Choosing the Best Bales for Straw Bale Building
Now that you have an understanding of what to consider about your land and you have a concept for a home design that fits that understanding, you need to know where your bales will come from. It is best to secure your bale source while designing so you know exactly what size the bales will be.
This is important during the engineering and/or framing design because you want to make sure that your frame is built such that the bales fit tightly into it. If the frame is 2″ too tall, for example, the bales will be loose, and the best you can do to remedy that is to stuff straw at the top of the wall. This does not provide enough strength to the wall, and each step after the initial baling (straightening the walls, cleaning the wall surface, plastering, etc.) will be negatively affected. Get this detail right: the union of bales and frame, and the rest of the job, will be significantly easier.
There are many farmers out there with available bales; however, don’t buy from just anyone. Instead, know what to look for and buy the best bales you can find in your area. The price difference should not vary much, so a little extra effort is worth it. We cannot stress enough the importance of a tight, quality bale in your project. You may be the best bale builder out there, but if you use subpar bales, your walls will show it immediately and forever. Take the time to find the best bales you can, and your home will thank you from start to finish. Here are some tips on how to get those bales.
Visual Inspection
Pay attention to the color of the bales. This simple detail is a telltale of the history of the bales. Have they seen the weather? Have they been stored properly with enough ventilation? The appearance of surface mold is a good indicator that the bales have been wet in the past or improperly stored. If there is a lot of white dust released from the bales when you hit them, they may have considerable interior mold; in other words, mold you cannot see on the surface of the bale.
To be sure that the dust released from the bales is mold and not dirt, use your nose. If it is mold, the smell is unmistakably musty. If you discover upon visual inspection that the bales are water damaged, moldy, or otherwise not in good condition, don’t investigate any further, as using these bales in construction will jeopardize the integrity of the house. They should be golden in color in most cases. Some crops, like rye and rice, tend to have a slightly green color, which is okay. It is important to ensure that the green is a residual color, though, and not the result of you looking at a stack of hay bales. We’ve seen it happen, so be careful. Remember that you want straw, not hay, to build your house. As our friends in the California Straw Building Association (CASBA) say: “Hay is for Horses, Straw is for Houses!“
One last thing to look for in your straw: make sure the individual strands of straw are long. The longer, the better. In dry years, it’s harder to find long straw because the crops didn’t get that tall; however, in average years, you should expect your straw to be around 16″ long or more. If you find a bale with 6″ lengths of straw, it has most likely been put through a shredder, and this will be a hard bale to work with on your project. One hint for finding bales with short straw is their size.
Modern baling machines that often include a shredder at the end of the line, right before baling, typically make bales of a slightly different size than the old-school balers. If you find a bale that is 16″ tall instead of 14″ tall, be sure to grab a handful of straw and see if you can pull it from the bale. If you end up with a handful of 6″ strands, it’s best to keep looking for a new source.
Bale Density
The density of the bales is another important factor to be aware of. Most building codes (IRC Appendix on Strawbale Construction) that recognize straw bale construction call out a specific density requirement. For example, the Oregon code says, “Bales…shall have a minimum calculated dry density of 7.0 pounds per cubic foot (1.10 kN/m3).”
If you do not know the density of the bales, you will not be able to assure the building inspector of the quality of the bales. A simple field test you can perform is to lift the bale by one string and gently bounce it up and down. The bale should not deform or fall apart in any way. If the bale holds its shape well, even after three or four bounces, it has an acceptable density.
Another thing to look at is the shape of the bale itself. It should be rectangular and evenly shaped. If one end of the bale is significantly shorter than the other, then the baling machine was not set correctly, and chances are that the bale will be unevenly tied. This can make for uneven settling in your wall, something you don’t want. A standard two-string bale should be roughly 14″ tall, 18″ wide, and 36″ long and should weigh around 45 pounds. That’s another good way to tell density. If a bale of that size weighs 20 pounds, it’s not dense enough. If it weighs 60 pounds, it’s either dense and an excellent bale for you to use, or it’s soaking wet and thus better used in the garden. Be sure of which scenario you have before you buy or use the bales!
Moisture Content
Perhaps the most important factor when choosing bales is their moisture content. If a bale reaches a moisture content of over 20%, it has reached the level at which mold growth and decay can take place and can be sustained. Once that level is reached, it is very difficult to reverse as the decay process produces the two things the bales need to rot: moisture and warmth. When measuring the moisture content of the bales, keep in mind that they will take on or lose moisture in response to ambient moisture in the atmosphere.
It is important to get accurate readings of the bales, not the atmosphere. In other words, do not measure the surface of the bales in the early morning when dew may affect the reading. Check the bales during the most neutral time of the day so that the reading is accurate and truly representative of the condition of the bales. We suggest using a standard moisture meter called a “hay probe” to read your bales. This will allow you to penetrate to the middle of the bale and get very accurate measurements. We try not to use bales exceeding 15% during construction, and most of our bales are closer to 8% when installed. Again, ambient, climactic moisture levels will impact this number to some extent.
There is a lot you can do to identify quality bales. Use your eyes, your nose, common sense, and whatever science your local codes require to make your decision. Use local bales if you can find them since the further away from the building site, the more impact on the environment they will have due to transportation. They will also be more expensive if they are transported a long distance. After all, transportation is not as cheap and clean as it used to be unless you can find a ride like the one shown here!
The bales should be of the best quality you can find; however, you could search for the perfect bale for the rest of your life. Once you find bales that meet your criteria and are within your price range, buy them and move on to the next step of the design/construction process.
You can even purchase your bales a year in advance as long as you have a way to properly store them so that no damage occurs between when you buy them and your build. Talk to the farmer. They may be willing to store the bales in their barn for you. If not, a simple pyramid-style stack on top of two levels of pallets will do the trick. Use quality tarps and check on them often. There are even tarps specially designed for bales. The barn is the best choice, but not all of us are that lucky!
