There are ecological, energy efficient, and economic reasons to build with straw. Aside from the beautiful aesthetic of the rounded walls, deep window seats and the organic look of a building with bales, benefits also include using a natural, renewable and completely biodegradable material. The big thick walls translate to nice, quiet, peaceful places.
There are two basic styles of straw bale construction:
- load bearing (Nebraska style) and
- non-load bearing (called infill)
We have used the non-load bearing style with the straw bales wrapping the post and beam structure. We then covered the thick straw walls with wire mesh strung tightly and sewed the bales to provide greater stability and strength. The last stage is the most time consuming of straw bale building and this is the plaster. The bales can be covered in plaster, cement stucco or other similar materials. For our current home, we used natural hydraulic lime plaster to lower our carbon footprint and increase breathability.
Local Renewable Resource:
We bought the straw bales from a local farm in nearby Creston, reducing our carbon footprint that comes from transporting construction materials long distances, a key concern of green-building advocates. Using straw bales diverts farm waste as straw is often burned, producing carbon dioxide. According to the American straw bale expert Matts Myhrman; "If all the straw left in the United States after the harvest of major grains was baled instead of burned, five million 2,000-square-foot (‘20-square’) houses could be built every year."
Using straw and natural hydraulic lime plaster provide an alternative to health-threatening paints, glues and toxins embedded in manufactured building materials used in conventional building. Straw bales, unlike hay bales, contain no nutrients to attract pests.
Straw needs only one season to grow and needs little energy to produce. Straw bales result in super insulated walls that offer between R-43 to R-48 (twice to three times) the insulation of typical frame wall systems. This reduces the life cycle cost of a straw bale house and results in big energy savings. For our previous home in Fernie, B.C. we were in an energy efficiency study with Canada Mortgage and Housing Corporation (conducted by straw bale builder and consultant Habib Gonzalez) and were found to be 38% more efficient than the same size house conventionally built. The interior plastered walls of our house increase the "thermal mass," which helps to maintain a constant temperature within the house.
Plastered straw bale walls have been proven to be a fire- safe envelope with a typical 2 hour fire rating. According to treehugger.com, engineer and straw bale advocate Bruce King, recently paid for an insurance-required test of fire resistance of straw bale walls, whereby “workers fired up a super-hot gas furnace next to a wall stuffed with straw in hopes of calming skittish insurers, bankers and building inspectors who have been reluctant to embrace big buildings insulated with bales of dried grasses.” The test wall satisfactorily withstood over two hours of 1,700-degree heat and the following hose-down.
Using straw as insulation can reduce construction costs by allowing the owner builder to build a large portion of the house, thereby reducing labour costs from specialized workers needed to build a house. Depending on choice of siding, type of insulation and interior wall finish, using straw has the potential to reduce material costs as well.
Straw bale building brings friends and family together for bale raisings. Just like old fashioned "barn raisings", we have held a straw bale raising for each house which is a wonderful tool to teach others about sustainable building methods. The raisings promote a fun, hands-on, empowering, community experience.