Here are basic instructions for assembling a straw bale wall in a post and beam structure. Nothing here should preclude the use of best construction practices.
The straw needs to be sickle-cut with a combine, not rotary cut, so the bale is made by folding long straws in half. The bale will have a cut side and a folded side. These bales will be able to be resized easily. Two-string bales are 14” high x 18” deep x ~34 – 42” long. Bales should be dry. Use a moisture tester to test their moisture content. Ideally bales will run in the 9-14% range, anything up to 18% is usable. If it has high moisture look to see if there are signs of mold, if so, do not use in walls. Bales should be tight enough that your fingers feel snug between the twine and the straw while lifting the bale. If picked up by one string the bale should still feel secure, not like it is about to fall apart. Bales do not need to be freshly cut but they will be less dusty than straw that has been stored awhile.
Bales are placed on a raised bed of gravel. Starting at a corner place the bales end to end in each direction from the corner. Place bales with the string side facing up, this is the structural way for bales to lay. For the next course you again start in the corner placing the bale so that it covers half of 2 bales with the joint between the 2 lower bales at approx. the center of the top bale. The same way you would lay bricks or block, in a running bond. Each time you get to the end of a course you might not have enough room for a full size bale. This is where resizing comes in. Continue stacking the courses in this way. Work your wall to keep it plumb. A large wooden mallet can be used to “persuade” the wall to be plumb. You can curve the wall with straw bales, the walls don’t need to be straight, but they should be plumb.
Bales can be resized to create a solid wrap at each course (row of bales). If the area needed to be filled is 9” or less stuff “flakes” straw into the space instead of trying to make a bale to fit. Bales are made up of a series of flakes that separate easily from each other. After the wall is built flake is also used to fill any holes in the joints where the bales meet. Resizing is best done with a partner, but you can do it alone. Determine the length of bale you need. Mark the bale and measure enough baling twine to go all the way around the “new” bale plus ~9 inches. Cut. You want to make two bales simultaneously so as not to waste the straw and you will probably need a bale just that size some place in the building. Measure and cut a string that will go around the other half of the bale plus the 9 or so inches. You will need to replace both strings on the bale so cut another set of strings to match the ones you just cut and set them aside. Take the 2 strings and thread the bale needle with them. Pull both strings into the needle so that the middle of the twine is at the eye of the needle. As you insert the needle into the bale you want to be careful not to cross the strings inside the bale. Do this by keeping both ends of one string in separate hands. Place the needle just to the inside of the existing string at the length you need. Keeping your needle perpendicular to the bale push it through. Your partner will remove the twine from the needle, noting which string came from which eye and which way it will go around the bale. Flipping the bale on its side make a block and tackle knot and tighten, making a tight bale. Now “re-sew” the other string on the bale. Once both sides have been restrung you can cut the original twine at the knot and remove. Keep this twine and use it for future resized bales.
After the straw is stacked it is reinforced for lateral strength. Place 2 bamboo stakes on either side of the wall every 18”. Wire them to each other using the bale needle and 16 gauge tie wire. Insert needle threaded with wire through the middle of the bale at each course. This is called pinning. Tighten the wire with pliers to pull the bamboo stakes tight to the bales submerging them slightly into the straw. Tightening will help straighten the wall. Then push the ends of the wires deep into the straw so they won’t interfere in plastering. The stakes should connect to both the top and bottom plates by screwing into the plates or attaching with a 2 hole strap or fence staple.
Windows & doors
Window and door bucks are pre-constructed. Brace them well to keep them plumb and square. Deep window sills are created when windows are placed to the outside edge of bale (recommended). In the kitchen, windows on a straw wall with counters can be non-operable windows or be set to the inside of the bale for ease of opening. If this is done be sure to detail for good sill drainage.
Plumbing & wiring
Wiring is placed on the surface of the straw. It can be placed in conduit (recommended) or used as is. You can use a plaster ring on your boxes which allows you to set the box so it will be flush with the final plaster layer. Plumbing we keep out of straw walls. Where plumbing comes up through the floor you can place fixtures on a straw wall, but where the plumbing needs to come through the wall place fixtures on an interior (non-straw) wall.
Kitchens cabinets can be mounted to straw walls by “bolting” a 2×4 to the wall using 1/2” threaded rod put through the straw wall, attach a 12” plywood washer and fasten. Tighten nuts again before plastering.
A healthy home needs to “breathe”. The best covering for straw is a natural lime and clay plaster applied inside and out. This plaster has been used successfully around the world for thousands of years. It is non toxic, easy to mix & apply and cleans up with water. The plaster is made with lime, clay and sand. Lime dissuades rodents and insects from entering your home. The plaster also acts as a carbon sink as it turns into limestone by drawing carbon out of the air over the life of the building.
Stucco & Mortar Sprayers
If you want to learn how to stucco, or want to apply stucco or mortar to a wall or straw bales, you will like this Stucco Sprayer for spraying traditional plaster, lime and natural earth plaster, and stucco and mortar mixes.
Straw bales offer an energy efficient home using a material that would otherwise be burned releasing carbon and other pollutants. By building with straw bales the carbon sequestered in the straw stays there, and the bales are rated a Class A fire resistive material making a safe, healthy and beautiful home.