Category A Healthy. House

Use of Sustainably Harvested Wood

The history of lumber harvest in the United States is long and complicated. On one hand, the relentless removal of the aboriginal forests built great cities and industries and made way for the agricultural abundance necessary for building a nation. On the other hand, the de­struction of the aboriginal forests in all regions of the country was for the most part wanton, complete, and without regard for ecological, biological, and human costs.

As a nation we have moved beyond the idea of limitless resources. Wood can be used in an ecologically conscious manner through sustainable harvesting and replanting, along with a commitment to building methods that produce structures with greater longev­ity than the growth periods of the trees from which they are built. A sustainably harvested forest is one in which the forestry practices are continuously monitored and improved to ensure the present and future quality of both the wood resource and the forest itself. This approach includes consideration of the eco­nomic and social impacts on the communities involved and the protection of regional bio­logical diversity.

Sustainably harvested wood can often be obtained for the same price as lumber har­vested by environmentally damaging methods such as clear-cutting. By specifying the use of sustainably harvested woods for a building project, you are helping to raise awareness and increase market demand. Specifying sustain­ably harvested wood can be done by describ­ing the standards the wood must meet in order to be classified as sustainable, or more simply by listing local suppliers of wood that has been reputably certified. In residential construc­tion, where the builder may not have a sizable research and purchasing department, the sec­ond method is more effective.

The Forest Stewardship Council (FSC) is a leading international organization that sets standards for sustainability and accred­its third-party, independent certifiers. In the

US there are currently nine organizations that are FSC accredited. These include the Smart- Wood Certification Program and Scientific Certifications Systems (SCS). The Certified Forest Products Council has now become Metafore. It is a nonprofit organization that provides information on sources for purchas­ing FSC certified wood, with state-by-state listings and more than 4,500 certified loca­tions on its website. It also provides sample specification language tailored for use in the Construction Specifications Institute (CSI) Master Format.

Home Depot, the worlds largest buyer of forestry products, adopted the FSC principles in 2001 and Lowes, the worlds second largest buyer, soon followed suit. Both now offer FSC products in a relatively wide range.

Oil Residue on Metals

Expanded metal lath and other metal goods are often shipped to sites coated in rancid oil residues left over from the manufacturing process. Such residues will be odorous for a prolonged period of time unless the metal is cleaned. When these oils are left in metal duct­work, hot air blown through the ductwork distributes these odors throughout the house. To avoid this unwanted pollution source, con­sider adding the following to your specifica­tions:

• Remove oil residue from all coated metal products using a high-pressure hose and one of the acceptable cleaning products listed in these specifications.

Some builders have found that the high-pres­sure hoses at self-service car washes are effec­tive for removing oil residues.

Metals and Conductivity

The role that metals play in the electrodimate of a building, along with proper grounding considerations, will be discussed in Division 16.

Metal Termite Shielding

Where floors are joisted, the proper applica­tion of metal termite shielding, as illustrated, will create a physical barrier that is effective against subterranean termites.

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.

For construction in colder climates, where higher insulation values are required than can be provided by mud alone, several methods

that combine earth with lightweight natural aggregates have evolved. These include mixing mud with pumice, volcanic rock, straw, wood chips, expanded clay, or vermiculite. In the US, clay-straw construction has become the most well-known of these methods because of the work of Robert Laporte of the Econest Build­ing Company, who has taught workshops and built clay-straw structures throughout North America. The Laporte technique uses a light­

weight mixture of clay and straw as an “outsu – lating” wall around a timber-frame structure. Clay-straw can also be used as an infill mate­rial between deep structural members.

Straw is mixed with a clay slurry so that each strand is coated. The wet material is then compacted into a 12-inch-wide formwork, which is removed the same day. The result is a precise wall that has enough texture to accept plaster without any further wall preparation

or lathing. The walls must be allowed to dry thoroughly. Because clay has the capacity to wick water away from the straw that it encases, mold growth has not posed any problem in this wall system if initial full curing takes place in a timely manner. A completed wall that ac­cidentally becomes wet will dry out without developing mold, but the walls must be fin­ished with materials that will allow for suffi­cient vapor diffusion. Earth and lime plasters, or wood siding with a vented air space and an air barrier of earth plaster on the clay-straw (for wetter climates with driving rain), are ideal for this purpose.

A clay-straw wall weighs approximately 50 pounds per cubic foot. The density can be var­ied to provide more mass on the south side of a building and more insulation on the north side, with weights of 60 and 40 pounds per
cubic foot respectively. The average R-value of a 12-inch-thick clay-straw wall has a range of approximately R-19 to R-24,7 making it ther­mally acceptable in all but the coldest regions of North America. The high thermal mass also makes it an excellent material for use in hot, dry regions. In areas with rainfall of more than 30 inches a year, an exterior sheathing of wood with a vented air space between the wood and clay-straw is advised.

Clay-straw is less suitable for locations that do not have a predictable dry season of at least three months duration for proper curing to occur. A similar technique combining clay and cedar wood chips has been used success­fully in wetter climates. These buildings can be dried from the inside out during the win­ter with a wood heat source. Many examples, including some that are several hundred years
old, can be found in Germany, which has an extremely damp climate. The older examples of mud and straw wall construction found in Europe are denser and have a higher clay con­tent than our modern formulas, which are de­signed to have higher insulation values. As with all natural systems, a good above-grade stem wall or plinth and large roof overhang will help protect the walls and increase lon­gevity.

Because clay-straw is non-load-bearing, permitting has been readily granted in many localities. However, if you are interested in building with clay-straw, check with your local building department to determine whether approval will be forthcoming. New Mexico has passed official guidelines for clay-straw construction, and this information, which is available on the Econest website at econest. com, may be helpful for obtaining approval from code officials elsewhere.

Throughout history, several methods for mud construction have evolved using wet mud fashioned into various shapes and stacked onto the wall while still plastic. The mud is then fused with the layers below it to create a monolithic wall. This type of construction has lent itself to laybuilders because it requires no formwork or special equipment and no pro­cessing other than onsite mixing. Two mod­ern innovations in this building method are of note.

In Germany, Gernot Minke has devel­oped a method called stranglehm for build­ing with extruded clay profiles. Casein or whey is added to the clay mixture to make the clay more water resistant. Minke has created a mechanized extrusion apparatus for use at the building site that can produce about six feet of material per minute. The uniformly extruded profiles, which are three by six inches and just over two feet long, are stacked one on top of another and pressed to adhere to the layer be­low. Construction joints are placed vertically between the ribbons and “caulked” with a mud mixture after the ribbons are dry so that shrinkage is controlled and air infiltration can be blocked. Being used as infill between wooden structural members, the system is not load bearing. Insulation must be added to the exterior in colder climates.

In North America, the Cob Cottage Com­pany has been responsible for the revival of cob, or wet mud, construction. Founders Ianto Evans, Linda Smiley, and Michael Smith have developed a stronger mix using a more con­trolled formulation process than their pre­decessors did. The Oregon Cob method that they have developed is characterized by small, free-flowing, sculpturally shaped homes with arched windows and doors and a strong solar orientation. Their designs emphasize maxi­mum space utilization through curvilinear

formations and built-in benches and plat­forms. In England, this traditional form of building has been revived by Katy Bryce and Adam Weismann of Cob in Cornwall Ltd.

Cob construction uses moistened earth containing suitable clay and sand content that is mixed with straw and formed into stiff loaves of a size that can be moved, person to person, from the mix site to the building site. The loaves are then piled onto a wall and blended with the previous layers. The result is a monolithic, load-bearing mud wall.

Cob has R-values comparable to adobe construction and is best suited to warmer cli­mates where less insulation is required and high thermal mass is effective. Cob is also valuable for adding thermal mass in the inte­rior of buildings, especially for heat storage in passive solar designs. Anecdotal evidence has indicated that it exhibits better seismic per­formance than adobe because the walls are monolithic.5

Rammed Earth

Historically, rammed earth construction has been found not only in hot, arid climates but also throughout the cold, wet regions of Eu­rope. Thousands of rammed earth structures, some dating back 400 years, can be found in the Rhone River valley.

Earth with the proper moisture, sand, gravel, and clay content is rammed into form­work in six – to eight-inch layers. When form­work is full it can be immediately removed and reused for the next sector of wall. Because of the low moisture content, the walls, if prop­erly constructed, will not shrink or crack. No curing time is required and construction can continue without any delay in sequencing.

The finished walls are thick, precise, and beautiful. Different colors of earth can be used to create decorative effects. Rammed earth walls are usually left exposed without any further finishing. Unlike adobe or stone masonry, where the joints are pathways for

erosion caused by the expansion of water, the monolithic surface of rammed earth has proven to hold up extremely well to freeze and thaw cycles. With modern comfort and en­ergy demands, this technique is most suitable in warmer climates. However, innovations, such as placing a two-inch board of rigid insu­lation at the center of the wall, have been used to adapt this method for cold climate use.

Of all the earth building techniques de­scribed in this chapter, rammed earth tech­nology has advanced the most through the use of modernized machinery. It has been cal­culated that historic homes of rammed earth took as many as 30 worker-hours per cubic meter of wall construction, whereas highly mechanized techniques can take as few as two worker-hours per cubic meter of wall.6 Ad­aptation to mechanization, improvements in formwork, high compressive strength, and short curing time make this type of earth con­struction suitable for large projects. Highly re­
fined, multistory buildings have been created using this technique, including the five-star Kooralbyn Hotel and Resort in Australia.

With more test data being accumulated in both the US and Europe on the structural properties of rammed earth, it is becoming easier for professional engineers to create re­liable structural designs and predict how the material will act under extreme conditions. In earthquake zones, some concrete has been added to the mix, and steel reinforcement has been used in much the same way as in concrete structures, allowing permits to be granted throughout earthquake-prone Cali­fornia, where David Easton, a pioneer and in­novator in the rammed earth revival, lives and works.

Earth is widely available at little or no cost. It is nonflammable, is infinitely recyclable, is

condensing. Even if water does condense, there is always an exit pathway for it. Natural building materials such as earth, cob, and masonry are es­pecially well suited for this task. To create a fully functional wall based on the flow-through design, any healthy home project must take into account all the climate-specific details of its location.

a. Max von Pettenkofer. Uber den Luftwechsel in Wohngebauden. Literarisch-Artistische Anstalt der J. G. Cotta’schen Buchhandlung, 1858.

b. Erwin Raisch/’Die Luftdurchlassigkeitvon Bau – stoffen und Baukonstruktionsteilen." Gesund- heitsingenieur. Issue 30 (1928).

c. Winfried Schneider. "40 Jahre Baubiologie – Klischees, lnnovationen, Trends."l/l/o/mung und Gesundheit. V0I.120 (2006), pp. 12-14. See also baubiologie. de/site/zeitschrift/artikel/120/12 .php.

d. M. Stiicker et al.’The Cutaneous Uptake of Ox­ygen Contributes Significantly to the Oxygen Supply of Human Dermis and Epidermis."Jour­nal of Physiology. Vol. 538 (2002), pp. 985-994.

e. W. Schneider and A. Schneider. Baubiologische Boustoffiehre + Bauphysik. Course Module 7 of

IBN Building Biology Correspondence Course 1998, p.67.

f. Moisture uptake of building materials within three hours while ambient air humidity in­creased from 40 to 80 percent. W. Schneider and A. Schneider. Baubiologische Boustoffiehre + Bauphysik. Course Module 7 of IBN Building Biology Correspondence Course 1998, p. 37.

Katharina Gustavs, BBEC, CT, is a Building Biol­ogy environmental consultant living on Vancou­ver Island, British Columbia, who specializes in electromagnetic field testing and healthy lifestyle programs for environmentally sensitive individu­als. As a professional translator, she is also translat­ing and researching the original Building Biology Correspondence Course from Germany for the International Institute for Bau-Biologie & Ecology in Florida. Contact her at gustavs@buildingbiol ogy. ca.

not subject to insect infestation, is a natural preservative, has excellent thermal mass stor­age capacity,3 has the ability to handle large amounts of water vapor diffusion and stabi­lize humidity without mechanical augmenta­tion, and, unlike postindustrial manufactured building materials, has a proven record of lon­gevity with intact examples dating back more than 7,000 years.

Earth is the predominant preindustrial building material. Earth construction, in all of its various forms, has not been codified on a national level in this country, and in spite of the fact that it is the wall-building material for more than a third of the worlds homes its use is considered by most building departments to be experimental. In Germany, simple stan­dardized tests for measuring various struc­tural properties of mud have been developed and codified. The work done there could pave the way for wider acceptance here if more per­formance-based criteria for code compliance are permitted in the future. For the most part, approval is currently at the discretion of the local building authority.

Earth Block Construction

Earth block construction is used in every hot, dry subtropical climate throughout the world. Examples have been found in Turkestan dating back to 6,000 BC. The historical core of Shi – bam in Yemen, consisting of eight-story build­ings, is constructed entirely of adobe. These magnificent buildings have scarcely been al­tered since the time of their last rebuilding in the mid-i6th century.

Earth blocks are primarily used in mod­ern construction in three forms. Adobes are mixed wet, poured into formwork, and then sun dried. Pressed blocks are made from moist soil that is compacted by a mechanical or hand press. Green bricks are extruded in a brick-making plant and used unfired.

In the US Southwest, adobe is a traditional building material that has remained in contin­uous use and is the material of choice for some of the most exclusive residences being built today. It has been jokingly called the building material for “the idle rich” or “the idle poor” because stacking the heavy blocks is labor in­tensive.

Because the R-value4 of earth blocks is fairly low, walls require additional insulation to meet energy requirements in all but the warm­est parts of North America. A higher R-value is usually obtained by adding foam insulation to the exterior of the building, which affects the “breathability” of the wall and creates a dubious marriage between natural and syn­thetic materials. Although most earth block is currently used in desert climates and for exte­rior wall construction, its excellent mass and

acoustic properties make it a superb product for interior mass walls in any climate where it is available or can be produced.

Adobe blocks are frequently “stabilized,” mainly to make them more water resistant and to prevent breakage during transport. The most common stabilizer is asphalt, a car­cinogenic material that should be avoided in the healthy home. Unstabilized adobes can be purchased from some adobe yards and can be special-ordered. Compressed earth blocks can

be made onsite with an adobe press, thereby eliminating the need to protect blocks during transportation. However, earth blocks that are not stabilized must be protected from ground water damage. This can be accomplished by holding the first course of blocks off the floor by installing a layer of concrete block first.

New Mexico has developed its own com­prehensive code for load-bearing adobe con­struction, which has served as a model for parts of Colorado and Arizona.

The breathing wall concept goes back to Max von Pettenkofer (1818-1901), one of the most accom­plished hygienists of his time and the pioneering founder of the occupational and environmental hygiene sciences as we know them today. He was instrumental in stopping the cholera epidemics in Munich, one of the largest cities in Germany, dur­ing the second half of the 19th century. By initiat­ing the construction of a central water supply and sewage treatment system, he greatly improved public health and achieved celebrity status.

In his dedicated search for better living condi­tions, von Pettenkofer introduced carbon dioxide measurement as an important indicator of over­all indoor air quality. His measurements of air ex­change rates in a room with brick walls, a masonry heater, and sealed windows led him to hypothe­size that the brick walls must let air pass through. Even with the keyhole and other cracks sealed, the air exchange rate dropped only about a quarter compared to the rate prior to sealing.3

He seems to have forgotten to consider the ef­fect the masonry heater would have on the ven­tilation rate. Thus he proceeded to demonstrate that when air is pumped through a brick cylinder,
sealed on the outside except for both ends, a can­dle flame at the other end could be extinguished. In his eagerness to prove his hypothesis, he over­looked the fact that the maximum natural air pres­sure across a wall of about во pascals is many times lower than the pressure required in his candle-ex­tinguishing experiment (between 700 and 10,000 pascals).

Von Pettenkofer’s celebrity status may have been one of the reasons his hypothesis of natural ventilation through walls was not scientifically de­bunked until the 1920s. b Though he never used the term "breathing wall," this concept took on a life of its own that continues to this day. The Insti­tute of Building Biology and Ecology Neubeuern in Germany recommends avoiding the use of the term because it does not reflect the reality of the complex processes occurring in a wall and usually leads to misconceptions.0

In Building Biology, a natural home is consid­ered to be a living organism in the sense that it should be — as much as possible — self-sufficient, energy-efficient, and built from materials that are part of the natural cycle and do not contribute to toxic waste. The roof and wall systems are often re­
wall made of unprocessed materials through which the flow of vapor is unhindered is called a breathing wall. The concept is central to the Building Biology goal of creating a healthy dwelling. (Tire term “breathing wall” is really a misnomer because the walls of course are not the primary ventilation source for the build­ing. The term “vapor-permeable wall” would perhaps be more accurate.) Another Building Biology concept is that of the building enve­lope being our third skin (clothing being our second skin). This analogy is a more useful one in describing how a breathing wall works. Our skin is the organ of contact with the outer en­vironment and regulates the balance of mois­ture and temperature of the body in relation to the environment. Skin must remain perme­able to facilitate a healthy interaction between the natural environment and the human or­ganism. So too, according to Building Biology,

ferred to as our third skin, implying that, just like human skin, the building envelope is in constant contact with the environment and plays a crucial rolein maintaininga healthy inner climate despite unfavorable weather conditions outside. Let us have a closer look at what does or does not perme­ate a wall with regard to air and moisture.

A constant supply of oxygen-rich air and the re­duction of carbondioxideareessentialtoa healthy indoor climate, but it is a misconception that walls can "breathe" air, especially massive walls built from earth, masonry, or solid wood, despite their varying degrees of porosity. The air pressure dif­ference between outdoor and indoor air is never high enough to promote an air exchange through such a massive wall. If air does get through a wall, it is not through the wall itself but through poorly sealed joints and cracks. This, however, is the least desirable way to supply fresh air because it pro­motes high heat loss in winter, makes for very un­pleasant drafts, and invites moisture problems.

To ensure the Building Biology recommended rate of about one complete change of air per hour, either mechanical ventilation with a heat recov­ery system or cross-ventilation through open win­dows several times a day is necessary. Massive wall systems are especially well suited for natural ven­tilation methods because their extraordinary heat storage capacity keeps heat loss at a minimum during brief opening ofthe windows in winter.

It is interesting to note here that human skin does not breathe air either. All oxygen for our in­ner organs is supplied by the air inhaled through the nose and mouth, which in keeping with the analogy of the third skin would be comparable to the windows and doors in a house. Though the outermost layer of our skin (up to 0.4 millimeters) can extract oxygen from the ambient air, the oxy­gen does not cross into the body. d

It is true that wall structures without vapor barriers allow for the free flow of moisture or wa­ter vapor. Moisture always moves from a warmer area to a colder one, from a higher vapor pres­sure concentration to a lower concentration. As a result, water vapor tends to flow from the inside out in the north and from the outside in down south. In mixed and moderate climate zones, it has a tendency to flow from the inside out dur­ing the winter and from the outside in during the summer.

must our third skin, the walls of our dwellings, remain permeable in order to achieve an opti­mal environment for health.

There is an intimate connection between the health of an individual and the health of the environment. All building processes in­volve the extraction of raw materials from nature and the disruption of the natural eco­system. The alternative materials and meth­ods described below use these materials in a minimally processed state with far less envi­ronmental impact than the highly refined and processed materials prevalent in conventional construction. When one considers that 40 percent of the material resources entering the global economy are related to the building in­dustry,2 it becomes clear that the building ma­terial choices we make have a global impact on the health of the ecosystem, the ultimate de­terminant of our own health.

In recent years, with renewed inter­est in environmental concerns and energy

Massive wall systems made from earth, clay, or solid wood also have a high capillary activity that is capable of wicking away liquid water. Though any wall system should be designed to prevent vapor condensation from occurring, the wicking capacity of natural building materials provides additional insurance that liquid water will not get trapped in the wall. This, of course, works only as long as all wall finishes are also highly permeable to water vapor.

The actual amount of water vapor an exte­rior wall can shuttle to the outside of a building is rather low. For example, in winter, when outside temperatures are low in northern and moderate climates, only about 1 to 2 percent of the indoor moisture can make it through a brick wall. e Again, it is obvious that the majority of the moisture that is usually generated inside a home needs to be re­moved through active ventilation, using windows and/or mechanical ventilation systems.

Building and finishing materials with a high moisture buffer or hygric capacity improve indoor air quality tremendously because they help miti­gate temporary humidity highs. Nearly all natu­ral building materials are highly hygroscopic, especially wood, earth, lime, and cellulose. Lime plaster (13 grams per square meter) or clay plas­ter (30 grams per square meter) can absorb large amounts of water vapor. But as soon as you fin­ish a lime plaster with a standard latex paint, wa­ter vapor absorption drops (to below 9 grams per square meter).f Therefore it is important to choose surface treatments that are highly permeable to water vapor, such as lime wash, silicate, or casein paint. Note that this moisture buffering effect re­lies on only the first 1 to 1.5 centimeters of the in­terior wall surface. Thus almost any wall structure can benefit from the moisture buffering effect of adding a material such as a clay plaster.

It is unclear why the breathing wall concept persists when it is riddled with misconceptions. What is clear, however, is that any building enve­lope has to meet two major challenges: first, not to let any water in and second, if water does get in, to let it out again. In contrast to the widespread use of polyethylene vapor barriers, which often makes no sense from a building science point of view, Building Biology favors the so-called flow­through design, which allows water vapor to pass through the wall assembly’s components without
efficiency, several alternative methods of building have enjoyed a limited renaissance among environmentally concerned home­owners, designers, and builders. Since the last edition of this book in 2001, the negative im­pact of human activity on the global environ­ment has become increasingly evident, and in our efforts to lessen this impact the green building movement has experienced expo­nential growth. The Bau-Biologie or Building Biology study course states that “there is al­most always a direct correlation between the biological compatibility and ecological per­formance of a given building material.” This statement is exemplified in the proper use of natural, minimally processed, and locally found and crafted building materials.

Introduction

Most code-approved building materials in North America are manufactured using in­dustrialized processes that create components of uniform size and form, with predictable performance characteristics such as fire resis­tance, permeability ratings, insulation values, and structural properties. Since the process of testing such materials for code approval is extremely expensive, only large manufactur­ers who intend to produce, package, and sell a product for wide distribution can afford to test. This product-oriented approval process is not geared toward the analysis and acceptance of nonproprietary unprocessed natural build­ing materials and it has all but closed the door on 9,000 years of preindustrial building tech­nology.

There is at least one exception to this trend that perhaps serves as a model in this coun­try for future code approval of other natural building materials. Wood is a naturally oc­curring, minimally processed building mate­rial that has universal code acceptance even though it is flammable and subject to shrink­age, comes with inconsistent structural prop­erties, and will rapidly deteriorate through rot and insect infestation if left unprotected. In spite of its embarrassingly preindustrial na­ture, it remains the dominant building mate­rial in residential construction, and building codes have succeeded in creating safe guide­lines for its classification and use.

Why consider alternative natural mate­rials such as earth and straw as an option for healthy housing? These historically derived methods of construction differ from standard cavity wall construction in that manufactured petrochemical-based barriers are not installed to retard the flow of vapor through the walls. Instead, vapor is allowed to flow naturally. The massive walls employ hygroscopic nat­ural materials to increase the capacity of the wall to handle the transfer of moisture from the interior and the exterior surroundings and

to release vapor back into the surroundings as climatic conditions change. Because temper­ature change occurs very slowly in the flow­through process, and because dried clay – based materials have the ability to absorb and desorb large amounts of moisture without de­teriorating,1 accumulation from condensa­tion is insignificant. When a home is properly constructed using these mass wall techniques it will be an extremely comfortable environ­ment with superior temperature and humidity stability. Furthermore, because the solid walls provide insulation and can be finished with a covering of plaster or furred-out wood applied directly to them, the need for synthetic exte­rior sheathing, batt insulation, gypsum board, joint fillers, and paint is eliminated. Many volatile organic compound contamination sources are thereby eliminated as well.

In the philosophy of Building Biology, a

Concrete can act as a wick for ground mois­ture, thereby promoting water damage and fungal growth in other materials through moisture transfer. A layer of coarse gravel under the slab with no fines smaller than half an inch will break capillary action. A layer of continuous, unpunctured polyethylene di­rectly under the slab will help prevent water vapor and soil gases such as radon from find­ing their way through cracks in the slab. A fully cured slab can also be sealed to further prevent moisture and soil gases from enter­ing the building and to create a more finished floor surface. Some sealers are solvent based and should be avoided. The following sealers are more benign:

• AFM Safecoat CemBond Masonry Paint:

Water-resistant coating for cement, con­crete block, and masonry

• AFM Safecoat DecKote: Waterborne coat­ing for use on concrete, magnesite, walk­ways, breezeways, and patios

• AFM Safecoat MexeSeal, AFM Safecoat Penetrating Water stop: Water-based seal­ers and finish coats

• AFM Safecoat Watershield: Water repel­ling sealer for masonry and painted sur­faces

• AgriStain for Concrete: Sealer and stain for concrete, plaster, and porous tiles

• Vocomp-25: A solvent-reduced, water – based sealer

• Weather-Bos Masonry Boss Formula 9:

A water reducible sealer for all above – grade concrete and masonry surfaces; helps reduce dusting, powdering, efflores­cence, spalling, cracking, and freeze-thaw damage

• Xypex: A nontoxic (according to manu­facturer), zero-VOC chemical treatment for the creation of moisture resistance and the protection of concrete; creates a non­soluble crystalline structure that perma­nently plugs the pores and capillary tracts of concrete. Xypex concentrate DS-i and DS-2 are dry-shake formulations designed for horizontal surfaces.

Further Reading

Timusk, John. Slabs on Grade. National Building Envelope Council, Building Science Treatise, Construction Canada 92-07.