Alternatives to Standard Building Methods Offer Some Green Advantages
Locally procured materials can be inexpensive
Many alternatives to standard wood or masonry wall construction were either revived or invented by builders — sometimes novices — taking part in the back-to-the-land wave of the 1970s. They most often used clay and earth, wood, stone, straw and other plant fibers, and salvaged and recycled materials. Interest in these approaches began growing again in the mid-1990s. Initially, these systems relied on indigenous and/or low-cost materials along with significant inputs of human labor, typically provided by the owner-builders themselves and/or inexperienced volunteers eager to learn these natural building methods. As the movement has matured in recent decades, however, many such homes have been built by professional builders. Contemporary examples are often beautifully crafted, with price tags to match. These nonindustrial wall systems, when professionally built, are reported to cost roughly 5% to 10% more than their more conventional counterparts, due to the higher level of handcraftsmanship. Proponents cite attributes such as performance (usually, thermal and acoustic), environmental benefits (i.e., materials that are nontoxic and low in embodied energyEnergy that goes into making a product; includes energy required for growth, extraction, and transportation of the raw material as well as manufacture, packaging, and transportation of the finished product. Embodied energy is often used to measure ecological cost.), costs (when the homes are owner-built), aesthetics, and occupant satisfaction.
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WAYS TO USE DIRT AND STRAW
Choose a method that works in your climate
Many building materials that seem unusual in North America have their roots in different countries and cultures, while other are the result of inventive minds looking for a viable use for a plentiful local material. If you are considering building a house from an alternative material, it's important to decide first if the material is available in your area and whether it is appropriate for your climate.
Remember as well that the cost-effectiveness of using unusual materials depends on their local availability.
Aren't green building systems already "alternative"?
Designing and detailing to make the most of a project's materials are at the root of green building. Because of this, many of the systems and concepts tend to be out of the ordinary. As time goes on and building methods are given a chance to prove themselves, they may migrate into the mainstream, where they can do good on a larger scale.
Find the right people for the job
Alternative wall systems, because they are nonindustrial by nature and differ substantially from mainstream wall systems, are best implemented by designers and builders who have prior experience with them. Their unique properties (e.g., size/width, structural capacity, thermal performance, and aesthetic attributes) need to be understood – and the design will ideally capitalize on them; they need to be detailed differently; and they utilize unconventional construction methods.
There are risks in using new ideas
Conventional building methods are just that — conventional. They have long precedents, large supporting industries, and public confidence. On further inspection, though, many successful sustainable technologies are based on time-tested principles that have been given new life. To improve a present situation, it can be valuable to look not just to the future, but also to the past, to see what worked or didn't work.
These alternative methods are labor intensive
Traditional and alternative wall construction methods are almost always more time-consuming than wood-frame construction, so they can be very costly if the client is paying for labor. That's why the methods are popular with owner-builders who may be able to invest their own sweat equity.
The code: Local officials might be unfamiliar and reluctant
Alternative, traditional, and "natural" wall systems are more likely to be approved by reluctant code officials if the nonstandard materials are relegated to an infill capacity; that is, use a bearing system that the officials are familiar with, such as timber, and the straw bales, leichthlehm, or what-have-you as a nonstructural insulating and finishing component.
Straw-bale building is supported by legislated guidelines or acceptance mandates in California, New Mexico, Nevada, and Oregon, and by code adoption in several municipalities in those states, as well as in Texas, Colorado, Arizona, and Nebraska. There are straw-bale structures in every American state, though not all have been built "with the benefit of code."
Cob construction, a more robust version of the "puddled adobe" used for some 1,000-year-old Native American buildings in the Southwest, suffers from almost no code adoption. Although there are cob houses from the 1500s in damp and chilly England, cob is in its infancy in the U.S. (despite scattered immigrant use in the 1800s in locations as far north as Rochester, N.Y.). Suffice it to say, contemporary code-approved cob houses in this country are rare in this country.
ABOUT ALTERNATIVE WALLS
Straw-bale walls perform very well
Of the many alternatives to conventional wood or masonry walls, straw-bale construction has gained the most adherents in the U.S. Other methods mentioned below also have their supporters, but most are regional or used by few people.
Tight and warm
Because most straw-bale walls are plastered on both sides, they have very little air infiltration. As with all building types, junctions of dissimilar materials — particularly around windows and doors — are weak spots for air infiltration and can do much to undermine an otherwise high-performing wall system.
Straw-bale walls also resist heat flow, though just how much is still an area of contention. The results of laboratory thermal tests on straw-bale wall systems have varied widely. After studying existing data and funding its own tests, the California Energy Commission adopted a nominal R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of 33 for plastered straw-bale wall systems. Although some enthusiasts cite a much higher R-value, R-33 still represents a significant improvement over most standard residential walls.
Straw-bale walls are susceptible to mold and rot if they get wet, so these homes should have wide roof overhangs, a good height above grade, and appropriate weather detailing. Rain-screen claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. may be an appropriate solution.
There are straw-bale structures in every American state. The oldest were built around 1900. The technique is supported by legislated guidelines or acceptance mandates in California, New Mexico, Nevada, and Oregon, and code adoption in several municipalities in those states, as well as in Texas, Colorado, Arizona, and Nebraska. For more information, see Straw-Bale Walls.
MORE ABOUT ALTERNATIVE WALLS
Adobe construction techniques are thousands of years old. Adobe bricks are made from soil that has a good ratio of clay to sand; the addition of chopped straw is optional. Mixed with water, the ingredients are formed into bricks. Once dry, the bricks are stacked in running bond to form walls, and mortared together using the same earthen mixture. The Getty Conservation Institute has developed systems in recent years that greatly improve the seismic performance of adobe buildings.
Cob walls are made from the same basic recipe as adobe: clay, sand, and straw. Unlike adobe, however, cob isn't formed into bricks — the word "cob" means "lump" or "loaf." Cob walls are assembled by hand, without forms, to create a monolithic wall. Completed cob walls are often plastered. As with all earthen wall systems, thermal performance is an important consideration.
Compressed earth blocks (CEBs) are a type of adobe block made using a machine that compresses the material into a form. Portable, automatic machines are generally used for production work, and a proportion of cement is typically used to stabilize these blocks. Manual block presses are also available. The technique creates a smooth-faced block that is denser than traditional adobe.
Cordwood walls are built from short sections of logs, each of which is as long as the desired wall thickness. The pieces of wood are stacked to form a wall, using two lines of mortar (or a cob mixture) — one to the inside, and one to the outside — with flowable insulation (usually sawdust mixed with lime) on the inside. Differential expansion and contraction of the dissimilar materials needs to be considered.
Earth bag construction uses bags of dirt to build walls. Woven polypropylene bags (burlap bags are rarely used) are filled with soil that is sometimes stabilized with the addition of portland cement. The bags are stacked in running bond, with two strands of four-point barbed wire providing a mechanical key between courses. Each course is tamped solid. This technique has been described as "flexible-form rammed earth," and "superadobe."
Earthships are partially underground passive solar homes with walls built from earth-filled automobile tires and aluminum cans. The construction method was developed in the 1970s by Mike Reynolds of Taos, N.M.
Leichtlehm (sometimes called "straw-clay" or "slip-straw") is a German technique for building infill walls between the posts of timber-frame buildings. Movable, reusable forms are filled with straw that is lightly coated with a slurry of clay and water, and the mixture is tamped into place.
Papercrete is a type of papier-mâché made from paper fiber, portland cement, and some sand. It can be used to make blocks, panels, or poured-in-place walls. Though beautiful and successful adobe-like examples exist, this is a highly experimental material and process that has also resulted in flammable, self-delaminating failures. Some papercrete recipes require more cement than a solid concrete wall. A variant called "padobe" uses clay rather than cement as a binderGlue used in manufactured wood products, such as medium-density fiberboard (MDF), particleboard, and engineered lumber. Some binders are made with formaldehyde. See urea-formaldehyde binder and methyl diisocyanate (MDI) binder. .
Rammed earth walls are built using movable, reusable forms. The forms are filled with soil that is ideally gathered on-site — a mixture of clay, sand, small stones, and sometimes portland cement — that is then compacted, either by hand or using pneumatic machinery.
Slipform stone walls were popularized in the 1930s by back-to-the-land pioneers Helen and Scott Nearing. Slipforms are movable, reusable forms. Walls built according to the Nearing technique are made from a mixture of concrete and fieldstones. The stones are carefully placed by hand in the forms so that the wall looks like a stone wall rather than a concrete wall when the forms are removed.
Straw-bale walls are built from stacked bales of straw. Both sides of the wall are usually finished with plaster. If the home includes posts and beams, the straw bales are nonstructural. Straw-bale walls can also be load-bearing. When plastered, straw-bale walls are relatively airtight and have good thermal performance.
Wattle and daub is an infill technique used to make walls between the posts of a timber-framed building. The wattle (a woven lattice of flexible sticks) is installed first, and then coated on both sides with daub (a damp mixture that contains soil, sand, clay, and sometimes straw or manure).
Buildingscience.com: Building Science for Strawbale Buildings
- Gary Williamson/Fine Homebuilding #131
- Mark Piepkorn
- Charles Miller/Fine Homebuilding #155
Feb 25, 2012 6:05 AM ET
Feb 24, 2012 6:22 PM ET