Choosing a Construction Method: Cordwood and Strawbale

We need to begin construction of our zero energy house by deciding how it will be built. This decision will impact our design, materials and process. In making this decision there will be tradeoffs and consequences that must be carefully analyzed and understood. No design or method can be entirely perfect. After examining our options, we will choose the method that works best for the goals of this project.

In the last article we examined rammed earth, earthships and earthbag construction. The two methods on our list for consideration here are cordwood and strawbale.

Cordwood 

In this system small, debarked pieces of wood between 12 and 18 inches long are stacked to create walls. A mortar mix is used to bond the pieces together. This mortar can be something more conventional using cement or something more natural such as an adobe or cob. Generally sawdust or some other light weight filler material is used within the wall or mixed in with the mortar to provide some insulation. Cordwood is similar in many ways to the rammed earth methods discussed earlier. They both make good use of natural materials to create an extremely environmentally friendly building. Unfortunately additional wood framing is usually required to support the load of the roof. The roof itself must also be designed separately. 

Cordwood walls being built

A demonstration video showing how to build a cordwood wall

Information on how to mix cob

Strawbale

This method has become a popular due to the tremendous insulation value of strawbales. Since they are so thick, a wall filled in with strawbales can easily achieve an R-40 insulation value. This high insulation is very valuable in the design of a zero energy home. However, like cordwood the bales themselves are not load-bearing. Although this is possible, it is limited to certain areas and requires a very careful and well engineered design to be successful.  A separate roof structure is again necessary.  

The definitive straw bale construction website. Contains videos, tutorials and additional information

Pros and Cons

The first important thing to realize is that both cordwood and strawbales are generally only used for non-load bearing sections of walls. We would prefer our method to be more all inclusive as was the case with earthbag construction. Since additional wood framing is necessary, our design becomes more complicated and more costly. Cordwood and Strawbale are both environmentally friendly and low cost, although not to the same extent as earthbag construction. Since cordwood and strawbale make extensive use of adobe and cob, there are also some climate issues to consider. These designs will be more difficult in areas that experience a thaw/freeze cycle or in areas that have perpetually high humidity and precipitation. These methods are also extremely labor intensive. While being superior in this regard to rammed earth and earthships, they again lose out to earthbag construction. In most cases we will again have trouble with conventional building codes depending on the extent to which we utilize conventional wood framing. The one area in which strawbale construction undeniably excels is in its extremely high insulation value.

Final Thoughts

These methods are just too limited in their use and applicability. They are also inferior to earthbag construction in most cases. As insulation however, straw bales are very appealing. Moving forward, we will keep this in mind and try to look for places where it might be possible to utilize straw bales as insulation.