EARTHBAGS! A newly FREE chapter inspired by Cal-Earth Institutes latest earthbag success! #BuildSimple #GreenerByDesign

Sometimes the Universe shows up so clearly there is NO way to ignore her.
This week was one of those moments. I got the following post sent to me three times in a few hours.

I knew there was a way I could share with people some tips about how to make earthbags work for them.
And it's time.

So, here is our Earthbags chapter. For Free. Yep, I mean it.
Tip: USE the details from Build Simply linked at the end of the article to get good design advice for seismic locations. And if you live in a humid place, consider all your other options before going with earthbags. These are the PERFECT quick build for emergency situations where the materials are available. But these are NOT a long term option for really humid locations, unless a supernatural amount of ventilation is possible (and preferable). Trust us, 'kay?

by Chiara Riccardi and Rachel Preston Prinz

Wall Type:                             Thermal Mass
Appropriate Climate:             All regions
Structural Capability:             Load-bearing
Suitable for Berm:                  Possibly
Natural:                                  Mostly
Learning:                                Easy
Doing:                                     Easy
Engineering Required:           If bermed
Kit Available:                          No

Earthbag construction is a natural building technique that evolved from military bunker construction and temporary flood-control methods. Rooms in earthbag structures often are circular in shape and have a dome roof, though square rooms are achievable with buttressing and/or interlocking of the bags at the corners. 

Earthbag building usually begins by digging a trench down to undisturbed stable subsoil. The trench is then partially filled with cobbles or gravel to create a rubble trench foundation. On this foundation, several rows of doubled woven bags are filled with gravel and placed into the trench, and another two courses are stacked above grade to form a water-resistant foundation dampcourse. Then the actual earthbag wall starts. 

The most popular type of bag is made of solid-weave polypropylene, like those used to transport rice or other grains. Polypropylene is very affordable and is resistant to water damage, rot, and insects. These bags can be purchased as mis-prints or bought used at agricultural warehouses and producers. Alternative bags include those made of hemp, burlap or other natural-fibers. Though, when exposed to air, water, and time, these natural options may deteriorate. 

Moist subsoil that contains 5 - 50% clay, enough to become cohesive when tamped, or an angular gravel or crushed rock is used to fill the bags. Portland cement, lime, or bitumen stabilizers can be used to allow earths with high clay content to withstand flooding. The addition of stabilizers in a ratio of 5-10% may be required to meet Code. The thermal insulating value of the fill material is directly related to both the porosity of the material and the thickness of the wall. Crushed volcanic rock, pumice or rice hulls yield higher insulation value than clay or sand. However, thermal mass properties are also an important consideration, particularly for climates that experience temperature extremes. Materials like clay or sand have excellent heat retention characteristics. 

Each successive layer of earth-filled bags is placed like bricks, with one or two strands of barbed wire placed on top to increase friction between each row of bags and improve tensile strength. Bags can be pre-filled with material and hoisted into position or filled in place. A light tamping and twisting of the bags serves to consolidate them and creates a wall with a strength between that of adobe and rammed earth. The same process continues layer upon layer, forming walls. 

The completed structure is then quickly covered with earth plaster to prevent solar radiation from degrading the polypropylene. Natural earth stuccos allow the wall to breathe and natural mineral pigments can be added to provide beautiful color effects. A standard mix for earth plaster for covering earthbag superstructures is: 1 part clay, 3 parts earth, 1 part straw, and 1 part lime.

Windows and doors can be formed with a traditional masonry lintel or by using earthbags in traditional masonry corbeling or brick-arch techniques using temporary forms. Light may be brought in by skylights, glass-capped pipes, or bottle bricks placed between the rows of bags during construction. 

A roof can be formed by gradually sloping the walls inward to construct a dome. This inherently limits the size of the space you can create and increases the size of the volume, because you want to use the minimum overlap on the bag that you possibly can: an inch or less of bag overhanging the bag below is best. Keeping the angle of the dome walls to no more than 60 degrees will usually work adequately. The trick with domes is waterproofing the roof; this can be difficult, and requires the use of commercial roof sealers. Using a traditional framed roof of panels or shingles is another option.

It is possible to combine earthbag building with earth-sheltering.

Self-built earthbag homes can start at $20 per square foot of floor space.
Earthbag Pros
·         Heat (or cold) penetration of the wall is slow and the internal temperature of the building remains relatively stable.
·         Allows the building to be constructed in culturally and regionally appropriate styles. This preserves the look and feel of the community.
·         The tools needed to complete an earthbag build are limited to those that are readily available pretty much everywhere: gloves, picks, shovels, hoes, hammers, barbed wire, twine…
·         Earthbag structures can easily be built solo or with just a few friends. The effort is much easier than that of traditional Earthships.
·         Earthbag homes are the only way to get an Earthship in some European countries like Belgium who have outlawed the use of tires in architectural projects.
·         Earthbag homes can range from cozy huts and domes to multi-story traditional homes.
·         Earthbag construction uses the least energy of any durable construction method. With on-site soil being used, practically no energy is expended on transportation. The energy-intensive materials that are used — plastic (for bags & twine), steel wire, cement or lime, and perhaps the outer shell of plaster or stucco — are used in relatively small quantities compared to other types of construction, adding up to only 1-4% of the total construction materials.
·         The buildings last a long time; however, when they are no longer useful they may simply erode with no serious threat to the environment, or even be recycled into new earthbag-constructed buildings.
·         Earthbag buildings last many years with low maintenance. Earthbag structures do not rot or mold and they deter pests including termites, roaches and the like, because there is no wood to chew through.
·         Building with earthbags means not contributing to the deforestation, air pollution, or build-up of landfill materials.
·         Only 1-4% of earthbag construction uses manufactured resources. The main materials used are dirt, straw, and water.
·         Earthbag structures can survive fire, flood, wind, tornado, hurricanes and earthquakes

Earthbag Challenges
·         The process of filling earthbags and tamping them requires a fair amount of physical strength for the self-builder; United Earth Builders has developed a skid-steer operated earth home building machine. It fills earthbag tubes of many sizes at a rate as fast as 400 feet per hour. At production speed, a crew could fill about 30 feet per hour of earthbag by hand (depending on bag width). Another option is using a small concrete-mixer on-site to blend materials.
·         Earth plasters are an acquired skill requiring practice to get the mix right. The difficulty is there is no list of definitive ingredients, and it all depends on your mud. 
·         Waterproofing earthbag buildings is a complex and sometimes expensive process for humid regions.
·         Earthbag buildings might take more work to meet with approval by building officials, bankers and insurers.
·         If an earthbag home gets damaged it is nearly impossible to fully repair. Large sections of the wall must be removed and replaced to complete a repair that could be considered more than a band-aid. Same with additions. They require a great deal of demolition if not planned for in advance.
·         Polypropylene, which the bags are most often constructed of, is a toxic agent known to cause cancer, allergies/immunotoxicity, organ system toxicity, and neurotoxicity. Though, rats and bugs are not keen on eating this material and rot is rarely a concern. Like tires, this material is encased, and may present no threat. That has yet to be determined.
·         Water Alert: earthbags cannot withstand prolonged soaking. 

Since 2010, earthbags have been used moderate and high seismic risk areas with new reinforcement techniques. A reinforced concrete footing or grade beam may be recommended. Additionally, corner reinforcing is required, since corners are one of the most vulnerable parts of buildings in earthquakes, and can often be pulled apart. A typical and easy-to-build solution suggests barbed wire should be cut to extend 24″ past each corner, and when the next course is laid and tamped, tightly pull this extra wire back up onto the upper course. Then lay the next set of bags and barbed wire, extending again out past the corners.  However, the Build Simple Institute, an architectural research firm in Placitas, New Mexico, suggests using a 2 foot deep buttress, extending each wall beyond the intersection at corners in earthquake prone areas. They have several alternatives if buttressing is not preferred, just visit their website at http://buildsimple.org/earthbag.php for details.