What is Natural Building?
Natural Building is a term often used to describe a more resource efficient, ecologically sound form of construction. In the book Alternative Construction: Contemporary Natural Building Methods edited by Lynne Elizabeth and Cassandra Adams, Natural Building is defined by not just the technique and materials used but by a set of ethics and a broader movement emphasizing a deeper connection to the earth as a living system into which we must integrate our built environment. Natural Building methods include the traditional and contemporary earth and fiber-based techniques (e.g. adobe, cob, rammed earth, straw bale), timber framing, stone masonry and various other indigenous forms. Another important aspect of Natural Building is using locally sourced, reused and recycled, and less energy intensive materials whenever possible.
What is Cob and What is Adobe?
Cob is perhaps the oldest, and simplest earthen building system, requiring no framework, ramming, or mechanized equipment. With no industrial additives, and only minimal training, cob has been used around the world for 10,000 years. As a natural building material, it is a combination of about 75-85% sand or aggregate, and 15-25% clay, found in most subsoils about a foot beneath the ground, throughout the world. Mixed with straw (a byproduct of growing wheat or rice) and water, cob becomes an incredibly strong and seismically resistant building material that can be sculpted, reworked, and reused with little degradation to the original ingredients.
Adobe is another millennia old building material and technique. Adobe, like cob is composed of clay subsoils with sand and straw to help hold it together and give it compression strength. The main difference between cob and adobe is that adobe is formed into bricks that are dried in the sun prior to building, whereas cob is built layer by layer without forming into bricks first. The Mission Dolores, built in 1776, is the oldest intact building in San Francisco, and having survived the 1906 and 1989 earthquakes, is a testament to the durability and beauty of building with adobe.
Considerations for Natural Building
As these materials are of the earth, they can breakdown into simpler elements if left exposed to rain for long periods of time. While 2,000 year old cob homes and buildings, up to 9 stories high, still stand in Shibam, Yemen, it is mostly due to low rainfall and proper maintenance. In areas that experience heavy rains, like Devon, England where a rich cob tradition is still in place, cob homes must be protected from wind driven rain by adequate roofs, and solid foundations that prevent groundwater from soaking into the mix.
For urban landscapes, cob and adobe benches (or other structures without a typical roof) are best sited under overhangs and eaves that prevent direct contact with rainfall. If that is not possible, several coats of earthen plaster (basically the same mix as cob but sifted for a finer texture) and finish coats of boiled linseed oil and beeswax can maintain a beautiful finish that is weather resistant.
Opuntia cactus, used for nopales or prickly pear fruit yields a mucilaginous additive to finish coats and plasters that make it even more weather resistant. Proper maintenance would include reapplying a linseed oil coat every 1-2 years, and reworking the finish plaster every 5 years – a great opportunity to create a community building gathering to bring people together and share in the rich tradition of earthen building that continues to this day around the world.
The Ecology Center of San Francisco – books on natural building, free cob and natural building workshops www.eco-sf.org
Emerald Earth Sanctuary – intentional community specializing in hybrid natural building systems www.emeraldearth.org
Solar Living Institute – classes on natural building, including cob, straw bale, and more www.solarliving.org
The Last Straw – international quarterly journal on straw bale and natural building www.thelaststraw.org