What is the perfect bale to use in a straw bale house? I am asked this question a lot. Most times, the question refers to what type of straw is the best. Some people say rice, others say wheat. I always tell people to buy what is most local as long as it is dense, dry, and clean. The other side of this question is in relation to the size of the bales to be used. Many people want to know if a 2 string bale is better than a 3 string bale for home construction.
Once again, I believe the best bales are those most local to your construction site. In general, most farmers are moving towards bigger bales and so that will have an impact on what you can find in your area. Three string bales stack more easily in the field and are more stable when moved by a squeeze (farm machine that moves large blocks of bales). For that reason, more 3 string bales are available today than 2 string, in most markets. So, first concept: buy local.
Here’s the advantage for two string bales: they are easier to work with. They are lighter, smaller, and generally easier to work with than 3 string bales. I prefer two string because I can handle the bales by myself whereas three string bales take two people to move and stack, especially after a long day of baling. The R-value on a 2 string bale is less than a 3 string bale; however, it is already so high, that the difference is not that noticeable. Unless you live in a VERY harsh climate (either hot or cold) the difference between 2 and 3 string bales will be hard to notice.
The advantage of 3 string bales is that they are more solid when stacked. As mentioned above in the field stacking ability of 3 string bales, they are very sturdy because of their larger base surface area. This translates into strong walls as well. I prefer 3 String bales when building load bearing for just this reason. In addition, because they are wider, you can cut deeper niche into them which is also a nice feature.
The reality is that both 2 string and 3 string bales have their advantages. See what is available to you locally and then decide which advantages best lines up with your plans to build. You may find that it really doesn’t matter to you which size you use. In which case, stick with the local kind.