What is rammed earth construction?
Rammed earth construction is the process of ramming a mixture of aggregates, like gravel, sand, silt and clay into a formwork to create walls. When the earth is dry the formwork is removed to reveal solid monolithic walls.
Rammed earth is an ancient form of construction, generally seen in drier hotter parts of the world. Although many rammed earth structures exist in this basic form, a new ‘stabilised’ rammed earth variant has been developed which adds a small amount of cement (5-10%) to the mixture to ensure strength and durability.
Traditionally, a wooden pole is used to ram the earth into the formwork, but modern methods now use a mechanical ram.
The process is labour intensive, but is considered to have a low environmental impact depending on materials used (cement content) and source of those materials. While some elements of the rammed earth wall will have a low embodied energy, cementitious products do not.
What does rammed earth construction look like?
The appearance of rammed earth will depend on the earth and aggregate used, in terms of colour and texture. However, rammed earth has a horizontal layered appearance which demonstrate the process used to construct the walls. Some like this feature of rammed earth, however it is possible to control it so that the layers are not visible. Rammed earth is often seen in a red/orange tone colour – a simple google image search will demonstrate this.
Rammed earth structures can be considered relatively basic and of simple form, or for eco enthusiasts. However many architects are now developing designs to use the process in contemporary projects, to spectacular effect. Check out some of the examples at the end of this post.
Rammed Earth Construction Guide
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 possibility of cracking and difficulty ramming around the reinforcement bars.
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 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.
Rammed earth construction is suited to warmer drier climates, there are relatively few rammed earth examples in the UK for this reason. It is a popular method of construction in Australia.
Walls should be protected from the weather as best as possible. Raised foundations should lift the wall at least 225mm above ground level, while 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.
Rammed earth example projects
DL Atelier Art Museum
Vo Trong Nghia Architects – Hanoi
NK’Mip Desert Cultural Centre – DIALOG
For more inspiration check out: