Earthbags: An Eco Building System

Earthbag Building

A Book Review: Earthbag Building: The Tools, Tricks and Techniques (Natural Building Series) by Kaki Hunter and Donald Kiffmeyer

The authors have been involved in the construction industry for the last 20 years, specializing in affordable, low-tech, low-impact building methods that are as natural as possible. The authors explain how Earthbag Building is an enduring, tree-free type of architecture that can be used to create arched and domed structures of great beauty. Few other building systems are as ecological and affordable.

With a shovel, some empty grain bags and some dirt, you are all set to build with this fire-proof, insect-resistant building system. A row of earth filled bags is laid, and then tamped down. Then two strands of barbed wire are laid across the top of the row of bags. Then the next row of bags is laid down and tamped.

The secret of this building system is there must be some clay content in the moistened soil that is used. Then the bags of tamped down dirt will dry out and set like adobe bricks. The bags help the dirt stay in the correct shape while drying. Later chicken wire or plastic mesh can be tied to the earthen wall. Plaster can then be applied to the wall for a smooth surface.

Earthbag building 1

Earthbag building 2

One of the most interesting parts of the book for me was the chapter on foundations. Poured concrete footing and stem walls are the conventional foundation system approved by current building codes. Cement is used heavily in most modern construction including bridges, sky scrapers, highways, sidewalks, swimming pools, etc. It takes a lot of energy to produce cement. In the USA it takes 4 gallons of gasoline or diesel fuel to produce 1 bag of cement. The production of one ton of cement emits one ton of carbon dioxide into the atmosphere. The authors suggest that humans learn to minimize their use of cement for the sake of the planet.

As an alternative to a solid cement foundation, the author uses bags of “Stabilized Earth Mix.” By adding 6 to 15 percent of cement mix to the soil, bags of cement-soil can be used as a foundation. For this mix, sandy soil with no clay is better. Two rows of cement-soil can be placed on top of a gravel filled trench, and this works well as a stable foundation. Once it is cured the fabric of the bag can be removed and the dry cement-soil has the appearance of stone. Above the two rows of cement-soil, bags of regular soil are used. However, a waterproof membrane should be placed between the cement mix row and the first soil row.

Another alternative is to use lime and soil for a stable foundation mix. Type S – Hydrated Lime comes in dry powdered form. It works well with soil that has some clay in it. Lime was successfully used as a soil stabilizer on roadwork in the 1920s. Lime is better choice for the environment as it takes much less energy to produce.

The “Earthship” houses designed by Mike Reynolds use old tires firmly packed with soil as a stem wall foundation. Rammed earth or gravel filled used tires make good use of a plentiful man-made product that is considered to be garbage.

To avoid using cement, regular soil can be used in an Earthbag foundation, if 2 inch rigid foam insulation is carefully placed around the bag wall. Heavy plastic sheeting can be used around the insulation to further protect the underground Earthbag foundation from water.

Earthbag building 4An Earth-Bermed or Earth-Sheltered wall can be successfully placed up to 4 feet below ground level. The author recommends building the structure in a round shape as it will better handle the stress of the dirt backfill up against the insulated walls. When the backfill soil puts pressure on the walls of a round structure, the compression is equally distributed. A French Drain should be placed around these structures to ensure adequate drainage.

Earthbag with post and beamOne common strategy for getting a building permit where building officials are not familiar with Earthbag construction is to use a Post and Beam frame as the load bearing structure. The Earthbags are then used to fill the spaces between and around the wood posts. One builder used load bearing concrete posts and beams to obtain building permit.

The electrical system and plumbing pipes are tied to the completed Earthbag wall, before the plaster layer goes on. Shelf brackets and be sandwiched between the rows of Earthbags to create a shelf attached to the wall inside the house.

earthbag bond beamAt the top of the Earthbag wall, a continuous bond beam made of wood or concrete is usually installed. The bond beam acts as a tension ring that ties all the walls together into one monolithic frame. This continuous bond beam is the building code design currently used in Adobe and Rammed Earth structures.

Earthbag dome

The Earthbags can be formed into a dome roof, or a more traditional wood or metal roof can be used. Many different interesting roofing options are available for Earthbag homes, including a grain silo roof, a spiral wooden roof, and a Yurt lightweight compression roof system.

Earthbag spiral roof

The book concludes with many resources such as how to make your own bag stand and tamping tools, and where to buy bags, etc.


Earth-Sheltered Houses

Earth-Sheltered Houses by Rob Roy

Earth-Sheltered Houses:  How to Build an Affordable Underground Home    by Rob Roy

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I am reading this very interesting book as part of my investigation into building a Sustainable Eco House (Earth-Sheltered Home).

Advantages: The author explains the thermal advantages of building an Earth-Sheltered house, in both summer and winter weather. The first 10 feet below ground level is very slow to heat up and cool down. This “thermal lag” saves a lot of energy cost for the Earth-sheltered home. The temperature in the first 10 feet of soil in most of the USA varies from about 40 degrees Fahrenheit in winter to 60 degrees Fahrenheit in summer. In the winter, the soil outside the walls of the Earth-Sheltered home is about 40 degrees, even if the temperature of the air above ground is below freezing. So the Earth-Sheltered home only needs to be heated up 30 degrees to be a comfortable 70 degrees inside. This requires much less fuel to heat the house than if the home was built on the surface. In the summer, the Earth-Sheltered home does not require air-conditioning. The earth outside the walls is about 60 degrees, and even if the air temperature above ground is very hot, the underground home will remain comfortable inside.

The Living Roof: The author points out seven advantages to having a 6 inch deep layer of soil and plants on the roof. (More than 6 inches of soil is not recommended as it may become too heavy when saturated, and would require more structural expenses.)

  1. Insulation: The first few inches where plant roots aerate the soil has good insulation value. The Earth roof also holds snow much better and the snow provides additional insulation.
  2. Drainage: The water runoff is slow and natural. It must fully saturate the earth roof before water drips off onto the ground around the house. A “curtain drain” or surface drain can carry the runoff away from the home.
  3. Aesthetics: It looks nice, especially with wildflowers growing on it!
  4. Cooling: The living roof stays nice and cool because of the shading effect of plants and the evaporation of rainwater.
  5. Longevity: The living roof is not damaged by the ultraviolet rays of the sun, wind and water erosion, and the freeze-thaw cycle. The water-proofing membrane under the soil is non-biodegradable, and should last 100 years.
  6. Ecology: Instead of a lifeless black tar-scape, the plants growing on a living roof replace your home’s footprint with cool green oxygen production.
  7. Protection: The living roof provides some protection from fire, radiation and sound. The earth roof can also provide some protection from tornado, hurricane and earth-quake.

Home Design: The author suggests using simplicity of design in the home, and consistency of structure style and line. The floor plan should be integrated with the structural plan. South facing windows provide more passive solar light and heat. Earth-roofed homes should have a very shallow pitched roof.

The Earth-Sheltered home needs insulation around the entire outside of the structure, and underneath it. Without insulation the 40 degree winter soil temperature will wick the heat out of the home. Also, moisture from the earth outside will cause condensation inside the Earth-Sheltered home. The author recommends using extruded polystyrene as insulation around the outside of the underground home. In a warmer climate, thinner insulation can be used.

Earth Sheltered homes can be all the way under the ground, partially under the ground, or built on top of the ground with earth berms up against the sides. Research shows that a home halfway submerged in the earth has 90 to 95 percent of the energy savings of a house that is fully underground. Having the home halfway underground makes it possible to get more light by placing windows at ground level. The author points out that in order to get a building permit, your home will need sufficient entry and exit doors, and windows large enough to climb out if there were a fire. So in other words, a Hobbit House hidden completely under a hill is not going to be approved for a building permit.

Earthships: Some great Earth-Sheltered home designs by Michael Reynolds are called “Earthships.”  These very creative designs use old tires and other recycled materials and are eco friendly. Here are some examples:

Earthship France