Adobe – The ABCs of Green Building Materials
Originally published on GreenBuildingElements.com
Green building materials are as diverse as Earth itself. Some of the most sustainable materials on the planet are modern inventions, and some are as old as the hills, like adobe. Familiarizing yourself with the best green building materials will help ensure your environmentally friendly projects enjoy sustainable success.
Over the next several weeks, watch for new posts in GBE’s new series, “The ABCs of Green Building Materials.” If you have a project in mind highlighting any great green building materials, give it a shout out in the comments below.
The ABCs of Green Building Materials
ADOBE – One of the Oldest Green Building Materials on Earth
One of the oldest green building materials on the planet, adobe is truly as old as the hills. For at least 4,000 years, the word “adobe” has been in use with pretty much the same pronunciation and meaning. Evolving from Middle Egyptian “dbt” or “mud brick,” to Coptic Egyptian, “toob,” and then from Arabic, “At-tuba,” the mud and straw brick became immortalized by the Spanish as “adobe.”
The arrival of Spanish-speaking people in the “New World” introduced the technique of brick-making, but the indigenous people of the Americas were already very familiar with the use of adobe for construction.
In hot, dry, desert climates, these buildings are very energy-efficient, offering naturally cool spaces during the hot days, due to the walls’ greater thermal mass. In the cool nights, they offer radiant warmth from the daily absorption of solar heat. Using only the most basic of natural resources, adobe structures are also highly resilient, even offering protection from fire.
DIY Adobe – The Original Mud Pie
The simplest of green building materials, all you really need to make an adobe brick is dirt, water and a hole in the ground to mix it by hand. Sounds as easy as making a mud pie, right? The dirt composition is critical, however, because if you don’t get it right the finished brick will crack into pieces or crumble completely.
Greater success rates are reported by using a mix of about 15 percent clay, 10 to 30 percent silt, and 55 to 75 percent fine sand. This can be checked by chemical analysis, but in many places around the world it’s judged by placing a handful of dirt in a glass container full of water and shaking it vigorously. Dirt settles first, followed by silt, and the clay stays suspended in the form of clouded water for varying lengths of time, depending on the percentage.
Wooden frames are commonly employed to standardize the finished brick shape, which can vary widely across cultures and locations. Of course, modern machinery like front end loaders and brick-making machines can also greatly speed up the process, but people are still making adobe bricks by hand all around the world.
Organic material, such as straw or manure, is also commonly added into the mix for additional brick strength. Once formed, the bricks are left to dry in the sun, moving them periodically to ensure uniform drying. Unlike standard kiln-fired bricks, adobe bricks maintain their great thermal insulating properties when dried in the sun.
Warning – Strong Back Required!
“Traditional New Mexico” size bricks are typically four inches thick, by ten inches wide, by fourteen inches long. A five-gallon bucket fully loaded with dirt will make around three adobe bricks of this size, so, depending on the size of the structure being build, a huge amount of dirt is needed.
A strong back is required, too, because each finished brick will weigh around thirty pounds. The foundation will also need to be carefully prepared to handle this kind of weight, because any settling or shifting under the load will likely result in serious structural damage.
Local building codes and desired material properties are major factors when choosing the most appropriate green building materials for a project. Because adobe brick walls are not high in structural strength, load bearing walls typically never rise over two stories high.
Building Code Considerations
US building codes commonly require load bearing walls to have bricks with sufficient compressive strength, typically 300 lbf/in2. US codes also commonly require that buildings must sustain a 1 g lateral acceleration earthquake load, meaning finished bricks must have a tensile modulus of rupture strength of at least 50 lbf/in2.
Rainfall amounts and water damage are also serious considerations when choosing green building materials. Adobe brick, while providing excellent protection from desert climates, doesn’t hold up well in the rain. Some builders stabilize it with the addition of about 10 percent emulsified asphalt or Portland cement, as this can provide extra protection from rainwater damage.
With or without stabilizers, both interior and exterior adobe brick walls are typically covered with a protective layer of mud plaster, stucco, or whitewash, depending on local rainfall measurements.
The Many Benefits of Adobe
Benefits include energy-efficiency and protection from both weather extremes and fire. As one of the oldest green building materials on Earth, adobe is still popular because it is inexpensive and convenient, providing a do-it-yourself housing solution for both temporary and permanent needs.
Many of the oldest buildings found on the planet are made of this wonderful material, and they are still in existence after thousands of years.