Building with Cob: Sustainable and Local

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Cob has the lowest environmental impact of all building materials. It’s natural, and non-toxic. The finished home is also energy efficient.

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Earth is the oldest building material. For thousands of years, walls have been made of mud, and many of those buildings still stand. The most well known are probably the old cob homes with thatched roofs found throughout the UK. They date back to the 1600s, which shows how durable they are.

Green building

Cob is the most eco-friendly building material there is.

It is local – you can make your walls from the land where the building will sit.

It is sustainable – it can melt back into the ground at the end of its life.

It is natural and non-toxic – subsoil is mixed by hand with water, straw, and sand.

There are no transportation costs, no CO2 emissions from machinery, no off-gassing, and no trees harvested for framing walls. Cob has a very low environmental impact.

Making mud, and building

Building with cob can be like an old-fashioned barn raising. Many hands make short work, and anyone can quickly learn the necessary skills.

Soil and straw are mixed with water. Depending on the structure of the soil, sand may need to be added. Oxen traditionally trampled it to blend it, but humans can dance on it for the same effect.

The Old English root of the word ‘cob’ is ‘lump’ or ‘mass’. When the mud mixture is of the right consistency, it is placed by handfuls (lumps!) in courses on a raised foundation. The climate and weather will determine how high to go for each course, since it needs to dry before applying the next.

Simple, durable, and energy efficient

Once a cob wall is erected, it’s done. No insulation or sheetrock are needed to finish it off. Wide roof overhangs and the raised foundation will protect it from the elements. Because the structure is one piece, it can withstand earthquakes, hurricanes, and high winds.

More than other earth building methods, cob is excellent for making soft, round lines, and relief sculptures and carvings. You can also salvage recycled doors and windows, because cob walls can be molded around them, like a custom fit. Your home will be unique, inside and out.

Benefits of cob

The finished structure is water resistant, so it does not mold or mildew. It is also fireproof, insect resistant, and rot resistant. Cob is suitable for any environment. If the climate is especially cold, added insulation might be necessary.

Earth is an excellent thermal mass for passive solar heating and cooling. It absorbs heat in winter to radiate out at night, and it absorbs heat in summer to keep the interior cool. It is also good mass and fire resistance for outdoor ovens, chimneys, and rocket stoves.

DIY natural building

Before you decide to build with cob, make sure your zoning laws allow it. It might be labeled ‘natural building’ or ‘adobe’ or ‘alternative’. But be sure to look into that first. Also check your neighborhood covenants for any restrictions.

When you have that go-ahead, take a workshop. You can find them all over the world. In a week, you can learn about site selection, materials, and design, and actually get your hands (and feet!) dirty doing some building.

If you are lucky, there is a cob builder near you that might help you with building. Maybe they would even hold a workshop on your land.

Cob is the most environmentally friendly and natural way to build. It uses the least amount of fossil fuels than any other method. If you’re looking to use local materials and reduce your carbon footprint, build a cob home.

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Nan Fischer

Nan Fischer has been living and building green for over 35 years. Nan’s emphasis on the BuildDirect blog is about how to make your dollar stretch further, while also moving toward a more sustainable lifestyle, as well as upcoming and existing technology to help us live in an ecologically-friendly way. Nan also authors posts on the website of her seed business, sweetly seeds.