Rammed earth buildings are thick, natural looking walls and are constructed using an ancient technique, combining soil, sand, clay and water in specific quantities that are compressed between forms to make a solid wall.
The wall is created in position on the site of the building by pouring the earth mix into casings, which are then removed after ‘ramming’ is finished. When finished, it can resemble a man-made sedimentary rock. Stucco is often used to protect the walls from the earth’s elements, particularly water, while the textural imperfections are a drawcard of the material’s look and feel.
The look can be found in centuries-old Asian and middle eastern villages, right through to multi-million dollar eco-friendly homes in California. Some of New Zealand's rammed earth homes were created in the 1800s and are still standing the test of time.
Although using these materials is labour intensive, rammed earth builder and director of Terra Firma Earth Building Paul Geraets says the sustainability and energy efficiency aspect of the material means the practice is becoming more popular.
“At the last three home shows we’ve definitely been getting more enquiries from a diverse range of people. Not surprisingly, they’re looking for natural feeling, sustainable ‘behaving’ options when they approach my stand,” Geraets says.
“What they learn if they’re prepared to go down the rammed earth path is that the sustainable building claims come not only from reduced carbon footprints due to more local material sourcing, but also for the longevity of the building.”
In fact, last year the 2017 World Architecture Festival’s Building of the Year award went to a rammed earth building in China last year. The technique was used to rebuild a village destroyed by the 2014 Ludian earthquake.
Geraets says this award is a great sign for sustainable building in New Zealand, particularly because it places the architectural needs of a community over developers’ profit margins, construction supply industries and banks.
However, he says in New Zealand, there’s still not enough recognition for the material’s benefits, particularly the way it can heat and cool a building with ease.
“The building industry here still holds standard wall insulation as the holy grail of thermal performance,” he says.
Geraets says he hopes the international recognition rammed earth buildings are now getting might buck the New Zealand trend to use weatherboard to insulate the walls so nothing can get in or out, saying this doesn’t help humidity. Instead, he says the ‘breathing’ qualities of rammed earth buildings can counteract this.
His engineer, Doctor Paul Jaquin, is an international expert on rammed earth buildings and is currently part of the team updating New Zealand’s earth building design codes.
Jaquin says with thermal mass in rammed earth buildings, the thick, cool earth walls store heat from the inside of the structure, which brings the internal temperature down.
When the internal temperature drops under that of the wall itself, the wall then releases the heat and warms up a cooler room.
“Let’s say for instance it was 30 degrees outside during the day, and 10 degrees outside overnight. During the day, the walls would absorb some of the heat, and during the night they transfer that heat to the inside of a building, so inside the building it can become an equalised 20 degrees,” Jaquin says.
Rammed earth buildings have a humidity level of around 55 percent. In terms of leaky homes, mould begins to grow when relative humidity reaches 70 percent.
Geraets says with the Healthy Homes Guarantee Bill passing in December that ensures every rental home in New Zealand meets minimum standards of heating and insulation, there’s an opportunity to look beyond insulation and heat pumps to solve this problem and decide what a healthy, well heated home really is.
“The main thing here is acceptance that rammed earth is an intelligent method of construction and that it is realistically affordable here in New Zealand,” he says. “Just think what you get for your buck: health, comfort, durability, low maintenance, low carbon footprint and of course a beautiful, original building.”
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