Earthbag homes are another way to build a home out of the earth. In this case, bags are filled with dirt and stacked like bricks. Earthbag construction is generally easier for a first-time builder to do without the help of a crew, which might cut down on construction costs. In earthbag building, the bags provide the form for the earth and are a little more user friendly than the wooden forms that you use for rammed earth homes. Rammed earth also requires a more specific mix of dirt and clay than the soils that go into earthbags, so it's easier to use on-site soil in earthbag building. However, because earthbag homes are usually built into small domes, there's more structural freedom with rammed earth homes. For more on the advantages and disadvantages of earthbag building, read How Earthbag Homes Work.
The French call rammed earth construction pisé de terre. David Easton, a rammed earth architect in California, has adapted rammed earth construction into a technique he calls PISE. It's an acronym for pneumatically impacted stabilized earth. Instead of building two-sided forms and ramming earth into them, Easton takes a pressure hose and sprays the earthen mixture against a one-sided form. PISE attempts to make rammed earth construction less time-consuming and more cost-effective, and the thick walls feature the same benefits as traditionally rammed walls. PISE is still fairly new, so it's not widely available. To learn more, see David Easton's Web site.
Challenges of Rammed Earth Construction
Mixing soils, building wall forms, ramming earth inches at a time…as you might guess, one of the main challenges of rammed earth construction is that it's very labor-intensive. In African and Middle Eastern countries, where labor is cheap, rammed earth construction is common and practical. In the United States, however, crews doing the same work can charge a pretty penny. Rammed earth builder David Easton estimates that a wall system in a rammed earth home can cost about 30 percent to 50 percent more than a conventional wood-frame house, which means the entire home might cost about 5 percent to 15 percent more [source: Fatsis].
In desert climates where the thermal mass of the walls can provide the sole means of heating and cooling, these construction costs might be a worthwhile investment. In other climates, additional insulation or energy sources might be needed for heating and cooling, which will further increase the costs. In rainy climates, for example, a rammed earth home might need additional insulation, as well as a larger roof, so that the overhangs protect the earthen walls. Rammed earth in rain-prone areas is acceptable, but the house site should be selected so that the home is protected as much as possible from the elements. Additional design features, such as good gutters and drainage systems that draw water away from the house, help protect against weather.
Like most alternative building methods, rammed earth homes might take more work to meet with approval by building officials, bankers and insurers. In the southwestern United States, there are several experienced builders and contractors, and rammed earth is starting to appear in building codes in that area. Outside of the Southwest, it's generally not mentioned and will require more research and persistence on the part of the person trying to get a construction loan, a mortgage or home insurance.
For more on rammed earth homes, including links to builders who specialize in this type of construction, see the next page.