "planters" (plants used for sucking up water/nutrients) are then used. When using regular planters as well, no chemical soaps/detergents, ... can be used.
The space where WOM, graywater pump panel, pressure tank, (first set of) batteries and POM (power organising module) and stored is in a small room referred to as the "systems package".
Earthships are designed to collect and store their own energy from a variety of sources. The majority of electrical energy is harvested from the sun and wind. Photovoltaic panels and windturbines located on or near the Earthship generate DC energy that is then stored in several types of deep cycle batteries. The space in which the batteries are kept is usually a special, purpose-built room placed on the roof. Additional energy, if required, can be obtained from gasoline powered generators or by integrating with the city grid.
Conversion and use
In an Earthship, a Power Organizing Module is used to take stored energy from batteries and invert it for AC use. The Power Organizing Module is a prefabricated system provided by Earthship Biotecture that is simply attached to a wall on the interior of the Earthship and wired in a conventional manner. It includes the necessary equipment such as circuit breakers and converters. The energy run through the Power Organizing Module can be used to run any house hold appliance including: Washing machines, computers, kitchen appliances, print machines, vacuums, etc. None of the electrical energy in an Earthship is used for heating or cooling.
The load bearing walls of an Earthship, which are made from steel belted tires rammed with earth, serve two purposes. First, they hold up the roof, and second, they provide a dense thermal mass that will soak up heat during the day and radiate heat during the night, keeping the interior climate relatively comfortable all day.
In addition to high thermal mass, some Earthships may be earth sheltered. The benefits of earth sheltering are twofold because it adds to the thermal mass and, if the Earthship is buried deep enough, allows the structure to take advantage of the earth's stable temperature.
Passive Solar Heating and Cooling
The Earthship is designed in such a way that the sun provides heating, ventilation and lighting. To take advantage of the sun, an Earthship (in the northern hemisphere) is positioned so that its southern wall, which is nonstructural and made mostly of glass sheets, faces directly south. This positioning allows for optimum solar exposure.
To allow the sun to heat the mass of the Earthship, the southern wall is angled so that it is perpendicular to light from the winter sun. This allows for maximum exposure in the winter, when heat is wanted, and lesser exposure in the summer, when heat is to be avoided. Some Earthships, especially those built in colder climates, use insulated shading on the southern wall to reduce heat loss during the night (Reynolds 2000).
The earthships usually use their own natural ventilation system. It consists of cold(er) air coming in from a front ("hopper") window, especially made for this purpose and flowing out trough (one of) the skylights that are placed on the eartship. As hot air rises, the system maintains itself and keeps sucking in (and out), air.
Earthships rely on a balance between the solar heat gain and the ability of the tire walls and subsoil to transport and store heat. The design intends to require little if any auxiliary heat. Some earthships have suffered from over-heating and some from over-cooling, because of a failure to adjust for local conditions.
Some earthships appear to have serious problems with heat loss. In these cases heat appears to be leaking into the ground constantly during the heating season and being lost. This situation may have arisen from the mistaken belief that ground-coupled structures (building in thermal contact with the ground) do not require insulation. The situation may also be due to large climatic differences between the sunny, arid and warm Southwest (of the USA) where earthships were first built and the cloudier, cooler and wetter climates where some are now being built. Malcolm Wells, an architect and authority on earth sheltered design, recommends R-value 10 insulation between deep soils and heated spaces. Wells's insulation recommendations increase as the depth of the soil decreases.
In very limited and specific situations, uncommon during the heating season, thermal mass can marginally increase the apparent R-value of a building assembly such as a wall. Generally speaking thermal mass and R-value are distinct thermodynamic properties and should not be equated. Thermal performance problems apparently seen in some earthship designs may have occurred because of thermal mass being erroneously equated to R-value.
According to the Kansas State University Extension Service the R-value of soil is about 1 per foot.