In "The Three Little Pigs" adventure, the straw house blows down first. Yet in the southwest, ancient adobe structures made from mixing clay and straw with animal manure still mark the dwelling sites of ancient Pueblo people.
Today, the combination of technology and sustainability allows consumers to consider locally available materials like straw as "green" alternatives. Straw bales, covered in stucco, can be used to build stand-alone structures like patio walls, or can be integrated into the walls of a framed house. Whatever the use, the end result has an organic appeal. This article will present guidelines for building a straw bale wall.
- Skill level:
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Things you need
- Dry 2-string straw bales 14 by 18 by 35 inches
- Bale moisture measure (available from Straw Bale Construction Management, Inc.)
- Pallets for bale storage
- Good quality tarp to keep bales dry
- Dust masks
- Hay hook
- Large wheelbarrow or small tractor
- Polypropylene baling twine
- Bale needle (made from a steel rod 5/16 inch by 3 feet long)
- Hay saw, machete, or chainsaw
- Circular saw
- # 4 rebar
- Cement mixer
- Composite lumber for forms and sill plate
- Tar paper
- Metal Lath (diamond stucco mesh) comes 36 inches wide and 150 feet long.
- Wire staples or lightweight wire for lath attachment
- Stucco or Gunnite
Design a patio wall to take advantage of the natural characteristics of bales. Select bales from a location that offers dry storage. Check the moisture content with a moisture meter to insure bales are very dry (less than 14 per cent moisture). Although you can cut bales to size, it's easier to plan the height of your wall to match a certain even number of bales (bale height is about 18 inches). For a patio wall, use two-string bales and turn them on edge to minimise the width of the footing. Later, apply stucco on the top of the wall. Set a 15-inch-wide footing at least 2 inches above grade.
Dig footing to code for your area. If you're worried about moisture, apply 2 to 4 inches of rigid insulation to the exterior of the footing edge. Two-by-fours or more flexible composite lumber can be used as cast. Straw bales can also be used as a form to hold wet concrete, but will result in some irregularities.
Pour concrete as a monolithic pour. Set #4 rebar (at least two per bale) at least 7 inches into the concrete. Make sure the rebar is long enough to reach at least halfway into the second course of bales. Rebar should sit approximately 9 inches from the bale ends and be centred on the bale width.
In wet areas, construct a sill plate to keep condensation from coming up through the concrete. Use waterproof composite lumber made from recycled plastic and wood chips, and insulate with rigid foam insulation in between composite lumber. Cover sill plate with tar paper. Install flashing with a drip edge at the base of the wall. Use a hay hook to place straw bales in place. Cover the first course of straw bales with building wrap, making sure it overlaps the flashing.
Stack the first course of straw bales by impaling them on the rebar. and offset edges. Use the hay saw to fit bales according to design plans. For tall walls (over 6 feet), consider adding additional rebar, starting at the fourth course and pounded down from the top of the straw bale wall.
Cut strips of 36-inch metal lath (diamond stucco mesh) to fit over the building wrap. Rip several strips at a time with a circular saw. Wear ear and eye protection. Cover wall completely, overlapping if necessary. Attach mesh to the wall by stringing polypropylene bailing twine through with a straw bale needle, or use large staples made from very rigid wire. A needle can be made by drilling a hole into a chain link fence tensioning bar. Sharpen edge into a point for easy pushing. Push staples flush against the straw. If using the needle threaded with polypropylene baling twine. sew lath onto the bale. The lath provides the surface and structure necessary for a good stucco bond.
Apply three layers of stucco: scratch coat, brown coat and finish coat (colour coat). Let each coat of stucco dry for at least a week. Spray with water daily. Seriously consider hiring a company to apply spray coats. This technique will cover the rough edges of the straw completely. Other spray cement products like gunnite produce similarly thick applications. Consider a wall cap mixture of hay and stucco for a rounded form on the wall's top.
How to build a straw bale patio wall
Tips and warnings
- Keep straw bales dry at all times.
- Adjust methods for your region.
- Check local building codes.
- Keep it small and simple.
- Use environmentally safe materials.
- While the wolf won't blow down a modern straw bale house built to code, there are some common concerns. In fire-prone regions, include fire retardants in stucco or plaster.
- Consider adding borax to plaster mixes, which acts as a fire retardant, fungicide and rodent repellent.
- Remember, humidity and water can damage straw bale construction. Damp straw during construction leads to rot or mould. Damage to the exterior stucco should be repaired immediately to prevent moisture or rodent invasions.
- Always wear ear and eye protection when working with power tools.
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