Introduction to straw bale construction:
In straw bale buildings, baled straw from barley, wheat, rice, flax, rye or oats is used to build the exterior walls of a house or shed. The building can have any of the traditional foundations used in Canada. Around the perimeter of the main floor a “curb” is built. The curb is a railing of two 2×3’s nailed to the floor on which the bales are set. Bucks (framing) are built to hold the window and doors. The bucks are temporally held in place with bracing to the floor. Baled straw is stacked on the curb in a brick like fashion around the bucks. Headers (a rail or top plate built of wood framing) are built to sit upon these straw walls.
Using the post and beam straw bale infill method on the second story
There are two common methods of building straw bale homes. The first method is called a post and beam with a straw bale infill. Here a wooden structure is built first and the bales are stacked between the framing and used as insulation. The second common method is called load bearing. Here the entire wall consists only of bales and there is little or no wood or steel framing in the wall. However, the load-bearing wall must be compressed with cables or wires to stabilize it. For either type of construction, the bales are covered with mesh which is stitched on with giant bale needles. On top of the mesh, two or three coats of plaster are applied. There are many different kinds of plaster which may be used, including earthen, lime or lime/cement.
Photo by Laura E. Taylor
A conventional roof or second floor and walls may be built on top of either type of wall system. The plaster provides ample structural strength, such that it will comfortably bear the weight of the roof and floors.
There is also a hybrid system, which combines some of the benefits of both load bearing and non-load bearing (infill) straw structures.
There are many advantages to straw bale construction, for example:
- Traditional “stick frame” homes of 2×6 construction usually have an insulating value of R14. (R-value of conventional home based on CMHC Technical Series “Energy Use in Straw Bale Houses”) With a properly insulated roof straw bale enables a person to build a warm winter home with an R factor of R35 to R50! (US Department of Energy, April 1995, “House of Straw”)
- The high R factor of straw homes has the added benefit of keeping the house cool in the summer!
- Straw bale homes offer a more solid look and feel and allows for greater artistic designs. All of which contribute to a more enjoyable and comfortable home.
- Straw homes utilize an annually renewable agricultural by-product.
- The interior and exterior plaster of straw bale houses increase the “thermal mass” of the home, which helps to stabilize interior temperature fluctuations.
- Big thick walls mean nice quiet places.
- Conventional foundations and roofs can be used with SB.
- Straw bale homes are low maintenance. The final coat of plaster can be mixed with a die to provide colour. As such, the owner may never have to paint it. When built with a steel roof and high quality windows, a straw bale home may have a virtually maintenance free exterior.
- Building with straw provides added income to struggling farm families.
- Finally there is the community factor. People can be more involved in the building of their straw bale home, a process that increases the owner’s sense of satisfaction with the product.