What Is Green Building?
(Page 5 of 8)
August/September 2005
By the Mother Earth News editors
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Cordwood
Excerpted from The Charm of Cordwood Construction by Rob Roy, Mother Earth News June/July 2003
This ancient building style — many references date it back 1,000 years — has known a substantial rebirth since the first articles about it appeared in Mother Earth News a quarter of a century ago. In cordwood construction, walls are constructed of log-ends — short logs, 12 to 24 inches long — mortared up transversely in the wall, similar to the way firewood is stacked.
In Canada, it’s commonly known as stackwall building. Log-ends can be cut from wood that is unsuitable for other purposes, such as fire-killed standing wood, ends and pieces from a sawmill, logging slash, and curved branches and trunks. Portland cement, mixed with sand, sawdust and builder’s lime, generally serves as the mortar between the “courses” of cordwood.
Why Build with Cordwood?
In 1974, Jaki and I bought land in northern New York to pursue our vision of a self-reliant lifestyle. In those days, the “natural building” structure of choice was the log cabin. We had helped with constructing a log home, and we knew from experience that fitting and hefting the large logs was a lot of hard work. We also knew that in our area, 15 miles from the Canadian border, we would not find logs thick enough to provide adequate insulation against the harsh climate. And building another internal insulated frame inside the log walls seemed to defeat the purpose of minimizing the use of materials.
About this time, we stumbled upon the April 1974 issue of National Geographic, which contained a picture of a cordwood home in Skowhegan, Washington. Immediately, we knew that we had found a method of building that satisfied our criteria. Building with cordwood masonry would be cheaper and more efficient than building with conventional methods, as we could salvage “unsuitable wood” to use for construction and we could build the home ourselves. Cordwood’s thick, stalwart walls also would buffer this region's temperature extremes. However, it was probably the unique beauty of these buildings that sealed the deal for us.
Over the past quarter century, Jaki and I have built four homes and innumerable outbuildings with cordwood masonry. In November 2002, we completed a beautiful new sunroom addition to Earthwood, our primary home and the home of Earthwood Building School, where we give workshops on cordwood construction. When people ask us why we're so enthusiastic about cordwood masonry, I am fond of listing what I call the “5-E Advantages.”
- Ease of construction. To lay up a cordwood wall, the builder need never handle anything heavier than a firewood log. Mortar is easily mixed in a wheelbarrow. We have found that the novice owner-builder readily learns the skills. For years, I have been saying that children, grandmothers and beavers can all build cordwood homes...and they do!
- Economy. Log-ends can be cut from less-than-perfect or salvaged wood — fire-killed standing wood, ends and pieces from the sawmill, logging slash, and curved branches and trunks unsuitable for lumber. Even old fence rails and driftwood have been used.
- Energy advantages. Cordwood combines insulation with thermal mass better than any other aboveground building system I can call to mind. The secret is the unique insulated mortar matrix that is woven around all of the log-ends. The mortar does not conduct heat directly through the wall because of an insulated cavity built into the middle third of the wall’s width. With a 16-inch-thick wall, for example, we use a 6-inch-wide insulated space between the inner and outer mortar joints. The insulation can be sawdust and lime (at a 12-to-1 ratio), which results in about R-3 of insulation value per inch of thickness. Other loose-fill insulation, such as perlite or vermiculite, also can be used. (Cellulose, which can trap moisture, is not recommended, and we no longer use fiberglass because of its high energy consumption during manufacture, as well as the danger of inhaling the glass fibers.) Unlike lightweight, wood-frame walls, cordwood walls contain tremendous thermal mass in the mortar. The log-ends themselves also possess both insulative and thermal mass characteristics. Because of this, cordwood homes do not suffer from wild temperature fluctuations; they are easy to keep warm and stay comfortably cool in the summer.
- Environmental harmony. Cordwood masonry makes use of natural, indigenous materials — and even “waste” destined for the landfill. To further mitigate the environmental impacts of construction, some cordwood builders concerned with concrete mortar’s high embodied energy use a cob mortar (clay, sand and straw) instead. My most-recent cordwood construction book, Cordwood Building: The State of the Art (on Mother’s Bookshelf), discusses this innovative technique.
- Esthetics. This acceptable spelling allows me to complete the “5-E” advantages of cordwood. To me, esthetics is just as important as any other consideration, because, ultimately, we must feel good about the house we call home. Jaki and I never tire of the appearance of our walls, which combine the warm colors of wood with the pleasing relief and texture of fine stone masonry. Cordwood offers an almost limitless outlet for creative expression. We like to incorporate special features into the walls, such as shelves and storage nooks. Colorful bottles embedded in the walls admit sunlight in all colors of the spectrum. Our sunroom addition features an Easter Island motif on one of the cordwood panels.
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