Building with Rammed Earth

Mud and dirt have been used as building materials for centuries, as ancient civilizations looked for ways to utilize what they had around them. These early methods eventually turned into a more reliable and robust building practice called rammed earth.

Rammed earth construction is considered one of the strongest and oldest methods of building, as can be seen in examples like the Great Wall of China, the Granada Alhambra in Spain, and many other structures that are still standing.

After thousands of years, modern builders have been experimenting with how to bring this technique back to home-building. When done right, rammed earth homes and buildings have a very low carbon footprint, are cost-effective, beautiful, and comfortable to live in.

This article will go over what you need to know when building with rammed earth.

What Is Rammed Earth?

Rammed earth buildings are made of various combinations of ground materials, whether it’s gravel, sand, clay, chalk, or silt. Stabilizers like lime or cement are sometimes added to the mixture, while coloring additives or other natural elements such as wood or stone can be included for effect.

If cement is added to rammed earth, it’s referred to as “stabilized rammed earth” (SRE), or “cement-stabilized rammed earth” (CSRE). If no cement is used, it is considered raw.

Rammed earth buildings have an earthen look that's similar to adobe or cob construction. However, the unique building process produces a distinct horizontal layered effect that makes for an interesting, definitive, natural aesthetic that blends in beautifully with the surrounding environment.

How Is It Made?

Historically, rammed earth walls were done by hand with a rod, which is incredibly time consuming and labor intensive. New technology uses pneumatically powered tools and machinery, which are faster and less laborious, but more expensive.

This mixture is poured into temporary wooden forms in small sections at a time, usually about four inches. These layers are then “rammed” or compressed to approximately half of their original size and allowed to dry. This action is repeated until the desired height is achieved.

The temporary forms are then taken away leaving a strong and durable wall. While the frames are temporary, they must be constructed well enough to hold the pressure and weight of the materials, and endure the compression process.

Environmental Benefits of Rammed Earth

The main benefit and reason for its newfound popularity is that rammed earth is a very sustainable building practice that also happens to be cost-effective. Soil is abundant, and using it to build has little to no environmental consequences.

The construction is the main cost to consider, as most people opt to use a mechanical tamper rather than rely on compressing by hand. Constructing the forms can also be labor intensive and costly, but prefabricated frames can also make the job go a lot faster.

Even with the cost of these modernized tools and forms, a home built with rammed earth technology can be done for a fraction of the price of regular building and done within a few days, depending on the complexity of the design and location.

Cost of Building

There are certain costs that make rammed earth building expensive, and that’s mainly the labor and machinery that's necessary to make the forms and compress the earth. The main building materials may not be expensive depending on how much soil is available to use on site for free.

If you design a simple one-story home with only a few walls, this will lower the overall price of construction. Good design will help with the cost, as solar and wind power can be utilized, even just in terms of where the structure will be built.

A smart geo-location can save energy based on how outside elements work in conjunction with windows, wind tunnels, trees, and other factors that influence natural heating and cooling with thermal mass walls. If the land is easy to build on, this will equate savings. If you are on a slope, or have difficult soil, excavating costs can quickly add up.

It's difficult to find an average cost per square foot since there are so many factors involved with rammed earth building. Just like a conventional home, simple will often equate cheaper, however, because soil should be free, you should be able to build a larger home out of rammed earth cheaper than a similarly sized standard home.

Can You Make Rammed Earth Yourself?

Yes, you can make rammed earth yourself, and even build your own home out of it. While you don’t necessarily need building experience to do it, it does require a lot of time, labor, and the right science. Some basic tools would be necessary, but most of it can be done with hand tools like shovels, tampers, and a hammer.

The ideal dirt mixture would be between 50-75 percent sand, and not too much clay. It needs to be sifted so that large rocks and other materials are screened out. The material needs to be protected or tarped from rain to keep a specific moisture content of no more than 10 percent.

A foundation of some kind is needed, and forms will need to be constructed. Once these are in place, the rammed earth can be shovelled into the forms in four inch iterations, each tamped down by hand until they feel solid.

This is just a basic step-by-step process that doesn’t take any of your climate or geographical characteristics into mind. Whether or not you can DIY your own rammed earth structure also depends on the size and weight of the structure, the necessary reinforcement, and whether you need permits or an engineer to begin work.

Climate

The freeze-thaw cycles of some American climates make building with raw rammed earth unstable, or even if reinforced properly, the durability may not be as long. Also, the costs and carbon footprint may go up as adding cement to raw earth takes away much of its eco-friendly benefits.

While the thick walls of rammed earth are excellent insulators, in extremely cold climates, extra insulation would be needed, as well as supplemental heating. Commercial insulation like fibreglass and spray foam, and the addition of HVAC systems would detract from rammed earth's sustainable badge, and increase yearly costs to the homeowner.

Rammed earth walls aren't recommended for areas that receive heavy, relentless rainfall, though they can withstand an average rainy season just fine.

Moderate climates and flat ground with an abundance of raw material is the ideal environment for building a raw earth structure. While they can technically be built anywhere, the need for modification ups the price of building significantly, and negates its low carbon footprint claim.

What Kind of Dirt Works Best?

Essentially the best dirt is the one that’s available, although many factors come into play. Just as climate and location can affect the extra materials needed to build with rammed earth, it also affects the soil mixture needed.

In general, a mix of mostly sandy soil with minimal clay content is ideal for moderate climates that don’t experience any extreme temperature fluctuations.

That said, the building method can be developed for the earth material being used, and not vice versa. Let the land dictate what mixture works best based on these environmental factors, and then reinforce and design as needed.

Rammed Earth vs Concrete

The actual building of rammed earth and concrete is very similar, as both use wooden forms to create the shape and various tamping methods to produce the cured effect. The aesthetic is therefore similar, as is the desired result.

Cement and concrete products are more expensive than free dirt, but the labor involved in rammed earth is also costly. Those two variables end up cancelling each other out in the long run, of course, depending on the structure and how much earth is available to use for free.

The main difference is the environmental impact. The production of cement accounts for 7 percent of annual CO2 emissions overall. Most concrete is between 10 and 15 percent cement. CSRE can be made with 1-10 percent of cement added to raw rammed earth, making it essentially a concrete product in the end.

If rammed earth can be kept raw, it far exceeds the carbon footprint of concrete products, especially if local soil is used and transportation is low. This also keeps the costs down, making it a superior choice to concrete in the end if these two variables are kept in check.

How Strong Is Rammed Earth?

Once constructed and fully cured, rammed earth is extremely durable and strong, with a compression strength of around 4 MPa or between 600 and 1500 psi, depending on engineers’ instructions. This is slightly less than concrete, but more than strong enough for the majority of one- or two-story building projects.

Walls built with rammed earth will be a lot thicker than a similar strength concrete wall, which also must be considered when building. This isn’t necessarily a negative, but something to consider when designing.

Rammed earth structures can also last thousands of years, and when built with re-bar, or other reinforcement techniques, are able to better withstand natural disasters like earthquakes, hurricanes, and tsunamis.

Thermal Mass

There are other attributes to rammed earth that often get overlooked when things like cost of materials and labor takes the forefront of people’s decisions. Rammed earth walls create a very warm environment, both in temperature and aesthetic.

Thicker walls are better at controlling the indoor climate, as outdoor temperatures will take 12 hours to reach the inside wall. This thermal capacity means that fluctuations in hot and cold won’t be felt as much as with other building materials like concrete or brick.

The thermal mass of rammed earth makes them very efficient at heating and cooling spaces, mainly because there wouldn’t be as much need for extra heating and cooling on a day-to-day basis.

Thermal mass increases the comfort of your home’s temperature in summer and winter, and reduces temperature fluctuations within the home. When paired with solar passive design and used correctly, thermal mass can have a major impact on reducing your energy usage.

Other Benefits

Thick walls reduce the transmission of noise which can be useful in cities or anywhere you want to create an indoor sanctuary. Museums, churches, and stadiums would benefit from this capability, while residential and commercial buildings would appreciate the lack of outdoor sound transfer.

Rammed earth is also known to create good indoor air quality. When clay is used in a rammed earth home, it’s been noted that indoor humidity levels are ideal, making the space healthy for humans, pets, and plants.

Natural materials are inevitably healthier in general as there is no off gassing or synthetic elements to worry about.

The last thing to consider is resale value. Homeowners are looking for ways to reduce their carbon footprint, and are considering these alternative building methods if it means they can live in an environmentally friendly and unique looking home.

These homes are also built to last, except on the market! Because of their exclusive nature, they are highly sought-after, making them a good investment to either build or purchase.

Styles and Design

The sky is the limit when it comes to structures that can be built with rammed earth. Residential homes, commercial spaces, museums, and any other architecture can be constructed with rammed earth.

The only restrictions on building with these materials will be climate and geography.

Versatility may be an understated benefit to building with rammed earth, as the ways in which it can be constructed are infinite. While rammed earth ceilings aren’t as common as walls, with the right reinforcement techniques, they can be fabricated.

Various textures, colors, and finishes are also available for those who are designing their own space. Walls can be left rough or polished smooth for a glossy look. Colour can be added, but the appeal of rammed earth is showcasing the natural hues of the local environment.

Buildings can be constructed in square or circular fashion, with single walls or feature walls and sculptures add to the design. Art can be incorporated into the building of rammed earth, and homes can be as big or as little as one desires.

Maintenance

Rammed earth buildings are very low maintenance. Once walls are sealed they are water-repellent, on the inside and outside, and will not require any further work or upkeep.

Walls don’t need to be painted or dry-walled, unless someone wants to add this to the design in areas.

Rammed earth buildings are fire-proof and termite-proof; the first being ever so important these days as wildfires rip across the country and the world deals with natural disasters from climate change.

Building with rammed earth is exciting because of the possibilities involved. If you are designing your own home, and have lots of land, materials can essentially be free if you are using the dirt around you.

While the cost-effectiveness of rammed earth depends on labor and type of design, it's overall an excellent investment when used in moderate climates.

Not only are the building materials sustainable, heating and cooling a rammed earth home is much better for the environment, and can add up in yearly savings for homeowners. The opportunities for a smart investment are there, as is the unique experience of living in a space that fits in with nature, rather than against it.