Catherine Wanek

Section: Planning and Design

Chapter: Building Naturally for Energy Efficiency--By Catherine Wanek

It’s a natural to use available, onsite materials in building our homes. Doing so conserves energy and resources--our own and planetary. And understanding the specific qualities of our onsite resources and how they can be combined, allows us to create efficient and elegant homes that require the least energy input and return the greatest comfort.

Beginning always with choice of building site, two effective strategies for energy-efficiency are solar orientation and earthcoupling. By simply designing window placement to capture the winter sun, a major part of our heating needs in many climates can be accomplished with minimal effort. If your site happens to be on a hillside, coupling your home with the constant yearround temperature of the earth below the frost line (about 55-65 degrees F), will keep indoor temperatures within relatively few degrees of the human comfort zone. Combining earthcoupling and passive-solar design enhances the effectiveness of both, but requires finetuning to climate, and works less well in cold climates, and where sunlight is scarce in the winter.

Thermal Mass, Insulation, and Structure. Common to nearly every building site is earth--in fact to build a sturdy foundation, it’s generally necessary to excavate. After the topsoil is set aside for gardening or landscaping, the subsoil must be dealt with. Very often it can be combined with other natural materials to form wall systems. Other materials often found onsite are stones and timber--both of which can be utilized in construction. But to utilize them appropriately and most effectively, it’s essential to understand what each material does best.

Although timber in our dry-land bioregion is a precious resource, it can still be harvested sustainably and used in construction. Wood has great structural strength, rigidity and beauty, and a medium insulation value. But it shrinks as it dries, so wooden wall systems are prone to small gaps that can let a lot of cold air in. Thus, for most sites, using wood structurally for your roof system probably makes the best use of available timber. Also, smaller trees not normally considered for building can be quite useful. The locally-ubiquitous Juniper tree grows slowly and in organic shapes, hence is not wellsuited for milling. On the other hand, this scorned tree is a member of the cedar family, so is extremely rotresistant and strong. It makes good structural posts, sills and trim, and when left in its organic shapes can be amazingly beautiful. Willow, maple and other saplings that often need to be thinned can also be used in wattleanddaub walls, or for pinning strawbale wall systems (instead of buying rebar.)

Stone and earth can also be utilized as structural materials. Their density makes them good "thermal mass," which means that they absorb heat or cold from the air around them. As the air temperature changes, a thermal mass will slowly equalize to match it, releasing the heat (or cold) stored in it. A thermal mass material absorbs heat most effective when it is dark colored and the sun hits it directly. Used well, this can help to warm or cool our homes, but misunderstood, it can be an energy drain or cause discomfort. The "heat island" effect of some urban areas is due to excess thermal mass (and lack of shading). Masonry buildings, asphalt streets, and concrete sidewalks soak up the hot summer sun during the day, and radiate it out during the night, keeping the city continually hot. This cycle can continue day after day, and require massive energy inputs to create human comfort zones.

Not often found onsite, but cheap and available in nearly every region, is straw. Since humans first began to build shelters, straw (or grass) has been used as a building material in combination with earth--in bricks, walls and floors. When the baling machine was invented, it became possible to turn straw into big, highlyinsulating building blocks. In bale form it can be used structurally, and it provides something few other natural materials can--excellent insulation. It is the deadair space contained within the hollow stalk of straw and around the individual stalks that make straw bales such a good insulator, provided the walls are well-sealed with plaster to prevent air infiltration.

Wall systems that combine thermal mass and insulation will, not surprisingly, perform somewhere in between. Although "definitive" R-values are not established for straw-clay, wood-chip-clay, cord-wood masonry, papercrete, fidobe and the like, these materials retain thermal mass characteristics with moderate insulation properties. In combination with passive-solar design and a well-insulated ceiling sealed against air infiltration, these materials can create a comfortable and energy-efficient home in moderate climates.

Still, good insulation in walls and ceilings best protects indoor environments from daily and seasonal temperature swings, providing the greatest comfort for the least energy input--which is why I favor straw bales for exterior wall systems. But bales take up a lot of space, so are less suited as interior partitions, where insulation isn’t needed. So, for inside walls, a thermal mass material is most useful, where it will serve to moderate temperature. Earth and straw combinations such as adobe, cob, straw-clay, etc., also offer infinite possibilities for sculpting interior spaces and builtin furniture. And clay has a preservative effect on straw and wood, reducing their vulnerability to moisture and rot.

More reasons to use earthen materials inside the home are its abilities to absorb sound, odors and moisture. Water vapor from bathing and cooking can build up inside and provide an environment for mold and fungal growth, but earthen walls and plasters resist this buildup, with their enormous capacity to moderate humidity. Used to create floors, earth provides thermal mass for direct solar gain and a surface to stand on that is easy on the body. And an earthen plaster covering interior walls adds up to a lot of thermal mass, augmenting passive-solar design.

While the cost of using onsite natural materials is often "dirt cheap," techniques vary in how much work they take. Even when using machinery, cob, strawclay, adobe, rammed earth etc., walls are quite labor intensive. But building with bales can go very quickly. So using bales for exterior walls and thermal mass techniques for interior walls is also consistent with conserving fossil fuel and human energy in constructing our buildings.

By simply orienting our homes to the sun and insulating thermal mass, comfortable shelter can be created primarily from natural materials. Understanding their properties and how they can complement each other will lead to energy-efficient and healthy built environments that nurture human life.

Catherine Wanek lives in an historic stone and brick lodge that faces north, with leaky old windows. The quest for energy-efficient comfort has led her to the above conclusions.

Resources--Books:
The Passive Solar House--Using Solar Design to Heat and Cool Your Home, James Kachadorian, Chelsea Green, 1997. This tome describes the timeless principles of solar design, including charts and tools to do solar calculations for a variety of latitudes. Suggested building materials are of a conventional nature.

Alternative Construction: Contemporary Natural Building Methods, Lynne Elizabeth and Cassandra Adams, Eds, New York: John Wiley and Sons, 2000. See especially Chapter 3: Natural Conditioning of Buildings by Ken Haggard, Polly Cooper, and Jennifer Rennick for a detailed description of the relationship between natural materials and passive solar heating and cooling.

Passive Solar Energy: the Homeowner's Guide to Natural Heating and Cooling. Second Edition; Bruce Anderson and Malcolm Wells. Brick House Publishing Co. Amherst, Mass.1994. An easy-to-read overview of strategies for passive systems, with sufficient detail to help you design a new building or retrofit an old one.

Workshops:
Build Here Now--a Natural Building and Permaculture Convergence; annually at The Lama Foundation, P.O. Box 240, San Cristobal, NM 87564 (505) 586-1269 registrar@lamafoundation.org

Natural Building Colloquium; annually, various locations. Contact: The Black Range Lodge, 119 Main Street, Kingston, NM 88042, (505)895-5652 resources@strawbalecentral.com