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Archive for September, 2010

Part 1 discussed the most efficient, cost-effective ways to build with earthbags. This post discusses a few related items.

Building site: Follow these steps and you’ll save lots of time preparing the site and reduce the risk of problems in the future. Choose a building site that’s clear of obstacles and naturally higher than the surrounding area so water will drain away from the structure. Do not build in flood-prone areas. Building on rocky ground or gravelly mineral soil on high ground is best. Make sure there is truck access.

Soil: Buy suitable soil (approximately 30% clay, 70% sandy soil) and dump it in several piles around the building to minimize labor. Trying to save a few dollars here by hand digging the soil will cost you a lot in time and labor. If you can, buy soil that’s free of large rocks and large clumps of clay, roots and other organic materials, and needs no screening, mixing or additives.

Foundation: The fastest foundation is gravel-filled bags on a rubble trench. Scoria-filled bags are my preference, but most any local gravel will suffice. Scoria is easy to work with, lightweight and insulating. For a small house, you can have a scoria insulated foundation built in about one or two day’s work with a few helpers.

Use salvaged materials when practical: I’m not recommending leaky single pane windows, of course. Most salvaged materials are a real bargain and usually impart a lot of character that’s missing in sterile modern homes. It takes time to locate recycled materials, but the effort is typically well worthwhile.

Use low cost natural materials: This can save you a ton of money: earthen plaster, clay, tamped earth floors, road base, sand, gravel, stone, small diameter wood, rice hulls for insulation, straw, reeds, bamboo, thatch.

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This article launches my new blogging gig at Mother Earth News, the leading US publication on sustainable living.

Recently, I had an epiphany in a building supply center while looking at the thousands of products used to construct modern buildings. Even though I’ve been in the building trades for over 35 years and made countless trips to purchase building supplies, this trip was different. You see, I’ve been immersed in writing a new earthbag building book and now the differences in the way I build and the way most of modern society builds has been brought into even sharper relief.

Read more at Mother Earth News Blog.

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What’s the most efficient, cost-effective way to build with earthbags? How can you enclose the most space with the least time, effort and money? Well, it depends in part on climate, individual skills and preferences as far as styles/building types. (Other factors will be covered in a future post.)

In general, round shapes are the most efficient. They create the most amount of floor space for a given wall length. This is easily demonstrated by drawing a circle and a square using the same lineal distance of walls. For example, draw an 18’ diameter circle, which will have an area of 254 square feet and circumference of about 56.5’. Divide 56.5 by 4 (= 14.1’) to obtain a square with the same total wall length. A square with 14.1’ per side has an area of about 200 square feet. So in this example there’s a gain of 54 square feet of floor space. (Draw this with your kids. It’s a great learning experience.)

So why do builders churn out square/rectilinear structures? Because modern building materials are rectilinear – plywood, OSB, sheetrock, etc. But we know these materials are energy intensive, costly, lead to monotonous designs and have negative impacts on the environment. Earthbag building frees us from these constraints and enables the use of more efficient round shapes. In addition, round shapes are inherently more stable. “Round is sound” as they say.

Size is also important. Large houses require much more time, labor, skill and materials and can easily wear you down, even more so for owner-builders. It’s far better to build only what you need. You can always add on later. Build with cash one stage at a time.

Another factor to consider is fill material – what goes in the bags. Lightweight materials such as scoria are much faster and easier to use than soil. This one factor alone can cut the labor by severalfold, because scoria is lightweight, easy to work with and requires less tamping. Scoria is insulating and so it’s ideal for extreme climates. Plus, scoria doesn’t rot, burn, attract pests, etc. One limiting factor is it’s less stable in certain applications such as straight walls and tops of domes that curve in too quickly.

And the winner is? I’ll give it a tie between roundhouses and domes, depending on the variables listed above. Small to medium sized roundhouses with simple roof designs have an edge in many cases, especially rainy climates and for those with carpentry skills. In dry climates, domes may be more efficient. Organic shapes that approximate circles are a close runner-up, although this often complicates roof construction.

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Here’s a new video by Guiding Star Creations. Text below is from their website.

Guiding Star Creations: Cultivating thriving environments through inner transformation, earth architecture, and well-being. Neil and Stella are committed to empowering others through facilitating workshops, teaching, and creating projects that combine thriving environments with co-creation and inner transformation. They are planning their projects for this year and are interested in being contacted from parties who resonate with their mission and want to follow their bliss through creation.

You can watch all the best earthbag videos on our Videos page.

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Patti Stouter has published another earthbag technical report. It is a summary of the state of testing to date, and also covers some of the codes related to earthbag. The following information is quoted from this report.

According to the new international earthen building standards, if earthbag walls with some reinforcing have shear strength equal to or greater than reinforced adobe they can be designed for building structures even in the most risky seismic regions. Since shear strength is related to friction between courses, soil filled poly bags were tested by a simple tilt table method to discover the approximate coefficient of static friction between the bags with barbed wire. Additional tests used barbed wire and metal pins, or pins alone. The force needed to pull barbed wire out axially from between bags was also tested.

– Results from more than 20 tilt tests indicated that full, moderately firm bags have coefficients of static friction between 1.5 and 1.9, up to 3 times higher than those needed to create an unreinforced geo-cell wall.
– Higher coefficients of friction (up to 2.7) resulted from providing small metal pins with 2 points. Length of barb did not appear to affect the coefficient of friction.
– Results from two axial tension tests indicated that barbed wire does not pull out until the barbs bend. Although static friction was overcome at 60- 80 pounds force, 120 pounds was required to remove the wire completely from between two partially cured bags.
– Instead of tearing the bags, all of the embedded barbs appeared to have bent.
– Barbed wire contributes to both the friction (related to shear strength) and the tensile strength of earthbag walls.

The full report is accessible from EarthbagStructures.com and EarthbagBuilding.com. Here, you can find all earthbag testing reports for easy reference.

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I just posted the recent news about gaining engineering approval for earthbag construction through PSE, Nabil Taha’s engineering firm in Oregon. He is licensed in 27 states and has developed an earthbag building system to meet international building codes. This is a major step forward for gaining widespread acceptance of earthbag building and we are very appreciative of his leading role and support.

The following engineering guidelines are quoted from the PSE website:
– Earthbag building utilizes the ancient technique of rammed earth in conjunction with bags and tubes as a flexible form. Earthbag construction does not require as much time, attention, or forms as adobe or rammed earth construction requires.
– The fill can be on-site soil or other local materials. Depending on the needs and uses of the completed project, certain materials are selected for either insulation or providing thermal mass. Generally, the fill is of a mineral composition and not subject to decay.
– Because these structures can take an endless variety of shapes, the need for traditional building materials, such as wood or steel, is negated. This saves both energy and precious natural resources.
– When construction is performed in the right way, earthbag buildings have been proven to withstand the ravages of fire, floods, hurricanes, termites, and earthquakes.
– Earthbags can be stacked for a number of different building types and shapes.
– Round is sound, round or circular shaped earthbag homes/buildings are very strong, and can resist the wind and seismic forces better than rectangular buildings.
– Earthbag buildings do not have to be round, circular or curved.
– The earthbag system, in conjunction with the design of monolithic shapes is the key to the earthbag structural integrity.
– Different materials have been successfully used for earthbag construction such as sand, dirt, crushed volcanic rock (scoria), etc.
– A good mix is approximately 70% sand and 30% clay.
– To prevent the earthbags from sliding relative to each other, barbed wire is always used between earthbag courses.
– Masonry equations can be used for earthbag wall designs.
– The Building Code requires a minimum amount of reinforcement to be used for earthbag construction. The following amount/area of steel can be included in the Code minimum requirement amount of steel: steel mesh in the plaster/stucco, steel bars in the bond beam, barbed wire or the joint reinforcement used between the courses/rows of earthbags.
– At the top of the earthbag wall, providing a concrete bond beam with 2- # 5 bars is recommended.
– Earthbag wall thickness should be 16 inches or more.
– Building codes do not allow generic prescriptive designs that can be applied to all earthbag structures. (Each structure must be analyzed on a case-by-case basis.)
– The best information we have found about bags for earthbag building is on Kelly Hart’s website under “Frequently Asked Questions.”

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We’re very happy to announce what is perhaps the greatest news ever for earthbag building. Nabil Taha, Ph.D., P.E., has developed an earthbag building design to meet building codes. This is a huge step forward for earthbag building and we feel very honored to have Nabil’s support.

Nabil Taha is the President of Precision Structural Engineering, Inc. (PSE) and is licensed in 27 states. PSE is a leader in green engineering and green design, offering services for a wide range of building systems, including earthbag, strawbale, bamboo and rammed earth. You would do well with your engineering career if you worked for PSE upon graduation.

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