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Location
Rammed earth construction is suited to warmer drier climates, which is why there are relatively few rammed earth examples in the UK. This construction method is popular in Australia, which was among the first countries to develop a national design guideline document for it. Before choosing rammed earth as your construction method, it is crucial that you thoroughly study your site location and climatic conditions. This is because the suitability of rammed earth can vary depending on local building regulations, available guidance, and soil conditions.

The extraction site may be the actual build site or a site nearby. The subsoil that lacks any humus or vegetable matter is used. The soil is typically dug and mixed with the crushed aggregates on site. This reduces the need for material transportation and helps to lower carbon emissions.

The soil conditions, as with any construction project, must be assessed to determine the most suitable foundation. This is typically a conventional concrete strip or slab foundation for rammed earth.

Construction
Formwork is essential for rammed earth walls and is typically made from plywood or steel panels. The formwork can also be mounted either on the foundation or an existing built up wall. Additional propping material may be used to ensure stability during construction.

There are different types of formwork that can be constructed, from movable to static, that can be both built on site or be prefabricated.

Once the formwork is in place, the construction process begins by filling the frame with a layer of damp earth mix. Traditionally, a wooden pole was used to compress this layer to about half its original volume but today more efficient pneumatically powered tampers are used. This process is repeated until the frame is filled with compacted earth. When the formwork is removed, a free-standing rammed earth wall remains. To see this process in more detail, check out the illustrated diagrams further down in this post.

However, despite these advancements, the process remains labour intensive and time consuming, which can impact the overall cost and timeline of the project.

Impact on the environment
Although the construction process is labour intensive, it is generally considered to have a low environmental impact, particularly when using locally sourced materials. However, it is important to note that the environmental impact will vary depending on the materials used. While some elements of the rammed earth wall will have a low embodied energy, cementitious products will not. The technique also allows for the recycling and reuse of materials on site, further reducing waste.

Structure
Rammed earth is considered to be strong in compression and suitable for load bearing construction. It is possible to introduce reinforcement to the walls similar to concrete, however this must be carefully designed due to the possibility of cracking and difficulty ramming around
the reinforcement bars.

Although many rammed earth structures exist in the basic form (RE), a new ‘stabilised’ rammed earth (SRE) variant has been developed which adds in a small amount of cement (5-10%) to the mixture to ensure strength and durability.

Durability
The walls are quite durable but should be protected from the weather as best as possible. Raised foundations should be used to lift the wall at least 225mm above ground level and roof overhangs should protect the walls from rain. All water should be drained away from the walls and moisture should be allowed to evaporate easily.

Some additives have been developed that are water repellent, these are added to the mix to allow the walls to be constructed in more exposed environments.

While rammed earth structures are known for their longevity (10-20 years) and low maintenance, they do require careful planning, particularly in terms of curing time and the integration of services.

Insulation
A feature often exploited with rammed earth structures is thermal mass. The thermal mass slows the movement of heat through the walls, then releases the heat when the surrounding temperature drops (at night). Thermal mass structures can even out temperature variations, creating a comfortable internal environment.

Insulating a rammed earth structure in cooler climates can require careful thought. Often designers would like to keep the external face of the rammed earth exposed for aesthetic reasons. Insulating the structure in the inside of the building will lose all thermal mass benefits. It is more beneficial to insulate the structure on the outside of the building which will protect the rammed earth but also allow the building to benefit from thermal mass.

Positioning and requirement of insulation will depend on location and climate, but it is worth noting that rammed earth is hygroscopic, meaning the walls must be able to breath, and allow evaporation. Any finishes must be vapour permeable to ensure condensation doesn’t build up within the assembly.

Fire and Pest Resistance
Rammed earth walls have high resistance to fire and pests. The absence of flammable components in the earth mixture means that these walls can withstand high temperatures without catching fire. Additionally, the solid, dense structure of the walls is inhospitable to pests, further contributing to the durability and safety of the building.

Soundproofing
Due to its density, rammed earth provides excellent soundproofing. The thick, compacted walls naturally dampen sound transmission and make rammed earth an ideal choice for buildings where noise reduction is a priority.

Indoor Air Quality
One of the significant benefits of rammed earth construction is its hygroscopic nature, which contributes to a healthier indoor environment by regulating indoor humidity levels, reducing the risk of condensation and mould growth.