Cordwood construction, also referred as Stackwall construction is building walls using short lengths of trees embedded in concrete with air space in the middle. Of course this is a simple analogy of the process, but in reality that’s about how easy it is. There is no need to shape the lengths of logs, just cut them all at a uniform length. Twelve to twenty four inches, determined by your skill in cement finishing and desired insulation
Some places have code requirements that mandate a post and beam type framework with cordwood walls used to fill in the openings. Though there is plenty of strength in a cordwood wall.
To prepare the basically stove length pieces of logs, it’s best to peel them. Nubs of branches sticking out are no concern, they will just be part of the unseen part of the walls.
Starting with a solid foundation, the process begins by laying down a bed of concrete in two rows. Space the two rows to match the length of your log pieces. You want to lay the logs across the two rows of concrete with about 1/2″ of wood sticking out beyond the concrete. as you lay down a row of cordwood, you add concrete to fill in between the cordwood pieces. As the wall rises you’re in effect building two narrow concrete walls with cordwood crossing between the two layers of concrete. This will leave a noticeable air space in the middle that will serve as a thermal barrier.
Wood will amount to 40-60% of the wall structure. Sometimes a material known as Cob can be used instead of concrete. Cob is a mixture of clay and straw, similar to Adobe, except it is not formed into bricks. Instead it is handled more or less by the handful, or a Gob of Cob. Plopped down on top of the previous layer. There is no stucco layer on top, so this type of construction is usually reserved to the south west, or areas of less precipitation. It is further required that large eve’s be built to protect the walls from rain and run off from the roof. Concrete will greatly reduce the amount of maintenance required of a Cob constructed wall.
A popular style of building is a circular structure. Cordwood buildings of this style are particularly attractive when the ends of the cordwood are varnished or painted. To increase the R value of a cordwood wall, you can fill the center cavity with insulation.
The wood you use doesn’t have to be round cordwood. You can use split firewood, branches, saw mill remnants, what ever wood you have access to. In fact some houses have been built with this type of construction using bottles in place of wood. You can get as creative as you want.
Cordwood houses have been around for well over a thousand years. Some very old examples are still standing in Greece and Siberia. According to William Tischler of the University of Wisconsin, present day cordwood construction originated in the 1800’s in Quebec Canada.
Wikipedia has more detailed information on Cordwood construction at this Cordwood Construction web site, including a picture of a circular cordwood building.
The next time you head for the wood pile for firewood, start thinking about how you can use that wood to build a back woods retreat. Build your next cabin using the resources that are right there on the property.