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The Organic Nature of a Cob House


Author: Rowan Kehn

Article:

My interest in cob building started four years ago when I visited my first cob house. It was a beautiful circular building with sculpted windows. The space felt calm and cozy. I was curious to learn more about earthen building and how it was created. A year later I saw a poster for a local workshop on cob building and decided to give it a try. 

Over the past three years I have taken two workshops and one course in cob construction. I love the organic nature of the building material and the way it feels when you work the walls with your hands. Cob works with the environment by using natural and available materials. I also enjoy getting muddy and working hard! After my third building experience in the winter of 2008, there was talk in our family of doing a project on our property.

Earthen buildings can be found around the world and in every climate. There are many different types of earthen buildings, such as straw bale, adobe, wattle and daub and rammed earth. For the most part the different styles of building have the same materials in common: earth, clay, sand and straw or some other binding and strengthening material, i.e. sticks.

Cob is a composite of sand, clay, straw, and water. These are mixed together to form a pliable building material. In cob building the walls are sculpted and continuous and no forms are used. Cob provides a thermal mass, similar to stone. It collects and holds heat, then radiates it out over a longer period of time. Cob has become more common in North America recently, but there are tens of thousands of cob homes in England and many have been used for more then five centuries. 

Once the decision was made to start a cob building of our own we picked a site. We considered sun and weather exposure. Salal, ferns, brambles and tree stumps had to be removed. The shovels, mattock, wheelbarrow and rake were put to use and a building site was cleared for a tiny cottage. We shovelled off of the topsoil until we reached the subsoil in order to remove organic material and minimize settling.

Getting to a final plan took most of a pad of graph paper. There was much pencil sharpening and head scratching. We fiddled with square footage, foot print, window placement and layout. The design had to accommodate the basic needs for a small living space excluding a bathroom, which we deemed unnecessary; an outhouse allowed us more space. Still, a lot of things had to fit into a small peanut-shaped space of 160 square feet. We glue-gunned a cardboard model to scale and were confident it would work.

We decided to combine a wood frame loft with the cob main level. That created some tricky problems. The posts, beams and framing of wood building had to meld with and attach to the free-form organic nature of cob walls. We consulted some building-savvy friends for their perspectives and ideas. 

The shovels and our backs were put to work for the rubble drainage trench, a one-and-a-half foot wide and two-foot deep trench around the perimeter. We sifted the dirt as we dug it out, re-used the rocks to begin filling the trench, and brought in extra drain rock to finish it.

My dream was to have a beautiful two-sided stone foundation but I had no experience building in stone. Neither did the rest of my family. We decided to enlist the help of a local mason. It took a little convincing, but he liked the idea of teaching my brother and I how to build in stone. We learned there is an art to picking rocks and that any old rock won’t do. It takes time to develop an eye for the ones that will be useful, with good shape, weight and angles. We were always on the lookout and started seeing perfect rocks wherever we went. We spent hours staring at rocks, trying them this way and that, willing them to work. The same rock would defy placement again and again until it finally worked, sometimes days later. The foundation tested our patience and took more time than we had anticipated – almost two weeks to build a two-foot high foundation. Looking back now that doesn’t seem very long at all.

Creating a workable cob mix involves finding the right kind of sand, good clay and straw. Luckily, the clay and sand are available where we live on Quadra Island, in fact right across the street. Straw was purchased at a local farm and feed store. Once we had the materials we experimented with mixes. A good batch of cob is wet enough to be pliable and dry enough to hold its form. 

Finally the cobbing could begin. We set up a five-day cob course and invited teens who were part of an alternative learning program—Self Design–which my brother and I also participated in. There were about 15 teens. Two women (from the MudGirls Natural Building Collective) and I facilitated and taught the course. All the support from family and the program staff made the course possible.

Once the mix was correct it could be applied. As we worked our way through weeks of cobbing the surface needed to be continually wet down before applying fresh cob. 

Every day started with an instructional session before cob mixing commenced. All the cob for the project was mixed with our, sometimes bare, feet on lumber tarps. It was a labour intensive process but was also the best way to get a feel for the quality and consistency of cob. The best way to mix was to music and the mixing tarps became our dance floors. Once all the materials were well mixed they could be applied onto the stone foundation. We built our walls to the standard one foot width and used foot long sticks as a guideline for the width. To maintain plum and keep an even surface, we trimmed excess cob with saws and frequently used our levels to keep things from sloping in or out. Over the five-day workshop we made about three feet of progress on the cottage walls. 

Like any building project there were hitches and set-backs. Maintaining momentum over the rest of the summer was a challenge. The cob needed to be up to the beams before the weather turned wet and windy. Over the summer we had many “work bees” with willing cobbers, WWOOFers (Willing Workers On Organic Farms) and friends. Without all their help we wouldn’t have been able to complete the walls by the end of September. 

This spring brings framing the loft, roofing, and plastering the cob. There is still a lot to do before this project is completed and the cottage becomes a liveable space.

This form of building takes groups of people and communities to be successful. It is neat to think about how much embodied energy is in the building from all the hands that worked on it. I think it has been a great experience for us as a family. It has been an intense learning curve for all four of us demanding adaptability, patience and a lot of hard work. We all learned far more than any workshop or course could teach. It was a huge challenge for me but I learned so much. Now every time I show it to others I am reminded how much I love what we’ve created and am excited to see what it will become.

This entry was posted on Friday, May 1st, 2009 at 9:39 pm and is filed under FEATURE. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

Synergy Magazine: Vancouver Island, BC, Canada