What exactly is rammed earth building ?

As a building method, rammed earth is one of the most sustainable materials to choose in home design. Rammed earth is an ancient form of building whereby a damp mix of aggregates—commonly gravel, sand, silt and clay—are rammed into removable frames (formwork) to create walls, foundations and floors. Stabilised rammed earth is a variant that includes the addition of cement to increase strength and durability.

Thousands of unstabilised rammed earth buildings around the world have given good service over many centuries. Traditional technology repeatedly rammed the end of a wooden pole into the earth mixture to compress it. Modern technology replaces the pole with a mechanical ram. The finished wall can be 100 to 600 mm thick, has a very high thermal mass and is natural and earthy in appearance.

Traditional technology repeatedly rammed the end of a wooden pole into the earth mixture to compress it. Modern technology replaces the pole with a mechanical ram. Stabilised rammed earth is a variant of 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 usually coated with an air-permeable sealer to increase the life of the material — it varies with circumstance.

Most of the energy used in the construction of rammed earth is in quarrying the raw material and transporting it to the site. Use of on-site materials can lessen energy consumed in construction. Rammed earth gives limited insulation but excellent thermal mass. The modern process of making stabilised rammed earth is both labour intensive and highly mechanical, requiring the use of powered rams.

Pros

Good thermal and insulative properties
Can use local unskilled labour
Uses whatever earth is on site
Strong and durable, fast
Gets straight lines and arches

CONS
Limited building standards in Australian codes
Hence performs badly in ratings assessments
Works on economy of scale, better for bigger projects

Rammed Earth in Australia

Rammed earth pioneers, Olnee Constructions, discuss the advantages of rammed earth walls on their website.  They claim they are perfectly suited for Australian climates because

• Rammed earth’s superior insulation qualities mean you’ll stay warmer in winter and cooler in summer. You’ll keep your heating and cooling costs down while helping to save the environment’s precious resources.
• Rammed earth walls don’t need to be rendered, painted, wallpapered or tiled, although if you want to add a finish you certainly can.
• Rammed earth walls require no ongoing maintenance.
• The strength and durability of rammed earth walls means they are practically permanent. They can handle virtually anything that Mother Nature can throw at them. With the introduction of new technology and waterproofing, Olnee’s rammed earth walls are even stronger and more durable than rammed earth walls of the past.
• The thermal mass of rammed earth walls will also help reduce noise, so they’re perfect for busy, loud areas.
• Earth doesn’t burn and neither does a rammed earth wall. This fireproof nature makes it perfect for bushfire-prone areas and is why rammed earth has been added to the Building Code of Australia’s list of recommended building materials for high fire risk areas.
• Rammed earth walls are excellent for load bearing, which reduces the need for structural supports. This can help reduce building costs and provide architectural possibilities that other materials can’t. Standard 300mm rammed earth walls can be used as load bearing in constructions up to four stories high!
• Termites and other pests are of little concern to rammed earth, so a rammed earth wall is deemed termite resistant under the Building Code of Australia.

Check out some of these resources:

Your Home – Australian Govt Guide to Good Building – rammed earth

CSIRO Building Tech file – rammed earth info

Earth Building Assoc of Australia (EBAA)

Australian Earth Building Handbook HB195 (Referenced in Australian Building Code)

The Rammed Earth Renaissance