Building Your House From Straw
by Jeff Johnston
Straw bale building construction has become popular with people looking to build an inexpensive, ecologically sound house or other structure. Straw bale construction was devised in the mid-1800s in the Sand Hills of Nebraska, and some straw houses are still standing in the American midwest. Such houses have been built recently in the United States for as little as $4 per square foot.
Straw bale construction is not just straw bales, of course. Left exposed to the elements, a straw house would soon be a sodden mass of rodent-infested fiber, or a heap of ashes resting on the foundation. The trick to preserving a straw house is to stucco it – inside and out – with concrete. This gives a level of fire resistance double that required by law in Canada.
The Nebraska style is the original, and most popular, method of construction. Straw bales 35 inches long, 18 inches wide and 14 inches high are piled on top of each other just like bricks, with each bale resting on the two immediately below it. Rebar (metal reinforcement rods) or poles are jammed through the bales (two per bale) to prevent the wall from falling apart. A top plate is added, and the roof sits on the plate, with the bales taking the entire load of the roof. After allowing two to four weeks for the building to settle, the walls are parged, or covered with concrete. These walls can be flimsy, and if they become infested or wet from leaking rain or water on the ground, entire walls can be damaged.
In the late 1970s, Louis Gagnon developed a building method he hoped would be used in the Canadian north because of the superior insulation properties of straw bales (walls have an R-30 value). This method became known as the Quebec style. Each bale stands on top of the one below, but each bale is totally encased in concrete – inside and out, as well as the ends, top and bottom. This gives the house much greater rigidity and strength, as the concrete takes the weight of the roof, unlike the Nebraska style. In addition, the walls are impervious to water, rodents and insects; if mice or rain do damage a bale, the harm is restricted to that one bale. Unfortunately, the Quebec style is almost as expensive as a conventional wood frame house. Gagnon and his team use concrete forms and pumpers to build a house, which will cost approximately ten to 20 percent less than a comparable wooden home.
David Cameron and Nancy Sherwood decided to build a straw bale house in rural Nova Scotia after a friend mentioned that he had seen Louis Gagnon build an inexpensive Quebec-style house and had Gagnon's rudimentary description of construction techniques. In a small booklet describing their building experiences, David writes, “We had been reading the book A Pattern Language by Christopher Alexander, et al. Their thoroughly researched patterns of construction elements, such as thick walls, alcoves, low windows, sunny places, courtyards, struck chord after chord in us. We wanted that kind of house – people-centered, hand-built over time, a minimum of straight and level and square. The straw house fit the bill perfectly.”
After altering their design plans three times, David and Nancy began construction. Six weeks later, their walls were up one story and parged on the exterior. The walls enclosed 1,200 square feet of floor space, and had cost less than $10,000, including the cost of hiring two helpers. In the process, they altered their construction method from the Quebec style to what David now calls the Nova Scotia style.
David Cameron's Nova Scotia style uses the same principles as the Quebec style. Bales are stacked directly on top of each other, with columns of concrete forming the load-bearing portions of the wall. Where this style differs is in the horizontal layer between the bales.
The Quebec style uses concrete as mortar, sandwiched between bales and holding them together. However, concrete has less strength when used horizontally. David and his friend/house designer Sterling McCann realized that two lengths of rebar on top of a row of bales would act the same way as a layer of concrete, especially once they were secured in the concrete columns. In addition, the rods could tie in to the corner construction. This modification took much less time and effort, eliminating the use of concrete forms at each layer and allowing them to build the walls three bales at one time.
The result is a first layer topped with concrete, onto which are laid all window frames, followed by six or seven layers with rebar rods laid horizontally, with concrete load bearing columns, solid concrete corners, and a three-inch thick concrete bond-beam on top of the last row of bales.
During wall construction, ensure that every wall is completely covered with plastic to protect it from rain and fog until both the outside and inside walls are parged.
David provides some tips and suggestions to keep costs down significantly.
First of all, he suggests, design your house in a standard shape so that prefabricated roof trusses can be used. David and Nancy's house required a custom roof built by carpenters, which took three weeks and was expensive.
Another tip that comes from experience is to design your house with only one story. As David and Nancy discovered, it becomes very difficult to move concrete up 15 to 20 feet without using ramps or expensive pumping equipment. David and Nancy made their second story of wood, which has a much lower insulation value compared to the straw bales.
David also suggests that anyone planning to build with straw bales contract with a farmer to grow a crop that gives good straw. Rye straw is best, oat straw second, and wheat straw third best. While the straw is growing, decide on your door and window dimensions, and what type of windows you want. Given the high insulation value of straw, and the 18-inch thick walls, don't use low emissivity windows, as you may have too much heat in the house from solar gain, even during the winter.
During wall construction, ensure that every wall is completely covered with plastic to protect it from rain and fog until both the outside and inside walls are parged. Finally, says David, build your walls in 12- to 16-foot sections that can be parged by a team of three people in one day. Each day's parge will have different gray shades, so unless you plan to paint the exterior, you'll want an entire wall in the same shade of concrete.
Nancy, a sculptor, appreciates the flexibility that building with straw bales permits in designing structures to fit the landscape. The lower cost also allows you to design a house that fits your needs and your dreams.
David and Nancy built their house for less than $45,000, including the second storey and the customized roof. As David observes in his booklet, “Philosophical motives were at the root of our desire to build with straw and concrete. We employ wage earners who, like us, could never afford to take out a $100,000 mortgage...Let's design and build a $25,000 energy efficient house.”
This article was published in Natural Life Magazine in 1995.
|
