Green Building - What's the deal with Rammed Earth Building?

What is Rammed Earth Building?
Rammed Earth construction is an age-old building method that has seen a revival in recent years as people seek low-impact building materials and natural building methods. Traditionally, rammed earth buildings are common in arid regions where wood is in scarce supply.

Rammed earth construction is a process of compressing a damp mixture of earth that has suitable proportions of sand, gravel and clay (sometimes with an added stabilizer) into an external supported frame that molds the shape of a wall section creating a solid wall of earth. Traditional stabilizers such as lime or animal blood were used to stabilise the material, but cement has been the stabilizer of choice for modern times. After compressing the earth the wall frames can be immediately removed and require an extent of warm dry days after construction to dry and harden. The structure can take up to two years to completely cure, and the more it cures the stronger the structure becomes. When the process is complete it is much like constructing a hand made wall of solid rock.

What are its benefits?

Rammed earth structures are beneficial for natural building because they can utilize locally available materials with little embodied energy and harmful waste. Earth is a widely available building material with virtually no side effects associated with harvesting for use in construction.The earth used is typically subsoil, leaving topsoil readily available for agricultural uses. Often the soil can be used on the site where the construction takes place reducing cost and energy used for transportation. It is also affordable to build with, as the materials are inexpensive or free. It is a viable building material for low- income builders with help from unskilled workers, friends, or family. Today more than 30 percent of the world's population uses earth as a building material.

Rammed earth is not only an economically viable construction technique, it results in pleasant, and energy-efficient buildings. The density and thickness of rammed earth makes it so that hot or cold temperature penetration has a slow rate of thermal conductivity. Warmth takes almost 12 hours to work its way through a 14 inch thick wall. The walls provide good thermal mass, which helps keep indoor temperatures stable, particularly in regions with dramatic daily temperature changes. The half-day rate of heat transfer and thermal mass of the material makes rammed earth a practical material for passive solar buildings. Rammed earth has been a popular choice for buildings where temperature fluctuations need to be kept to a minimum. It can be used in cooler climates but must be protected from heavy rain and insulated with vapor barriers.

Typically rammed earth walls are about 12 to 14 inches thick making them ideal for humidity control and noise barriers from traffic, furnaces, compressors, fans or ducts. Rammed earth also allows more air exchange than concrete structures allowing the building to breathe and not become clammy without significant heat loss as the material mass absorbs the temperature as the wall breathes. source: wikipedia and www.lowimpact.org

some examples: high rises in Yeman.