Before I get into the specifics with what I'm learning in this internship at Strawbale Studio I thought I might give an overview on what exactly a straw bale or cob home is and why they are important.First off, both of these are forms of natural or green building. What makes something a natural building depends on the embodied energy it takes to build the structure. Embodied energy being the total amount of energy consumed in the process of production from mining and processing of materials to the manufacturing and delivery. So a green building would be something with low construction impact, resource efficiency, should be long lasting, non toxic, and beautiful! Straw bale and cob homes meet all of these criteria. The literal definition of cob is a "lump" or "mass" but basically, cob is a mixture of soil containing clay and sand mixed with water and straw. One of the reasons building with cob is so great is because these materials are available almost everywhere, they are inexpensive, and can very often be found on-site. Cob can easily be made with your feet, a tarp and some friends!
Cob building is pretty straightforward since it requires no formwork and very few tools so it isn't surprising that one third of our world's current population are living in unbaked earth. It is most commonly found in Africa, the middle east, India, Asia, Europe and south and central America. There is evidence that cob building began as far back as 800 years ago deriving from Europe. Because building with cob reduces the use of wood, steel and toxic building supplies it can cost as little as $10 a square foot to build! Once you have your foundation all you basically have to do is start piling it on! Although there are many cob homes out there, the major disadvantage to building a strictly cob home is that it provides very little insulation. Insulation is measured as relative resistance to heat flow or better known as the R-value. R-value requirements for building varies through the different states and climates, however it ranges from R-13 to R-21. Building with cob alone only gives you about an R-6, however, cob walls do have a lot of thermal mass. Thermal mass is the ability a material has to absorb and store heat energy. So in places that have a big fluctuation in temperature from day to night it's great because the cob's high thermal mass absorbs in heat energy through the day and then releases back through the house at night to provide warmth at night once it's cold outside. (Check out the link for visual descriptions) This is where straw bale homes comes in. Straw bales are extremely insulative with the R-value being about 1.5 per inch when laid flat and R-2 when laid on edge. Even though this is still less than commercial cellulose insulation per inch which would be anywhere from R-3.1 to R-3.8, the fact that straw bales can be anywhere from 14 to 24 inches is what makes the difference making a bale around R-28. A straw bale home is built by stacking straw bales on top of each other and then plastering over using a recipe very similar to the cob, the only difference being you will generally use more water and a shorter fibre such as chopped straw no longer than two inches. I will eventually do a separate blog on natural plasters.
So, why should you consider building a straw bale or cob home? If you are someone who has any interest in the preserving our environment then you should be interested! Today we are living in a world where people have no direct connection to our homes. The book "Building Green" gives the examples of the eskimo's who built their igloos using the thermal mass of the ice to protect them from the cold and the ancient Egyptians who used an intricate system of screens and ventilation to protect them from the desert heat. Homes that are built today are designed to be able to work in any climate or environment by being plugged into adjustable life-support systems that provide light, temperature and air circulation as well as provide water and flush out waste. Although these all seem beneficial, it doesn't allow us to have that intricate interaction and connection that humans once had with their homes, also meaning that our survival is completely reliant on our system not failing. More importantly, much of modern housing is dangerous to our health as well as our earth. With the off-gassing of synthetic materials, chlorine in drinking water and the damage that is done to our planet to create the materials used to build are only some of the negative effects modern housing has. There is also a huge amount of erosion, loss of wild life habitat from forest clearing, pollution from burning coal to produce electricity, and wasteful resource depletion that ends up in our dumps. If we continue to live the way we do we will destroy our beautiful planet ending life as we know it. This is what makes straw bale and cob homes so great! You not only save money, but you get to connect with your living space and people around you by working with others to build your own home in a way that minimally effects the environment and allows you to learn and grow as a person, as well as contribute to a better world. Not to mention, the finished product is incredible!
Deanne's straw bale home at Strawbale Studio in Oxford, MI
Click HERE for some more fun images of cob homes. I hope you enjoyed this post and have a better understanding on this type of natural building. The information provided in this post was collected from a mixture of Deanne Bednar and the books Building Green by Clarke Snell & Tim Callahan as well as The Cob Builders Handbook by Becky Bee.