This article was originally printed in the 2003 Resource Guide
Compiled and updated by Joyce Coppinger from the writings of Judy Knox, Kim Thompson, books on strawbale, and US Department of Energy.
In most cases, it is advisable to find a source for your bales early on in your project planning as the size of the bales may influence how you lay the bales in the walls or bale orientation, wall spans, ceiling heights and other design considerations. And, be sure that the bales are stored under cover, preferably in a barn or storage building, until they are taken to your construction site.
Twenty Tips on Bale Buying
1. Purchase bales following the harvest when bales are usually inexpensive and abundant. You may need to contact local farmers during planting season about growing and custom baling.
2. Make sure the bales are stored high and dry from the time they come out of the field until they are installed in your building’s walls.
3. Don’t rely on hearsay about the size and condition of any bales you might buy. Check out the bales yourself.
4. Bales should be “bright” and dry with no sign of moisture, mildew or mold.
5. Test some portion of the bales you select to make sure they have always been dry.
6. Bale moisture content should be 14 percent or less. (Use a digital probe or moisture meter.)
7. An ideal proportion of a bale in size is twice as long as it is wide. This simplifies maintaining a running bond in courses.
8. Commonly available bale sizes: two-string, 14 inches(36cm) high x 18 inches(46cm) wide x 35-40 inches(91-96cm) long, weighing about 50 pounds(40 kg); three-string, 16-17 inches high x 23-24 inches wide by 42-47 inches long, weighing about 75 pounds(60 kg).
9. Try to get bales of equal size and length. If they do vary in length, as many will, lay ten bales end-to-end. Measure this entire length and then divide by ten. This is the average bale length to use for planning and designing purposes.
10. Bales should be free of weeds and mostly free of seed heads.
11. Wheat, oats, rye, barley, rice or flax are all good bale materials. Some grasses can be used for bales (switchgrass, for example). Do not use alfalfa or other brittle stemmed plants. Other materials are now being baled, such as paper and cardboard (See TLS #42/New Systems).
12. Look for thick, long-stemmed straw. Straw of 3-4 inches or 7.5 to 10.2 cm is not recommended. The stem length will vary depending on the type of baling machine used.
13. The R-value and other properties of your bale (tensile strength, moisture content, burnability, for example) will vary depending on the type of plant or crop residue used.
14. Dealing directly with farmers may give you more say about bale quality and consistency.
15. Expect to pay extra for transportation and storage.
16. Wholesale brokers offer direct access to the bale supplier and often offer commercial transportation.
17. Retail outlets and feed stores are the easiest source to access, you will probably pay more for your bales than those you buy from a broker or directly from the farmer.
18. Bales must be tightly tied with durable material, preferably 240-lb. knot strength polypropylene (usually won’t decompose) or hemp twine or 16-gauge galvanized baling wire (usually won’t rust). Avoid bales tied with traditional natural fiber baling twine (sisal, for example).
19. When you lift the bale, it should not twist or sag. The flakes (sections within some bales) should not pull apart easily.
20. Make sure the bales are uniform in size (as much as possible – there will be some variance) and are well compacted.
Bales can be laid flat (strings between courses, the wider side laid parallel to the ground). When the narrower of the two sides is laid parallel to the ground, the bale is being laid “on edge.” Bales can also be placed on end in small spaces where vertical stacking is required. The recommended placement for two-string bales is flat. Three-string bales can be used either flat or on edge. The R-value for two-string bales is believed to be approximately the same regardless of placement.
Flat placement provides maximum wall thickness and is more stable during construction. It also offers greater resistance to vertical compression. If a wire or string fails, expansive forces will be parallel to the wall and will be contained by the surrounding bales. Notches up to 5 inches can be cut into bales without severing a string or wire. Beveled bales can be more easily created for filling in the eaves of a peaked roof.
Placing bales on edge creates more wall height and bales can be cut parallel to the strings for placing windows. It also makes attaching stucco netting easier, because it can be fixed directly to the strings.
Storage should be off the ground, preferably in a barn or storage building. If outdoors, preferably on pallets, to keep ground moisture from being absorbed, and covered with high quality tarps to keep the bales dry. The tarps should cover each side of the stack of bales by at least one bale. The stack should be crowned (built to a peak at the top) to keep water from standing on the tarps and perhaps leaking into the middle of the stack through cuts or holes in the tarps. Best if the top row of bales (around the perimeter of the stack of bales) has a slight overhang to help protect the sides of the stack.
Inexpensive tarps and rolls of plastic are not preferred as they may tear or puncture easily, making moisture penetration into the bale stack more likely. Covering the bale stack with plastic sheeting and then covering the sheeting with tarps could help keep moisture away from the bales. Anchoring the bales securely is not always easy, but it’s very important, especially to protect the bale stack from strong winds and storms. Weighting the bale stack down with old tires, cement blocks, or logs tied to the end of a rope and attached to grommets in the tarps’ edges is a good method for anchoring the sheeting and tarps.
Most bales are easy to move around and stack. However, two people lifting and moving the bales will speed up the work and reduce body strains. Baled material can be scratchy and itchy as well as dusty – so long-sleeved shirts and pants, dust masks and gloves should be worn. Hay hooks can be helpful.
Lifting and throwing bales can be eased by using your body weight and the momentum of a swing or toss. Probably best not to try to just muscle them around when moving and lifting the bales. Use a wheelbarrow or large wheeled dolly to help with bale moving and, in some instances, heavy farm or construction equipment such as a small crane, a tractor with lift, could be helpful.
Bales can be used for stairs and as scaffolding – but caution is the word, as baled material can be slippery. And, keep loose straw raked and stacked away from the bale walls and the construction area, as it is highly flammable and dangerous underfoot.