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Mountains and Domes: A B&B in Thailand built using rice husks

By Asia, Design, Earth Buildings, Issue 70, Roofs No Comments

This article first appeared in The Owner Builder 192 December 2015/ January 2016. www.theownerbuilder.com.au

By Maggi McKerron

Ten years ago I fell in love with a mountain. Mt Chiang Dao rises 2173 metres out of the forests of northern Thailand, its jungle covered peaks dressed in swirls of clouds. I leased a piece of land on a small hill facing the mountain. Under half a hectare, the land slopes down to a small rural Thai village under the mountain, clustered around the nationally famous Chiang Dao Cave.

Planning a B&B

I was approaching upper middle age and realised I needed to make some sort of plan for older age when my life might possibly slow down a little. This piece of land would be perfect for a B&B!

I did not have the money to develop the land, so I took off for the UK to make some. Although I am British, I was born in India and have always lived in Asia. Going to the UK to work was a challenging experience, as I had to learn to live in a western culture for the first time, at the age of 56.

mckerron-_24

Earthbag B&B

While in the UK I took the opportunity to study natural building, beginning with an inspirational earthbag building workshop taught by Paulina Wojciechowska, author of the first book on earthbag building. Making a dome out of earthbags sold me on domes and round dwellings. I was determined to build round domes back in Thailand!

Rice husks

But using earth as the building material did not sit right with me. I am mildly asthmatic and need dry air and did not relish the thought of being enclosed in an earthen dome during six months of monsoon rains. I thought about rice husks. This is a product that no one wants. It takes ages to break down if added to compost, and is difficult to burn. It is also a desiccant, which means that it will draw moisture out of the atmosphere. Perfect!

After seven years in the UK I finally had enough money to return to Thailand. At least I hoped it was enough. There was no way I could calculate the costs of the buildings in any detail, as I did not really know how I was going to build my rice husk domes. I couldn’t find any information on the internet: no plans available, no books on building with rice husks. I worked out a financial guesstimate, which I finally reached in savings, and I bought a one way ticket back to Thailand.

My beautiful land was covered in towering brush and it was not until a team of machete wielding villagers cleared it that I discovered how steeply it sloped. What a challenge this was going to be!

I should mention here that where I was building, out in the scarcely populated countryside, planning permission, although preferred by the local council, was not an issue. In towns and cities I would have had to submit plans. My local council signed off the building after it was finished.

Beginning the build

Ready to begin my adventure, I posted on social media that I would welcome anyone who would like to help with the project, and people turned up. I hired some local day labourers from the village. We found the flattest area, at the top of the property, and one of the first steps was to prepare for a concrete base. I had been warned by locals that the termites were ferocious and there really was no alternative to concrete.

We marked out a circle 5.5 metres in diameter with some bamboo stakes. Then we got some tubing and filled it with water, and tried to find a level. No one believed what the water in the tubes was telling us, so I went and bought a spirit level. This confirmed the water’s message; there was still a big slope, even though compared with the rest of the land it looked practically flat. Leveling the area was our first task.

My very rough plan showed a concrete cap on the dome, as this was all I could think of to keep out the monsoon rain, so our next task was putting up six concrete posts to carry the weight of the concrete cap. Then the base of sub soil and stones went in, pounded flat
by enthusiastic volunteers, a trellis of bamboo for strengthening, a sheet of plastic as a damp proof membrane to stop moisture leaching upward, some sand and a final topping of concrete.

The dome

Now I needed to seriously consider the dome. I could not for the life of me work out how to construct it. Unlike earthbags, which are load bearing and could support a concrete cap, I was working with lightweight, not at all solid, bags of rice husks. I spent ages in hardware stores, second-hand wood shops and looking through books. I asked various local builders, but one after the other they shook their heads, mystified with the ideas of the crazy foreign lady.

At one point I decided to forget the dome and just build a hexagonal roof using the steel for conventional roof frames. One of the volunteers said: ‘But Maggi, your dream is a dome. You must follow your dream.’ So I thought again.

Weaving the bamboo

Weaving the bamboo

Bird cage

I found reinforced steel rods, rebar, bendable and long. I could buy quite thick pieces and long enough to go from one side of a dome to the other. First a piece of rebar was bent into a circle to go around the building, sitting on the top of the concrete posts. Then up went the rebar making the dome shape and we wired it onto the posts and horizontal rebar. Using different thicknesses of rebar and adding bamboo we made a dome shaped trellis.

The bamboo for the trellis in the dome came from bamboo poles we harvested from the land. These we cut and prepared and wove as needed. We used the same trellis idea for the walls, and our bags of rice husks would be attached to this frame. The whole thing looked like a giant bird cage!

The windows and doors were added as we built the bamboo trellis. This was complicated as the walls were going to be quite thick, so windows and doors needed frames to sit in. We learned as we went along. At no point in the building did we use any electrical tools – there was no electricity!

Rice husk walls

Filling in the walls came next. I found a place that sold second-hand polypropylene bags and had bought several hundred. Then I found a rice mill that agreed to fill the bags for me with their waste husks, 200 a week. These we had been collecting in preparation.

The first layer of bags was filled with gravel to guard against water and moisture damaging the walls, with a layer of sand on top of that, then the bags filled with rice husks. We experimented with different types of string, and different knots and found the method that worked best. They went up quickly and easily in a couple of days, and soon we were at the level where the curve of the dome began.

The bags were too big. They would be too unwieldy and heavy to attach. We had to empty them, refill them with less rice husks, then tie them up in the shape of a sausage. Our sausages were quite complicated to put up as we were attaching them to the inside of the dome to continue the inside line of the walls.

The dome looked wonderful! The next step was to put on the concrete cap. We used plastic sheet covered with chicken wire and put the concrete on top. We made deep overhangs to protect the walls.

mckerron-_15

Finished dome

Mud render

The last step was the mud on the walls. It took a while to perfect our recipe as putting plaster on bags of rice husks is not the same as putting it onto earthbags or straw bales. The bags were not solid, so plaster had to be built up slowly in several layers until it was firm and strong. Then a final layer of lime plaster, followed by some decorations, and our dome was finished!

The big lesson I learned was never to put a concrete cap on a dome in the kind of climate found in Thailand. It cracked, and cracked again! But because the rice husks dry out so easily it has not caused any lasting problems. The second lesson was to attach the bags to the outside of the dome trellis. Much easier!

Three years have gone by since the beginning of the adventure. I have three domes and five roundhouses with thatched roofs. All the buildings with their thick walls of rice husks covered with earthen plaster are cool in summer and warm in winter. I have a beautiful home, made from three of the five metre roundhouses, joined by thatched walkways. My B&B is up and running. And every day and all day I can see my mountain. My dream has come true.

Maggi will be running a roundhouse building workshop in November 2017.  See website for details: www.chiangdao-roundhouses.com

Links & resources

Maggie’s Blog

Sharing her adventures of living – and building – in Chiang Dao, northern Thailand.

maggimck.wordpress.com

Chiang Dao Roundhouses

Set on the side of a hill overlooking the spectacular Mt Chiang Dao, offering rice husk workshops and B&B accommodation.

www.chiangdao-roundhouses.com

Building an Energy Efficient Straw Bale Home: Design criteria for Inglewood straw bale

By Bales, Design, Issue 70, Straw Bale Construction No Comments

This article first appeared in The Owner Builder 196 August/September 2016.  www.theownerbuilder.com.au

By Brian Hodge

As we embark on our 20th owner-built home, I reflect back over the progress since purchasing property last year.

We were surprised the property didn’t have power, sewer, or water but discovered it actually had sewer connection just over the back fence. We were somewhat pleased when we received the quote for electricity connection of $5,050. Mind you, that did not include the connection of the power to our meter box.

Having mentioned the meter box, I am flooded with the memory of its incorrect positioning in my unavoidable absence and the challenges that we were faced with as a consequence (see TOB 195 June/July 2016). But who can complain. The end result was that we have revisited the design and now have a better one that is more interesting.  And who can forget the bonus sewer connection at the back of the block, which will save us around $10,000 that we would have spent for a septic system.

A place to run courses

When we first went looking for land our primary motivation was to get a low cost piece of land on which we could run the practical part of our owner-builder straw bale building workshops. This was a precursor to being willing to sell the straw bale house in Ladys Pass. To be a straw bale building consultant with nowhere to do courses and nothing to show people was not an option and the solution had to make financial sense.

Consequently, I did an internet search for ‘land under $50,000 Victoria.’ The result was land in Loch Sport, which was too small and, from previous experience, has too many mosquitoes, and land in Inglewood, Victoria. Inglewood is in central Victoria about 35 minutes north of Bendigo with a population of a bit over 1,000. It was established in 1859 and is still a great place to find gold. It has a good supermarket, hospital, permanent doctor, pharmacy and most important, a couple of good old fashioned pubs for great meals. It is also the town where my youngest son, his wife and two of my grandchildren are located. However, the criteria were primarily price and size.

There was an 8000m2 block for around $45,000 near a light industrial area, a 2000m2 for $70,000 or a 1000m2 for $35,000. We put in an offer of $33,000 on the last block, which was accepted.

Position, position…

The only issue, which was a big one, was its orientation. It is only 20 metres wide and faces north-west. In order to control heat input and get some passive solar benefit in the design, we had to design a house that is twisted on the property. This option consumes a lot of land, which was complicated by our need for wide eaves for a straw bale house. Regulations stipulate that living area windows must have a minimum of 1000mm of clear sky from the boundary, which meant that we had to be set in from the side boundary a minimum of 1900mm to allow for the 900mm eaves. We also needed truck access to the backyard to take deliveries of bales etc. for workshops, further restricting our build space.

We finally settled on the concept of building a U shaped house with a central courtyard as this would enable us to get passive solar benefit in the master bedroom and living area. Not a huge amount, but enough to make a difference. It also provided us with a outdoor private area, which is important to us as we have lived on country properties for the past 12 years.

U-shaped floor plan

U-shaped floor plan

Energy rating

I had our energy assessors check to see what difference this adjusted orientation would make on stage one of the construction, as opposed to building parallel to the front boundary. We were surprised that the energy rating actually went up from 5.4 stars to 6.3 stars even though there is only one window that faces north.

As we are building in central Victoria, the energy rating is primarily directed toward the energy required for winter heating. However, we get some really nasty weather in summer with temperatures reaching high 30s and even mid 40s. Consequently the design criteria also included resistance to summer heat. The central courtyard faces due west, however it has a deep verandah to protect smallish windows from the afternoon heat from the west, and the windows facing east are limited.

One of the big concerns for restricting heat input in summer is to avoid doors that open directly into the house from the north, as it is the north wind that brings high temperatures to the area. I have therefore included a good size entry on the northern end of the house with the external door facing east, which will dramatically reduce the impact of those hot northerly winds.

Airflow manipulation

The cooler summer breezes often come from the south-east, so we have included casement windows on the south-eastern boundary to funnel those cool breezes through the house. The benefit of correctly hinged casement windows is that they tend to trap the breeze and funnel it into the house rather than simply working with straight airflow. When you are trying to get cool air into your home it is best to open the windward windows fully but close the windows on the opposite side of the house to 50%, as this creates a vacuum resulting in greater airflow.

As this is a residential block I expect that airflow will be a bit of a challenge as we have boundary fences which will restrict it. I have also incorporated a flat ceiling in part of the house in order to accommodate ducting for an air circulation pump to force the early morning cool air through the house if the temperature in the house is higher than the temperature outside. Our previous straw bale house in Ladys Pass had the same issue, which was overcome using an evaporative cooler as an air circulation pump. The cooling function of the unit was hardly ever used, and would not have been missed, so I am planning on simply fitting an air pump this time.

The master bedroom window faces north onto the central courtyard, however the window is not within the shadow of the verandah roof so we will get good passive solar benefit in winter. It also means that we have a private outlook, and with Molly, our big guard dog, we are assured of security! (Molly is a miniature Maltese Shiatsu)

As this is house number 20 for us personally, it was difficult to find something a bit different to do, so we eventually settled on a curved roof with a curved ceiling. This will be achieved by building box trusses on site. It is a very cost effective method of roof construction and I am looking forward to trying it out, as I have never done it before.

With all the design, engineering and building permit issues behind us it is now time to get to work and build it. I am going to take my time and enjoy the process as I suspect this will be the last home that I build, although many people scoff at this idea, thinking that I am either crazy for building so many or that I am addicted to the process. Personally I am not sure, but I am going to enjoy this project as if it is my last.

Brian Hodge is the director of Anvill Straw Bale Building Consultants. He has nearly 40 years experience in the building trade, and now consults predominantly on straw bale construction. Brian is the author of ‘Building your straw bale home’ and will be blogging about his build. Anvill Straw Bale Building Consultants: Whether you are building a mansion or to a strict budget, we are here to help.  www.straw-bale-houses.com

Healthy Living, Healthy Building (Building an EcoNest)

By Bales, Design, Issue 62, Straw-Clay, Walls No Comments

By Elaine Brett

Finished WallsTwelve years ago I had never even heard of building with straw.  I lived in a four-bedroom colonial house in a subdivision in Maryland.  The conventional American Dream – good job, big house, nice cars, the monthly lawn service, the health club membership, 24/7 access to shopping …

Then on my 49th birthday came the American nightmare.  A wake up call from Mother Nature.  Sometimes she needs to smack you hard to get her attention.  My wake up was a cancer diagnosis that sent me spinning into a quest of asking questions and trying to understand “how could this happen to me?”

One path of my quest (probably driven by my background as a chemist) sent me questioning the chemicals in my environment: the food I was eating, the air I was breathing, the water I was drinking, the lifestyle I was living, the buildings in which I was residing and working.  The answers took me beyond the overt pollution of urban air and water to the hidden nooks of micro pollutants in synthetic materials, chemical food processes and endocrine disrupters in simple everyday products.

The quest also took me on another path.  I began looking for a place to live clean and chemical free, or at least as clean as is possible.  And that’s how I came to a small town in the North Fork Valley (www.northforkvalley.net) in Western Colorado.

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Straw House Patent (Feuillette House Follow-Up)

By Bales, Community, Design, Issue 62, Straw Bale Construction, Technical, Walls No Comments

As an update to this post about the Feuillette House in France, here is a patent in the United States for straw bale construction.  It was filed on June 6, 1921 and is a very interesting read for the bale construction history buffs out there. The author was Emile Feuillette himself and approved on June 6, 1921.

This is not the oldest patent on bale construction as we documented back in Issue #21 in the Winter of 1998.  That title goes to Josiah M. Leeds (of Indiana, not Nebraska) in 1880.  The article describes and contains illustrations of three subsequent straw bale building patents (1885, 1903, and 1905).  Issue 21 can be ordered on our CD of the first 40 Issues here.

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Traditional and Contemporary Natural Building in Korea

By Bales, Design, Energy, Floors, Issue 62, Plaster, Straw Bale Construction, Straw-Clay, Walls No Comments

By Kyle Holzhueter

Editors Note – This article is a feature length pictorial look at the various aspects of natural building in Korea.  The full-length article will be in the upcoming issue of The Last Straw and is available in its entirety right here on the website for subscribers.  Make sure you have a subscription soon so you won’t miss this stunning array of natural building techniques.

Traditional Korean Architecture

Traditional Building in Korea relied primarily on natural and local materials.  Buildings were traditionally designed according to the 間 (Korean: ka, Japanese: ken) module, a common measurement found in east Asia.

East Asian Modual

East Asian Module

Traditional Korean homes generally have a timber frame with adobe or wattle and daub infill, though regional variations are found throughout the country.

Traditional House

Traditional House

Regional Variation

Regional Variation

Especially on Jeju Island where volcanic rock and strong winds are abundant, homes traditionally consisted of a double wall system with an exterior wall of volcanic rock surrounding an interior wall, creating a protected corridor around the house.  This in turn, protected the interior walls from wind and rain and improved the thermal performance of the home.  Also because of the strong winds, thatched roofs were generally secured by a net of straw ropes.

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Straw Bale and Building Science: Growing Up Together

By Building Science, Design, Energy, Issue 62, Plaster, Straw Bale Construction, Technical No Comments

by Chris Magwood

Making Things Air-Tight

Making Things Air-Tight

The straw bale revival of the 1990s reintroduced builders to a pioneer building method that showed remarkable potential for building in a modern context. The nature of the basic components of a straw bale wall system – bales with plaster applied directly to bales – combined several obvious advantages over other wall systems while simultaneously raising some serious questions.

The advantages are familiar to TLS readers: low environmental impact, simplicity and well placed thermal mass. The serious questions and attempts to answer them were the lifeblood of TLS: What about moisture? Air tightness? Cold climates? Humid climates? Longevity of the straw in all these conditions?

There was a lot more going on in the construction world of the 1990s than the straw bale revival. The housing industry was recovering from multiple moisture-related disasters, many caused by overly airtight but under-ventilated homes and/or the use of un-vented “waterproof” exterior cladding systems. The research into these issues, among other factors, led to a rise in prominence of “building science” as a distinct engineering discipline. The straw bale revivalists were extremely lucky to have the attention of some of building science’s leading practitioners, in particular John Straube, who authored several key articles and studies about straw bale walls that were essential to answering the question of why bale walls were so resilient, despite some seemingly obvious moisture concerns.

Simply put, building science attempts to quantify the movement of heat and moisture through building assemblies and help designers and builders to make decisions that lead to structures that adequately deal with the moisture and temperature regimens of their particular climate and use.

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A Straw-bale Home in Idaho – TLS #55

By Bales, Design, Plaster, Roofs, Straw Bale Construction, Walls One Comment

This article originally appeared in TLS #55 and was the feature article in that issue.

house1by 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

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

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.

diningWhen 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

Finishing Bale Walls with Siding – TLS #57

By Bales, Building Science, Design, Plaster, Straw Bale Construction, Technical, Walls, Water 2 Comments

This article appeared in TLS #57.

Loose Strings: Technical Discussions
by Jeff Ruppert – Colorado, USA
T e c h T i p s

A little known fact in the bale building realm is that a handful of people scattered across different continents have experimented with the idea of finishing their bale walls with wood or some type of manufactured siding. The technical term for siding over a bale wall assembly is a “rain screen.” The use of a rain screen (sometimes referred to a “multiple defense assembly”) on a bale wall plays the role of keeping rainwater off of the bale portion of the wall. This is in contrast to the standard way of finishing a bale wall with plaster and allowing moisture to come into contact with it on a regular basis (also referred to as “faceseal” walls). In fact, almost all of the literature to date on bale-wall construction makes the assumption that they are faceseal assemblies.

In this article, we are going to take a look at the pros and cons of in-stalling siding over a bale wall. To some people the idea of not having a plaster finish on a bale house would seem weird, mainly due to aesthetic reasons. However, for those who have chosen to use siding, aesthetics take a backseat to function due to high rates of rainfall throughout the year, as well as constant high humidity. The option of allowing bale walls to even get wet in the first place is not an option and therefore other systems must be considered.

For those of us who live in drier climates, the consideration of moisture is not as dire, therefore giving us more choices. However, doesn’t the siding option make sense if you are concerned about moisture at all? If you would like to design a building with mixed finishes, such as a combination of plaster, masonry and siding, this would open up the opportunity to include bale walls as an option on those projects. In fact, by installing a rain screen over bale walls are we not greatly reducing the potential for moisture damage, as David Eisenberg puts it, by “designing problems out of the project” from the start? We will explore these issues and hopefully offer you another choice in your search for solutions.

Rain Screens
In the old days, a rain screen was simply an exo-barrier that was attached to a building to catch rainwater and shed it before it could hit the structure behind it. The Norwegians titled this approach the “open-jointed barn technique,” since originally it was used in conjunction with the construction of barns1.

With tighter construction and newer forms of finishes, the technology of rain screens has evolved into a science. One of the advantages of using a rain screen on a bale wall is that, no matter
how you do it, it will probably add a significant layer of protection that would otherwise not exist. This assumes that you do not install the siding to accidentally direct water into the wall. The potential exists for this to happen, so just like any other type of finish, pay attention to the details!

Siding over bale walls

Siding over bale walls

No matter what type of wall you build, the driving forces of moisture will be:

  • Air pressure difference (gradient)
  • Gravity
  • Surface tension
  • Capillary action
  • Rain drop momentum.

The dominant force acting on your walls will be the difference in air pressure across the siding itself.  As the wind blusters around your house, there are pockets of less and more pressure ever changing within and around your wall assemblies. The main goal is to minimize any pressure differences so water is not accidentally driven into the wall assembly. By minimizing pressure differences, the main force acting on nearby moisture will then be gravity, drawing water down to the ground where it belongs, before it reaches your bales.

In order to equalize pressure, an air gap behind the cladding (siding) needs to be well ventilated to the atmosphere. This can be achieved through different methods, but whatever you do, make sure not to create a gap for wind to blow rain behind the cladding. This means providing ventilation behind the siding so air can pass through easily, but including a barrier at the points of ventilation to keep wind-driven rain from entering.

The advantages of using a rain screen are:

  • Adds another option for finishing bale walls (aesthetic),
  • Keeps moisture completely off the bale portion of the wall assembly,
  • Provides replaceable/changeable finish,
  • Has low or no maintenance (depending on material),
  • Uses local materials in northern climates near forested areas.

The disadvantages of using a rain screen are:

  • Plaster finish is not an option on a bale wall,
  • May not be as durable as some types of plaster,
  • Materials may not be sustainable or even available in your area,
  • Aesthetic of siding may not match your project.

Rain Screen Concept on Bale Walls

It is important to remember that no matter how we finish bale walls, they must be sealed with plaster. This means that even if we choose to use a rain screen, we must apply at least one coat of plaster. One way to install siding on bale walls is to first install nailers for the siding. These can be in the form of 2-in.x2-in. wood strips attached to the sill plate and beam at the top of your bale wall.
We recommend attaching the nailers before stacking the bales, but you can do it afterwards if you like. Once the nailers and bales are in place, one coat of plaster is applied between the nailers. A rough coat of plaster over the bales is all that is necessary. Little or no troweling is required because no one will ever see the results. After plastering, building paper is stapled to the nailers and the siding is then installed, leaving a gap behind the paper for ventilation and drainage.

One issue of concern with this method is the gaps that can occur between the plaster and nailers as the nailer wood shrinks over time. These gaps can allow air to ?ow in and out of the bale wall, creating a loss of insulating value, as well as a path for insects and/or rodents. Extra care and/or the application of caulk can take care of these gaps. Also, these gaps can be eliminated if the nailers are installed after plaster is applied. Whatever you do, be sure that a gap remains between the back of the siding and the plaster.

This is but one way to install siding on to a bale wall. There are variations to this concept, but the goals remain the same – keeping rainwater and back-splash off your bale walls. Pay attention to the details and remember the forces that are acting on water that comes into contact with your walls. Holding these basic concepts in mind will help you design your wall system. And most important, do your homework first!

Happy wall building!

Resources
1. Rainscreen Cladding: A Guide to Design Principles and Practice.Anderson, J.M. & Gill, J.R. Butterworth-Heinemann, 1988.
www.shildan.com/Rainscreen/History.htmlhttp://irc.nrc-cnrc.gc.ca/pubs/ctus/17_e.htmlwww.greenhomebuilding.com/pdf/RainScreen.pdfwww.cmhc-schl.gc.ca/en/inpr/bude/himu/coedar/loader.cfm?url=/commonspot/security/get?le.cfm&PageID=70139

Ed.Note: Jeff encourages TLS readers to send in questions and comments to The Last Straw. There may be outstanding issues that builders are dealing with that most laypeople may not aware of. There are always many questions from people new to straw-bale construction. With this in mind, this column is offered and intended to encourage everyone to educate themselves to the fullest extent regarding building construction, and we are here to help in any way we can. This forum endeavors to offer the best of our knowledge, with no claim to its completeness, but to the spirit of bale building as a continuing evolution of one form of habitat within the larger realm of natural building. We offer this forum for dialogue, with no implication of being right or wrong. This forum is for you, the learner, artisan and teacher.

Jeff Ruppert, P.E., Principal, Odisea LLC, Ecological Building, Engineering and Consulting, P.O. Box 1505, Paonia CO 81428, 970.948.5744  <[email protected]> www.odiseanet.com
Jeff has been in the construction trades for over 25 years, beginning as a laborer and draftsman on his father’s construction projects. He has spent many years working on construction projects he designs, and is a licensed engineer in Colorado.

Newsflash! Straw-bale Infill Meets U.S. Building Codes – TLS #54

By Building Science, Community, Design, Straw Bale Construction, Technical, Uncategorized No Comments

codes1This article originally appeared in Issue #54.  This issue includes a table of straw-bale building codes, guidelines and mandates in the U.S., and links to straw-bale codes, guidelines and supporting documentation; and an extensive review of the status of straw-bale codes and permitting throughout the world.

by Sigi Koko – Pennsylvania, USA

The bottom line is that yes, using straw bales for non-loadbearing infill walls meets existing building codes for both residential and commercial structures throughout the United States. Why is this true? Because building codes are not written to exclude new or alternative construction materials and methods. Rather, each building code begins with an inclusive statement such as the following from the CABO 95 Preface:

“…there are construction materials and practices other than listed in this code which are adequate for the purposes intended. These other methods represent either seldom-used systems or performance-type systems which require individual consideration by the professional architect or engineer based on either test data or engineering analysis and are therefore not included herein.”

The intent of building codes to ensure that materials are used safely and suitably, not to limit the use of appropriate materials. The burden of proof is to demonstrate that an alternative construction method meets the intent of the building code for durability, effectiveness, and safety (including fire resistance). This means showing how straw-bale infill wall systems meet the requirements of the building code for insulation value, flame spread, smoke development rating, and fire rating. Demonstrating compliance with the building codes is possible thanks to many pioneers that have dedicated time and money to sponsor third-party ASTM (American Society for Testing and Materials) tests. The results of these tests show that straw-bale wall systems not only meet the building code but, in most cases, surpass the intent of the code compared to standard stud-and-drywall construction.

Several states and counties throughout the U.S. have adopted building code amendments that specifically address straw-bale construction, though most regions do not yet include such provisions. Obtaining a building permit for straw-bale infill in regions without a specific building code is not impossible, but rather entails a non-standard process. The question is not whether you can get a building permit for infill strawbale, but rather how to best communicate with local building officials that strawbale is a viable method of construction that meets the existing building code.

David Eisenberg has written extensively and with great eloquence about how to communicate effectively with building officials, and I encourage anyone wanting more detailed information to review his writings on the topic. I have used the following strategy with success:

1) Schedule a pre-submittal meeting with the permitting official to communicate your intentions to build with strawbale. If they are not already familiar with straw-bale construction, provide printed information and additional resources. (Don’t overload with information unless it is requested; like all busy people, building officials are less likely to review a daunting pile.) Bring to the pre-submittal meeting:

• drawings of the proposed building

• an overview of straw-bale construction (I use “House of Straw: Straw Bale Construction Comes of Age” by the US Department of Energy, available at www.eere.energy.gov)

• copies of ASTM testing data (fire-related ASTM tests are at www.dcat.net)

For the final permit submittal, my experience is that stamped structural drawings greatly facilitate the speed and ease of the permitting process.

2) Remember that your building official is your ally not your adversary, and has the same goal as you: to ensure that what gets built is safely built.Acknowledge your common interest for occupant well being and safety. You will create connection instead of confrontation and open a dialog on how to achieve your common goal.

3) Be informed or hire an advocate that has experience in straw-bale construction, including how to build appropriately in your climate. The building officials will generally have more confidence in your project when they know someone on your team fully understands this non-standard construction technique. At a minimum, be prepared for the following common questions:

  • How does your wall system handle liquid water and vapor?
  • What is the fire rating and smoke development rating of the wall system?
  • Will the straw bales attract pests, such as termites and rodents?
  • What is the insulating value of strawbale?
  • How is electrical and plumbing installed?

I have to date not experienced any delays during the permitting process using this method of interaction with building officials. Increasingly, I find that building officials already possess some level of knowledge about straw-bale construction, which was not the case in this region of the country (Mid-Atlantic states) even five years ago.

Finally, I would like to address the issue of adopting existing codes and details in different climates. I design structures in a wet, humid climate with hot summers and cold winters. However, many of the now-standard straw-bale details have mostly developed in arid and temperate climates that are not necessarily durable in this mixed climate. For example, I do not recommend using rebar inside a straw-bale wall in a humid climate, since the cold metal creates an artificial dew point inside the straw wall. The result is elevated moisture around the rebar, which can lead to rotting the straw over time. Instead, I recommend external pinning or using materials that are “warm,” such as bamboo. Similarly, pea gravel at the base creates an artificial dew point, as well as creating a thermal break along the entire base of the wall. My point is not that the originally developed details are inadequate, but rather that they are specific to an arid climate. So when adopting codes and details in different regions with different climatic concerns, ensure that what you propose will perform durably in your climate.

Sigi Koko, the founding principal of Down to Earth, a design and consulting firm specializing in natural building, has obtained construction permits for many straw-bale buildings in her area. With a Masters of Architecture and several years of in-the-field construction experience, she has developed written specifications and architectural details for straw-bale and cob construction. www.buildnaturally.com

Siberia 2008 (Altai Project, Builders Without Borders)

By Bales, Community, Design, Plaster, Straw Bale Construction, Walls 2 Comments

This is original content and has not appeared in the printed version of The Last Straw.

In mid August of 2008 we saw ourselves back on the plane to Siberia.  This was our second trip as a group of builders and teachers to this far-away and exotic place we now consider our most remote home away from home.  Paul Koppana (Crestone, CO), Cindy Smith (Durango, CO) and myself, Jeff Ruppert (Paonia, CO) were much more comfortable this time traveling half-way around the globe having made a trip for the same reasons back in the summer of 2005.  We were to teach and transfer our knowledge and skills building a straw bale structure to a group of eager folks near the city of Barnaul.  While the goals were similar, the region and our sponsors the same (The Altai Project, Builders Without Borders) , the exact location and the participants for this year were very different.  We looked forward to meeting everyone and seeing some old faces from our previous trip.  This is the story of our time in Southern Siberia in 2008.

Bale Walls with Clay Clip

Bale Walls with Clay Slip

img_0374

Model of the Building

We departed from Denver International Airport on August 16th and flew to Atlanta where we boarded a flight straight to Moscow.  We were greeted at the airport by our Czech cohort and friend Jakub Wihan (Kuba) who speaks enough Russian to translate for us.  Kuba was present on our 2005 trip and was now playing multiple roles.  Not only was he going to be teaching his skills of wall building but he was to also translate for us when he could with his limited Russian.  In 2005 we were escorted by our leader, Alyson Ewald of the Altai Project, who organized and raised the funds for our travel.  While she was still in the capacity of the two latter roles, she was raising a newborn back home in Missouri on Red Earth Farms.  We missed her on this trip but new she was doing something much more important.

We landed in Moscow on August 17, met Kuba and made our way into the city for a long wait (12 hours) until our flight to Siberia.  The temperature was nearly 100 degrees (F) and the humidity was hovering around 90%.  We ate food, exchanged money and slept on the floor of the airport as jet lag caught up to us despite our best efforts to remain alert.  Kuba was fresh from his travel from England so he remained awake while we caught some much needed sleep.  We boarded our flight around 11p on Aug 17 and attempted to sleep during the five hour flight through three time zones to the east.  We landed around 6a on August 18 very tired and happy to see our Altai friend and hosts.

Sill Plates with Coal Slag Insulation

Sill Plates with Coal Slag Insulation

While the region and some of the folks were familiar to us, the project for this trip was different than 2005.  We were asked to help build a gallery/conference building with attached office and kitchen space for the Institute of Architecture and Design in Barnaul on their “Dacha” land which is directly south of Barnaul about 20 kilometers as the crow flies.  The building was designed by the architecture students over the past couple years as an ongoing project within their curriculum.  The result was a beautiful building using straw bale walls that stood about 14 feet tall.  The design of the building incorporated large overhangs and wrap around porches to protect the walls from the harsh winter conditions of Siberia.  To say that we were impressed with the design would be an understatement.  We thought it was magnificent, but we had doubts as to our ability to tackle all of the work needed for the walls, and then have a roof installed.  Our Siberian friends would astound us with their abilities and hard work, but more of that later.

After landing in Barnaul we spent the next few days attending and participating in a seminar for many of the Institute’s important administrators and local officials, we traveled into Barnaul for an art exhibit by one of the students who was also one of our translators, and we visited family of one of the professors and ate dinner.  We spent these days talking with Lena and Sergei, our main hosts and the Deans of the Institute directing the project, about building details and what materials we would need.  There were already bales on the site and the foundation was freshly poured.  There was no wood for the frame, nor any mesh or clay for plaster.  Cindy and Kuba immediately began looking for a source of clay which would prove to be a long and difficult task.

Our first step was to have the carpenters install the sill plates.  These turned out to be 6×6 timbers that were nailed into the foundation with blocking every several feet.  The spaces between the sills were filled with coal slag, which it seems is commonly used as an insulating material in Siberia.  On Aug 21 we built the first post as an example for the carpenters, which they copied many times to creating all of the window and door bucks, as well as corner framing.  The top plate was to be flat 2x material layered with joints staggered at post locations.

Bale Stacking

Bale Stacking

By the 23rd of August the posts were installed and braced around the main gathering space.  We were pressed by our hosts to teach a “workshop” and educate everyone in bale-stacking.  Paul and I described how stacking bales worked and showed them how to re-tie a bale.  The bales were of marginal quality so treating them delicately was very important.  The eager participants soon took over and were stacking away.  Within an hour three walls were substantially complete and we made everyone stop due to the questionable weather approaching.  We needed to cover our work before it was soaked by rain.  The carpenters also needed to construct the top-plate assembly so the top bales could be installed.

All of the bales on the main room were installed by the 25th and we began using plastic lath, or mesh, to reinforce the joints between straw and wood.  Without a stapler, we attached the mesh to the wood with nails bent over and we had some of the students make pins out of wire for attaching the lath to the bales.  Much of this work was loose by the time we began plastering, but it was still good to have it held in-place with something.  By this time, no clay had been found despite a few forays by Kuba and Cindy into the neighboring countryside.  It seems that any people with a pit of clay did not want to share it.  We were in an ancient floodplain where the river had deposited silt and sand, but left little clay exposed that was available for use. It seemed very frustrating as loads of “clay” would show up that was not suitable as a plaster material.  Cindy was becoming frustrated and unable to find a solution.

By the 27th clay arrived as Cindy and Kuba had found a source.  It was good quality so Cindy had the volunteers begin applying a clay slip to the walls while others prepared cob to stuff into voids.  The work was fun and we could finally see the project happening.  Our hosts, however, had bigger plans.  We were asked our opinions about how far we could go during our three week visit.  We were scheduled to leave on the 31st which was less than a week away.  We strongly encourage our hosts to focus on the main structure and get a roof installed before attempting any more new walls.  They charmingly went ahead with their plan of having the lower walls framed, bales stacked and the shed roof framed.  At this point a group of twenty or so students showed up to work for a few days.  The results were nothing short of miraculous.  Where we thought they were flirting with disaster, they used all of the skills we taught them and managed to not only frame and stack the lower walls, but plaster them with two coats of plaster before we left.  We were amazed!

Having witnessed how slow things can go in Russia, we could not believe the motivation that was instilled by our hosts in their students and other volunteers.  Not only were they dealing with the workshop, but they had a budget that was running out and needed to be refunded by the Institute.  If they failed to meet certain deadlines the building would not be finished.  We watched Lena and Sergei expertly navigate a sea of regulators, engineers, administrators and volunteers, all the while smiling as we appraoched never missing an opportunity to treat us like family.  The experience was humbling to say the least.

Students and Volunteers

Students and Volunteers

As the clay slip was applied to the building, we asked about electrical wiring.  No electrician had been hired and we were getting ready to seal the walls.  I created an electrical plan with Lena and some students, some wire was produced along with boxes.  The boxes were nailed to posts and lathed in-place.  Wiring was run up the posts through the top plate where all wiring would be figured out later.  We decided on the location of the electrical panel so I could plan where runs would be made later.  It was another last-minute detail, but we were able to do what we needed before it was too late.

Most of the plaster was mixed by hand due to a malfunctioning mixer.  We limped the mixer along until it was completely dead and then had the students team up in groups to make plaster.  They were able to keep up well with the dozens of people applying it.  By the time we left, a slip coat and one coat of plaster had been applied to the entire building.  Plastic tarps were used to protect the tops of the walls and drape over the rafters of the lower roof.  We held our breaths praying for dry weather.  We had seen rain on and off most of our visit, but not in large quantities.  All we could do was hope for the good fortunes of our amazing friends to continue.

We received pictures of the final building just before Christmas.  The building has been completed!  They have lime-washed the earthen plaster and installed siding where needed.  The roof is on and the interior is finished.  There are two truth windows that are the largest we have ever seen.  They didn’t seem to be swayed by opinions such as “the plaster is a rigid part of this structure.  Leaving it off large expanses of wall may not be desirable,” or “If bugs and rodents do get inside your walls, it will be like a movie theater for visitors.”  The desire of these folks to push their limits gave us pause at times and we are impressed by their resolve in the face of possible disaster.

Clay Delivery

Clay Delivery

Lessons were learned about working with the locals even if it meant doing something in the wrong order or what seemed to be the wrong way to us.  They have their ways of doing things and even though we thought we could help them, there was great resistance to our ideas at times.  Stepping back and letting the owners of the project remain in control no matter what was happening seemed to give them a sense of determination that would not be derailed.  It turns out that they did not ignore or resist our ideas as we had thought.  They listened and integrated them into their program in the best way they could.  What became clear to me was that we were working with formally trained architects and students of the classical ways of architecture.  They paid attention to details and form.  On this project the function drove their form more than what seemed typical.

Finished Building

Finished Building

This building took all of the lessons they were taught about bale buildings and integrated them in a very functional way.  They used large overhangs.  There was not a single bale wall over 2 feet in height that was not protected by a wrap-around porch.  They used earthen plasters even in their extreme climate where temperatures reach -50 degrees (F).  They finished the plasters with a lime wash that will be easily maintained over time.  They installed two huge masonry fireplaces as thermal mass.  There is almost no solar gain due to the dense forest so they reduced glazing on all walls to what was necessary and functional.

Truth Window

Truth Window

We left Krona on August 30 after a quick award ceremony where everyone received some thank you certificate and a book on the design of straw bale houses – a first of it’s kind in Russia.  Our next stop was the old building that we helped build back in 2005.  That project was 6 hours south by car so we kicked back as best we could in the smallest car we could imagine and rested until we arrived in the heart of the Altai Republic and back in Chemal at The Milky Way.  We were interviewed by a video production group and welcomed generously by our previous hosts.  They had erected a handful of wood-framed cabins for guests and used the bale building as a tourist attraction and gathering space.  The plaster is holding up much better than we thought.  It is also earthen with a lime wash.

The 2005 Project near Chemal

The 2005 Project near Chemal

On Sept 3 we were in Barnaul and boarding a plane back to Moscow and then onto Colorado.  It was another magical trip and one that was more successful than any of us thought possible.  The memories of bania (sauna) with friends every other night, meeting the families of our Siberian friends, working alongside our gracious hosts Lena and Sergei, and dancing around the campfire with all the volunteers who showed up for two weeks to help us and learn how to build with bales made for a deeply rich experience.  We look forward to seeing everyone again some day and to visit those two important projects that brought straw bale construction to the Altai region of Siberia.

We would like to thank the following organizations for their contributions and hard work:

The Altai Project
http://altaiproject.org

Trust for Mutual Understanding
http://www.tmuny.org

Builders Without Borders
http://builderswithoutborders.org

Institute of Architecture and Design in Barnaul

Fund for 21st Century Altai

Sustainable Living in California – TLS #59

By Bales, Design, Walls No Comments

This article appeared in TLS #59.

semmes1Turko Semmes is a licensed general contractor from San Luis Obispo County, California, and one of the foremost experts in straw-bale building techniques.

semmes2A 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.

semmes4The 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.

semmes5Turko Semmes, Semmes & Co. Builders, Inc., Atascadero CA
<[email protected]> www.semmesco.com
semmes3Photo credits: Semmes & Co. Builders, Inc.

 

 

 

Better Quality, Ecological Correctness through Sustainable Design – TLS #59

By Bales, Community, Design, Fire, Uncategorized, Water No Comments

This article appeared in TLS #59.

by Ken Haggard and Polly Cooper – California, USA

Adopted from an article that appeared in Home Power Magazine.

Straw-bale cottage during construction.

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.

cottage2

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 built 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

interiorThe 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, powered by 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

exteriorOne 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 <[email protected]> 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.

Straw-bale Sound Isolation and Acoustics – TLS #53

By Building Science, Design, Sound, Straw Bale Construction, Technical, Walls One Comment

This article appeared in TLS #53.  The topic of this issue is Moisture.  It contains an extensive article about Moisture Basics and Straw-Bale Moisture Basics (by John Straube, edited by Bruce King)  it also includes articles on moisture meter accuracy, moisture sensors, seismic resistance, and plaster testing.

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

table1The 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.)

table2In 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.

<[email protected]>

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).

House of Straw? – Reprint from TLS #57

By Bales, Design, Straw Bale Construction 2 Comments

 

build-our-house-out-of-straw2Build our house out of straw?

by Stephen MacDonald – New Mexico, USA

This article appeared in The Baley Pulpit,TLS#7/Summer 1994.

“May we look upon our Treasures, and the furniture of our Houses, and the Garments in which we array ourselves, and try whether the seeds of war have any nourishment in these possessions, or not.”

– from the Journal of John Woolman an 18th Century Quaker

“Build our house out of straw?” When our neighbor suggested the idea as a solution to our housing problem, both my wife, Nena, and I reacted similarly. “You must be kidding!” Even when he showed us a copy of Fine Homebuilding with an article in it by Gary Strang (1985) on a studio built out of straw bales, we were dubious. It was just too weird (images of rotting hay, mouse hotels, and pig stories readily came to mind). The idea was too simple and straightforward to be believed.

Try as we might, however, we kept returning to the idea of it. It did seem to fit our condition: Using straw bales was 1) low cost…we were near broke, having used the last of our meager savings to buy a small piece of land; 2) a way to stay cool (and warm)…having just moved to southwest New Mexico from Alaska, I was scared to death of the heat; 3) fast and physically easy to build…I just couldn’t face the slow, heavy work of adobe; and 4) ecologically sound…besides being energy efficient, a straw-bale building uses a renewable resource (often viewed as a waste product) that was locally available. Done right, building with straw uses very few trees.

In the end, we decided to go for it. Seven years later, we have no regrets. Just the opposite. We didn’t know it at the time, we were not the only ones interested. Through Strang’s article and newly formed friendships with Susan Mullen, a permaculturist and close neighbor, and an enthusiastic Matts Myhrman in Arizona, we learned of a small but dedicated network of straw-bale aficionados. Nor were any of us particularly innovative. The true trailblazers of straw were the folks from the Sandhills of Nebraska who, out of necessity, started a tradition of building their homes out of native hay and straw beginning back in the late 1800s and continuing up through the early 1940s.

The work of the Nebraska homesteaders remains the key. It took a fact-finding journey to Nebraska in 1989 by Matts and Judy Knox, his wife, to finally convince us that we, like most of those early Nebraskan straw-bale builders, could further simplify our technologies by using straw bales as load-bearing walls without the time and expense of poles or posts. We modern practitioners of straw have come to call it building “Nebraska style.”

It is this style of building that has captivated my imagination and been the thrust of our most recent building endeavors. Much good work needs to be done to revitalize the straw-bale building tradition and get it accepted into common practice. Tackling the building codes is part of that work along with trying (and sharing through The Last Straw) new and innovative techniques. I have no doubt in my mind that sooner, rather than later, this Earth will demand it of us.

 

 

Nena in front of the MacDonald’s straw-bale home.

Nena in front of the MacDonald’s straw-bale home.

Meanwhile, here are some of this straw-bale builder’s rules of thumb.

I. Keep it small. How much space do you really need? Be honest. Be creative with your space. Small is easy to heat and keep cool. It’s easier to keep clean. It takes up fewer of the earth’s resources and takes up less of its space. You finish the job, at a lower cost, so you can devote money and energy to more useful work. If your teenagers need distance, have them build their own outbuilding or addition. They need to learn the skills, anyway.

2. Keep it simple. Control your impulses to make your house a complicated, “artsy” statement. Simple, small and rectangular houses are beautiful when made of straw and other natural materials. Let form follow function. Again, spend all the time and money you saved by being – out in the woods, feeding the poor, or playing with your children.

3. Build it yourself. Trust yourself. You can do it, especially if you build with straw…and especially if you follow rules 1 and 2. Read building books and magazines.

Ask questions of builders. Build it on paper and as a model first. Track the details. Use your common sense. Be creative with your mistakes. Don’t be intimidated by the “experts.”

4. Stay out of debt. Pay as you go. Assemble the parts as you have the money and time.

5. Use local materials. Use more rock and adobe. Use locally milled lumber and poles. Your neighbor needs the work and you need to know firsthand what demands you’re asking of the forests and the fields.

6. Be energy conscious. Build to maximize passive heating/cooling strategies. Superinsulate your ceiling. Stay off the electric power grid if you can. Put up a windmill or use a solar pump. Build a composting toilet. Raise a garden.

7. Make yourself a home. Don’t just build a house, make yourself a home. Learn to be at home. Do no harm.

6 June 2005 Update

It is hard to believe that 18 years have somehow flowed by since Nena and I first built our little house of straw here in rural New Mexico. Two kids fledged, one now married and making his way at the edge of the Adirondacks in New York, the other just back in the United States after months of solo travel through Europe and western Russia.

Our little house continues to do well. We finally added a small greenhouse to the southwest corner of the place, and several years ago built a really first-class outhouse off the shop. I keep meaning to replace the salvaged (and very inefficient) casement windows we have, and one of these days I’m going to get around to finally plastering the outside of my Nebraska-style office/former teenage daughter ‘cabin.’ “Margosh, margosh” as my Mongolian friends would so often say – tomorrow, tomorrow.

Stephen MacDonald lives with wife Nena, son Orien (and co-author with his father of A Straw-Bale Primer), and daughter Aili, in their owner-built houses of straw in Gila, New Mexico. Steve and Nena live their Quaker faith in numerous ways including active participation in The Friends of the Gila River, working to create a cooperative ecosystem-based Gila River Ripiarian Management Plan with all stakeholders. Steve returns to Alaska each summer to continue biology mammology field work in the bush, and touch base with his northern home for over 14 years in the 1970s to early 80s… and stay cool.

“Somehow Nena and I have survived our various mid-life crises, finding new balance as we age and continue along our now 32-year journey together. I am still very much engaged with my work on far northern mammals (now through the Museum of Southwestern Biology), while Nena, having let her nursing license lapse, spends her days here at home.”

[Guest Editor’s Note. Stephen and Nena’s small straw-bale house has been an inspiration to many. It still inspires because it so effectively embodies the basic principles Stephen outlined of what a home should be a nice place to live in.]

Post Editing Note: If this information is valuable to you, there is much, much more in the published, official version of The Last Straw.  Please subscribe at The Last Straw online.

Panel-built Classroom in Northern Arizona

By Bales, Design, Products, Walls No Comments

This article originally appeared in TLS #49.  Articles on straw-bale wall panel systems are included in issues #30, #42, #47, #48, #55.

panels1-300x224by Matt Robinson – Arizona, USA

Northen Arizona provides an ideal climate in which to build with straw bales and has been the site of many such structures since the 1990s. Ed Dunn has been the principal designer and builder of straw-bale homes here for over a decade. In May‘04, Western Strawbale Builders (WSB) was formed by Jason Radosevich and Matt Robinson, former crew members of Ed Dunn. The focus of WSB is to increase the scope of straw-bale building to include affordable housing as well as top-of-the-line custom housing.

With affordability in mind, systems using prefab panels seem to us the most promising avenue of approach to building with straw bales. In order to spare you the well covered details of this method of building, you can reference several articles published by TLS including: Chris Magwood in TLS#42, Canada Guy TLS#47, and Brett KenCairn in TLS#48.

Western Strawbale Builders was able to show off our skills in a project this past Fall here in Northern AZ. Designed and overseen by Ed Dunn, this project was an additional building done for The Star School, an off-grid solar-powered charter school on the borders of the Navajo Reservation in Coconino County. Star School teaches middle school students subjects, including permaculture, cultural awareness, and sustainability. Proprietors Mark and Kate Sorrenson therefore wanted to build a structure that reflected these values while fitting into their budget.

Ed Dunn designed this structure to utilize passive solar principles, trombe walls and a greywater planter. It is to be used as a combination classroom, performance hall, and wrestling gym, as well as any other creative uses Mark and Kate come up with.

We decided to hold the bid on this project to the regular bid price for stick-framed structures in our area to see how well we could compete. To our mild shock and great relief, we were able to build to these numbers and still afford our business a modest profit. With a four-man crew including ourselves and the exceptional abilities of carpenters Alden Catherman and Phil Mason, the class room was completed in eight workweeks, beginning to end.

We feel that this project, although relatively simple in scale and design, can serve as an example of an affordable option for people who love the idea and feel of straw-built houses. Hopefully this structure and others like it will help in bringing straw-bale houses into the mainstream.

Matt Robinson and Jason Radosevich own and operate Western Strawbale Builders in Flagstaff, AZ. Contact: or westernstrawbale.com

Where to Draw the Line – TLS #50

By Bales, Design, Technical No Comments

This article appeared in TLS #50.

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

table3We 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

graph

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, <[email protected]> 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.