Choosing a Construction Method: Rammed Earth Variants

We need to begin construction of our zero energy house by deciding how it will be built. This decision will impact our design, materials and process. In making this decision there will be tradeoffs and consequences that must be carefully analyzed and understood. No design or method can be entirely perfect. After examining our options, we will choose the method that works best for the goals of this project.

Rammed Earth, Earthships and Earthbag Construction

Let’s start at one end of the spectrum and work our way across. These methods are the ultimate in environmental sustainability. The load bearing structure of the house is formed from the earth beneath your feet. Often the same soil excavated to prepare the site can be used. In pure rammed earth construction a mixture of sand, clay and silt is packed down tightly within a formwork. The result is thick, rock hard, earthen walls.

More information about the soil mix in rammed earth

Building rammed earth walls using fixed formworks

Building rammed earth using a moveable formwork

Earthships are an improvement upon this idea. Earthships use discarded vehicle tires as a form. Since the rammed earth has additional stabilization from the tires the soil mix is more flexible, allowing earth from the site to be used in most cases.

The definitive guide to building Earthships

Making a rammed earth tire

Earthbags are probably the best application of these ideas. In this system polypropylene bags serve as the earth formwork. Using bags makes filling and compacting much easier. Additionally, earthbag buildings are often formed as domes, allowing earthbags to form the entirety of the structure including the roof. This is not possible in either rammed earth or earthship construction.

More information about earthbag construction

Time-lapse of a small square earthbag construction project (set to speed metal music??)

Pros and Cons:

Pros

Environmental Benefits:

The materials used are completely natural and usually taken from the building site; there is virtually no environmental damage whatsoever. In the case of Earthships, there is actually a large environmental benefit since large quantities of discarded tires are upcycled.

Low materials cost:

The materials are earth and formwork; there is virtually no material cost.

Low skill requirement

The process is simple, easy to learn and quite tolerant of small mistakes.

Strength and Longevity

Rammed earth style homes of nearly any style are essentially indestructible. Earthbag buildings even perform well in earthquakes making them resistant to all but the most catastrophic natural disasters. I would not be surprised to see most rammed earth style buildings able to survive small explosions. These structures will last centuries without significant damage.

Cons

Labor:

This is by far the most significant drawback. The time and labor required to build any of these variants is quite intensive. You need either a large volunteer crew or some other way of getting a workforce together.

Insulation:

While rammed earth has excellent thermal mass, it has poor insulation value. Thus for climates that experience prolonged periods of either hot or cold, additional insulation is needed. 

Scalability:

Due to the extremely high mass of rammed earth walls, any sort of multi-story building would require extremely thorough engineering that is beyond our expertise.

Building Codes:

Unfortunately we need to consider the well established building codes that dictate home construction. In most cases, getting approval for these structures will take a significant amount of time, stress and money. In some cases it may be impossible to get approval altogether.

Final Thoughts:

Labor and building codes are the defining challenges here. We want our design to be as easy and adoptable as possible. The bottom line is that getting approval and securing the necessary labor will be challenging for most. The builders of rammed earth style homes tend to be dedicated in a deeply personal way. They are willing to put forward an incredible amount of time and willpower.

I want to end by taking one last look at the potential of earthbag construction. The ingenuity and functionality of these structures are difficult to ignore. In addition some of the conventional difficulties with rammed earth listed above are beginning to be addressed through earthbag construction. Instead of filling bags with earth, naturally insulating materials such as basalt, scoria or pumice have started to be used. These materials are widely available under the name ‘red lava rock.’ This solves the majority of the insulation problem. There are also existing and emerging methods to offset the significant labor needs. Devices known as pneumatic tampers make the compacting process much easier and are available to rent. In addition, there are emerging technologies that automate the process of filling the bags. This machine by Ensor Equipment is one such example.

Should these kinds of machines become more widely available earthbag construction may prove much more viable than originally thought. In any case, the earthbag style of construction will be a significant contender for our final decision.