by Kaki Hunter and Doni Kiffmeyer – Utah, USA

We live in the heart of the great Southwestern United States, surrounded by examples of one-thousand-year-old ruins left behind by the ancient civilizations of the Anasazi, Hohokam, Pueblo and many others. It was these original natural builders that inspired us to consider building with earth as a way to create beautiful, low-impact, energy-efficient housing that has endured the test of time to this day.

We started by teaching ourselves how to make adobe bricks, the most common earthbuilding technique native to the U.S. Making adobe bricks turned out to be a lengthy process that involved mixing the mud, pouring it into forms, lifting the forms, and then turning the blocks over the next several days to facilitate even curing. The blocks then had to be stacked and protected until ready for use. Manufacturing the adobes required a considerable amount of space for both the pouring process, as well as for storage of the dirt needed to make them, and then the storage of the adobe bricks themselves until they were ready for building. We live right in the heart of a small town, which made this process a little tight.

The dirt for adobe block and most other forms of earthen architecture require a specific ratio of clay to sand, ideally about 25 to 30 percent clay to 75 to 70 percent well-graded sand. In some cases, a stabilizing agent may be added to an earthen soil to increase its compressive strength and make it resistant to the affects of water. Some earth building techniques like cob require copious amounts of straw fiber added to the mix. In most cases, adobe brick also benefits from the addition of straw or some other kind of natural fiber.

Honey House

After our initial foray into homemade adobes, we read about the work of international award-winning architect Nader Khalili. Nader is an Iranian-born architect who abandoned a successful career designing skyscrapers to follow his heart, which led him to create an innovative sandbag/superadobe/earthbag architecture as a means of providing low-tech, enduring affordable housing. Inspired by the ingenious monolithic adobe buildings of his homeland of Iran, Nader conceived the idea of building domed and vaulted structures with…bags of earth. We took a one-day workshop with Nader and we were hooked! We returned home excited to build our first earthbag-wall project, a privacy wall opposite the busy baseball field across from our house. However, our interest quickly zeroed in on the building process itself. We began innovating tools, tricks, and techniques that we felt made the building process more enjoyable and the results cleaner and predictably solid. We coined the acronym FQSS which stands for Fun, Quick, Simple and Solid. The process has to be Fun, which makes the work go Quickly as long as the procedure is kept Simple and the end results are Solid. Hence the FQSS stamp of approval became our dirtbag golden guideline.

Earthbags (as we were soon to discover) had the advantage of being able to use a wider range of soil types than traditional earth building techniques – “Wow, this dirt’s just got five percent clay and it still works!” We have been able to adapt soils for use in earthbags that have ranged from zero clay to 50 percent clay content. No type of fiber was needed within the soil. Since the bag acts as a textile container for the earth, the woven fibers do the job of stabilizing the soil in place so the soil can have a lesser quality binding strength than required for most other types of earthen construction. When necessary, even dry sand can be used as fill, as could be the case in providing emergency relief shelter. The Earthbag System is a contemporary form of earthen construction that uses modern woven polypropylene feedbags (usually misprints) or long tubes as a flexible textile container (or what we call a flexible form) preferably filled with dampened soil. The bags or tubes are filled in place on the wall being built so there is no heavy lifting. After a whole row is laid, the bags are compacted from above with hand tampers. The compacted earth later cures to a cement-like hardness. Two strands of four-point barbed wire are laid in between every row that act as a “Velcro” hook-and-latch mortar, cinching the bags together while providing continuous built-in tensile strength. Tensile strength inhibits the walls from being pulled apart during stressful conditions like earthquakes, floods, hurricanes, and load-bearing and lateral forces. The combined strength of the four-point barbed wire sandwiched in between the woven textile fabric of every row of earthbags adds a significant degree of tensile resilience that is lacking in most traditional forms of earthen architecture.

The soil we selected for our initial earthbag building projects was delivered from our local gravel yard at 80 cents per ton. That was ten years ago. Today we pay about $1.80 per ton. Reject sand or crusher fines are common names for the clay fines that are the byproduct from the manufacture of washed sand and gravel produced at most developed gravel yards. Often, this reject material has sufficient clay-to-sand ratio to produce strong compacted earthen blocks. However, over the years, we have had considerable success with using almost any type of soil available on site by paying particular attention to adjusting the moisture-to-soil ratio that produces the optimal strength block.

Building the earthbags around temporary rigid box and arch forms creates door and window openings. After compaction of the keystone bags, the forms are then removed. Wood-strip anchors are installed during the wall-building process, providing an attachment for bolting on doorjambs, cabinetry or wood-frame intersecting walls, electrical outlets and plumbing systems.

Wall plastering options range from thick natural earthen plaster applied directly over the surface of the bags (yes, it sticks!) or, for additional protection, lime plaster can be applied over an earthen plaster. Cement/lime based plasters perform well when the earthbags are filled with a stable, well-draining sandy soil and applied over stucco mesh (chicken wire). Plasters can be applied by hand or sprayed on with a pressurized plaster sprayer for a unique contoured effect that accents the shape of the bags or tubes.

Earthbag Architecture can be designed to suit a wide variety of climates. Since the woven polypropylene bags are virtually rot proof, earthbags are an excellent choice for underground structures: root cellars, storm shelters, bermed homes and greenhouses. In climates where wood is scarce, whole houses can be built exclusively with earthbags including the foundation and roof, as is the case for corbelled earthbag domes. Earthbags also combine well with other natural building materials that can be combined together to create hybrid structures. Straw bales can be interlocked with earthbags to build sturdy arch entryways or to add thermal mass to the interior wall of an attached sunroom. Or we may choose to use earthbags for the sunken first level of a structure and then switch to strawbale, post-andbeam, cob or adobe brick for the rest of the wall above grade to make use of an available resource or add aesthetic variety.

The advantage of combining two alternative natural building mediums: load-bearing earthbag walls provide mega-thermal mass, while an exterior straw-bale wrap provides mega-insulation.

Insulation strategies for earthbag walls offer a variety of options. Narrow tubes provide a sturdy load-bearing wall with plenty of thermal mass, while straw bales secured to the exterior of the wall provide ample insulation. Now, we have mega mass coupled with mega insulation to provide the best use of both of these materials in one building. Another way to add interior mass is to build our interior walls with earthbags and our exterior walls with straw bales alone. Another approach we have experimented with is mixing a percentage of 3/4-inch pumice to a quality rammed earth soil that captures air spaces within the earthbag itself. A 50/50 mix of suitable earth and pumice make the bags one third lighter than their normal all dirt weight yet still makes a nice hard compacted earthbag.

Building codes

The advantage of combining two alternative natural building mediums: load-bearing earthbag walls provide mega-thermal mass, while an exterior straw-bale wrap
provides mega-insulation.

The earthbag building system has been extensively tested by Nader Khalili in conjunction with the ICBO (International Conference of Building Inspectors) and the Hesperia Building Department in Hesperia, California, at the California Institute of Earth Art and Architecture for earthquake resilience, loadbearing, and shear strength stability, all of which were proven to far exceed conventional code standard acceptance. (See Building Standards issue Sandbag/Superadobe/ Superblock Sept-Oct 1998 for a full article on the merits of Earthbag structural nitty-gritty).

Resources

Sources for bags and tubes can be found on the Internet under woven polypropylene feed bags. Our favorite U.S. supplier for both pillow-pack and gusseted misprint bags is www.innpack.com, toll-free 800.622.3695 in Tennessee. Typical prices for 50-lb misprints are approximately $.17 each (USD), and 100-lb bags are $.25 each (USD). Both come in bales of 1,000 bags. Smaller quantities for bags and tubes are available from a Kansas City, Missouri, source www.centralbagcompany.com 816.471.0388. Ask for Chris Klimek for prices and selection. Also try 800.521.1414 www.fultonpacific.com.

For step-by-step nitpicking details about building with earthbags, check out our book Earthbag Building, the Tools Tricks and Techniques by Kaki Hunter and Donald Kiffmeyer, New Society Publishers, 2004. Or call us at 435.259.8378, or visit our web site www.okokok.org.

Donald Kiffmeyer and Kaki Hunter have been involved in alternative construction since 1993, specializing in affordable, low impact and natural building methods. Inspired by the work of visionary architect Nader Khalili, the grandfather of Sandbag/ Superadobe/Earthbag architecture, they wrote a screenplay entitled “Honey’s House,” a film about truth, justice and affordable housing. From these innocent beginnings, they were launched into the alternative building movement where they were encouraged to share their combined innovations to establish the Flexible Form Rammed Earth technique. Together they co-authored the book Earthbag Building, the Tools, Tricks and Techniques by New Society Publishers. They live in Moab, Utah, where they continue to focus on the research and development of fun, quick, simple and solid natural and alternative building techniques that are inspired by this fabulous planet.

Slope pan flashing to outside.

Included in TLS #49 (Myths and Realities, Spring 2005) was a discussion of ways to deal with moisture at the bottom of windows. David Eisenberg shared a written design detail for a pan under the window to carry water away from rather than down the wall. We wanted to share a drawing of this detail and David kindly provided one for us to share in Tech Tips.

Here’s the portion of the discussion in which David details this design idea.

“Protecting the bales beneath the windows requires that you catch the water under the window and make sure it gets all the way out of the wall. In other words, ideally, you would have a pan of sorts under the window, sloped slightly to the outside, extending a bit beyond each side and with a lip at the back and on each end (so water can’t just run off the ends), and extending out beyond the exterior wall surface, with a drip edge – so that any water that leaks through or runs down the sides of the window ends up in this pan and is shown the exit. You can make these pans out of metal, plastic, ice and water shield, cast this shape into a concrete sill, anything that will keep the water from leaking through it, but the principal thing here is to make sure that the water can’t get into the wall below the window. You can put your window sill material, whatever it is, on top of this pan flashing being careful not to punch unsealed holes when you install the sill. It can take a little thought and ingenuity to do this, but it assures you that, when the windows leak, the water leaves the building.

Concept of pan flashing turned up at back and sides extending beyond exterior finished wall with drip edge. Extending behind finish or trim at each side of opening.

“That old practice of just putting roofing paper or plastic over the top of the bales and setting your windows on it and then plastering over it just leads the water down inside the plaster to the bales wherever the water protection ends unless it runs continuously down the wall under the window to below the bales (and we don’t recommend doing that).  It just temporarily moved the problem down, didn’t solve it.”

by Wayne Bingham and Colleen Smith – Idaho, USA

Our interest in straw-bale construction grew out of our concern for energy efficiency. Our research into building energy efficiency grew into an awareness of sustainable building practices. An urge to build an energy-efficient home of materials that are sustainable grew as we explored these issues.

As we examined the site conditions for our home in Idaho, we found prevalent winds came from the southwest, passive solar orientation was due south, and views were predominantly southeast toward the Teton mountain range. The homestead to the west anchored the place visually and the rolling grass and grain fields to the north and east held their own hypnotic beauty.

We asked ourselves, “How do we place a building here and what would it look and feel like?”

From Small Strawbale by Bill Steen, Athena Swentzell Steen and Wayne J. Bingham. Published by Gibbs Smith

We walked the site many times over several years, searching for the right place to build and the right kind of structure to build to respond to the soil, views, and
weather. When the irrefutable drive to build overwhelmed us, we went to the land and stayed for three days, walking, feeling, talking, and looking for the right place. We examined alternative ways of achieving solar gain while maintaining prominent views and avoiding challenging weather patterns.

The summer sun in our high mountain desert can be intense. The days can be hot, evenings cool down fast when the sun goes down, and the nights are cold. So a porch wrapped around straw-bale walls made sense to us. It can protect us from the sun, provide outdoor living space, and allow the straw bales and the internal thermal mass to moderate and maintain a relatively even temperature inside the house. The porch would also serve to protect the earthen-plastered bales from the weather.

We wanted the house to sit lightly on the land and allow the rolling surface of the earth to flow unimpeded past the house. We raised the porch surface only six inches
above the adjacent ground around the entire perimeter to require only one step to grade.

We have visited and experienced several houses that deeply impressed us and we developed several drawings to reflect this approach. They were approximately square, had hip roofs and wrap-around porches. The deep porches were occupied with plants, chairs, tables, firewood, clotheslines, and other apparatus for living out-of-doors under cover.

After consideration of many schemes, we settled on one that is 34-ft. square, providing 1,156 gross sf and 961 net usable sf. Seventeen percent of the total area is in straw bales and the house is 83 percent efficient. It has a kitchen/living area, one bath, a master bedroom and guest room. There is a loft for the grandchildren.

Photos by Wayne J. Bingham

Colleen had researched the area for organic straw bales that were 14-in. high x 18-in. wide. We found a farmer in Blackfoot, about 90 miles away, who had grown straw without herbicides or pesticides. Because the crop had matured and there was rain forecast, he cut and baled the straw. We had been working to have the house dried-in before taking delivery of the bales. We were able to place the bales under the newly finished roof before rains. Bale installation took only one week, notching and fitting under the roof and between columns and windows and doors.

Several friends called out of the blue and said that they heard that plastering was about to happen and could they come to help. Yes! Stan, John, Joe, Susan and I spent the weekend hand applying the beautiful chocolate colored earthen plaster mixed with long fibers of straw. We were at the end of summer and we wanted the plaster to dry before it could freeze, rendering earthen plasters no good. We were able to apply a rough coat on three walls over a three-day weekend. Brian and I finished the final wall in two days. The first weather coat had taken about one week. The building season ended and we left for the winter, planning to return the next spring.

When we returned in June 2003, we turned our attention to the final plastering on the main house. Sift clay, chop straw, mix clay to water, add straw and sand and apply to the rough coat completed last year. Check proportions, read the newly published book Natural Plasters, do tests and define how we want to do the work. Out of the research and study and questioning came a process we are very pleased with. We applied an infill coat of stiff plaster to the existing hand-applied rough coat using wood floats. We then brought the surface to within 1/4-in. of the /finish surface using a plaster that has more sand and less straw, sent through the chopper a second
time.

The final coat was applied with a steel trowel with curved corners, and polished with stainless steel Japanese trowels. It turned out quite nicely, with soft rounded corners and the bottom edge flared out to meet the metal drip edge.

We had read of clay “alis” paint. We read recipes in the two books and called the Steens asking for their advice. “Start with one part wheat paste glue, add two parts water, add clay until it covers your finger without showing a print.” We added one small scoop of burnt umber and about four cups of medium-sized mica flakes. We painted it on with 4-in. brushes, allowed it to become almost dry, and then polished with a damp (not wet) sponge.

Wow! What a difference it made. When plastering, the joints between one day’s work and another were visible, even though we tried diligently to feather it out. The alis unified the whole surface, and no joints were visible. It has a soft sheen from the mica, and it invites touch, as everyone who comes to the house exemplifies. Some have said it looks like leather. We think it looks like the earth around the house, but is refined by plastering and polishing. It looks like it belongs to its surroundings.

Building our house started out as a dream, a desire to do something sustainable, to build with one’s hands. Our project then became something physical, real, as we worked with the foundations, concrete, rebar, straw bales, earthen plaster, roofs, wiring, and all the rest.

In the summer of 2004, we installed a photovoltaic system to serve electrical needs of the house. We mounted the solar collectors on the garage porch. Batteries and inverter are in the garage with underground feeds to the house.

Well drilling estimates came in at $20,000, so we looked for another alternative. We built an 18,000-gallon underground cistern for a fraction of the cost that takes rainwater from the house and garage that passes through a filter before going to the tank. Before use in the house, it also goes through a charcoal and UV filter. It filled completely the first winter. With the exception of propane for heating and cooking, we are entirely off-the-grid. What a feeling of freedom!

Our home developed meaning for us beyond our wildest expectations. There has been a profound change in direction of our lives and satisfaction since we explored ways of becoming involved in sustainable building and focused on strawbale as a preferred method. Thirty-five years of life energy are focused on building our home. Feeling through our needs, responding to the site, and building the house day-by-day have been the most satisfying and meaningful experiences of our lives.

———————————————————————–

Wayne J. Bingham and Colleen F. Smith, a husband and wife team, have been involved since 1998 in straw-bale design and building. Their interest is an outgrowth of an exploration of energy efficiency and sustainable building techniques. In the mid-1990s, they attended several American Institute of Architect Green Building conferences where they began to understand the need for finding new ways to build without endangering the earth and its resources or future generations.  Seeking a direction of their own, they went on a natural building odyssey to the Southwest U.S. evaluating cob, adobe, rammed earth, earthship and straw-bale buildings, visiting or staying in each. They evaluated thermal performance, beauty, the feel, construction techniques and concluded that straw-bale building held the greatest possibility to satisfy their interest.

They attended The Canelo Project straw-bale and earthen plaster workshops and came away with a love affair with strawbale and earthen plaster that has not abated. Wayne immediately plastered their concrete block garden wall in their backyard with earthen plaster (see p 11 of this issue). They returned to the Steens in 1999 to spend a year involved with workshops, construction and collaboration with Bill and Athena on the development and production of Small Strawbale published in 2005 by Gibbs Smith Publishers.

Avid photographers and travelers, Wayne and Colleen have searched out and documented indigenous buildings in the United States, Greece, Great Britain and Italy and have developed a large library of images that were the start of the book. They took additional trips to explore and further record specific straw-bale buildings that now constitute a new book called Strawbale Plans.

In addition to Wayne’s working with owners and builders on straw-bale home designs and conducting workshops, Colleen and Wayne have put their experience into building this straw-bale home of their own in Teton Valley, Idaho. www.wjbingham.com

by Rene Kilian – Denmark

Save money on your black and grey water while protecting the environment!

Reeds and iris clean the wastewater in the planted filter.

All properties without sewage facilities in rural areas of Europe must meet minimum standards for wastewater treatment. It can be expensive joining on to the main sewage lines. A planted filter’ – a modern kind of reed-bed system with vertical waterflow – has low operating costs and is an inexpensive alternative.

Approximately 30 of these filters have been built in Denmark. The systems are planted with wetland plants, and occupy around 16m² per dwelling.

The system complies with the latest Danish standards, which are stricter than the European standard.

Along with this, environmental impact is reduced and the homeowner can save money on sewage connection and payments.  The investment can be paid for through savings in less than five years, when compared to a standard sewage connection. Here is an example.

Reuse of treated wastewater
Søren Raffnsøe built his own straw-bale house, went about it in a way that was as environmentally and economically friendly as possible. The way that water comes in and out of the house has
been considered in a holistic manner, and is the first of its kind in Denmark.

The house has its own planted filter to treat wastewater. The system is only 8m2 because the house has a composting toilet.

The planted filter is a biological-cleaning system. The system, designed by René Kilian, is an effective alternative to a sewage connection. The system can even be integrated into a garden where it could resemble a garden bed growing with thatching reeds, iris and bullrushes.

Figure 1. A recycling system with the planted filter where water is reused in the washing machine and garden. 1. Sedimentation Sedimentation tank for grey wastewater only. The source of the water may vary depending on local codes or regulations but might include water from bath, washing machine and kitchen. 2. Pump well with a level controlled pump. 3. Reed bed system or constructed wetland. 4. Tank for treated wastewater and treated rainwater. 5. “Green” pipe for reuse water to washing machine and garden. 6. Water vitalizer in drinking water pipe. 7. Fine filter for treatment of rainwater. 8. Untreated rainwater toward sand catcher and infiltration unit. 9. “Black”’wastewater from toilet to compost container. 10. Urine from toilet to urine container Design by Kilian Water Ltd., Denmark

The recycled water becomes so clean that you can reuse it to flush the toilet, wash clothes and water the garden. As compost toilets don’t use water, Søren uses the water only in his washing machine and garden. See Figure 1.

Along with this, he saves 50 percent in his usage of drinking-quality water. To collect the excess recycled water, he has made a little pond in the garden, where there is an extra cleaning process that created a habitat for plants and animals. The drinking water itself is also special. He has installed a ’vitalizer’ in his drinking water pipes. This revitalizes the water so it attains the same quality as spring water.

Payback in less than five years

A planted filter of 16m2 suitable for a normal household, will cost around 60,000 Danish kroner/$11,083.80 USD. Connection to public sewage costs one household around 40,000 kroner/$7,389.21 USD. The investment can be paid back in less than five years, as you can save on annual wastewater bill payments. Ongoing costs for a planted filter are 0 kroner /m3; there is just a government tax of 1.60 kroner /m3. Costs for sewage are approximately 35 kroner /m3. This means a dífference of nearly 33.50 kroner / m3. With an average consumption of 170m3 per year, a household would save around 5,700 kroner/$1,052.96 USD per year, or 140,000 kroner/$25,862.20 USD after 25 years.

The planted filter at 8m2 in front of the newly built straw-bale house.

If you chose a reuse system in addition to this, and saved 50 percent on water consumption, you save 7,000 kroner/$1,293.11 USD per year. After 25 years, you will have saved 175,000 kroner /$32,327.80 USD. With the correct wastewater solution, you can really save money and protect the environment.

This is the second of a two-part article on creating a poured adobe or earth floor. See Earth Floor, TLS#52, for the first article describing how to prepare for and install a poured adobe floor.

By Tom Lander – New Mexico, USA

Now, weeks later after your floor is 100 percent dry, it’s time to seal and fill the floor with Linseed oil. Here in the South West our floors can dry in a matter of a few weeks but in humid climates error on the safe side.

Materials:

Linseed oil. We prefer raw linseed oil, less petroleum additives then the common boiled linseed oil but the boiled works if you are not concerned about petroleum out gassing. Even raw linseed oil has carcinogenic warning labels. Ask for an MSDS sheet. Linseed oil is made from flax seed.

Citrus Solvent (thinner) or mineral spirits, again petroleum out gassing

We are still learning how to estimate coverage and quantity so I’m not sure how much material is needed for your size floor. Maybe buy 2 gallons each for starters; you can buy linseed oil in 5-gallon lots.

Equipment:

4” paintbrushes, natural bristle is always best but pricey

Electric hot plate or gas camp stove

Large pot or kettle

Approved vapor mask

Safety glasses or goggles

Fan for air circulation/expelling fumes if you feel this is necessary

Rags,

Gloves

Prep floor:

Sweep or vacuum any loose debris and dust. You might want to do a light mopping or sponging. Give yourself time for the moisture to dry before applying the oil.

Procedure:

Heat the linseed oil to almost boiling (do not boil). We are just trying to heat the oil to aide in soaking, absorbing in. This must be done outside with caution, flammable. Another option is to pour the oil into a large deep baking pan, cover with a piece of glass and let it sit out in the sun. Leave an air gap. With either method start with a small batch to get the hang of heating and applying.

Transfer the oil into a suitable container. You can paint the material on or if you are quick, you can pour some onto the floor and swoosh it around with the brush. The only risk here is that you will not get an even distribution of material. Try it. Be consistent and watch how the floor is absorbing. If more than one person is applying, then you might get varying results but by the time you are done it shouldn’t matter. Use up your first small amount then decide how much more (a large batch) to heat for your next go at it. For reference keep track of how much material you use for each coat and offer this info to others.

The floor will soak up this first coat and there should not be any pooling of the oil on the surface. Plan your route of attack so you end up working yourself out the door, window or hallway. You should be able to go back to the start and do a second full strength coat right a way. Remember your shoes will be picking up dirt and dust from the outside so take steps to minimize this. There are disposable booties one can buy to cover their shoes.

What we are trying to do is seal the floor but think of it more like filling the floor. Filling all the little air voids between the sand and clay particles with oil.

The floor will dictate the timing and how much material. Watch how the material soaks in. You might be able to continue with more heated, thinned coats the same day, unless you are tired or sick from the fumes and not wearing a vapor mask.

Diluting:

The first two coats can be applied full strength. For the third and fourth coat combine 75% oil with 25% thinner, heat and apply. Watch the absorption, watch for pooling or puddling but also give the material some time to soak in; you just don’t want it to dry on the surface. Have a rag and thinner handy to wipe up any excess otherwise the material dries on the floor and becomes sticky. If this happens then it’s quite a job to use thinner and rags to clean the floor. Apply at least two coats of this first diluted mix.

Next is a 50% to 50% heated mix. Hopefully by now you have learned if pouring and brushing works for you (certainly faster) or just brushing or maybe it’s time now to just brush. Isn’t this fun learning as you go? Like all earthen materials, they tell you when and what to do, what’s the word? Experience.

Remember, oily rags and brushes are flammable so hang out to dry and do not leave a pile of rags unless it’s in the middle of a gravel driveway and you want to have some fun.

www.bioshieldpaint.com

Sunny Side http://www.gillroys.com

This article appeared in TLS #59

by Tim Beatley – Virginia, USA
Reprinted with permission from Residential Architect magazine, November 2005.

We live in disconnected times. We occupy space but know little about it. Instead of joining communities or neighborhoods, we buy houses and make real estate investments.

Sustainable design offers us the chance to rekindle these lost connections, to rebuild knowledge of place. New residential development is commonly thought to bring more cars and traffic, higher taxes, overcrowded schools, diminished views, and open spaces. But there is a way to turn this around – if we can imagine new growth connecting with and strengthening our sense of place. This kind of green design might take many forms, but just a few possibilities are mentioned here.

Acting locally

One idea is to locally source building materials. In our globalized economy, such materials can originate hundreds or thousands of miles away from where they are eventually installed or assembled. They contain a high embodied energy, and their extraction often entails substantial ecological impact. Paradoxically, much of the practice of green building has emphasized materials, such as bamboo flooring, that are transported great distances.

We need to look much closer to home, to materials that nurture local livelihoods and reconnect us to place and land. An innovative sustainable wood initiative here in Virginia holds some clues and offers some inspiration. Operated by Appalachian Sustainable Development (ASD), it supports the local economy by working with small wood-lot owners who are willing to manage and harvest sustainably. The wood produced is beautiful, durable, and distinctive (more of the tree is used, with knotty “character” wood a key result), and it is certified under ASD’s Sustainable Wood label. It is then dried in a solar- and wood-waste-powered kiln and cut into flooring at ASD’s mill.

My family and I recently installed ASDcertified white-ash flooring in our home. As a result, I know where the wood was grown, and I have some assurance that the result for the landscape is not destructive but rather restorative. In this case, a sustainable material close to home was actually less expensive than its standard commercial alternative. It is a small expression of commitment to
sustainability but an important step on the way to a deeper connection and duty to place.

Using local materials is a growing practice in sustainable design communities. Innovative green projects like BedZED, the Beddington Zero Energy Development in the London borough of Sutton, have explicit targets for local materials. At BedZED, more than half of the building materials arrive from sources within a 35-mile radius of the site. Wood siding comes from local municipal forests, bricks from a local brick company.

In Western Australia, there has been a creative effort to nurture furniture building and wood artistry. Rather than exporting logs (or allowing them to be converted to low-value wood chips and then exported), there is a growing sentiment that these resources can be the foundation of a highvalue-added, labor-intensive economy, of which sustainably managed forests can serve as a linchpin. Among other steps, a forest heritage center and school of fine furniture making has been established there, and the number of outlets for locally made wood products and crafts is growing.

Much of our food comes from very far away. It typically travels some 1,500 miles from where it is grown to where it is eaten, according to the 2001 report “Food, Fuel, and Freeways,” and we are usually oblivious to these origins. New developments could begin to think more carefully about the food needs of their future residents, perhaps developing long-term relationships with local growers. This is essentially the concept of Community Supported Agriculture (CSA) residents buy a share in a local farm that provides (often delivered) a basket or box full of produce each week during the growing season. CSA farms are growing in popularity – there are now more than 1,500 of them nationally – and they could be offered as part of the package that goes along with a new home (or at least as an option).

Designing in opportunities to grow food directly is another way of promoting sustainability (and healthier living), strengthening place, and re-earthing us. This is a trend in Europe, where ecological, mixed-use projects such as Viikki in Helsinki, Finland, have left green fingers between major buildings for garden plots. Single-family homes might be designed to facilitate this as well. A model sustainable home in the Perth, Australia, suburb of Subiaco, for instance, includes extensive edible landscaping and a built-in raised-bed vegetable garden in its backyard. The garden is large enough to produce all the vegetables a typical family needs.

Energy use is another way to reconnect with local places. Every place has opportunities to generate its own power, whether through wind, sunlight, or biomass. Strong European examples exist of communities that have been able to redirect community resources to local energy production. In Aeroe Island, Denmark, which aspires to be 100 percent energy independent, small power plants generate energy from the sun and from locally grown straw and hay. Expenditures for energy stay local and help to strengthen, not diminish, the region’s economy.

A more urban example is the redeveloped district of Vastra Hamnen in Malmo, Sweden, where a variety of renewable energy technologies and design ideas have been incorporated into dense housing and the ambitious goal of 100 percent renewable energy from local sources has been met.  Energy production is a visible element of the community, with vertical solar hot-water-heating panels feeding into a district heating grid.

BedZED again offers inspiration with an on-site combined-heat-and power plant fueled by wood waste from tree trimmings. In Freiburg, Germany, the Solar-Fabrik solar-technology factory burns oil from locally grown rapeseed in a carbon-neutral cycle, further demonstrating the power of combining green and local.

The energy consumed by residents and the embodied energy associated with new building materials might also be compensated for in ways that creatively restore and renew bioregions. In the U.K., the Carbon Neutral Company works with banks and building societies to offer a carbon neutral mortgage, which provides for the planting of enough trees to cover the carbon footprint of the home and lifestyle of its occupants. In Australia, similarly, several banks are now offering carbon-neutral car loans. Habitat and place restoration can happen in many ways, of course, but local tree planting holds potential for productively harnessing the green sensibilities of people on behalf of place.

In an increasingly turbulent and globalized world, rebuilding lost place and human connections in a host of creative ways provides solace, strength, and reassurance. Sustainable design must strive not only to reduce its overall ecological impact, but to do so in ways that enable us to be truly native to place.

Resources
Residential Architect magazine www.residentialarchitect.com

Appalachian Sustainable Development
www.asdevelop.org/sustainable_woods.html

www.bedzed.org.uk
Beddington Zero Energy Development, an environmentallyfriendly,
energy-efficient mix of housing and work space in
Beddington, Sutton, United Kingdom.

Viikki Eco Neighbourhood Blocks – Finland
www.cardiff.ac.uk/archi/programmes/cost8/case/holistic/viikki.html

Malmo, Sweden
naturalspace.com_broadband/swedentext.htm
The CarbonNeutral Company, United Kingdom
www.carbonneutral.com/pages/reducingCO2.asp

Sustainable Communities

Toward Sustainable Communities: Resources for Citizens and
Their Governments by Mark Roseland, Sean Connelly, David Hendrickson and Chris Lindberg.

Developing Sustainable Planned Communities by Richard
Franko, Jo Allen Gause, Jim Heid, and Steven Kellenberg.

Sustainable Communities: The Potential for Eco-neighbourhoods
by Hugh Barton.

Designing Sustainable Communities: Learning from Village
Homes by Michael Corbett, Judy Corbett, and Robert L. Thayer.

Fostering Sustainable Behavior: An Introduction to Communitybased
Social Marketing by Doug McKenzie-Mohr and William Smith.

Ecovillages: A Practical Guide to Sustainable Communities
by Jan Martin Bang.

Sustainable Communities: Learning from the Cohousing
Model by Grahm Meltzer.

Green Cities: A Guide for Sustainable Community Development
by Michael Bloomfield and Michael Lithgow.

Sustainable Communities Network www.sustainable.org
Links citizens to the resources they need to implement innovative processes/programs.

Intentional Communities www.ic.org
Information on ecovillages, cohousing, intentional communities, urban housing cooperatives and other related projects.

School of Living www.schoolofliving.org
Nurturing healthy, Community Land Trust Communities.

New Urbanism www.newurbanism.org
Many choices for living in more sustainable, convenient and comfortable places.

Tim Beatley is the Teresa Heinz Professor of Sustainable Communities at the University of Virginia. This article is based, in part, on ideas discussed in his book Native to Nowhere: Sustaining Home and Community in a Global Age (Island Press, 2004).
www.residentialarchitect.com

This article appeared in TLS #59.

Turko Semmes is a licensed general contractor from San Luis Obispo County, California, and one of the foremost experts in straw-bale building techniques.

A graduate from the Architecture Department of Cal Poly State University in 1978 with a degree in Construction Engineering, he has been self-employed since that time, running a custom home building business specializing in energy efficiency and sustainable building techniques. Turko is a co-founder of the California Straw Building Association. He has built several custom homes, agricultural buildings, and wineries throughout central California. He has taught classes and workshops on sustainable building systems to community groups and to students at the elementary, secondary, and university level. He is recognized as an expert on passive solar design concepts and other energy efficient techniques, as well as nontoxic and sustainable building materials.

The Semmes southwest-style straw-bale home (pictured here) is nestled in the Los Padres National Forest in a setting that joins nature with natural building. The courtyard/pool area is an inviting setting filled with flowers and hand-painted artwork at the main entry door leading to Turko’s office and the family den. The lower terrace provides space for relaxing poolside with an outdoor shower nearby. The upper terrace is a covered outdoor cooking and dining area. The formal living and dining rooms and the master bedroom face onto the meadow with views toward the mountains of the Santa Lucia Range. The cool and calming color palette of the master bedroom contrasts with the bright and lively colors of the other living spaces.

Turko Semmes, Semmes & Co. Builders, Inc., Atascadero CA
<turko@semmesco.com> www.semmesco.com
Photo credits: Semmes & Co. Builders, Inc.

by Ken Haggard and Polly Cooper – California, USA

Adopted from an article that appeared in Home Power Magazine.

Straw-bale cottage during construction.

Like many other architectural firms in California, San Luis Obispo Sustainability Group architects had been designing building that utilized passive solar for many years. Like many other architectural firms around the country, and around the world, in recent years we found ourselves shifting our design work to “sustainability,” an extension of passive solar design concepts.

The definition of sustainability we use in our work is to use resources that meet our needs but do not compromise the ability of future generations to meet their needs. As our firm and the work we do evolved, our practice has evolved to encompass broader issues including life cycle impacts of materials, miniaturization of infrastructure, health issues in buildings, permaculture and landscape regeneration.

By 1994, we had developed a comfortable working environment, consisting of a mix-used passive solar complex that included an office, shops and a residence on an old trout farm adjacent to the Los Padres National Forest, 12 minutes north of the city of San Luis Obispo. Little did we imagine that we would endure the trauma of losing nearly everything we owned or that this tragedy would afford an opportunity to redevelop our complex based on our new knowledge of sustainability. In August 1994, the 41 Wild Fire that burned 40,000 acres/16,200 hectares in our area destroyed our entire complex, and forced us into applying these broader principles of sustainable design for ourselves. Once we got over the initial shock of losing an extensive library, slide collection, office and home, it became more and more obvious what an opportunity our natural fire-oriented local ecology offered us – we could start from scratch and build sustainably, without the problem associated with retrofitting existing structures.

One of the first things we realized was that the fire had left us with a large inventory of building material. (We had several strawbale benches on the site before the fire. They turned out to be more fire resistant than most of the stucco-, tile- and metal-clad buildings in the canyon.) It had killed most of the mature trees (except for 2/4 of the fire-adapted oaks), and these trees were now available to use as lumber. We would never have dared touch them while they were alive. In addition, the massive opening-up of the landscape afforded by the fire allowed us to examine our aging infrastructure. We realized it could be redone in a much more sustainable way. Landscape regeneration became an everyday reality, not some theoretical subject. We suddenly could do things that we had only talked about, but never had the time to do – like getting off the electrical grid.

Completed straw-bale cottage.

Right after the fire, it was necessary to develop a base of operations – a place to store tools, plan from and live in. We attempted to combine this need with several others, such as providing future retreat for guests and visitors, as well as a demonstration workshop for our senior sustainable design architecture class at Cal Poly State University. The result was a 500 sf/46m2 cottage that we uilt on a slab that was left from a shed we had removed long ago. his was one of the few slabs in the canyon not destroyed by the re, because it supported no flammable building at the time. For the structure of this building, we used fire-damaged telephone polls with a truss joist frame. We built the walls from rice straw bales laid on edge, which provide good insulation. In addition, the stucco finish provides interior distributed thermal mass. For the ceiling, we used wheat straw bales laid flat between TJI rafters, which also provide good insulation. The roof is corrugated steel sheet, and includes a 4-ft.x 8-ft/1.2mx3.4m skylight with skylid (movable insulation) unit. Our electrical power came from a Pelton wheel (a microhydro system) on the creek connected to storage batteries.

The construction of this building used healthier building materials that produced less waste. The unused straw was used for erosion control on the site. The building also gets much of its heat from the sun, and uses waste as a resource. In addition, the structure served as a prototype to test details that we planned to use in the larger buildings.

Sustainable Materials

In sustainable design circles, there is a lot of talk about the advantages of using regional materials. As practitioners, we always had nagging doubts about how much of this is truth and how much is idealized theory. Once construction of the guest cottage was underway, we turned our attention to testing this theory. There were several stands of mature trees on the site, especially in the creek areas. The oaks, Sargent cypress and several pine species were native. The Douglas fir and redwoods were not, although their natural range on the coast extends to just 10 miles/48 km north of the site. They were planted 33 years ago when the trout pods were developed. After the fire, all the redwoods put our new growth immediately, and three-quarters of the oaks sprouted from at least part of the remaining trunks. The other trees were killed. We now had an opportunity to do what passive solar applications do – use resources directly on the site rather than importing them from far away and exporting the impact elsewhere.

We felt obligated to mill the dead trees into lumber for reconstruction. We hired sawyers to do this during the fall of 1994, suing a wood Miser portable mill. Both we and the sawyers were amazed at the quantity and quality of wood produced in this relatively small area. We harvested 22,000 board feet of lumber, enough for construction of the other buildings with enough left over to be a storage, rain and sun protection chore. The economics of this also created the unusual condition of using straw-bale construction in conjunction with heavy timber construction, as it was more economical to mill big pieces rather than small ones.

The result of this experience was very interesting. The wood we obtained cost about the same as it would have from a lumberyard, but the quality was much higher. In addition, all phases of the life cycle of this material – source, transport, processing, use and source regeneration – happened on the site. Waste could not be exported elsewhere. It became a resource used for erosion control and organic matter for the regenerative process.

It became obvious to us that although the first costs of both milling our own lumber and buying it from a lumber yard were about the same, the long-range environmental costs of milling our own was much less. These costs are not often accounted for in our present economic system.

The Studio/Office

The next step was construction of the studio and office, completed at the end of March 1995. Because of the function of this building, we placed great emphasis on natural lighting in addition to the passive solar design. The studio/office is also off-grid, poweredby photovoltaic (PV) panels over the library/research area, with a Pelton wheel on the adjacent creek for use as backup in the winter when the water is high. (Two streams fed by the nearby mountain range flow through the property.) The studio/office is heavy timber-frame construction with straw-bale infill.

The south side of the office is configured to allow maximum sun
penetration in the winter and begins to shade itself in early April. During the summer months, it is totally in shade, picking up sun again in late September. Parts of this facade are view windows, part unvented 12-in./30cm Trombe walls that also act as shear walls, and part 9-inch-thick/23cm water tanks below the south-facing window on each end that act as indirect gain passive heaters. The Trombe walls and water tanks are painted with a selective surface paint on the sun-facing side.
The wiggly light shelf on this south facade serves two purposes: providing summer shading of the windows and low water tanks and throwing light deeper into the building in winter. This office is also designed for maximum night ventilation. Summer breezes generally flow from southwest to northeast, so the air moves through the long dimension of the office. These breezes, coupled with the large amount of distributed thermal mass in the building, keeps the interior temperatures below 79oF/26oC, even when daytime summer temperatures are quite hot, occasionally reaching 110oF/43oC.

The Residence

The two-story residence of the complex was completed in October 1997. We used construction techniques similar to those in the office, except that the heavy timber structure is placed 6 in./15cm inside the straw-bale walls. This configuration allowed us to expose the beautiful timber frame and create a continuous two-story straw-bale wall without interruption of the north side. The curves of this wall were very easy to achieve with straw bales without any added expense. This is the best arrangement of the timber structure and bale walls we’ve found to date. There are remarkably few cracks in this wall. The contrast to the stuccoed wood shear walls on the east side is very telling.

The residence uses interior 8-in./20cm concrete block walls as shear walls, thermal mass and decorate “gates.” Besides south-facing glass, skylights provide direct gain, with skylids as thermal control. We’ve found that this system offers more flexibility in the fall and spring than fixed overhangs.  The El Nino weather pattern sometimes produces a very unusual cool late spring, which we cannot respond to in the studio with its fixed overhangs. The skylight/skylid arrangement in the residence did allow us to respond to these unusual climatic conditions. The residence is also off-grid, powered by the PV system and Pelton wheel backup that provides electricity to the rest of the complex.

Landscape Regeneration

One of the unexpected joys of this whole ordeal has been to experience the rapid regeneration of the landscape following the fire. Fire is such an integral part of the native California landscape that everything is set up for it. The first spring was dominated by delicate fire poppies, which only appear in newly burned areas. In this case the seeds had been waiting 60 years for their chance – it had been that long since this area last burned. The next year was dominated by morning glories, which spread all over the armature of the burned branches of earlier plants. The third year was the year of low herbal plants – sages, bush poppies, soap roots and others. In the fourth year, we found the Ceonothus (wild lilac) dominating. The regeneration of oak and cypress trees then began to be much more noticeable.

The best wood for reconstruction turned out to be the Sargent cypress, used for the structure and trim. Alder was the best for cabinets. The cypress trees regenerated naturally because they were a fire species whose seeds are stimulated when they are burned. When the office was done, to commemorate the wonderful alder cabinet it contains, we planted several times the number of alders in the creek than were there before the fire.

Better Quality, Ecological Correctness

We’ve found that the application of our design theories to our own situation has helped convince clients and others that sustainability is more than just another theory. It is a way of achieving better value while simultaneously having far less impact on our planet. In fact, once we get beyond the fears of scarcity that haunt our industrial culture, we will see that these two values – better quality and ecological correctness – are interrelated.

Ken Haggard and Polly Cooper are principals with the San Luis Obispo Sustainability Group, 16550 Oracle Oak, Santa Margarita, California 93453; 805.438.4452, fax 805.428.4680 <slosg@slonet.org> www.slosustainability.com

Ed.Note – An article about the curved wall straw-bale workshop building (not pictured in this issue) at Ken and Polly’s complex will be included in TLS#60/Details, Details, Details. It’s amazing in its design and structure.

by Chris Newton – Queensland, Australia

Can you design and build straw-bale homes for a hot and humid climate? Living in Queensland, Australia, I am frequently asked to identify an invisible line on the map where “she’ll be right” applies on one side of the line and “don’t go there” applies to the other. The part of me that fears litigation wants to respond with “ask me in 20 years time,” the technical part of me feels it has to be evidence based, and the logical part knows the answer already exists in the local environment. So I take on board here these three points and discuss how I attempt to find that line on the map in our building history, current research and the observation of the environment we live and build in.

Macro Climate

Queensland extends from 10 degrees south to 29 degrees south of the equator, covering more than 1.72 million square kilometres. Queensland is more than twice the size of Texas. Within Queensland, we live in monsoonal, tropical, subtropical, grassland and desert climate zones.

The table below represents summer (December though March) in the climate zones of Queensland. Summer is dominated by the monsoons making this a hot, wet and humid season. All zones in Queensland have mild and dry winters.

Microclimate

We can create a microclimate in and around our homes. Changes in air movement, moisture load or sunshine can significantly change the wetting and drying potential of a section of the building. When designing the house and gardens in a humid climate, we need to be aware of creating microclimates that cannot dry out.

Relative Humidity

Humidity is the water vapour held in the air. This is the ratio of the actual amount of water vapour in the air to the amount it could hold when saturated; it is expressed as a percentage. The capacity for air to carry water vapour increases as the air temperature increases. Air with a temperature of 30°C/86°F can hold more than three times as much water vapour as air at 10°C/50°F.

The dew-point temperature is temperature in which air must be cooled in order for dew to form. Droplets of water can be deposited within the straw-bale wall when air cools below the dew point and water vapour condenses.

Wood can absorb moisture content up to 25% from a relative humidity 98% (See Straube report in Resources at end of article). Straw is hygroscopic with its large surface area and internal pores having the ability to absorb moisture. A bale whose moisture content is at 8% will weigh less than the same bale with a moisture content of 20%.

Wetting Potential

Table Daily Humidity in relation to Temperature Changes Source: Australian Bureau of Meteorology

We have a copy of an 1860 encyclopedia. It’s only damage is some yellowing and a few small brown spots (mold). This book had no special storage other than to sit on a bookshelf in subtropical Brisbane. So it seems that humidity alone may not be enough to cause decomposition of straw bales. However, I know through talking to people from Cairns that it is the norm to have molds growing on curtains, furniture and shoes throughout their summer. Newspapers and photos curl from the moisture they absorb. So humidity alone is enough to support mold growth in the tropics.

Historically, bathrooms have remained an area with high failure rates from moisture; this is true in any building type. Protection for straw-bale systems in wet environments exists. This can be in the form of vapour barriers, water barriers, design considerations, and attention to detail. It would be fair to say that, over the life of a building, some houses despite best efforts will experience elevated moisture levels in part of the wall system. Concentrated moisture only becomes a problem if the ability to dry is not timely for the given climate conditions. Remember that molds grow rapidly in hot and humid conditions, and are dormant in cold conditions.

Drying is the balance for wetting. The measure to ensure this includes a capillary layer below the bottom straw bale and a render with high permeability. Water vapour moves from low concentration to high concentration. High humidity will reduce the ability for the wall system to dry. In the tropics, rain may persist over several days. Attempting to dry clothes in the shade will take a long time during which they will acquire a moldy smell. You can not expect a wall system on the south side of the building to dry as efficiently as those on the north. High humidity will further compound this. (Note that we live in the southern hemisphere.)

Can you build with straw bales in a high humidity climate?

The line that removes high risk for straw-bale construction is unlikely to be a latitude line. Maybe it is a line that farmers have already identified. Grain farmers look for a climate dry enough so the grain dries adequately before harvest. The dry grain is then suitable for storage. Humidity is not a problem for the sugar cane growers who harvest the crop with high moisture content and send it straight to the mills where the juice is squeezed from the cane. So maybe the invisible line is found on an agricultural plan.

Resources

How Straw Decomposes, Matthew D. Summers, Sherry L. Blunk, Bruan M. Jenkins. www.ecobuildnetwork.org/pdfs/ How_Straw_Decomposes.pdf

Straw Bale House Moisture Research, CMHC (Canadian Mortgage and Housing Corporation). www.cmhc-schl.gc.ca/ publications/en/rh-pr/tech/00-103-E.htm

Moisture Properties of Plaster and Stucco in Strawbale Buildings, Dr. John Straube. www.ecobuildnetwork.org/pdfs/ Straube_Moisture_Tests.pdf

Monitoring the Hygrothermal Properties of a Straw Bale Wall, Dr. John Straube and Chris Schumacher. www.ecobuildnetwork.org/pdfs/Monitoring_Winery.pdf

Bureau of Meteorology–Australia. www.bom.gov.au/ weather/qld/

Chris Newton, Earth-n-Straw, Queensland, Australia, 0413 195 585, <chris@newtonhouse.info> www.newtonhouse.info. Chris, an owner/builder, educator and trainer in strawbale, plasters and other aspects of natural building, is the new President of AUSBALE, the Australia and New Zealand straw-bale building association.

by Rene Dalmeijer – The Netherlands

In June 2003, Jasper van der Linden, a building engineering student at the Eindhoven Technical University, Eindhoven, The Netherlands, tested the sound isolation of an earth-plastered straw-bale wall. Rob Kaptein of RAMStrobouw and I assisted in carrying out the test. The test was executed in a true acoustic test chamber according to ISO 140-3. We were able to execute a consistent test giving a good indication of how well a plastered straw-bale wall retards sound.

Based on the outcome of the test, it is to be expected that a reasonably well-designed and built straw-bale wall without acoustic defects (like protruding post-and-beam members) will perform in the region of 53dB and upwards (55dB with A weighting; “A-weighting” means the impedance is corrected to approximate human hearing sensitivity, which varies depending on frequency). The 2dBA increase in performance when compared to the test is mainly because we used very thin (worst case) plaster thickness in the test sample. Normally earth plaster finishes would be thicker. This puts the performance of a straw-bale wall at more or less the same level as a decoupled brick cavity wall and even exceeding it in the critical low-frequency region.

Most everyone who has been in a straw-bale building has had the sensation that interior sounds somehow seem louder, because interior sounds become more distinct for not being drowned out by background noise coming from the outside. This is a clear indication that straw-bale walls work very well as an acoustic insulator. Normally built structures depend on high mass for good sound insulation. But there is also another way of achieving good sound insulation, which depends on a damped cavity surrounded by two not-sostiff membranes with sufficient mass. A straw-bale wall, specifically with earth/clay plasters, is an excellent example of this alternative way of achieving good sound insulation, as the test result clearly illustrates.

The Test

The test was executed in the acoustic lab of the Eindhoven Technical University. The test and test facility is according to ISO 140-3 which is to test the sound isolation of building aperture of two acoustically separated chambers (the test sample is placed in an aperture between the chambers). Although I am aware of the limitations of the test facility for testing a wall system, we have endeavored to make this test as accurate and as representative as possible. The aperture’s size (ISO 140-3 std) is 1.88m² /20 ft². The tested straw-bale wall section had the following configuration:

• Two-string (460mm wide building quality bales laid flat density 120-130kg/m³)
• Earth/clay straw plaster 25mm and 35mm (intentionally asymmetrical cover)
• No reinforcing plaster netting or mesh or any form of pinning

The chosen sample structure was to be as representative as possible of a normal earth/clay plastered straw-bale wall structure as used by the experienced straw-bale builder Rob Kaptein of RAMstrobouw. Rob was also responsible for manufacturing the test sample. The graph and table summarize the test result.

[Rene’s comment on the measured performance: The result can be expressed as 53dB according to A-weighting. Actually expressing the sound isolation value in one number (i.e., 53BA) is a simplification. In actual fact, giving the performance at each of the various frequencies is much more meaningful.]

Generally this is done at either one octave intervals (1/1oct) or at one-third octave intervals (1/3 oct), the last giving even more detailed information.The graph and table show both measurements (not A-weighted). The dip at around 250Hz is due to the transition between the masws and damped cavity odes of operation of the test sample and should be largely disregarded as part of the vagaries of a test.

The 53dBA test result might seem low but in fact is very good. Most conventional wall systems including a brick cavity wall with much higher mass have a lower performance. Specifically interesting to note is the 2-3dB better performance at very low frequencies of the straw-bale test sample when compared to brick-wall systems. Nearly all wall systems, including stick frame, are able to sufficiently subdue high-and mid-frequency sound, but low-frequency sound is problematic. In practice, better performance at low frequencies is worthwhile because it means that the ever-present background noise in suburban areas is perceptibly reduced.

Recipe for Straw-bale Wall Acoustic Isulation

Besides sheer mass, low stiffness with sufficient mass and acoustic decoupling are very imortant for acoustic sound insulation. The relatively low stiffness of a straw-bale wall with earthen plasters is ideal. The fact that the cavity between the two plaster shells is filled with straw provides excellent acoustic damping. Beware and be careful to fill all cavities and voids with very light straw/clay. Avoid any direct mechanical contacts between the inner and outer plaster shells, as these will seriously degrade sound damping performance. Contrary to what you would expect, loosely packed bales will perform better than very tightly packed bales. Extra thick (>35mm) earth plaster specifically improves low-frequency performance. Cement and lime plasters perform almost as well but earth plaster with lots of straw is the best due to a lower modulas of elasticity (stiffness). Applying significantly asymmetrical plaster thicknesses helps to avoid coincident reverberation of the inner and outer plaster layers. The thicker plaster layer should be on the sound source side of the wall. Pay a lot of attention to all openings and edge details; these are the weak points. An air leak of only one sq. mm will seriously degrade performance. Door openings and windows are literally acoustic holes in the wall; these need special detailing and attention to even remotely approach the acoustical (and thermal) performance of the surrounding walls. Even double doors generally show poor performance compared to the wall. The gaskets and seals in the doors should be double or even triple, but even then there is a problem as, over time, the seals will degrade and leaks will occur. The type of door you are aiming for is more like a steel watertight door in a ship than a house door with multiple closing bolts and tightening clamps. (All of this only if acoustical performance is essential.)

In conclusion, I would like to emphasize that, due to the nature of a straw-bale wall (an excellent sound barrier), the wall is not the problem; the connections between the

wall and all other elements incorporated or surrounding it are. In other words, it is the same issue as with thermal and moisture performance. I strongly suspect that most sound isolation tests executed on straw-bale walls are measuring the defects of other structural components or mistakes in the test procedure (a non-calibrated sound source, background noise, and such).

Room Acoustics

Here are some simple rules of thumb depending on the type of acoustics you want, e.g., very lively to very well damped. Soft acoustic instruments require a “live” (reflective) room. Loud amplified sound needs a “dead” (absorbtive) room. The single most important parameter is the reverberation time and level. The harder the surfaces, the livelier the sound. A bathroom is lively, hence your strive to sing even if you can’t. The opposite is standing on top of a snow-bound hillock [small hill or mound] – virtually no sound reflects back to your view. The bigger and harder the room, the longer the reverberation time, e.g., a cathedral. Next the relative dimensions: an oblong box (like Concertgebouw Amsterdam) approaches the ideal. Preferably the relative dimensions are approximately 2 to 3 to 5; this ratio will avoid the formation of dominant harmonic resonance and standing waves. The exact ratios needed for a given acoustical requirement depend on the size and acoustic reflectivity. I personally prefer rooms without parallel surfaces, thus avoiding standing waves. I think if you finish a room with earth/clay plaster on straw-bale walls, with wooden flooring and a well-pitched ceiling, you will have quite acceptable acoustics for musical performances. If it’s too lively, you can always add some damping afterward by placing soft furnishings in the room or hanging curtains on the windows. A bigger audience also helps.

Good acoustic isolation is definitely one of good merits of straw-bale walls. It should be seriously considered for purposes where sound isolation is of importance. It would be hard to find a more affordable solution to building sound studios, quiet houses in noisy neighborhoods, or noisy workshops in residential surroundings.

<Rene.dalmeijer@hetnet.nl>

Rene Dalmeier has been interested in straw-bale building since 1998. In June 2005, he finally took the plunge and turned his hobby into a profession by becoming a full-time straw-bale builder.

A whisper = 15 dB … Normal conversation = 60 dB. dB: Abbreviation for decibel(s). One tenth of the common logarithm of the ratio of relative powers, equal to 0.1 B (bel).