What is a Cob House? Simple Earth Architecture

Sturdy Houses Made of Mud & More

Cob house under construction, Greyton, Western Cape Province, South Africa.
Cob house under construction, Greyton, Western Cape Province, South Africa. Photo by Mike D. Kock/Gallo Images/Getty Images (cropped)

Cob houses are made of clay-like lumps of soil, sand, and straw. Unlike adobe and straw bale construction, cob building does not use bricks or blocks. Instead, wall surfaces are built up with lumps of damp cob mixture and sculpted into smooth, sinuous forms. A cob home may have sloping walls, arches and lots of wall niches. In Old English, cob was a root word that meant lump or rounded mass.

Cob homes are one of the most durable types of earth architecture.

Because the mud mixture is porous, cob can withstand long periods of rain without weakening. A plaster made of lime and sand may be used to windproof the exterior walls from wind damage.

Cob architecture is suitable for the desert and some people claim cob is even good for very cold climates, because of the great wall thickness. Small cob structures, like tiny homes and garden sheds, are very inexpensive Do-It-Yourself projects. It's the architecture of choice for survivalists and preppers.

More Definitions:

"Cob is a structural composite of earth, water, straw, clay, and sand, hand-sculpted into buildings while still pliable. There are no forms as in rammed earth, no bricks as in adobe, no additives or chemicals, and no need for machinery."—Ianto Evans, The Hand-Sculpted House, 2002, p. xv.
cob "A mixture of straw, gravel, and unburnt clay; used esp. for walls."—Dictionary of Architecture and Construction, Cyril M. Harris, ed., McGraw- Hill, 1975, p. 111.
cob wall "A wall formed of unburnt clay mixed with chopped straw, gravel, and occasionally with layers of long straw, in which the straw acts as a bond>"—Dictionary of Architecture and Construction, Cyril M. Harris, ed., McGraw- Hill, 1975, p. 111.

How Do You Make Cob?

Anyone with even a little experience in the kitchen knows that many of the finest foods are put together with simple recipes.

Homemade pasta is simply flour and water, with an egg added if you want egg noodles. Shortbread, that rich, crumbly cookie confection, is a simple combination of flour, butter, and sugar. Ingredient amounts vary with each recipe—the "how much" is like a secret sauce. The mixing process is the same—make a well (an indentation) in the dry ingredients, add the wet stuff, and work it together until it feels right. Making cob is the same process. Mix water into clay and sand, and then add straw until it feels right.

And that's where the expertise comes in. When does it feel right?

The easy way to make cob is with a portable cement mixer, which does all the labor-intensive mixing of the clay, sand, water, and straw. But a sturdy mixer can cost $500 even on Amazon.com, so "natural builders" like Alexander Sumerall at This Cob House use what is called the tarp method. The process of mixing is like making pasta, but on a larger scale. The ingredients (clay and sand) are placed on the tarp, which is used to help mix the ingredients. Folding the tarp moves the cob ingredients, and the movement mixes it. Add water, and the fun begins. Sumerall's logo, a footprint with the outline of a house in the arch, makes a lot of sense when you watch his video on How to Make Cob—use your bare feet to mix in the water and eventually the straw.

Put most of your energy into the heel of your foot to flatten the mixture like a pancake. Then use the tarp to roll the mixture into a form. Repeat the process until it feels right.

Clay is an abundant natural resource in many parts of the world. It is inexpensive and has been used to build "mud huts" since architecture began. Clay will have different moisture contents, which is why different amounts of sand are used to create cob. The straw acts as a fibrous binder. To build a cob wall, balls of the mixture are thrown together and sculpted atop a pre-made base (foundation).

How strong is a cob house? When you examine the geology of bricks, you discover that clay is the main ingredient of the common building brick. Just like cob.

Learn More:

  • Aprovecho in Oregon is a non-profit organization offering "hands-on, experiential education programs for youth and adults." Their aim is "to inspire a sustainable culture."
  • Building with Cob: A Step-by-Step Guide by Adam Weismann and Katy Bryce, 2006
    Buy on Amazon
  • The Hand-Sculpted House: A Practical and Philosophical Guide to Building a Cob Cottage by Ianto Evans, Linda Smiley, and Michael G. Smith, Chelsea Green Publishing Company, 2002
    Buy on Amazon
  • The Cob Builders Handbook: You Can Hand-Sculpt Your Own Home by Becky Bee, Groundworks, 1998
    Buy on Amazon