Rammed earth is a technique for building walls, foundations and floors using natural raw materials such as earth, chalk, lime or gravel. It is an ancient building method that has seen revival in recent years as people seek more sustainable building materials and natural building methods.
Earth walls are constructed by ramming a mixture of aggregates, including gravel, sand, silt and a small amount of clay, into place between flat panels called formwork. In modern times the most typical form of constriction is called stabilised rammed earth. This is a variant of the traditional rammed earth that adds a small amount of cement (typically 5-10%) to increase strength and durability. Stabilised rammed earth walls need little added protection but are typically coated with an air-permeable sealer to increase the life of the material.
The colour of rammed earth will vary depending on the earth and aggregates that were used in the construction. During the ramming process layer upon layer is applied, this introduces a horizontal stratification appearance to the wall. This can be controlled as a feature or can be eliminated.
The thickness and density of rammed earth walls allows the absorption of heat transfer through the material and then releases that heat when the surrounding ambient temperature goes down. Used correctly, and in the right climate, the thermal mass of rammed earth can delay heat flow through the building envelope by as much as 10 to 12 hours. Rammed earth is not recommended for tropical climates where high mass construction can cause a house to hold too much heat and cause thermal discomfort.
As a corollary to its high thermal mass, rammed earth has limited thermal insulating qualities. Insulation can be added within the thickness of the wall, it will provide the benefits of both excellent thermal mass and a good thermal insulation, while retaining the desired aesthetics and adhering to standards.
The thickness and density of the walls means that noise transmission is very much reduced from both the exterior of the house and internal connecting rooms. CSIRO tests quoted in Bulletin 5 Earth-Wall Construction indicate a sound transmission rating of more than 50 decibels for a rammed earth wall of 250mm.
Durability & Moisture Resistance
Rammed earth is highly durable and moisture resistant. While you need to prevent continued exposure to water at the top and bottom of the walls, most Australian rammed earth walls do not require additional waterproofing. Earth building has 100-400 years on proven durability in Australia, Europe, England and the middle east, offering longevity. Increased confidence in the stength and resistance of the product has been created by the addition of modern stablizers, concrete foundations and steel reinforcement.
There are no flammable components in a rammed earth wall, as earth doesn’t burn. CSIRO tests showed that a 250mm earth block wall achieved a 4-hour fire resistance rating. A 150mm earth block wall achieved a rating of 3 hours 41 minutes.
Termites and other pests simply are not interested in the rammed earth. There are no cavities in earth walls for pests to live in, or to use as a route to the roof or other timbers.
Earth structures are maintenance free. Each panel is constructed as a fully articulated monolith so stress fractures due to any shrinkage are eliminated. Similar to all solid masonry, the base of the walls must be kept a minimum of 50mm above the surrounding group level to prevent rising damp. The top surfaces of the walls require capping.
Building with rammed earth is more environmentally friendly than building with any other solid masonry product. Earth is an unprocessed, widely available building material with virtually no side effects associated with its quarrying or use. Earth walled building saves on construction and energy resources, doesn’t pollute and last practically forever, inevitably this makes the decision to build with earth a wise investment in the future of our planet.
For more information on why you should turn to green building solutions see our blog post ‘Reasons to Build Green’
Earth Building Association of Australia. 2012. www.ebaa.asn.au
Earth-wall Construction, Building Technology File 06, Publisher: CSIRO Building, Construction and Engineering http://www.publish.csiro.au/pid/2981.htm
Rael, R. 2012. Earth architecture — Australia & New Zealand. http://eartharchitecture.org