Rammed Earth: the longest standing building material....
For thousands of years our ancestors have been building with rammed earth. You can see structures made with this technique on every continent other than Antarctica. Early examples exist in China along the Yellow River and the Silk Road, as well as in Portugal and France. Around 2000 BCE rammed earth was a common building technique used for walls and foundations in China. Examples of rammed earth exist in Canada and North America as well, more common in the southern states; notably South Carolina. However one of the early Canadian examples exists not far from Toronto, in Shanty Bay, Ontario.
St. Thomas Anglican Church began construction in 1838. Wet clay and straw were compacted into forms until dry and then covered with siding or plaster to protect from the elements. The church is now a provincial heritage site and still runs service every Sunday. This is only one example of the longevity of rammed earth as a building material.
Nowadays rammed earth structures in Canada are comprised of a 8” wythe of rammed earth on the interior and exterior, separated by minimum 6” of insulation, and connected with fiberglass or stainless steel reinforcing bars.
Rammed earth buildings have a high thermal mass, and ductility and when designed with intersticial insulation will reduce heating and cooling costs substantially. It is an extremely useful material for Passive homes due to its durability, longevity, and low embodied energy.
Creating rammed earth in southern Ontario is less energy intensive since our accessibility to the materials needed is in abundance. Gravel pits are typically within a few km of the site. They create the base soil mixture of clay sand shale for rammed earth and then it is trucked to the site. This is combined with agregate, small amounts of water, and only 4% cement. Regular concrete is typically 10%-20%. The final mix also has earth plasters for colour and Plasticure, a waterproofing material. Once the rammed earth mixture is ready it will be dry poured into the forms and compacted down with a pneumatic tamper. Although this was done traditionally , site soils cannot be used as it is harder to control the ratios and keep it free of organic material.
Hardships are also experienced with rammed earth. Although it is an ancient material, most countries lack regulation, making it complicated to be approved as a building material. Typically an Alternative Solution to the Ontario Buidling Code is required. Due to the structural nature of the solution we use structural engineer, Tim Krahn of Building Alternatives Inc., who has successfully administered our buildings through the OBC.
Once rammed earth get approved as a building material, the next challenge is finding an experienced contractor. Luckily we are one of the most experienced rammed earth architecture firms in Ontario and have great relationships with both Aerecura Rammed Earth Builders and Tapial Homes. Lastly, make sure you don't waffle on your window and door placement, once it is built, it is almost impossible to change them, as they are literally set in stone.
The pros definately outweigh the cons. It is a great material offering energy savings, a beautiful look and durability to last hundreds of years. Insulated rammed earth has been proven to be able to meet the Passive House standard in Ontario. It was presented by Terrell Wong at the Darmtadt PHI conference a few years ago. Interested in learning more feel free to contact us. Aerecura hosts monthly open houses, so that you can see it first hand. www.aerecura.ca