How to Choose the Right Straw Bales

The first decision when designing and building a straw bale house is what size of bales to use. There are at least three options:

  1. two-string bales measuring 14″ tall x 18″ wide x 36″ long;
  2. two-string bales measuring 16″ tall x 18″ wide x 45″ long;
  3. three-string bales measuring 14″-17″ tall x 24″ wide x 48″ long.

The actual measurements of all these bales may vary depending on the baling machines employed in the fields. You will need to know the exact size of the bales you will use when you are designing the structure. It is good practice to design to the size of the bale.

Moisture content is another important factor in deciding which bales to purchase. Moisture content of up to 20% is considered safe although the less moisture the better. I use bales that have a moisture content of 8-10%. Moisture content will vary with ambient moisture, so areas with high humidity may have bales with more moisture. Be sure to keep the levels below 20% at all times.

There is a way to calculate moisture content in bales mathematically; however, hand held moisture meters are the easiest way to check moisture content.

Density is important. A tightly strung bale will create a solid wall and strong backing for the plaster. A general rule of thumb is that when you lift the bale by one string, there should be very little shape deformation. Also, bales should not greatly deform when dropped from a pickup truck bed.

Finally, visually inspect the bales. If they look like they have gotten wet, be sure to thoroughly test the bales for moisture readings. Bales that have a golden color are the best option. The lighter the straw in color, the more likely they have never seen water!


Andrew Morrison has a passion for straw bale construction that is matched only by his desire to teach his knowledge to others. He has a wealth of experience in designing and building both conventional and straw bale homes. After years of building, he has moved his practice entirely to consulting and teaching. He shares his knowledge with thousands of people via his DVD series and this website and teaches roughly six-eight hands on workshops each year. For more on his workshops, please visit  Andrew received a BA degree from Hampshire College in 1995 for Glacial Geology. He also has a degree in construction technology.

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