Wood insulated concrete forms (WICFs) were invented of necessity in Europe follow­ing World War II. Massive rebuilding was required and there was a shortage of conven­tional building materials. Waste wood was plentiful, and insulating forms made by mix­ing mineralized (clay impregnated) wood chips with cement proved to be a good way to conserve both precious fuel and scarce con­crete. These wood and cement masonry units had many excellent building properties. They were lightweight and noncombustible, had a high strength-to-weight ratio, and were di­mensionally stable, insulative, and resistant to freeze-thaw, rot, insects, and fungus growth. The resulting structures were more durable, energy efficient, and economical than struc­tures built by prewar methods. In continu­ous use since the 1940s under various brand names, WICFs are still a preferred method of construction throughout Europe.

In North America, WICFs are avail­able through Durisol, Faswall, and Healthy Buildings Made Easy. They come as inter­locking hollow blocks similar to cinder or masonry unit blocks. They are dry-stacked (without mortar) and filled with concrete and reinforcing steel. Durisol produces special thermal units that can incorporate mineral fiber insulation inserts to reach an R-value of 28. Faswall is a shorter, heavier block with thicker walls that can incorporate different in ­sulation inserts to produce an R-value of 26.

Although all the cores are usually filled with concrete, a more ecological application is to use concrete only in the cores where steel re­bar is required and to fill the other cores with natural insulation or earth. WICFs are consid­ered to be a form of vapor diffusible or breath­ing wall construction.

Aerated Autoclaved Concrete

Aerated autoclaved concrete (AAC) was first developed by a Swedish engineer between 1920 and 1932. It has since been refined into a concrete-based block material with high in­sulation used for both load – and non-load­bearing walls. AAC is manufactured from quartz sand, lime and/or cement as the bind­ing agent, aluminum powder, and water. The aluminum powder reacts with calcium hy­droxide and water to form tiny hydrogen gas bubbles. At the end of the foaming process the hydrogen escapes into the atmosphere and re­acts with air to form water, and air replaces the hydrogen in the formed bubbles. The finished block does not contain aluminum. The final block form is autoclaved under heat and pres­sure to reach full strength.

AAC block construction uses standard masonry skills and is installed in a manner similar to regular cinder block, using a thinset instead of a cement mortar. Where reinforcing is required by code, special units with bored cylindrical holes can be vertically stacked and filled with rebar and cement grout, thus

minimizing the use of cement. No blocking is required, and shelving and other attach­ments can be screwed directly into the walls. The blocks can be sawn, cut and shaped with woodworking tools. The solid, lightweight walls combine thermal mass and high insu­lation values. They have outstanding seismic, acoustic, and fire performance. The walls can be plastered inside and out and are inert and stable, with no toxic outgassing. This system has worked well for people with chemical sen­

sitivities, but sensitive individuals should pre­test the thinset mortars for acceptability. In North America, aerated autoclaved concrete is manufactured by Aercon, Contec, Huma – built HumaBlock, and TruStone.

Conclusion

A variety of natural materials can be used to create heirloom quality buildings that are eco­logically sound, promote health, and have

outstanding energy efficiency. In short, natu­ral building materials may be superior in all these respects to the standard building systems prevalent in industrial countries. An owner choosing to use a natural alternative building system is a pioneer who may be well rewarded for an adventuresome spirit. Regional factors such as drainage, rainfall, temperature, hu­midity, freeze and thaw cycles, and the avail­ability of natural materials will make some natural building systems more suitable for certain locations than others.

When planning to build with alternative materials, make careful inquiry to determine the status of these materials with local build­ing authorities to ensure that the alternative you choose will be permitted in your jurisdic­tion. Each of the model building codes used in the United States has a provision for alterna­tive methods and materials. Building officials of the jurisdiction in which a project is located have the authority to approve any building they deem adequately meets the intentions
and provisions of the code. It may be necessary to educate a building official about the materi­als you intend to use, and it is worthwhile to gather information about code approvals that have been granted elsewhere for the same ma­terials. If a building official is unable to make a determination about the alternative material you are presenting, it may be possible to move forward with approvals by creating a legal document holding the building department harmless. DCAT is a nonprofit organization dedicated to addressing the challenge of insti­tutional barriers to sustainable building and development found in building codes.

Earlier in the 20th century it was incum­bent upon industrial manufacturers to prove to code officials that their products performed as well as their preindustrial counterparts. The powerful forces of industry, with their finan­cial capability to test manufactured products, have now completely reversed the situation to the point where nonproprietary materials and methods of construction are viewed as inferior.

Ironically, this is so in spite of the thousands of years of research and development that have gone into the refinement of natural building techniques. In order to gain more widespread acceptance into mainstream building venues in this country, each example of natural build­ing mustbe well-conceived, well-documented, and based on a sound knowledge of the laws of nature. In fact, a thorough understanding of building science is even more important for designers and builders using these alternative systems because of the high degree of experi­mentation involved in adapting ancient tech­niques to modern comfort and performance demands.

We would like to emphasize that the use of natural construction materials does not automatically create a healthy home. The ma­terial used in the buildings walls is only one of many components that go into creating a home environment. However, when the alter­native systems described in this chapter are
used in conjunction with the other principles of healthy building outlined in this book, it is possible to produce buildings of exceptional vitality.

Further Reading

Baker-Laporte, Paula and Robert Laporte. EcoNest: Creating Sustainable Sanctuaries of Clay, Straw and Timber. Gibbs Smith, Publisher, 2005. Chiras, Daniel D. The Natural House. Chelsea Green Publishing Company, 2000.

Cob Cottage Company Earth Building and Cob Revival: A Reader. 3rd ed., Cob Cottage Company, 1996.

Easton, David. The Rammed Earth House. Chelsea Green Publishing Company, 1996.

Elizabeth, Lynne and Cassandra Adams, eds. Al­ternative Construction: Contemporary Natural Building Methods. John Wiley and Sons, 2000. Evans, Ianto et al. The Hand Sculpted House. Chelsea Green Publshing Company, 2002.

Kennedy, Joseph et al., eds. The Art of Natural Build­ing. New Society Publishers, 2002.

King, Bruce. Buildings of Earth and Straw. Solar Liv­ing Center, 1996.

The Last Straw: Vie International Quarterly Journal of Straw Bale and Natural Building. See thelast straw. org.

MacDonald, S. O, and Matts Myhrman. Build It With Bales: A Step-by-Step Guide to Straw-Bale Con­struction. Treasure Chest Books, 1997.

McHenry, Paul G. Adobe: Build It Yourself Univer­sity of Arizona Press, 1985.

Minke, Gernot. Earth Construction Handbook: The Building Ma terial Earth in Modern Architecture. WIT Press, 2000.

Roodman, David Malin and Nicholas K. Lenssen.

A Building Revolution: How Ecology and Health Concerns Are Transforming Construction. World­watch Paper 124,1995.

Steen, Athena Swentzell et al. The Straw Bale House.

Chelsea Green Publishing Company, 1994.

Steen, Bill et al. Built by Hand. Gibbs Smith, Pub­lisher, 2003.

Wanek, Catherine. Vie New Straw Bale Home. Gibbs Smith, Publisher, 2003.

Weismann, Adam and Katy Bryce. Building with Cob: A Step-by-Step Guide. Green Books, 2006.

Straw Bale

Although straw has been an important com­ponent of natural building for centuries, straw bale is a relatively new form of alternative con­struction that appears to be an innovation of the early settlers of the Nebraska plains, where unsuitable soils and a scarcity of wood made necessity the mother of invention. The high insulative value of straw bale (between R-33 and R-57, depending on the type of bale and the testing facility) and the aesthetics of the thick walls have quickly made it a popular al­ternative building material.

Because much of the straw grown in the United States is heavily sprayed with pesti­cides, we recommend looking for straw that

has been organically grown. The Last Straw, listed in the bibliography at the end of this chapter, has published a list of organic straw sources.

Because cellulose is aperfect food for mold, bales of straw often contain mold. This means that it is very important with straw bale build­ing to incorporate rigorous water and mois­ture management strategies into the design. If the walls are allowed to breathe — that is, if

they are not covered with impermeable mem­branes that will trap any moisture in the wall — in theory the bales will always remain dry enough so that mold will not be a problem. Us­ing earth-based instead of cement-based plas­ters on interior walls will help keep water away from the bales and allow them to dry out more readily when they do get wet. On the exterior of the building, earth-based plasters that are augmented to prevent water penetration may prove more desirable from a moisture move­ment standpoint than cement-based plasters, which are less flexible, tend to crack more, and allow less vapor diffusion. Should water become trapped in the wall through roof fail­ure, plumbing leaks, poor drainage, or other building systems failures, mold can become a problem.

Many techniques have evolved for straw

bale construction. Building permit approval is greatly simplified when structures are non­load-bearing and most straw bale construc­tion relies on a variety of structural systems, including exposed and buried post and beam, steel posts, and poured or masonry concrete piers. Load-bearing straw bale examples have been built in Colorado, Arizona, and Canada. Several jurisdictions have adopted straw bale codes, including New Mexico and California; Pima County and Guadalupe, Arizona; Aus­tin, Texas; Boulder and Cortez, Colorado; and McCook, Nebraska. Nevada has a legislative mandate to ensure that local jurisdictions de­velop building codes allowing straw bale con­struction. While some jurisdictions permit load-bearing straw bale construction, others permit straw bale only as a non-load-bearing wall system.

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Section through pumicecrete wall.

Pumice-Crete

In this method, 14- to 24-inch-thick walls are created by mixing pumice, a very porous vol­canic rock, with a light, soupy concrete. The mixture is poured into formwork. The result­ing walls have both thermal mass and a high insulation value, and are ready to accept plas­ter without further preparation. When used with a concrete bond beam at the top, the walls are load bearing. In Europe, pumice and other naturally occurring lightweight volcanic aggregates have been used with mud in place of the concrete. However, these walls are not used in a load-bearing situation.

Because of the simplicity of this system and the absence of organic matter in the wall construction, pumice-crete is very suitable for persons with chemical sensitivity, who are often also highly sensitive to wood terpenes, mold, and pesticides that may be found in small quantities in other building materials. Since the wall uses cement, the rules for con­crete formwork and cement composition, out­lined in Division 3, must be followed.

Pumice can be radioactive. Samples should be tested with a Geiger counter to be sure they are free of radioactive material. (Refer to the section on radiation in Division 13 for testing
methods.) Because pumice is highly porous, it can readily absorb odors and it is prudent to specify that pumice be free of acquired odors when it arrives onsite and protected onsite and in place from pollution sources. Once the walls are plastered, this should no longer be of concern.

To help stabilize indoor humidity levels and create further thermal mass storage ca­pacity, clay-based plasters can be applied to interior surfaces and will adhere well without the use of lathing.