Thirty years ago, my wife, Becky, and I built our mortgage-free cordwood home in northern Wisconsin. Since then, as directors of Cordwood Construction Resources, we have written books, conducted workshops, organized the 2005 Cordwood Conference and provided consultation for potential cordwood builders.
In winter 2007, the Friends of the Merrill School Forest (an organization in Madison, Wis., that supports the school district’s forest) along with the Evjue Foundation, the charitable arm of the Capital Times in Madison, Wis., decided to use cordwood construction to build an education center on the school’s 764-acre woodland site in Merrill, Wis. The committee of “Friends” asked us to be the consultants and cordwood construction instructors for the project. The center would be used as a classroom, nature center and winter shelter, and would serve as a model for sustainable building and energy efficiency.
The committee had explored various green building methods and ultimately chose cordwood. Cordwood construction utilizes a low-cost, renewable, local building material — chunks of firewood — as the infill in timber frame construction. Cordwood has historical roots in Wisconsin. Door County, Wis., has numerous fine examples of turn-of-the-century cordwood structures (called “stovewood” at the time).
The Friends drew up plans, which were code approved, for the Evjue Cordwood Education Center. Volunteers cut 25 cords of tamarack during that winter (one cord is a pile 4 feet by 8 feet by 4 feet). In the early spring, the crew peeled the bark from whole logs with draw knives and peeling spuds, and later that spring, they used a portable sawmill to cut the timbers, posts and paneling. For the cordwood infill material, we used a buzz saw attachment on a John Deere tractor to cut logs to 16-inch lengths. Then we covered the rows and rows of split tamarack that were left to air-dry.
Sustainable All the Way
The framework of massive white pine corner posts and tamarack middle posts went up in spring 2008. Local high school construction classes came out to learn the art of timber framing and cordwood masonry. The general contractor gave lessons in safety, construction techniques, and the proper methods of squaring and leveling. An energy-efficient truss roof was erected and topped with standing-seam metal roofing. This roof truss design allows for thicker insulation for greater energy efficiency.
The building was oriented south for optimal passive solar gain. After establishing the solar exposure, we harvested the surrounding trees for firewood. To take full advantage of the solar gain, we used Energy Star efficiency guidelines in every phase of building. Generous local merchants and community organizations helped out: The Merrill Rotary Club donated a beautiful Vermont Castings Encore woodstove to provide auxiliary heat. Eleven casement windows, two steel doors and the attractive, split-faced construction block came from local businesses.
In fall 2008, volunteers arrived daily to learn the old-fashioned art of cordwood construction. They laid short lengths of logs (16 inches) in a mortar matrix of two 3-inch mortar beads (see photo, below left). Next, they filled the center cavity with dry sawdust mixed with hydrated lime for added insulation. According to thermal resistance tests conducted by the engineering department at the University of Winnipeg, this 16-inch wall has an R-value of 24 (more than the recommended R-19 for standard 6-inch fiberglass batt insulation).
Volunteers mortared recycled colored bottles (also known as “poor man’s stained glass”) into the walls among the log ends. These provide bright spots in the wall when the sun strikes the bottle ends. The builders also set stones, gems and animal tracks into the mortar. The cordwood infill took five weeks to complete. As the walls slowly took shape, the inherent beauty of the building became apparent. The building was finished in winter 2008 as the gable ends, interior ceiling and lighting were installed.
The solar, in-floor radiant heat system was installed in 2009. The Midwest Renewable Energy Association in Custer, Wis., provided three used flat-plate solar collectors to heat the water for the radiant heat. To pump the water for the radiant floor heating system, we purchased DC pumps and a 75-watt photovoltaic panel from a local renewable-energy buff. This solar hydronic system has 600 feet of PEX tubing located within the insulated slab. This system illustrates how to install solar heat and electrical power at a remote site.
Students visit the center every day for classes on nature, ecology and forestry, and an open house and family fun day are held every winter. Community members learn from and take note of the old-fashioned natural methods of building combined with the newest solar technology used in the community cordwood center.
Richard and Becky Flatau are cordwood building consultants and instructors in Merrill, Wis. You can contact them at 715-212-2870, or visit their online bookstore.