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 insulated 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.
The Availability of Straw Bales
One of the most abundant byproducts from the farming industry is 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 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 a 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.
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 suns 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 every day 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 suns energy and warmth through angling your home towards the path of the sun, incorporating large windows and earthen, thermal mass into your home, and insulating (with straw bales, for example, the “cold” side of your 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 a 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.
Straw Bale Homes for the Future
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. 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.