An intentional community is a planned residential community designed from the start to have a high degree of social cohesion and teamwork. The members of an intentional community hold a common social, religious, or spiritual vision and follow an alternative lifestyle, they share responsibilities and resources. Intentional communities include collective households, cohousing communities, ecovillages, communes, survivalist retreats, kibbutzim and housing cooperatives. New members of an intentional community are selected by the community's existing membership, rather than by real-estate agents or land owners; the purposes of intentional communities vary in different communities. They may include sharing resources, creating family-oriented neighborhoods, living ecologically sustainable lifestyles, such as in ecovillages; some communities are secular. One common practice in spiritual communities, is communal meals. There is a focus on egalitarian values. Other themes are voluntary simplicity, interpersonal growth, self-sufficiency.
Some communities provide services to disadvantaged populations. These include, but are not limited to, war refugees, homeless people, or people with developmental disabilities; some communities operate learning and/or health centers. Other communities, such as Castanea of Nashville, offer a safe neighborhood for those exiting rehab programs to live in; some communities act as a mixed-income neighborhood to alleviate the damages of one demographic assigned to one area. Many intentional communities attempt to alleviate social injustices that are being practiced within the area of residence; some intentional communities are micronations, such as Freetown Christiania. Many communities have different levels of membership. Intentional communities have a selection process which starts with someone interested in the community coming for a visit. Prospective community members are interviewed by a selection committee of the community or in some cases by everyone in the community. Many communities have a "provisional membership" period.
After a visitor has been accepted, a new member is "provisional" until they have stayed for some period and the community re-evaluates their membership. After the provisional member has been accepted, they become a full member. In many communities, the voting privileges or community benefits for provisional members are less than those for full members. Christian intentional communities are composed of those wanting to emulate the practices of the earliest believers. Using the biblical book of Acts as a model, members of these communities strive for a practical working out of their individual faith in a corporate context; these Christian intentional communities try to live out the teachings of the New Testament and practice lives of compassion and hospitality. Communities such as the Simple Way, the Bruderhof and Rutba House would fall into this category; these communities, despite strict membership criteria, are open to visitors and not reclusive in the way that certain intentional communities are.
A survey in the 1995 edition of the "Communities Directory", published by Fellowship for Intentional Community, reported that 54 percent of the communities choosing to list themselves were rural, 28 percent were urban, 10 percent had both rural and urban sites, 8 percent did not specify. The most common form of governance in intentional communities is democratic, with decisions made by some form of consensus decision-making or voting. A hierarchical or authoritarian structure governs 9 percent of communities, 11 percent are a combination of democratic and hierarchical structure, 16 percent do not specify. Many communities which were led by an individual or small group have changed in recent years to a more democratic form of governance. Community garden Cooperation List of intentional communities Utopian socialism Christian, D. Creating a Life Together: Practical Tools to Grow Ecovillages and Intentional Communities New Society Publishers. ISBN 0-86571-471-1 Curl, John Memories of Drop City, the First Hippie Commune of the 1960s and the Summer of Love: a memoir.
IUniverse. ISBN 0-595-42343-4. Kanter, Rosabeth Moss Commitment and Community: communes and utopias in sociological perspective. Cambridge, Massachusetts: Harvard University Press. ISBN 0-674-14575-5 McLaughlin, C. and Davidson, G. Builders of the Dawn: community lifestyles in a changing world. Book Publishing Company. ISBN 0-913990-68-X Lupton, Robert C. Return Flight: Community Development Through Reneighboring our Cities, Georgia:FCS Urban Ministries. Moore, Charles E. Called to Community: The Life Jesus Wants for His People. Plough Publishing House, 2016. “Intentional Community.” Plough, Plough Publishing, www.plough.com/en/topics/community/intentional-community. Intentional community at Curlie Intentional Communities website Intentional Communities Wiki Intentional Community For Media and Spirituality Diggers & Dreamers UK directory & Journal eurotopia European Directory of Communities and Ecovillages The Twitter Age Embraces Communal Living – slideshow by The New York Times International Communes Desk
Permaculture is a set of design principles centered around whole systems thinking simulating or directly utilizing the patterns and resilient features observed in natural ecosystems. It uses these principles in a growing number of fields from regenerative agriculture, rewilding and organizational design and development. With its system of applied education and citizen-led design permaculture has grown a popular web of global networks and developed into a global social movement; the term permaculture was developed and coined by David Holmgren a graduate student at the Tasmanian College of Advanced Education's Department of Environmental Design, Bill Mollison, senior lecturer in Environmental Psychology at University of Tasmania, in 1978. The word permaculture referred to "permanent agriculture", but was expanded to stand for "permanent culture", as it was understood that social aspects were integral to a sustainable system as inspired by Masanobu Fukuoka’s natural farming philosophy, it has many branches that include, but are not limited to, ecological design, ecological engineering, regenerative design, environmental design, construction.
Permaculture includes integrated water resources management that develops sustainable architecture, regenerative and self-maintained habitat and agricultural systems modelled from natural ecosystems. Mollison has said: "Permaculture is a philosophy of working with, rather than against nature, they include: Observe and Interact and Store Energy, Obtain a Yield, Apply Self Regulation and Accept Feedback and Value Renewable Resources and Services, Produce No Waste, Design From Patterns to Details, Integrate Rather Than Segregate, Use Small and Slow Solutions and Value Diversity, Use Edges and Value the Marginal, Creatively Use and Respond to Change. Several individuals revolutionized the branch of permaculture. In 1929, Joseph Russell Smith added an antecedent term as the subtitle for Tree Crops: A Permanent Agriculture, a book which sums up his long experience experimenting with fruits and nuts as crops for human food and animal feed. Smith saw the world as an inter-related whole and suggested mixed systems of trees and crops underneath.
This book inspired many individuals intent on making agriculture more sustainable, such as Toyohiko Kagawa who pioneered forest farming in Japan in the 1930s. In Australian P. A. Yeomans' 1964 book Water for Every Farm, he supports the definition of permanent agriculture, as one that can be sustained indefinitely. Yeomans introduced both an observation-based approach to land use in Australia in the 1940s and the Keyline Design as a way of managing the supply and distribution of water in the 1950s. Holmgren noted Stewart Brand’s works as an early influence to permaculture. Other early influences include Ruth Stout and Esther Deans, who pioneered no-dig gardening, Masanobu Fukuoka who, in the late 1930s in Japan, began advocating no-till orchards and gardens and natural farming. In the late 1960s, Bill Mollison and David Holmgren started developing ideas about stable agricultural systems on the southern Australian island state of Tasmania. Dangers of the growing use of industrial-agricultural methods sparked these ideas.
In their view, these methods were dependent on non-renewable resources, were additionally poisoning land and water, reducing biodiversity, removing billions of tons of topsoil from fertile landscapes. They responded with a design approach called permaculture; this term was first made public with their publication of their 1978 book Permaculture One. Among some of the more recognizable names who received their original training within Mollison's PDC system would include Geoff Lawton and Toby Hemenway, each of whom have more than 25 years experience teaching and promoting permaculture as a sustainable way of growing food. Simon J Fjell was a Founding Director of the Permaculture Institute in late 1979 and a teacher of the first Permaculture Design Course, having first met Mollison in 1976, he has since worked internationally and is listing a major social enterprise on NASDAQ. By the early 1980s, the concept had broadened from agricultural systems design towards sustainable human habitats. After Permaculture One, Mollison further refined and developed the ideas by designing hundreds of permaculture sites and writing more detailed books, such as Permaculture: A Designers Manual.
Mollison lectured in over 80 countries and taught his two-week Permaculture Design Course to hundreds of students. Mollison "encouraged graduates to become teachers themselves and set up their own institutes and demonstration sites; this multiplier effect was critical to permaculture’s rapid expansion."The permaculture movement spread throughout Asia and Central America, with Hong Kong-based Asian Institute of Sustainable Architecture, Rony Lec leading the foundation of the Mesoamerican Permaculture Institute in Guatemala and Juan Rojas co-founding the Permaculture Institute of El Salvador. The three core tenets of permaculture are: Care for the earth: Provision for all life systems to continue and multiply; this is the first principle. Care for the people: Provision for people to access those resources necessary for their existence Fair share: By governing our own needs, we can set resources aside to further the above principles; this includes re
A wetland is a distinct ecosystem, inundated by water, either permanently or seasonally, where oxygen-free processes prevail. The primary factor that distinguishes wetlands from other land forms or water bodies is the characteristic vegetation of aquatic plants, adapted to the unique hydric soil. Wetlands play a number of functions, including water purification, water storage, processing of carbon and other nutrients, stabilization of shorelines, support of plants and animals. Wetlands are considered the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal life. Whether any individual wetland performs these functions, the degree to which it performs them, depends on characteristics of that wetland and the lands and waters near it. Methods for assessing these functions, wetland ecological health, general wetland condition have been developed in many regions and have contributed to wetland conservation by raising public awareness of the functions and the ecosystem services some wetlands provide.
Wetlands occur on every continent. The main wetland types are swamp, marsh and fen. Many peatlands are wetlands; the water in wetlands is either brackish, or saltwater. Wetlands can be non-tidal; the largest wetlands include the Amazon River basin, the West Siberian Plain, the Pantanal in South America, the Sundarbans in the Ganges-Brahmaputra delta. The UN Millennium Ecosystem Assessment determined that environmental degradation is more prominent within wetland systems than any other ecosystem on Earth. Constructed wetlands are used to treat municipal and industrial wastewater as well as stormwater runoff, they may play a role in water-sensitive urban design. A patch of land that develops pools of water after a rain storm would not be considered a "wetland" though the land is wet. Wetlands have unique characteristics: they are distinguished from other water bodies or landforms based on their water level and on the types of plants that live within them. Wetlands are characterized as having a water table that stands at or near the land surface for a long enough period each year to support aquatic plants.
A more concise definition is a community composed of hydric soil and hydrophytes. Wetlands have been described as ecotones, providing a transition between dry land and water bodies. Mitsch and Gosselink write that wetlands exist "...at the interface between terrestrial ecosystems and aquatic systems, making them inherently different from each other, yet dependent on both."In environmental decision-making, there are subsets of definitions that are agreed upon to make regulatory and policy decisions. A wetland is "an ecosystem that arises when inundation by water produces soils dominated by anaerobic and aerobic processes, which, in turn, forces the biota rooted plants, to adapt to flooding." There are four main kinds of wetlands – marsh, swamp and fen. Some experts recognize wet meadows and aquatic ecosystems as additional wetland types; the largest wetlands in the world include the swamp forests of the Amazon and the peatlands of Siberia. Under the Ramsar international wetland conservation treaty, wetlands are defined as follows: Article 1.1: "...wetlands are areas of marsh, peatland or water, whether natural or artificial, permanent or temporary, with water, static or flowing, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres."
Article 2.1: " may incorporate riparian and coastal zones adjacent to the wetlands, islands or bodies of marine water deeper than six metres at low tide lying within the wetlands." Although the general definition given above applies around the world, each county and region tends to have its own definition for legal purposes. In the United States, wetlands are defined as "those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, that under normal circumstances do support, a prevalence of vegetation adapted for life in saturated soil conditions. Wetlands include swamps, marshes and similar areas"; this definition has been used in the enforcement of the Clean Water Act. Some US states, such as Massachusetts and New York, have separate definitions that may differ from the federal government's. In the United States Code, the term wetland is defined "as land that has a predominance of hydric soils, is inundated or saturated by surface or groundwater at a frequency and duration sufficient to support a prevalence of hydrophytic vegetation adapted for life in saturated soil conditions and under normal circumstances supports a prevalence of such vegetation."
Related to this legal definitions, the term "normal circumstances" are conditions expected to occur during the wet portion of the growing season under normal climatic conditions, in the absence of significant disturbance. It is not uncommon for a wetland to be dry for long portions of the growing season. Wetlands can be dry during the dry season and abnormally dry periods during the wet season, but under normal environmental conditions the soils in a wetland will be saturated to the surface or inundated such that the soils become anaerobic, those conditions will persist through the wet portion of the growing season; the most important factor producing wetlands is flooding. The duration of flooding or prolonged soil saturation by groundwater determines whether the resulting wetland has aquatic, marsh or swamp vegetation
Energy conservation effort made to reduce the consumption of energy by using less of an energy service. This can be achieved either by using energy more efficiently or by reducing the amount of service used. Energy conservation is a part of the concept of eco-sufficiency. Energy conservation reduces the need for energy services and can result in increased environmental quality, national security, personal financial security and higher savings, it is at the top of the sustainable energy hierarchy. It lowers energy costs by preventing future resource depletion. Energy can be conserved by reducing wastage and losses, improving efficiency through technological upgrades and improved operation and maintenance. On a global level energy use can be reduced by the stabilisation of population growth. Energy can only be transformed from one form to other, such as heat energy to motive power in cars, or kinetic energy of water flow to electricity in hydroelectric power plants; however machines are required to transform energy from one form to other.
The wear and friction of the components of these machine while running cause loss of quadrillions of BTU and $500 billions in industries only in USA. It is possible to minimize these losses by adopting green engineering practices to improve life cycle of the components; some countries employ carbon taxes to motivate energy users to reduce their consumption. Carbon taxes can force consumption to shift to nuclear power and other energy sources that carry different sets of environmental side effects and limitations. On the other hand, taxes on all energy consumption can reduce energy use across the board while reducing a broader array of environmental consequences arising from energy production; the state of California employs a tiered energy tax whereby every consumer receives a baseline energy allowance that carries a low tax. As usage increases above that baseline, the tax increases drastically; such programs aim to protect poorer households while creating a larger tax burden for high energy consumers.
One of the primary ways to improve energy conservation in buildings is to perform an energy audit. An energy audit is an inspection and analysis of energy use and flows for energy conservation in a building, process or system with an eye toward reducing energy input without negatively affecting output; this is accomplished by trained professionals and can be part of some of the national programs discussed above. Recent development of smartphone apps enables homeowners to complete sophisticated energy audits themselves. Building technologies and smart meters can allow energy users, both commercial and residential, to visualize the impact their energy use can have in their workplace or homes. Advanced real-time energy metering can help people save energy by their actions. In passive solar building design, windows and floors are made to collect and distribute solar energy in the form of heat in the winter and reject solar heat in the summer; this is called passive solar design or climatic design because, unlike active solar heating systems, it does not involve the use of mechanical and electrical devices.
The key to designing a passive solar building is to best take advantage of the local climate. Elements to be considered include window placement and glazing type, thermal insulation, thermal mass, shading. Passive solar design techniques can be applied most to new buildings, but existing buildings can be retrofitted. In the United States, suburban infrastructure evolved during an age of easy access to fossil fuels, which has led to transportation-dependent systems of living. Zoning reforms that allow greater urban density as well as designs for walking and bicycling can reduce energy consumed for transportation; the use of telecommuting by major corporations is a significant opportunity to conserve energy, as many Americans now work in service jobs that enable them to work from home instead of commuting to work each day. Consumers are poorly informed of the savings of energy efficient products. A prominent example of this is the energy savings that can be made by replacing an incandescent light bulb with a more modern alternative.
When purchasing light bulbs, many consumers opt for cheap incandescent bulbs, failing to take into account their higher energy costs and lower lifespans when compared to modern compact fluorescent and LED bulbs. Although these energy-efficient alternatives have a higher upfront cost, their long lifespan and low energy use can save consumers a considerable amount of money; the price of LED bulbs has been decreasing in the past five years due to improvements in semiconductor technology. Many LED bulbs on the market qualify for utility rebates that further reduce the price of purchase to the consumer. Estimates by the U. S. Department of Energy state that widespread adoption of LED lighting over the next 20 years could result in about $265 billion worth of savings in United States energy costs; the research one must put into conserving energy is too time consuming and costly for the average consumer when there are cheaper products and technology available using today's fossil fuels. Some governments and NGOs are attempting to reduce this complexity with ecolabels that make differences in energy efficiency easy to research while shopping.
To provide the kind of information and support people need to invest money and effort in energy conservation, it is important to understand and link to people's topical concerns. For instance, some retailers argue. However, health studies have demonstrated that headache, blood pressure and worker error all increase with the common over-illuminat
Greywater or sullage is all wastewater generated in households or office buildings from streams without fecal contamination, i.e. all streams except for the wastewater from toilets. Sources of greywater include, showers, clothes washing machines or dish washers; as greywater contains fewer pathogens than domestic wastewater, it is safer to handle and easier to treat and reuse onsite for toilet flushing, landscape or crop irrigation, other non-potable uses. The application of greywater reuse in urban water systems provides substantial benefits for both the water supply subsystem by reducing the demand for fresh clean water as well as the wastewater subsystems by reducing the amount of wastewater required to be conveyed and treated. Treated greywater has many uses, for irrigation. Greywater contains some traces of excreta and is therefore not free of pathogens; the excreta comes from washing a person's anal area from the laundry. The quality of greywater can deteriorate during storage because it is warm and contains some nutrients and organic matter, as well as pathogens.
Stored greywater leads to odour nuisances for the same reason. In households with conventional flush toilets, greywater makes up about 65% of the total wastewater produced by that household, it may be a good source of water for reuse, because there is a close relationship between the production of greywater and the potential demand for toilet flushing water. Misconnections of pipes can cause greywater tanks to contain a percentage of blackwater; the small traces of feces that enter the greywater stream via effluent from the shower, sink, or washing machine do not pose practical hazards under normal conditions, as long as the greywater is used correctly. In Hong Kong regional usage, an alternative term for blackwater is "foul water"; the separate treatment of greywater falls under the concept of source separation, one principle applied in ecological sanitation approaches. The main advantage of keeping greywater separate from toilet wastewater is that the pathogen load is much reduced and the greywater is therefore easier to treat and reuse.
When greywater is mixed with toilet wastewater, it is called sewage or blackwater and should be treated in sewage treatment plants or onsite sewage facility, a septic system. When it is kept separate, it may open up interesting decentralized reuse options. Greywater from kitchen sinks contains fats and grease and high loads of organic matter, it should undergo preliminary treatment to remove these substances before discharge into a grey water tank. If this is difficult to apply, it could be directed to the blackwater system or to an existing sewer. Most greywater is easier to treat and recycle than blackwater, because of lower levels of contaminants. If collected using a separate plumbing system from blackwater, domestic greywater can be recycled directly within the home, garden or company and used either or processed and stored. If stored, it must be used within a short time or it will begin to putrefy due to the organic solids in the water. Recycled greywater of this kind is never safe to drink, but a number of treatment steps can be used to provide water for washing or flushing toilets.
The treatment processes that can be used are in principle the same as those used for sewage treatment, except that they are installed on a smaller scale at household or building level: Biological systems such as constructed wetlands or living walls and bioreactors or more compact systems such as membrane bioreactors which are a variation of the activated sludge process and is used to treat sewage. Mechanical systems In constructed wetlands, the plants use contaminants of greywater, such as food particles, as nutrients in their growth; however and soap residues can be toxic to microbial and plant life alike, but can be absorbed and degraded through constructed wetlands and aquatic plants such as sedges and grasses. The global water resources are worsening. According to a report from United Nations states that 2.7 billion people will face the problem of water shortage by 2025, which means 1/2-1/3 of the total population of the world will be affected by this problem. Reusing the wastewater has become a good way to solve this problem, wastewater reuse is called recycled or reclaimed water.
Demand on conventional water supplies and pressure on sewage treatment systems is reduced by the use of greywater. Re-using greywater reduces the volume of sewage effluent entering watercourses which can be ecologically beneficial. In times of drought in urban areas, greywater use in gardens or toilet systems helps to achieve some of the goals of ecologically sustainable development; the potential ecological benefits of greywater recycling include Reduced freshwater extraction from rivers and aquifers Less impact from septic tank and treatment plant infrastructure Reduced energy use and chemical pollution from treatment Groundwater recharge Reclamation of nutrients Greater quality of surface and ground water when preserved by the natural purification in the top layers of soil than generated water treatment processesIn the U. S. Southwest and the Middle East where available water supplies are limited in view of a growing population, a strong imperative exists for adoption of alternative water technologies.
The potential economic benefits of greywater recycling include Can reduc
Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics, indirectly using concentrated solar power, or a combination. Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Photovoltaic cells convert light into an electric current using the photovoltaic effect. Photovoltaics were solely used as a source of electricity for small and medium-sized applications, from the calculator powered by a single solar cell to remote homes powered by an off-grid rooftop PV system. Commercial concentrated solar power plants were first developed in the 1980s; the 392 MW Ivanpah installation is the largest concentrating solar power plant in the world, located in the Mojave Desert of California. As the cost of solar electricity has fallen, the number of grid-connected solar PV systems has grown into the millions and utility-scale photovoltaic power stations with hundreds of megawatts are being built.
Solar PV is becoming an inexpensive, low-carbon technology to harness renewable energy from the Sun. The current largest photovoltaic power station in the world is the 850 MW Longyangxia Dam Solar Park, in Qinghai, China; the International Energy Agency projected in 2014 that under its "high renewables" scenario, by 2050, solar photovoltaics and concentrated solar power would contribute about 16 and 11 percent of the worldwide electricity consumption, solar would be the world's largest source of electricity. Most solar installations would be in India. In 2017, solar power provided 1.7% of total worldwide electricity production, growing at 35% per annum. As of 2018, the unsubsidised levelised cost of electricity for utility scale solar power is around $43/MWh. Many industrialized nations have installed significant solar power capacity into their grids to supplement or provide an alternative to conventional energy sources while an increasing number of less developed nations have turned to solar to reduce dependence on expensive imported fuels.
Long distance transmission allows remote renewable energy resources to displace fossil fuel consumption. Solar power plants use one of two technologies: Photovoltaic systems use solar panels, either on rooftops or in ground-mounted solar farms, converting sunlight directly into electric power. Concentrated solar power plants use solar thermal energy to make steam, thereafter converted into electricity by a turbine. A solar cell, or photovoltaic cell, is a device that converts light into electric current using the photovoltaic effect; the first solar cell was constructed by Charles Fritts in the 1880s. The German industrialist Ernst Werner von Siemens was among those who recognized the importance of this discovery. In 1931, the German engineer Bruno Lange developed a photo cell using silver selenide in place of copper oxide, although the prototype selenium cells converted less than 1% of incident light into electricity. Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the silicon solar cell in 1954.
These early solar cells cost 286 USD/watt and reached efficiencies of 4.5–6%. The array of a photovoltaic power system, or PV system, produces direct current power which fluctuates with the sunlight's intensity. For practical use this requires conversion to certain desired voltages or alternating current, through the use of inverters. Multiple solar cells are connected inside modules. Modules are wired together to form arrays tied to an inverter, which produces power at the desired voltage, for AC, the desired frequency/phase. Many residential PV systems are connected to the grid wherever available in developed countries with large markets. In these grid-connected PV systems, use of energy storage is optional. In certain applications such as satellites, lighthouses, or in developing countries, batteries or additional power generators are added as back-ups; such stand-alone power systems permit operations at other times of limited sunlight. Concentrated solar power called "concentrated solar thermal", uses lenses or mirrors and tracking systems to concentrate sunlight use the resulting heat to generate electricity from conventional steam-driven turbines.
A wide range of concentrating technologies exists: among the best known are the parabolic trough, the compact linear Fresnel reflector, the Stirling dish and the solar power tower. Various techniques are used to track the focus light. In all of these systems a working fluid is heated by the concentrated sunlight, is used for power generation or energy storage. Thermal storage efficiently allows up to 24-hour electricity generation. A parabolic trough consists of a linear parabolic reflector that concentrates light onto a receiver positioned along the reflector's focal line; the receiver is a tube positioned along the focal points of the linear parabolic mirror and is filled with a working fluid. The reflector is made to follow the sun during daylight hours by tracking along a single axis. Parabolic trough systems provide the best land-use factor of any solar technology; the SEGS plants in California and Acciona's Nevada Solar One near Boulder City, Nevada are representatives of this technology.
Compact Linear Fresnel Reflectors are CSP-plants which use many thin mirror strips instead of parabolic mirrors to concentrate sunlight onto two tubes with working fluid. This has the advantage that flat mirrors can be used which are much cheaper than parabolic mirrors, that more reflectors can be placed in the same amount of space, allowing more of the available sunlight to be used. Concentrating linear fresn
A natural building involves a range of building systems and materials that place major emphasis on sustainability. Ways of achieving sustainability through natural building focus on durability and the use of minimally processed, plentiful or renewable resources, as well as those that, while recycled or salvaged, produce healthy living environments and maintain indoor air quality. Natural building tends to rely on human labor, more than technology; as Michael G. Smith observes, it depends on "local ecology and climate. To be more sustainable, natural building uses abundantly available, reused or recycled materials; the use of renewable materials is a focus. In addition to relying on natural building materials, the emphasis on the architectural design is heightened; the orientation of a building, the utilization of local climate and site conditions, the emphasis on natural ventilation through design, fundamentally lessen operational costs and positively impact the environment. Building compactly and minimizing the ecological footprint is common, as are on-site handling of energy acquisition, on-site water capture, alternate sewage treatment and water reuse.
The materials common to many types of natural building are sand. When mixed with water and straw or another fiber, the mixture may form cob or adobe. Other materials used in natural building are: earth, straw, rice-hulls and stone. A wide variety of reused or recycled non-toxic materials are common in natural building, including urbanite, vehicle windscreens and other recycled glass. Other materials are avoided by practitioners of this building approach, due to their major negative environmental or health impacts; these include unsustainably harvested wood, toxic wood-preservatives, portland cement-based mixes and derived products such as Autoclaved aerated concrete and other coatings that off-gas volatile organic compounds, waste materials such as rubber tires in regions where they are recycled, some plastics. Many traditional techniques and materials are now experiencing a resurgence of popularity; this differs around the world based on climate appropriate building design and the availability of local materials.
One of the oldest building methods, adobe is clay and sand mixed with water. Chopped straw or other fibers are added for strength; the mixture is allowed to dry in the desired shape. Adobe is shaped into bricks that can be stacked to form walls. Various claims are made about the optimal proportions of sand; some say that the best adobe soil contains 15% - 30% clay to bind the material together. Others say equal proportions of clay and sand are best to prevent cracking or fragmenting of the bricks; the blocks dried, or pressed into blocks. Adobe colored with clay and polished with natural oil makes an resilient floor. To protect the walls and reduce maintenance, adobe buildings have large overhanging eaves and sizeable foundations. Adobe can be plastered over with cob or lime-based mixes for both protection. Adobe has good thermal mass, meaning that it is slow to transmit cold, it is not a good insulator, however, so insulation can be added, or a double wall built with airspace or insulation in between.
The traditional thick, un-insulated adobe has proven to perform best in regions without harsh winters or where daily sun is predictably available during those cold periods. The term cob is used to describe a monolithic building system based on a mixture of clay, sand and earth; the construction uses bricks or wooden framework. Various forms of "mud" building have been used in many parts of the world for centuries, under a variety of names, date from at least 10,000 years ago. Cob building began use in England prior to the 13th century, fell out of favor after World War I, although it is seeing a resurgence today. Cob is one of the simplest and least expensive building techniques available, though it is very labor-intensive. Cob's other great advantage is versatility. While cob building was falling out of favor in England by the late 19th century, thousands of cob structures have endured to the present, it is estimated that from one third to one half of the world's population lives in earthen dwellings today.
Although associated with "low-rise" structures, in Yemen and other Middle-Eastern countries it has, for centuries, been used in "apartment" buildings of eight stories and more. Cob-like mixes are used as plaster or filler in several methods of natural building, such as adobe, earth bags, timber frames and straw bales. Earth is thus a primary ingredient of natural building. Cordwood construction is a term used for a natural building method in which "cordwood" or short lengths of pieces of debarked tree are laid up crosswise with masonry or cob mixtures to build a wall; the cordwood, becomes infill for the walls between posts in a timber frame structure. Cordwood masonry can be combined with other methods to produ