New home construction comes at a tremendous expense to the planet. Building 1.7 million homes with traditional wood, steel and concrete frames consumes the same amount of energy as heating and cooling 10 million houses each year, according to the Consortium for Research on Renewable Industrial Materials. The environmental costs stem largely from the manufacture of the materials. Cement production, for example, requires an astounding amount of energy and results in water and air pollution and industrial waste that is usually not recycled. Using natural materials that require minimal processing or refining reduces these environmental impacts.
Natural building offers a way to construct a home with renewable, naturally occurring and locally available materials, as opposed to industrial or man-made products. Many of these materials are available throughout the world, so the costs and pollution associated with the transportation of these materials across the country falls. Using natural materials also reduce toxins in the home. As a bonus, many of these methods are energy efficient, inexpensive and easy to build with little construction knowledge. In this article, we'll look at 10 natural building materials that are being used today.
It's much easier to build with perfectly shaped bricks or slabs of concrete, but it's possible to build beautiful homes with locally available rocks. The rocks can be mortared with earthen plasters such as sand and clay or lime. Rock walls have very good thermal mass, which means that they absorb the outside temperature, hold it in and then radiate it through the home. Insulation, on the other hand, stops heat from flowing in and out of the building.
Thermal mass is best used in desert climates because of the difference in day and night temperatures, and the release of heat is cyclical. During a hot day, walls with thermal mass will absorb and store the sun's heat while the inside of the house remains cool. At night, when outside temperatures drop, the daytime heat stored in the walls radiates inward to warm the home. Thermal mass can be energy efficient since the house heats and cools itself, instead of relying on a furnace or air conditioner.
Rock structures are extremely durable but very labor-intensive. Sticks and straw spelled doom for some famous little pigs, but on the next two pages, we'll see how these natural building materials can create stable and sturdy homes.
9. Straw Bales
Straw bales provide an extremely strong building block for homes. They can act as the actual structural building block or as the fill for insulation in a traditional post-and-beam structure, where the frame supports the home, as opposed to the straw bale. After the bales are stacked, the walls are plastered. The thick walls provide excellent insulation and are about 75 percent more energy efficient than conventional homes [source: Morrison]. Contrary to what you may think, straw bale houses are not a fire hazard. Rather, they provide roughly three times the fire resistance of conventional homes [source: Morrison]. Because the bales are so tightly packed, there's no oxygen and no chance of combustion.
If you'd rather leave the straw bales to the farmers, there are plenty of other options for natural building materials, including the next one that panda bears like to munch on.
Decorative bamboo has long been fashionable in home design, and bamboo floors are beginning to become popular in the United States. In Asia and South America, houses are frequently made out of the wood. Bamboo is an extremely strong wood, so much so that it's being used for highway and bridge construction in Asia.
This strong wood is a renewable resource because it's one of the fastest growing plants. It has a shorter growing cycle than timber, and harvesting bamboo does not affect the roots of the plant. Bamboo does have to be treated with some chemicals in order to ensure that it's waterproof and insect-resistant, and it requires some different building methods, particularly in joining different pieces of bamboo. However, bamboo is an extremely flexible building device because it bends, and it's immensely durable.
If you like the look of log cabins, but are hesitant to go through that much lumber, cordwood building might be a good compromise. Cordwood building uses wood that is cut into short lengths, about the size of firewood, which might otherwise go to waste. You can check with local sawmills, furniture manufacturers and even log home builders to see if they have any scrap wood, or you can use dead trees.
The pieces of cordwood are laid into mortar so that the length of the log makes the wall. The ends of the log stick out of the mortar on either side. The mortars that are commonly used include mixes of cement, lime, clay, sand or sawdust. Cordwood is a natural building material that offers both good insulation and good thermal mass. The logs provide insulation that keeps heat in the building, while the mortar provides the ability to store and release heat into the building. The wood might expand or shrink over time and crack the mortar, but you can remedy this problem through caulking.
6. Rammed Earth
For many people, wood is neither affordable nor available, so resourceful builders use what they have: the ground beneath their feet. To build a rammed earth home, a mixture of soils is packed down into a temporary wall form that shapes the mixture. The form is usually wooden, and it must be strong enough to withstand the compression of the ramming. Ramming can either be done by hand or by machine, and once it's completed, the forms can be removed, leaving an earthen wall about 18 inches to 24 inches (46 cm to 61 cm) thick.
Rammed earth walls require a cross-grade of soils, but too much clay will cause the walls to crack. Walls can be plastered with stucco or left bare; bare walls usually are internally stabilized with a small percentage of cement. When properly constructed, rammed earth walls are extremely durable, holding up in bad weather, as parts of the Great Wall of China can attest. They also provide energy savings because of their thermal mass.
If you prefer your earth neatly bagged rather than rammed, read on.
You may have seen pictures of flood barriers and military bunkers created out of stacked sandbags. With their ability to hold back rushing waters and protect soldiers, you can see how sandbags are inherently strong. Earthbag homes, which are made of polypropylene or burlap bags stuffed with dirt and stacked like bricks, are similarly strong.
But how do a bunch of dirt bags form a home? The dirt in the bags presses down after each layer is placed, and this compression makes the dirt into a kind of self-supporting brick. Barbed wire serves as the mortar between the layers, and the compression makes the dirt bricks so sturdy that even a stray hole won't affect the wall's durability. The walls are plastered to add to their durability. These homes usually have domed roofs, which are formed by stepping in the bags gradually until the bags come together to close the dome. Structural tests have shown earthbags to be seismically sound and able to withstand the elements.
If you happen to have a bunch of old car tires littering your landscape, you'll definitely be interested in the next natural building material we'll discuss.
Michael Reynolds got the idea for earthships after watching a television special about the possibility of a looming garbage problem. Soda cans were made out of steel, so they weren't recycled, and Reynolds saw their potential as a building material. During the energy crunch of the 1970s, he discovered that packing dirt into recycled tires created good thermal mass. The earthship was born from these revelations [source: Cooper].
To build an earthship, you fill old car tires with earth and stack them like bricks. Because the tires are so thick, you don't need a foundation, and the tires are plastered after stacking. Internal walls are made from aluminum cans or bottles. These materials would otherwise be thrown away, but when assembled properly, they can save a good deal on heating and cooling costs. Earthships commonly are built right into the ground, with the exposed wall made out of tires pointed out to the sun.
To read about more earthen dwellings and how you can live underground, keep reading.
It turns out hobbits had the right idea. Earth-sheltered homes, such as the underground dwelling of Bilbo Baggins in "The Hobbit," are energy efficient, soundproof and fire-resistant. They can also be built above ground, with the sides of the home or the roof covered with earth. Underground earth-shelters aren't completely dark; windows and openings provide heat and natural light.
Water drainage systems must be designed to channel the water away from the structure, and it's best to build earth-sheltered homes in soils that are permeable, which allows the water to drain, as opposed to a cohesive soil like clay, which will expand with the water [source: U.S. Department of Energy]. Soils also should be tested for their load-bearing capabilities. The construction materials for building the inside can be natural, including earthbag, rock, local wood or straw. An earthship is a type of earth-sheltered home.
If you want to get up close and personal with your building material, cob might be the way to go. Cob is a combination of earth and straw that you usually mix with your feet, and then form into lumps that you mash together by hand to form the wall. Cob comes from an Old English word meaning "a lump or rounded mass" [source: Smith, Evans].
Cob lends itself easily to creative, free-form construction that includes curvy shapes and sculptural forms, and it requires minimal tools or construction experience. When the cob dries, it's like concrete, thanks to the reinforcement of the straw; however, waiting for the cob to dry is essential before placing the next layer of cob lumps. Building on top of wet lumps will cause the building to sag, so cob building is very time intensive. Cob walls also cannot be built very high, but when completed, cob walls, like all of the earthen methods on this page, provide thermal mass that cools homes in the summer and warms them in the winter.
You may not have heard of many of these natural building materials before reading this article. After all, how many of your neighbors live in earthbag homes? But you probably will have heard of this last one we'll discuss on the next page.
Adobe is one of the oldest forms of building with earth, with examples all over the American Southwest, the Middle East, South America and Africa. Adobe is made by pouring a mix of clay, sand, water and sometimes straw into a form, most commonly a brick. The forms are left to dry in the sun, and then the forms are removed. This curing process can take some time, and it requires a continuously dry climate so that the bricks can solidify without getting wet. As the bricks dry, they shrink, so they should be inspected for cracking. Adjusting the ratio of clay and straw can help to prevent cracking; because the levels of ingredients vary widely among adobe bricks, it's best to make some test bricks to determine if they'll crack.
Adobe bricks are stacked just like conventional masonry and typically connected with a mud mortar. However, adobe walls are vulnerable to moisture and usually need large roof overhangs and elevated foundations in wet climates. In addition, adobe buildings are not a good idea in earthquake-prone areas, although concrete can be added to bricks to stabilize them.
To learn more about natural building and how to design your own eco-friendly home, visit the links on the next page.
Lots More Information
- 10 Sustainable Buildings
- Aluminum Quiz
- Metals Puzzles
- Materials Science Pictures
- 10 Reasons to Use Geothermal Energy
- Bamboo Technologies. "About Bamboo, the Giant Grass." (Feb. 29, 2008)http://www.bambooliving.com/bamboo.html
- Branch, Quentin and Julie Szekely. Rammed Earth Solar Homes Inc. Personal communication. April 2, 2008.
- Consortium for Research on Renewable Industrial Materials. "Environmental costs of home construction lower with wise choices, reuse of building materials." Aug. 24, 2004. (March 4, 2008) http://www.corrim.org/reports/pdfs/UWArelease.pdf
- Cooper, Diane. "The Earthship--A Living Vessel Sailing the Seas of Tomorrow." (Feb. 29, 2008)http://www.spiritofmaat.com/archive/apr2/eship.htm
- Hart, Kelly. "Adobe." GreenHomeBuilding.com. (Feb. 29, 2008)http://www.greenhomebuilding.com/adobe.htm
- Hart, Kelly. "Cob." GreenHomeBuilding.com. (Feb. 29, 2008)http://www.greenhomebuilding.com/cob.htm
- Hart, Kelly. "Rock." GreenHomeBuilding.com. (Feb. 29, 2008)http://www.greenhomebuilding.com/rock.htm
- Hunter, Kaki and Donald Kiffmeyer. "Earthbag Building." New Society Publishers. 2004.
- Kennedy, Joseph F. "An Overview of Natural Building Techniques." (Feb. 29, 2008) http://www.networkearth.org/naturalbuilding/overview.html
- McHenry, Paul. "Adobe: A Present from the Past." Building Standards. September-October 1998. (April 1, 2008) http://www.greenhomebuilding.com/pdf/buildingstandards_adobe.pdf
- Morrison, Andrew. StrawBale.com. (Feb. 29, 2008)http://www.strawbale.com
- Rammed Earth Solar Homes Inc. "Rammed Earth Flyer." (Feb. 29, 2008) http://www.rammedearthhomes.com/pdfs/Rammed_Earth-Flyer.pdf
- Roy, Rob. "Expert Advice: Cordwood." (Feb. 29, 2008)http://www.greenhomebuilding.com/QandA/cordwood/find.htm
- Smith, Michael and Ianto Evans. "Questions and Answers about Cob." (Feb. 29, 2008)http://www.networkearth.org/naturalbuilding/cob.html
- U.S. Department of Energy. "Earth-Sheltered Home Design." (Feb. 29, 2008) http://www.eere.energy.gov/consumer/your_home/designing_remodeling/index.cfm/mytopic=10100
- Wilson, Alex. "Cement and Concrete: Environmental Considerations." Environmental Building News. March 1993. (Feb. 29, 2008). http://www.buildinggreen.com/auth/article.cfm/ID/1263/