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Straw Bale Homes And Passive Solar Design

Is it possible to stay warm during winter without a fossil fuel powered central heating system? Straw bales are one of the most common left over products from farms in the United States. In many places, excess straw bales are burned leading to huge amounts of contamination. Straw bales, however, are some of the most insulative construction materials available. When designed together with passive solar design, a straw bale home is a natural construction method that combines beauty and functionality as a self-heating home.

Problems with central heating in conventional homes

The U.S. Department of Energy estimates that close to 50% of all the energy used in American homes is for heating and cooling purposes. While it is nice to be able to walk barefoot in one’s home during the dead of winter, that luxury comes with a price that most of us don’t take into account.

The Energy Information Administration (EIA) notes that residential carbon dioxide emissions have been steadily growing at a rate of around 1% per year. While most household appliances and home energy implements have become much more energy efficient (think LED lighting), the amount of energy used to actually heat and cool a home has continued to rise.

While your grandparents may have had a wood burning stove in their home, the vast majority of households in the industrial world depend on fossil fuels for heat. As noted above, this dramatically increases the ecological footprint of your home. Furthermore, as we continue our steady march towards peak oil, we need to seriously begin to consider how we are going to stay warm once cheap and abundant fossil fuels are no longer an option.

In Europe alone, over 40,000 people died in 2015 due to extreme cold temperatures. When the electricity goes out, most people have absolutely no idea how to stay warm. Our dependence on fossil fuel energy, then, is not only dangerous for the planet, but also a threat to our survival.

The availability of straw bales

One of the most abundant byproducts from the farming industry are straw bales. Straw bales are made from the stalks of grains including wheat, oats, rice, barley, and others. Since tractors and combines are designed to only harvest the seed head from the grain, the stalks from these grains are left on the field.

While organic, no-till farming methods such as the Fukuoka natural farming method would have farmers leave this straw on the field as a natural mulch and organic fertilizer, most farmers either burn the crop residues or use a baler to block the straw into manageable masses that can either be sold, used to feed livestock, or left to rot in the corner of a field. The burning of straw bales is a major cause of pollution that adds significant amount of carbon dioxide emission to our already saturated atmosphere.

What few people know, however, is that straw bales can be used as a low cost and highly insulating wall material. Instead of simply burning tons of straw bales or leaving them to rot, it is completely possible to take this farm “waste” product and turn it into a durable, cheap, and ecological home.

burning wood stove for heat in straw bale home

Insulative properties of straw bales

One of the most important characteristics of straw bales for home construction is its insulative properties. The construction industry measures the insulative value of different types of building mediums through the R-value. The R-value is the ability of a certain material to resist the passage of heat from one side to another.

While regular brick only has an R-value of 0.80, straw bales are considered to have an R-value of anywhere between 25 and 35. The synthetic fiber glass insulation that is usually placed between the exterior of a home and the dry wall interior adds insulation to traditional homes. However, straw bale walls would need no extra insulation because of their natural insulative properties.

The small spaces that exist between the individual strands of straw in a straw bale are what create such a high R-value. These small spaces allow for air to get “trapped” in the wall, thus not allowing the passage of heat.

Designing your straw bale home with passive solar design

So how do you go about designing a straw bale home to take maximum advantage of their insulative properties? Since straw bales will keep the heat in your home, a central heating system installed into a straw bale home would be much less used. Whereas your heating bill might come out to around $200 dollars a month with a traditional brick home, the energy bill for a straw bale home would be significantly less.

You could also install a wood burning stove into a straw bale home. The heat produced by the burning of wood would stay trapped within the walls of your home thus increasing the efficiency of the wood heat.

There is, however, an alternative design strategy that aims to take advantage of the sun’s energy and natural ability to bring heat into a home.

Our earth travels around a ball of fire that is continuously emitting enormous amounts of heat and energy. The sun is perhaps the most underutilized source of energy. We spend millions of dollars to develop technologies to dig fossil fuels out of the ground, refine them, and burn them, when everyday our homes receive between 8 and 16 hours of direct exposure to the largest source of energy in our solar system.

Passive solar design is simply the process of designing a home to best take advantage of the sun’s energy and warmth. There are four main principles to passive solar design:

  1. Angle your home towards the path of the sun (south in the northern hemisphere and north in the southern hemisphere). In winter, the sun drops in the horizon. Without sunlight directly overhead, the only way to take advantage of that sun is through angling your home so that it receives the most direct sunlight.
  2. Build large windows that allow for maximum solar gain. You need to get the energy and warmth from the sun’s rays into your home. Building large windows on the sun facing side of your home will allow for the sun to heat your home during the day. Since windows also can let heat escape from your home, it’s important not to build too many windows (or none at all), on the cold side of your home (north facing wall in the northern hemisphere and vice versa). If you live in an extremely cold climate, double pane windows can add an extra layer of protection and insulation.
  3. Build lots of thermal mass into your home so that the sun’s heat can be stored overnight. It would do little good to design your home to capture the sun’s rays if you had little way to “store” that heat. And how can you store the heat from the sun?
    Certain earthen materials are known as thermal masses because they have the ability to absorb the heat of the sun and hold it for long periods of time. The rock or brick mantles of fireplaces follow from the same principle. The heat generated by the fire is “sucked up” by the rock or brick so that even after the fire subsides, these thermal masses continue to slowly release the heat from the fire. Some options for thermal mass materials to capture the sun’s heat include earthen floors, adobe or cob walls, or stonework and masonry.
  4. Insulate well, especially on the cold side of your home. Once you get the sun’s heat into your home and stored in a thermal mass, you want to make sure to keep that heat in your home for as long as possible. Insulating your home, especially on the cold sides of your home (north and east in the northern hemisphere), is important for passive solar design. One of the best insulative building materials are straw bales.

timber framing for straw bale home

Primer on how to build with straw bales

Since straw bales are not load bearing, you will need to build a frame that will hold up the roof structure. Timber framing is a beautiful natural alternative that combines well with straw bales which will be infill for the walls. Cedar posts are naturally resistant to termite infestation and also very attractive.

Straw bales need to be lifted off of the ground to avoid any contact with water which will cause them to begin to rot or mold. A rock stem wall placed on top of a rubble trench is one easy foundation that can be adapted to straw bale construction.

To build your straw bale wall, you will have to stack the straw bales as if they were individual bricks. You can think of the straw bales as blocks that need to be staggered for added strength. To connect each layer to the next, sharp stakes of either rebar, bamboo, or some other strong and sharp material are pushed through the bales to bond them together.

Some cities in the United States have specific building codes related to straw bale construction. Almost all codes require there to be a solid connection between the foundation, walls, and roof. A piece of threaded rebar cemented into the foundation that goes through the straw bale walls can easily be then connected to the roof beams to comply with code.

Once your wall has achieved the desired height, you can connect your walls to the roof beam that will support your roof either through the pieces of threaded rebar or with straps that tie the wall together with the roof.

Straw bale walls need to be plastered in order to resist the elements. A simple cement and lime based plaster for the exterior walls will keep your walls protected. If you ever notice a crack in your exterior stucco, you need to re-plaster right away to avoid any sort of moisture from getting into your wall. Earthen plasters are a great option for the interior walls offering a natural feel to the home.

When combined with passive solar design, a well built straw bale home may very well be able to heat itself with nothing more than the warmth of the sun.

Concluding section

Finding alternative ways to stay warm in the coming post fossil fuel age is a task we shouldn’t take lightly. Passive solar design and straw bale construction are two methods, that when combined offer a completely natural heating system. To learn more about straw bale construction, “The Straw Bale House” by Athena Swentzell Steen, Bill Steen and David Bainbridge is a great resource to get the information you need to start building your own natural home.

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