An Overview of Natural Building Techniques
Over the past several decades, numerous vernacular building methods have been investigated and, in some cases, revived and improved upon by a new breed of visionary designer-builder. These techniques are often grouped under the label natural building, a building philosophy that relies on materials and techniques which are ecologically sound, culturally sensitive, reliant on local resources and skills, and are within economic reach of local inhabitants, many of whom cannot currently afford shelter.
Natural building has emerged as a response to an increasing concern for our built environment. Natural materials are an alternative to toxic substances which have led to widespread environmental illness. Those seeking to simplify their lives can build their own homes using such techniques, with community help and local, inexpensive materials. Those who recognize the environmental, social and economic costs of our current ways of construction believe that natural building provides part of the solution to the complex worldwide problem of sustainable living.
While interest in natural building has surged in the Industrialized West, many ancient roots have been lost in traditional areas in favor of capital- and energy-intensive industrial building methods. In the name of progress, crucial cultural and technological riches continue to be abandoned for concrete blocks, tin shacks and other degraded symbols of an untenable Western dream. Ironically, some builders in industrialized countries are now turning to these very cultures for solutions to their building problems. It is to be hoped that a resurgence of interest and research into vernacular building systems will increase respect for these timeless ideas in their native lands. And through diligent efforts, many of these techniques are indeed being revived, studied and implemented throughout the world.
Though often appropriate in their original contexts, many ancient techniques are benefiting from scientific and engineering study, creating applications for a variety of new situations. These techniques are being validated by modern structural and other code tests, which also point out directions for further research and improvement.
Adobes are sun-dried mud bricks stacked with a mud mortar to create thick-walled structures. These thick earthen walls provide what is known as thermal mass which helps to modulate interior temperatures by absorbing excess heat during the day and slowly releasing it at night. (In chilly climates, thermal mass needs to be insulated to prevent creating a net heat loss in winter.) The use of adobes dates back centuries in traditional earth-building areas such as North Africa, the Middle East, South America and the United States Southwest. While in some areas this building method is in decline, it is still in widespread use in others. Dramatic examples of vaulted and domed structures built entirely of earth bricks still stand after centuries in the Middle East, testament to adobes timeless beauty and structural integrity.
While in developing countries its use is mostly confined to those too poor to have access to other building materials, in the Southwest U.S., adobe is often used by the very rich, illustrating its wide appeal. Adobe is appropriate in areas which are labor-rich and capital-poor, because it is labor intensive, using local materials and simple tools.
Adobe bricks are made with a completely saturated mixture of clay and sand (and sometimes straw or manure), poured or pressed into forms, which are removed either immediately or after the brick has partially dried. Adobes can take an infinite number of shapes and sizes which are utilized for specific techniques (i.e. small flat square bricks used to build leaning arches and domes in Iran). After the bricks have dried for several days, they are turned on edge for further drying, then stacked for transport or for use on site. The adobes are laid on an appropriate foundation (usually stone or concrete) using typical masonry techniques with thick joints to take up the difference in size of the adobes. Typically, mud mortar is used, but a concrete- or lime-based mortar can also be used. Various stabilizers for the adobes themselves have been developed, with most, however, relying on cement or asphalt-based compounds.
While adobe is widely appropriate, precautions must be taken to ensure the durability of construction. Wide eaves are often necessary to protect the walls from rain and foundations must protect the walls from ground moisture, while gutters are used to prevent splashing. Mud plaster is traditionally used to finish adobe structures, only requiring replenishment every few years if the walls are unprotected.
Cement stucco has also been used in an effort to provide longer-lasting exterior coatings, but in many cases has proven to be destructive, as the brittle stucco can crack, letting in water which dissolves the underlying adobes. Because the stucco often hides this damage, buildings can collapse before anything is sensed to be wrong. In addition, indoor water vapor cannot escape fast enough and builds up on the inside of cement stucco, eroding the wall. Because of this, there has been a return to traditional plasters using mud, straw and other natural materials.
Because the mortar can be a weak link in adobe construction, building codes typically place severe restrictions on it. While other, monolithic techniques, such as cob and rammed earth may fare better in earthquake-prone areas, these, along with adobe are essentially limited to the desert Southwest.
Bamboo is the largest of the grass family of plants. It grows very quickly, providing renewable material for building, tools, and utensils as well as edible shoots. Common in the tropics, many species of bamboo grow in temperate climates as well. Strong and beautiful, bamboo has seen a recent resurgence in popularity with builders.
Bamboo as a building material is not commonly known in North America because of limitations on the import of living plants, lack of knowledge of traditional techniques, and because there are so few native species. This ignorance is beginning to change, however, as timber prices rapidly escalate, and western builders become aware of innovative uses of bamboo that have originated in Asia, Central America and South America.
Utilized for millenia on these continents, bamboo is often used, as the west uses wood and steel, for structural purposes. It can replace rebar in certain concrete applications, be used as pins in straw-bale construction, to create trusses and other structural members, as decorative elements, and has even been used as plumbing.
Its widespread use in tropical areas, as well as unsustainable harvest for export, can also be dangerous however, as indiscriminate cropping can decimate stands and endanger interdependent ecosystems. To address this danger, efforts to create sustainable growing programs similar to those for tropical hardwoods are in development.
Cob is an ancient technique of building monolithic (meaning all one piece) walls using cobs of moist earth and straw that has similar thermal properties to adobe and rammed earth. It is being rediscovered as a multifaceted building material applicable to a number of conditions. Virtually unknown in North America, cob was reintroduced by Welsh architect and permaculturist Ianto Evans, who started the Cob Cottage Company with his wife Linda Smiley after intense interest in his $500 self-built cob home. A sculptural technique which lends itself to curved organic shapes, cob requires minimal tools and can be built by young and old alike. Oregon cob is quite a different process than traditional methods, improving some aspects of the technique through increased attention to design, materials selection and application procedures.
The process of building with cob entails mixing local subsoil with sand and/or clay (depending on the composition of the base earth) and straw or other fibrous materials to create a stiff mud which is formed into small loaves (cobs). These cobs can be tossed to the builder on the wall who mashes them together to form a monolithic wall on top of a stone or concrete foundation. Cob can also be forked as a mass onto the wall, then shaped into the next layer.
The relatively thick walls (they have been known to be up to six feet thick) proceed in layers or lifts from 6 to 18 high. Attempts to build higher than this can result in slumping. After a period of time to let each layer solidify, work can continue. Irregularities can be shaved off with a spade or other sharp tool as work progresses.
A particular favorite of natural builders for its ease, sculptural qualities, strength, and thermal mass, cob is also useful in combination with other techniques. Windows and other details are cobbed into place, and niches and reliefs are easy to create. While extremely economical for owner-builders, cob is very labor intensive and time consuming, with walls taking up to a year to fully cure. In addition, the curving architecture currently advocated is not to all tastes.
Cob has been used mostly in informal or experimental buildings in the U.S. while code-testing procedures are investigated, but now several isolated projects are receiving permits. Traditional cob construction is undergoing a revival in England as well, where proponents are rediscovering five hundred year old houses in perfect condition, and new projects are reinvigorated this nearly-lost craft.
Compressed earth blocks are similar to adobes, with the main differences being they are not fully saturated with water, are more dense than adobes, and are usually significantly more uniform. These blocks are created using a variety of machines. Some, like the Cinva-Ram invented in South America, use human labor and are relatively inexpensive. Expensive fuel-powered machines, on the other hand, can produce thousands of bricks in a day.
Because of their uniformity, compressed earth blocks need little mortar, and can even be dry-stacked. This uniformity also speeds up the laying process and results in straighter walls. A house was built several years ago by CRATerre, a French earthbuilding education and research group, in a total of 24 hours using compressed earth blocks.
More recently, an inexpensive, innovative machine has been invented in Auroville, India, which can make a wide variety of sophisticated block shapes using human power. This machine was demonstrated at the UN Habitat II conference in Istanbul, where a domed prototype house was built in a week by volunteers and local labor.
A technique traditional to Northeast America and other heavily forested areas is the use of small lengths of wood as a masonry unit mortared with a cement-based mortar. An insulation layer of sawdust is used between the inner and outer mortar layers. This construction technique has been most prominently advocated here by Rob Roy, who has built a number of houses and saunas using the technique.
Cordwood can take advantage of small-diameter trees not useful for other building purposes where these trees are plentiful. It is relatively quick and easy to build. Differing rates of contraction can result in small gaps between the mortar and wood, leading to air or insect infiltration. Recent experiments have utilized cob as a replacement for the cement mortar, with good results.
Earthbags are soil-filled fabric sacks or tubes used to create walls and domes. Commonly used for flood control and by the military to create bunkers, this method of construction has been recently turned to a variety of natural-building purposes. This technique has been used by Gernot Minke of Germany and is currently being pioneered in the U.S. by Persian architect Nader Khalili of the California Institute of Earth Art and Architecture (Cal Earth), who has dubbed the technique superadobe.
The use of earthbags is still in its infancy, but holds much promise as a quick, easy and forgiving technique which uses minimally-processed soil and few tools. To build with this technique, moistened soil is placed into a bag set in place on the wall, the bag is lowered into place, then compressed using a hand tamper.
Heavy earth mixtures can be used with weaker burlap bags as the compressed soil makes the bags redundant once it sets, while stronger, structural polypropylene bags are preferable for sandy soils. The polypropylene deteriorates with prolonged exposure to sunlight, so it is important that the structures are plastered quickly. Long tubes of the bag material are filled and stacked like a coiled ceramic pot. Recycled sacks are often available free or at minimal cost.
In earthquake prone areas, a layer of long-barbed wire is used as mortar between the bags to contain slipping. Domes using these materials are easily achieved with a corbelling system. An experimental lightweight dome was created at Cal Earth by stuffing the bags with a straw-clay mixture, which were dried and then placed.
Numerous natural builders have taken to using the bags as simple foundations for straw-bale or cob structures, or for simple site walls. Recent projects in Mexico, Nova Scotia and New Mexico have used gravel-filled bags as foundations for straw-bale walls to minimize rising damp.
Disadvantages with earthbag construction are that resulting structures may seem excessively organic to some and also require quite of lot of plaster in order to create smooth walls. Advantages of this technique include the opportunity to build in wet conditions and in sites prone to flooding. Cheap and easily transported, the bags could also be used for temporary or disaster relief housing. Successful ICBO-approved testing has been undertaken by Cal-Earth, and a code-approved public project is currently underway in Hesperia, California.
The use of tamped or poured earth mixtures to create floors is currently undergoing a renaissance in the Southwest U.S. These floors can provide an excellent source of thermal mass in passive solar designs. Methods range from the African use of fresh cow dung sealed with ox blood, to earth mixtures sealed with linseed oil and beeswax.
The technique involves pouring or tamping one or several layers of an earth mixture over a substrate of gravel, pumice or sand (a sublayer of straw-clay has also been used for insulation by builder Robert Laporte). Hardening agents such as blood, lime, cement or glue may be added. This mixture is allowed to dry and any cracks are filled with more mud mixture. Cracking can be allowed to occur at random, resulting in a flagstone-like pattern, or can be controlled by incising the floor to create a tile-like effect. When the floor is entirely dry, it is sealed, most commonly with successive applications of linseed oil and turpentine. The floor is most often coated with wax to protect the surface.
Minor disadvantages of this system are its relative damageability and need for maintenance. This labor-intensive system can also be time consuming to install because of long drying times. Advantages include its aesthetic values, softness to the feet, and reliance on cheap, often free local materials.
Earthships are the name for the independent living structures utilizing passive-solar design and recycled materials developed by Michael Reynolds of Solar Survival Architecture. While not exclusively reliant on natural materials, Earthships replace some conventional materials with recycled trash which is found all over the planet.
Earthships are a system rather than a technique: initially, the structure is dug into a south-facing hillside; soil-filled tires are then stacked like giant bricks to form side and interior walls providing a source of thermal mass. Old bottles and cans are used to create interior walls and a variety of detail features, and to fill in gaps between tires. The building is framed in wood on the south side and roofed to collect rain water. Other systems include integrated wastewater treatment, photovoltaic electrical systems, solar hot water and passive-solar heating.
Advantages of the system include near-total self-sufficiency, the use of recycled materials and local soil, and technical and aesthetic sophistication. Disadvantages include the complexity of building such a structure and the sometimes-overwhelming amount of labor required. Summer overheating can also happen.
The Earthship concept has become a well-known and popular alternative building system, especially in northern New Mexico. Several Earthship communities have been built, and the system has received widespread media attention. Other builders have used the stacked tire concept to build houses which dont contain all of the systems of Reynolds designs.
Hybrid buildings are a fascinating outgrowth of the efforts of a few visionary natural builders and the sharing of ideas in the Natural Building Colloquia. The basic concept is that several techniques can be combined for increased building efficiency or unique artistic effect. An example is to combine a thermal-mass technique such as cob or rammed earth on the south side of a house, with an insulative system such as straw bales or straw-clay on the north, east and west sides, taking advantage of the best qualities of each system. New solutions to common problems have begun to evolve from such creative combinations.
A disadvantage of this approach is the lack of practitioners with wide experience in a number of techniques, pointing to the need for increased communication and sharing of ideas, and the elimination of dogmatic insistence on the preference of one system over another.
Leichtlehm (literally light-loam) is a German technique of coating loose straw with a clay slip and tamping it into forms as an infill for timber-frame structures. This technique was introduced to North America by Robert Laporte, a Canadian timber-framer, and by Frank Andresen, a builder with extensive natural building experience in his native Germany.
The technique consists of surrounding a frame structure with a thick infill of the straw-clay mixture. The frame is usually fully expressed on the interior of the building to take advantage of the beauty of the timber frame joinery. A lighter frame of wood is built on the eventual outside face of the building as an anchoring system for the straw-clay walls.
Loose straw and a clay slurry are tossed with pitchforks or mixed mechanically, then allowed to age for up to several days in order to allow the straw to absorb the extra moisture and thus create a stickier, more durable and more easily-tamped mixture. For higher insulation values lighter tamping or less clay can be used. Slip forms are set up between the framing members, and the straw-clay mixture is tamped by hand and foot in layers.
Occasional horizontal members spanning between the exterior frame are placed in order to lock in the straw-clay mass. Frank Andresen places the ends of these horizontal members at the upper ends of vertical slots in the frame in order to allow for shrinkage of the straw-clay as it dries. Once each layer is complete, the slip form is moved up and the next layer is tamped until the wall is complete. The walls are allowed to dry before final plastering occurs. Any shrinkage is taken up by stuffing more of the mixture into the cracks.
Robert Laporte commonly uses straw-clay stuffed loose between rafters as insulation, with the clay discouraging pests. He has also used it as an insulating layer underneath earthen floors. Frank Andresen has demonstrated a system of straw-clay tiles which can be placed between roof rafters as insulation and as a plastering surface. Hes also introduced straw-clay bricks that can be used like lightweight adobes.
A variant on the straw-clay technique utilizes wood chips or other materials mixed with clay; the resulting mixture is poured into removable forms. This technique can also be used to create lightweight bricks.
Highly accurate buildings are possible with the timber frame and straw-clay technique, allowing a natural structure which compares in looks to conventional stick-frame housing, making it an appealing option for some homeowners. Some disadvantages of the technique include its highly labor intensive nature, and the long drying time. The straight walls achievable with this method, however, are desired by builders in southern countries who seek a western look in their houses, and to whom an organic structure is old-fashioned.
Hemp and other fiber-producing plants as kenaf and sawgrass are currently being investigated as potential building products. Commonly used for numerous purposes before drug laws made its cultivation illegal, non-psychoactive hemp is being rediscovered as a source of fiber, oil, and hurd; these can replace less ecologically sound wood or petrochemical products in a variety of building applications.
Examples include a company using hemp to create a pressed board product to replace plywood, and another which uses the inner pith or hurd as an additive for a lime-based concrete-like material. Similar studies and experiments are being done with Kenaf and other fibers.
Hemp and other fibers have several advantages as they provide four times the usable fiber per acre as wood, grow in degraded soils, and need little chemical processing. Such advantages are leading these annually renewable crops to be considered more and more seriously. Several European countries, including England, Hungary and the Ukraine, have joined major hemp producers such as China to grow this neglected and useful plant for a variety of uses.
Drawbacks include the reliance on expensive imported fiber because of misguided laws which outlaw the growing of non-psychoactive strains of the plant in the U.S. Domestic manufacturers are also hampered by the lack of modern processing machinery.
The Archibio architecture group in Quebec as well as rammed-earth builder David Easton, have updated the ancient sod roof of Europe with a concept called the living roof. This type of roof has several advantages: it is an aesthetic feature, helps the house blend into its environment and provides climatic stabilization. While it is particularly useful in wet snowy areas, it has limited applicability in dry climates.
A living roof is built on top of a sufficiently strong frame with carefully applied waterproofing, as it is very difficult to locate leaks once the growing medium is in place. The living roof itself is a compost-based system, usually a base of straw left to decompose, within which native or introduced plants can then take root.
The living roof will need ongoing tending, and it could be a fire hazard in hot dry climates. It also doesnt provide much insulation value when wet, which must be considered for heating needs. It is advantageous in that it protects the waterproofing from damage by ultraviolet radiation, and precludes the need for tiles or other shingles.
Before the advent of portland cement, most earthen and masonry structures were protected by mud- or lime-based plasters. While still common in other parts of the world, lime and mud plasters are relatively rare in the U.S. The advantages of these plasters include breathability, softness to the touch, aesthetic qualities, workability and easy reparability, as well as economy of materials. Because they can erode unacceptably in wet vicinities, exterior mud plasters are generally used in drier climates or with wide overhangs.
Less brittle than cement-based plasters, those based on lime or mud adhere and move with the underlying wall, lessening cracks and often making stucco netting unnecessary. They have fallen into disuse in the U.S. because of their disadvantages: slow curing times, the need to renew them every several years and discrimination against their use by building codes. Proper lime putty traditionally used for building is unavailable in the United States, forcing builders to rely on the much-inferior dried hydrated lime.
However, as the limitations of cement-based plasters become increasingly evident, many natural builders are returning to ancient plastering techniques from around the world. Traditional plaster and paint recipes and application methods can be found inThe Straw Bale House,Build It With Bales, andThe Earth-Builders Encyclopedia.
Printer Eric Patterson of New Mexico rediscovered a use for his (and anyones) waste paper. He re-pulps this paper and mixes it with cement, making lightweight, strong and easily-worked paper blocks. Builder Mike McCain is currently advocating the system with low-tech mixers and block-making techniques which can greatly speed the building process. His mixture has also been used to plaster earthbag domes. While most recipes call for as much cement as is used in a solid concrete wall, some practitioners are experimenting with clay as a binder to make a lightweight earthen wall. These walls can be extremely susceptible to water damage. Concerns also include flammability with some examples having burned, and the effects of freeze-thaw. Relatively new in the US, only a few examples of this system currently exist, including some domed and vaulted structures, with varying degrees of success. Some reports have indicated this material was manufactured and used extensively in Europe, but is no longer preferred because of performance problems.
Rammed earth is an ancient earthbuilding technique currently undergoing a renaissance in the U.S. and abroad. It has been revived in France by CRATerre, in Australia by Giles Hohnen and others, while its main proponent is the U.S. is David Easton, author ofThe Rammed Earth House. Usually more expensive than conventional construction,this technique has been updated with improved engineering, sophisticated forms, and innovative design to make rammed earth competitive with conventional construction, even in earthquake-prone California. While rammed earth is in limited use in the U.S., builders in western Australia have captured up to 20% of the housing market in many areas.
Rammed earth has the advantage of excellent thermal mass (which in some climates would be a detriment unless insulated) as well as strength, comfort and beauty. Rammed earth can be built with simple forms and tools with less handling than other earthbuilding techniques, as the material cures in the wall, and can be built in a variety of climates. Walls do not need to be plastered and will last for hundreds, even thousands of years (the great wall of China is partially built of rammed earth). It has been used to build structures of up to seven stories in Yemen.
First setting up forms on top of an appropriate foundation (usually stone or concrete), a soil mixture with a clay content of 20% and a moisture content of 10% is then rammed in layers or lifts of 6-8 inches using mechanical or hand tampers. Different soil types can be layered to create decorative effects and the whole is topped by a concrete bond beam which then holds the roof. Procedures are discussed in detail inThe Rammed Earth Housebook.
To build efficiently for the North American market, David Easton has developed sophisticated forms and tools which decrease time and labor costs. It is still extremely labor intensive, and codes demand intensive reinforcing in earthquake-prone areas.
In an effort to make rammed earth even more competitive, Easton has developed a system called Pneumatically Impacted Stabilized Earth (PISE). In this system moist earth is sprayed against a single form allowing thick walls to be built extremely quickly.
In an effort to lessen waste, many builders are seeking to reuse materials which would otherwise end up as trash. Many structures, especially in urban areas, can be effectively rehabilitated, saving immense amounts of new construction costs, maintaining important cultural links, as well as avoiding massive amounts of landfill waste. Other structures can be carefully dismantled, saving lumber, bricks and other recyclables for new projects. High quality old-growth timber has been salvaged from old barns which is then used for new homes.
Waste wood can be reused to create a number of board products. Many of these, unfortunately, depend on toxic binders, but efforts to make healthy alternatives continue. Additionally, sawdust and recycled plastic have been used to create long-lasting lumber substitutes. Efforts in these areas have been spearheaded by the Wood Reduction Clearinghouse.
Windows, doors and other fixtures can be refurbished and reused, saving valuable architectural heritage and creating unique resources for owner-builders. Others use junk in innovative ways.
The advantage of this approach is the obvious environmental benefits as well as the aesthetic possibilities. Disadvantages include the time, labor and cost to build with old treasures because of refurbishment, special detailing necessary, and the time spent to find, dismantle and transport these resources.
The use of baled straw to create superinsulated walls has become an extremely popular method of construction in recent years. Most common in North America, bale buildings have been built around the world. Originally used by the pioneers of the Nebraska sandhills, straw bales are cheap to buy and easy to build with, lending themselves to barn-raising parties, where structures and community are created at the same time.
Straw is an annually renewable crop, available wherever grain crops are grown. It is indeed a waste product, much of which is currently burned in the field. The thick wal