What is Natural Building?
Natural building Methods and materials
Natural Building involves a range of building systems and techniques that prioritize the use of minimally processed, locally available, abundant and renewable materials. Natural building walls systems are going to look different depending on where you are in the world, who is building the structure, and what the needs are of the building once it is done. Part of what defines natural building is the buildings relationship to place. A building that is built of and for a place and reflects the available materials and needs of that place.
These are clay Obos of the Musgum people in Pouss, Cameroon.
Earth in its many forms is not only the most common material used in natural building systems; it is also the most common building material used at all.
What makes sense in one location is not always the best option in another location. I have spent most of the last 15 years living in desert locations where earthen is a very common, and appropriate building materials. Both due to the abundance of buildable soils, but also due to the high thermal mass helping to mitigate the diurnal temperature extremes. I have also worked a fair bit in Alaska, where thermal mass is not what creates a comfortable structure, and with such a wet short building season, earth is not very easy to work with. Wood is a much better option for such a climate and situation. Ever since humans began building permanent houses 10,000 years ago, earth has been the most common building material. All inhabited continents and even most countries have a history of building with unbaked earth in some form. Even today, more than one third of all humans live in homes built of earth.
The Hakka roundhouses of Fujian were built to house hundreds of people
The style of earthen buildings and their materials vary greatly from one region to another, and sometimes from one village to another within the same region. This diversity is due to the materials at hand, the local climate, and the skill and knowledge passed down through the generations as tradition. Different methods of earthen building have developed organically over generations to fit with different cultures needs and available materials. Most of these structures are some combination of aggregate, clay, fiber and water, but the different proportions of these materials can produce a multitude of techniques and composite materials for a large variety of uses. For example, the fiber used can range from horse hair to branches, the aggregate may range from sand to large stone. In all these parts of the world earthen architecture reflects the local environment and the spirit of the builders, dwellers, and history of that place. This is due to an understanding of the importance of a sense of place, as well as a necessity to use the materials at hand. Without the means of mechanical transportation, we would all be building with the materials found closer to our building sites, and our structures would inherently reflect the natural and cultural surrounding.
Currently, over 1,500,000,000 people live in unbaked earth homes. In developing countries, it is estimated that about 50% of people live in earthen homes. In Africa the earthen building may be more widespread than anywhere else on earth. From banks in Niger to granaries and humble huts in Cameroon, to town houses in Mali, earth is by far the dominant building material. In the Middle East earthen architecture also has a long history. Techniques of barrel vaults and domes were perfected in Iran, and in the southern region of Yemen there are cob buildings more than 10 stories high. In China, in the provinces of Henan, Shanxi, and Gansu, more than 10 million people are estimated to live in homes dug out of the loess layer of earth. These living earthen building traditions are not limited to developing nations. In Germany houses that are ½ timber framed with an infill of clay and straw fibers still can be found in abundance. In England the countrysides are still covered with several hundred-year-old cob buildings. In the southwestern part of the US there is still a plethora of adobe buildings.
With the development of modern day transportation, our ability to transport building materials was born. People no longer had to rely on their local environment for materials. As the transportation systems developed and increased, so did the homogenization of our built environment. Today building materials are transported all over the world, enabling the ability to create identical buildings in all parts of the world. Today’s natural building movement is rooted in getting back to using local materials.
Modern Day Natural Building
The natural building movement that we are experiencing today is based on our own choices and philosophy, rather than it being the only way to build that our ancestors experienced. Today’s natural building is based on a philosophy that places the highest value on social and environmental sustainability. Natural building is about integrating our built environments into their local ecologies and communities with a minimal amount of adverse effects on local and distant environments and societies. We believe that natural building improves lives in many ways. It allows us to show deep respect for our immediate environment and gives us the chance to make responsible decisions regarding distant environments.
Hybrid earthen house in Southern CA
This house is made of several different types of earthen wall systems, including Cob, Earthbag, light straw clay, and more.
Most of our grandparents, including those of us from the industrialized North, practiced natural building. Before the advent of standardization, mass production, and long-distance transport, people relied on locally available materials to house their family. During the last century there has been a shift towards the import of building materials, causing disastrous effects on ecosystems, cultures, and communities. But we have a choice. By exchanging earth and straw bale for concrete and cement, by choosing locally milled lumber and roundwood over lumber that has been unsustainably harvested, and opting for natural clay plasters, washes, and paints instead of dangerous chemical varnishes, stuccoes and paints, we can exert a force to affect change in our economies and in our lifestyles.
Wall Building Systems
Cob is s a load bearing, monolithic method of building with earth. It is a combination of enough clay to hold together the sand, enough sand to keep the clay from cracking, enough straw to give it tensile strength, and enough water to make the mixture malleable. The material is worked into the wall while still wet, creating a monolithic wall. Typically no forms or dried bricks are used, but rather hand or spadefuls of materials are built directly onto the foundation and wall.
Cob
Students building with cob during a workshop
Adobe is a sun dried block or brick made of mud, sometimes with the addition of straw. Adobe blocks are traditionally shaped by hand or with wood or metal molds; today they are often made by machines.
An adobe building in Tucson, AZ
Rammed Earth is a method of compressed earth using frames. This creates a monolithic wall, which often has a cement stabilizer added to the earthen mixture. The ‘ramming’ or compaction can be done by hand, but is mostly done with machinery.
Straw Clay is very clayey soil mixed with water to create a clay slip, and than mixed with straw. There is enough clay to coat the straw and ‘glue’ the straw together. This material is then compacted into temporary forms either in place, or in molds to make bricks or wall panels. This method of building can also incorporate wood chips, sawdust, pumice or perlite as a substitute for the straw.
Wattle and Daub is a non load bearing method of wall building. The wattle is a lattice of flexible branches or twigs woven together to form a surface to apply the daub. The daub is a earthen mixture similar to cob. This is ‘daubed’ on to the wattle. This method of building is used for thin, often interior, non-load bearing walls. This is perhaps the first building method used, as humans daubed mud onto branches to fill holes.
Materials
It is important to understand the properties of the materials you use, rather than simply memorizing the common building techniques or recipes. By understanding the function each material serves, you are not limited to using just the materials you know. Once you understand the properties of the materials, then you can improvise and use the variety of materials you have available, and not be limited to the ones you have seen someone else use, or read about in a book. Every site and location has different materials available, opening our eyes to be able to see them is often the most challenging part. I am going to go through the different materials used commonly in earthen building.
Clay is perhaps the most common earthen building material. When we say ‘clay’, we simply mean sediment with some clay content in it; many naturally occurring sediments are a mixture of clay, sand, silt and gravels, the amount of clay in the sediment can range greatly. Clay works like glue an earthen building. The higher the percentage of clay in the sediment, the more of other materials you need to add to produce the proper mixture. Clay can be found in most places throughout the world. The few places where clay can not be found are geologically young regions (e.g. volcanic terrain) or high energy depositional areas (e.g. beach shore breaks).
Clay, unlike aggregate, makes a chemical bond to water molecules, and therefore expands when it is wet. When it dries it then shrinks, which is why we add aggregate to the mixture. If the aggregate is already locked together and touching each other, it inhibits large cracking when the clay dries and shrinks. There are a few ways to test to see how much clay your soil has. Since clay cracks when it dries, one way to find clay is to look for cracks on the surface of the ground. This is usually found in places where the clay was suspended in water (due to its ability to bond to water molecule), and the water evaporated. If you don’t have clay on the surface, dig down 2 or 3 feet to look for a clay layer. Clay can often times be confused with silt and one way to tell them apart is to do a shake test. Fill a mason jar ½ full with soil, than fill it about 2/3 full with water. Shake the jar until all the sediment is fully dissolve in the water. When you set it down, the heavy particles will settle first (pebbles and large sand) than the finer particles, and last the clay. The clay may stay suspended in water for a day or more. Another way to check for clay is to go wash your hands. Clayey soil will not wash off your hands by simply running them under water like sand or silt, with clay you will need to rub your hands together and rub off the clay.
Aggregate is any stone, gravel, pebble, or sand component added to an earthen mix. Sand is the primary ingredient is some earthen walls, such as cob. Cob walls are more of a sand wall with just enough clay to glue it all together. Like I have mentioned before, sand is most often used, but there are other options. The aggregate is a material that does not expand when wet or shrink when dry. This is an essential part of your earthen wall, because it keeps the clay from cracking. The sand particles are already touching and locked together while the material is wet. So that when it dries it doesn’t crack. It is best to use the coarsest sand available, so that it locks together and does not roll around itself.
Fiber gives the wall tensile strength. This serving the same function as rebar in cement. Straw is the most common modern day material used, however you can use a variety of materials based on what you have. Most grasses will work, although you will want them dry, and with as little seeds as possible. In some places dung and animal hair is a very common additive.
Water is often over looked, but if there was no water in your mix, you would not be able to build.