Design of Straw Bale Buildings Introduction

INTRODUCTION

The oldest known straw bale structure in the world reached the century mark in 2003, an anniversary of both sentimental and technological significance. The historic Burke house in the little town of Alliance, Nebraska (United States) would not necessarily catch your eye as an architectural wonder, or even oddity, yet its presence there is intimately connected to the book in your hands. Had that modest little home and many like it not survived to this day, then straw bale construction might never have caught the skeptical interest of a few builders, this book’s authors, or the public at large.

Those first straw bale structures in the Sand Hills of Nebraska were built by European settlers entering the area from the 1800s onwards. Having few other means to shelter themselves, they were driven by necessity to improvise; there was little stone or cement, the sod was often too sandy to cut or too valuable as cropland, and most of the available lumber was what little had come on their wagons. Using the newly invented horse-powered baling machines, they bundled the grasses that surrounded them, stacked the bales to form walls, and applied mud plasters inside and out. Many of those homes still exist in good shape, as do a few more in other parts of the world where baling machines had appeared over the subsequent decades. This was the birth of a promising and completely new building technology, yet with roots in various historic forms of earth and straw-based construction that were widespread in Europe. Nonetheless, as the Industrial Revolution spread in the form of railroads and modern building materials, interest in straw bale construction faded.

In the 1980s the American West witnessed a revival, initially sporadic, generated by some obscure published articles and the scattered efforts of a few architects and owner-builders. In 1989, some of those latter-day pioneers gathered in Oracle, Arizona to play, collaborate, and imagine how best to build with bales; a few newspaper articles followed, interest blossomed, and the straw bale revival suddenly was and still is exploding in size. As more architects, engineers, inventors, and builders began to try this new material, a variety of styles and techniques began to emerge. There are now straw bale health clinics in Mongolia and China, wineries in Australia and California, a prince’s palace in Saudi Arabia, a post office in New Mexico, a Buddhist monastery in New York, retail stores, schools, police stations and high-end luxury homes in California, and thousands of houses of every style all over the world. Field experience and laboratory experiments have taught some basic lessons that will be articulated in this book, but straw bale construction remains very much a developing technology. As is the case with any building material, there is no “right way” to build independent of climate and rainfall, soils and earthquake hazard, building usage, and architectural style. There are many right ways to build with straw bales – and many wrong ways. Many bale building techniques, first rediscovered almost entirely from a short article by Roger Welsch published in the book Shelter(1), were inherited from the first Nebraska settlers. Steel or wood pins driven down through the bales to stabilize them, for example, were codified in the first modern straw bale guidelines. But “pinning” is no longer thought to contribute strength or be worth the trouble, and has been largely abandoned. In any event, publicity fueled popularity, and to this day public interest worldwide has stayed well ahead of engineering knowledge about straw bale structures.

The explosive rise in interest has resulted in thousands of built straw bale structures throughout the globe, and a small and increasing number of books on the subject. (For more general discussions of straw bale construction, and access to a wealth of photographic images, see the Resources section at the end of the book.) To date, however, there have been relatively few resources to help architects and engineers design straw bale structures to endure the driving rain, humidity, extremes of hot and cold, fire, wind, and earthquakes that routinely cause the early demise of buildings of all types around the world. In responding to the question “How will this building perform?” we have relied mostly on intuition and anecdotal evidence.

Now, with the completion of many tests in recent years, we have a much clearer picture of how straw bale buildings behave under the normal range of stresses that affect structures. This book is a review of all those tests and of the anecdotal knowledge gained over a hundred years (particularly the last fifteen). It is also a studied effort to digest and present that knowledge in a way that can be of practical use. This is architecture and construction at its most elemental: we try things out, we make mistakes, we learn, we adapt, and we thus build our knowledge of how to build. It may be that an architectural straw bale vocabulary will emerge as our understanding of the material evolves – just as it did with stone, wood, structural steel, and reinforced concrete – and the intent of this book is to lay down a rational foundation on which to develop the architecture of straw bales.

Context

The re-emergence of straw bale construction over the past fifteen years has occurred within a particularly hospitable environment, in the United States and around the world. Green building in general has become a commonplace term, referring to the design, construction, and maintenance of buildings that are careful in the use of material, human, and energy resources to create shelter, with great regard given to protecting not only the building occupants but also the local and global system of life from which those resources are drawn. Green building means building with the welfare of future generations, not just this one, and not just human, in mind. Straw bale construction, by virtue of being unusual and photogenic – and thus the star of innumerable media pieces – has been the introduction for quite a few people to the wider concerns of green building for healthy interior environments, energy efficiency, and waste reduction. It is also a classic example of what has been dubbed Industrial Ecology, i.e., the idea that one industry’s waste can be another’s feedstock. What the farmer throws away, the builder turns into warm, durable houses.

The Internet has also been key to the growth of straw bale construction, as the sudden ubiquity of Web access has made it astonishingly easy for the nascent straw bale community – for lack of a better word for a very loose-knit worldwide group of inventors, builders, scientists, architects, and engineers – to communicate, collaborate, and learn from mistakes. And, as straw bale construction remains almost completely in the public domain, there is little protection of secrets or glossing- over of mistakes. Quite in contrast with other building technologies that are jealously guarded, the non-proprietary nature of straw bale building – with a few exceptions – has kept innovation, refinement, and failures out in the open for all to learn from.

Finally, it bears mentioning that straw bale construction is perhaps the most visible part of a revival of interest in “natural” building, generally understood to mean use of minimally-processed materials with roots in historic or indigenous (i.e., pre- Industrial Revolution) ways of building. Before fossil-fueled engines enabled us to move any material anywhere in the world, and to make building materials themselves from oil, we had to build with what was at hand. The extraordinary range of styles and material uses that evolved over the centuries is being rediscovered for the ingenuity and experience that went into them. (See, for example, Built by Hand(2).) What are routinely derided as “mud huts” and “grass shacks” often, if not always, turn out to be very effective means of shelter (as architectural conservators the world over already know). The adobe buildings of the American Southwest, the lime-plastered timber-frame houses of medieval Europe, and the Roman concrete monuments, to choose just three examples, have all proven themselves to be in many ways superior to the “modern” structures that now surround them. Thus, building professionals who have taken an interest in straw bale construction have been startled to discover that there is so much to be learned from the old ways – that we have very nearly thrown out the baby with the bathwater in abandoning everything old in favor of anything new. Perhaps the preeminent example is what we’ve learned about the interrelationship of moisture and buildings. We invented plastic sheeting and then figured we could shrink-wrap our buildings to keep all the water out – and ended up trapping it in and getting great mounds of mold. Ditto with cement plaster, which has been applied to ill effect over historic earthen buildings around the world, and which can cause – and hide – moisture degradation in wood-framed walls. Slowly we’re re-learning what our ancestors had always understood: buildings get wet no matter what you do, so in your design and construction, always provide a means for them to dry out. In the case of straw bale construction, for example, this knowledge of the old ways has led to favoring vapor-permeable earthen and lime plasters over more brittle cement-based plasters, while utilizing modern steel or plastic reinforcing meshes and fasteners to deal with earthquake forces.

This is not to suggest an anti-technology or neo-Luddite view of building so much as to point out that, as with all other domains of life, it’s worth knowing a bit of history. The most effective way of building any particular project employs not so much primitive or modern, but appropriate technology. ( John F.C. Turner best defined this by saying, “Truly appropriate technology is technology that ordinary people can use for their own benefit and the benefit of their community that doesn’t make them dependent on systems over which they have no control.”) As the easy availability of fossil fuels decreases with the attendant rise in fuel costs, there will inevitably be a trend towards building with what is near at hand. We won’t return to “mud huts” and “grass shacks”; we’ll simply learn to be smarter in the way we build, and we’ll eliminate the very concept of waste.

Systems thinking – no material is an island

This book may be unusual just for advancing our engineering perspective on a hitherto obscure building material: straw bales. It is also somewhat unusual for addressing several engineering properties under one cover, i.e., structure, moisture, durability, fire, and thermal insulation. This is reflective of the fact that a plastered straw bale assembly is structure, insulation, air barrier, finish, and fire resistance all in one – as opposed to most building materials, which typically perform only one or two of the requisite functions of a building enclosure.

The book is also organized to reflect an emerging development in the way buildings are thought about and designed. The past several decades have seen increasing specialization in the architecture and engineering professions, spawned in large part by rapidly increasing proliferation of and knowledge about building methods and materials. A moderately large or complex project may have design architects, project architects, landscape architects, construction administrators, disability access specialists, lighting and energy consultants, interior designers, and engineers of every stripe: structural, mechanical, electrical, civil, acoustical, etc. Each specialist addresses his or her own aspect of the design, theoretically under the watchful, knowledgeable, capable, and all-seeing eye of the project architect. Sometimes the system works; sometimes it doesn’t. This is not said as a criticism of architects so much as to point out that without some form of capable and holistic overview, on the designed building may not function as intended, or even fail outright. Those who design with straw bales are generally aware of this, and thus have discovered and embraced both collaborative design – working and communicating as a team from start to finish – as well as the emerging body of knowledge known as building science, which comprehensively considers the effects of temperature, moisture, vapor, air flow, and structural stresses – along with aesthetics – in designing a building enclosure or detail. You get the big picture, or you get problems: good design is important, yes, but a pretty house that cracks, leaks and rots is no longer pretty.

This is intended to serve as an engineering guidebook. It has been written as much as possible to be accessible to any building professional, or even layman, but will inevitably have sections that are obscure without an engineering background. Nevertheless, in contrast with many other engineering texts, no problem-and answer sections are provided. More importantly, the book offers few cookbook formulas that might delude the reader into a false sense of design confidence. It is simply not yet possible to comprehensively delineate a prescriptive way of designing or building with straw bales, if in fact it really is with any building material. The technology, as mentioned, is still rapidly developing, so we have focused on identifying rules where they have become clear (“Keep those bales dry!”). Otherwise our aim is to present underlying principles by which the reader can work out site-specific building challenges. Common sense, and a knowledge of local culture and climate, have always been and will continue to be the overarching guidelines for any building designer.

In the hundred years since straw bale building was first pioneered, the basic technique has remained as straightforward as stacking the bales and plastering both sides. Our knowledge of the material properties of these walls has blossomed in tandem with the extraordinary revival of the past fifteen years, and we now are now equipped, at least roughly, to design for any conditions. That there are enormous environmental and energy-conserving benefits to straw bale construction is now without question, so any strategy to move the construction industry towards a sustainable course must allow for and encourage this intriguing new building technology. This text offers to designers and builders a sound scientific and common-sense basis for exploring and contributing to the development of plastered straw bale architecture.

	The First Permitted Earth-Plastered House in California (with Lime Plaster Finish) Design by Kelly Lerner and Pete Gang photo courtesy of Kelly Lerner

Endnotes
1
Welsch, Roger 1973. Shelter Shelter Publications, Inc, Bolinas, California

2
Steen, Bill and Athena, and Eiko and Yoshio Komatsu, 2003. Built by Hand Gibbs-Smith Publishers, Layton, Utah