Cob

Cob is a very old method of building with earth and straw or other fibers. It is quite similar to adobe in that the basic mix of clay and sand is the same, but it usually has a higher percentage of long straw fibers mixed in. Instead of creating uniform blocks to build with, cob is normally applied by hand in large gobs (or cobs) which can be tossed from one person to another during the building process. The traditional way of mixing the clay/sand/straw is with the bare feet; for this reason, it is fairly labor intensive. Some of the process can be mechanized by using a backhoe to do the mixing, but that diminishes the organic nature of it. Because of all the straw, cob can be slightly more insulating than adobe, but it still would not make a very comfortable house in a climate of extreme temperatures. The wonderful thing about cob construction is that it can be a wildly freeform, sculptural affair. I've seen some very charming homes made this way. Cob was a common building material in England in the nineteenth century, and many of those buildings are still standing.

A variant of cob is what is commonly called "light straw/clay". This is made with the same long fibers of straw which is tossed like spagetti with a sauce of clay slip. The idea is to coat the straw fibers with enough of the clay to get them to stick together, but not so much that it makes a gummy clump. This material is then tamped into a form and left to set up enough to remove the form. Light straw walls could be useful for interior partitions and even exterior walls if it is thick enough. Such walls would be quite a bit more insulating than cob, but they require a timber frame of some sort because the straw itself would not be load bearing.

Photo courtesy of inhabitat.com

Plans
Solar Oval One
John Fordice, Architect

SOLAR OVAL ONE is a compact  passive solar design with a loft which can be an outbuilding for many possible uses.  It has many valuable and green/sustainable features:

• Potentially able to be constructed without a building permit
• Cob wall construction 
• An impervious base wall below the cob for moisture protection of the cob
• A South facing wall of windows and french door for passive solar heating
• An earthen floor for solar mass and economy of construction 
• An interior cob bench for built-in seating and rocket mass heater
• A built-in desk or kitchenette area with side storage niches
• A north wall closet for storage space and insulation
• Small East and West end side windows for views & area lighting
• A sleeping loft accessible by a built-in ladder
• Roof framing which needs only minimal small dimension lumber 
• The roof framing can be easily adapted to your insulation needs
• A corrugated sheet metal roof
• The structure is designed to include seismic stability components
• A pleasing curved design 
• Low cost if you build it yourself

Building with cob allows the use of local sustainable materials.  In many areas the earth at your site can be used and only water, sand and straw will need to be brought to your site to make your cob.  The cob is mixed right where you are building and stacked up on an impervious foundation. There are no forms needed to make a cob building.  Curving sculptural walls are easily created.  Your imagination is set free when you build with cob.

For more information about this plan, and many others, visit our sister site www.dreamgreenhomes.com, where you will find a wide range of plans for sustainable homes, greenhouses, small buildings, garages, and food storage space for sale. Dream Green Homes is a consortium of outstanding architects and designers, who have pooled their talent and expertise for your benefit.

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I specifically disclaim any warranty, either expressed or implied, concerning the information on these pages. Neither I nor any of the advisor/consultants associated with this site will have liability for loss, damage, or injury, resulting from the use of any information found on this, or any other page at this site. Kelly Hart, Hartworks LLC.