Archive for August, 2009

Why earthbag building is one of the best building methods.

Sometimes we delve into esoteric aspects of earthbag building. For those new to building with bags, here is a summary of advantages.

• Low cost (if you build simply and do most of the work yourself)
• Durable (rammed earth structures such as earthbag can last for centuries)
• Owner-builder friendly (easy to learn and few tools required)
• Environmentally friendly (uses primarily local, natural materials)
• Comfortable (cool in summer, warm in winter, quiet)
• Excellent insulation (when filled with an insulating material such as crushed volcanic rock)
• Excellent thermal mass (when filled with tamped soil or gravel and/or thick plaster on the interior)
• Strong (almost 10 times compressive strength as conventional stud-frame housing; test results in California exceeded ICBO requirements)
• Disaster resistant: floods, hurricanes, tornadoes, earthquakes, fire, bullets
• Insect and rodent resistant, safe, mold-free and will not rot
• Proven technology (over a century of military use, plus many hundreds if not thousands of modern examples)
• Highly adaptable (ideal for curved organic-shaped walls, domes, roundhouses, small vaults, straight walls, underground or above grade, earth-bermed, privacy and retaining walls, furniture)


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Road base is a mixture of clay and gravel used in road building throughout the world. As an engineered material designed to withstand extreme loads (trucks and cars), you are assured of good working properties for earthbag building. While site based soils are less expensive and require less transport, the working properties are unknown and so you will want to do a series of tests to determine the best clay to gravel ratio. With road base, no additional tests are necessary and you can begin building right away.

Moisten road base slightly before filling bags.

Moisten road base slightly before filling bags.

Road base is typically very inexpensive, largely because the mixture is just clay and gravel. With huge quantities needed for road building, many suppliers are available to meet demand. That often means a truckload can be delivered to your site in short order from a nearby gravel pit.

Road base is a uniform mixture without clumps of clay or large rocks. Using road base eliminates digging for soil on your land, thus preserving the natural beauty of your site and freeing up your time for building. And since it is delivered by truck, you can have it stockpiled around your house just where you need it to minimize labor. Road base excels in compression, and therefore is ideal for dome building. It dries almost rock hard, creating incredibly strong walls. You can use the same material under your house to raise the building site.

Note: road base is a generic term and the mixture may mean different things in different places. Ask for a clay/gravel mixture as used in road building (not just sand/gravel). You need the clay portion, which acts as the binder.

If you live in cold climates, then consider using lightweight fill material such as scoria, perlite or vermiculite for high R-value and ease of use. See Insulated Earthbag Houses for more information.

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Internship program
Cost for 6-week internships: $1,200

The Geiger Research Institute of Sustainable Building announces a building internship training program in Sakon Nakhon, Thailand starting November, 2009. The internships largely involves a learning by doing approach with some classroom time. It encompasses earthbag building, sustainably harvested wood, earth plaster and floors, CEBs, adobe, thatch, and low-fired brick, as well as most aspects of general carpentry – setting doors and windows, tile, etc. through all stages of construction.

Perhaps the most interesting aspect of the program is excellence in building design. Over the next two years, we will be building a series of unique buildings that have been carefully chosen for magazine articles and a future book: a roundhouse office, guesthouse, roofed dome, earthbag pantry. One project includes this office. Each building will focus on the best, low cost building techniques: what works best and why.

Interns will work directly with Owen Geiger (now a Mother Earth News Magazine Green Building Expert) and Thai builders learning a multi-cultural way of building with natural materials – where east meets west, so to speak. Students will rotate through on an ongoing basis, enjoy exceptionally low cost living (nice, new apartment = about $75/month plus utilities, 15 cent taxis, etc.), go on field trips and attend workshops at no additional charge. Class size is limited to a few students, so please apply early. Send a brief summary of your skills and interests to: strawhouses [at] yahoo.com.

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We often get questions from people wondering how many bags they need to have on hand for some particular project. Is there a formula to figure this out?

First you need to calculate the total square footage (or square meters) of  the wall you intend to build. This can be done by simply multiplying the length times the height, and then to be precise, you can deduct the size of the windows and doors from this…but I usually don’t do this because it is better to over-estimate how many bags you might need, and also, you always need some partial bags to keep the brick pattern going.

If your wall is curved you’ll need to figure out the running length of the wall by either making a scale drawing and measuring the length that way, or in the case of a circle you can use the formula Length = 3.14 X the diameter for this.

Figuring out the surface area of a dome is obviously more complicated, partly because there are many shapes for domes. If the dome is close to hemispherical (not recommended for structural reasons) the formula would be 3.14 X the diameter squared. If the dome more closely resembles a cone, then the formula would be 3.14 X the radius X the radius plus the length from circle at the base to the top of the cone. Either of  these formulas could be used to estimate approximately what the area of your dome might be, especially, if that total is then padded by not deducting openings, or simply rounding upward.

As far as bag coverage goes, it depends on the size of the bag how much square footage it will cover. I used what were labeled 50 lb. rice bags to build my house. These measured roughly 5″ X 20″ when laid in a wall and compacted. That is approximately .7 of a sq. ft.  A nominal 100 lb. bag might actually be considerably larger than what I used, so you’ll need to run some tests to determine what kind of coverage to expect. The 50 lb. bags I used measured about 18″ X 30″ when laid flat.

Once you have figured out what the area of one bag might be after it is filled and tamped, then you can  divide that figure into your total wall space to get the total number of bags needed. For instance, with the 50 lb. bags that I used, you would divide the area by .7 to get the total number of bags needed. In this case, for example, a 100 square foot wall would require roughly 143 bags.

Happy calculating!

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