Bale Construction

If you’re reading this in a house or smallish building in the United States, chances are the walls around you are built with a frame of wooden sticks. At some point early in the process of designing the building, a decision was made to use wood framed construction - a decision of profound consequence - but one that was likely made with little consideration. The choice of a building’s wall system is fundamental insofar as it dictates the need for numerous additional materials and sets limits on the building’s potential long term quality and performance across a range of measures. The choice of wall system has a major influence on the building's overall economic and environmental costs, both at the time of construction and over the many decades of its useful life. It is surprising, therefore, that wood framed construction, despite a long list of flaws and drawbacks, remains, overwhelmingly, the default system for millions of projects every year.

At the center of a wood framed wall is a row of vertical sticks we call studs, usually 2x6 boards spaced sixteen inches apart. To create a useful wall from this row of studs, we attach several layers of additional materials, each selected to provide some aspect of safety and shelter. The walls need to be strong, to resist both the gravity loads of the roof above and the horizontal forces of wind and earthquakes. For this, we add countless larger pieces of lumber and steel brackets alongside the studs, and then clad the exterior face with sheets of glued-up plywood. To insulate the interior from temperature swings outside - we stuff the spaces between the studs with insulation - often made of fiberglass or petroleum-based foams. The walls need to protect us from wind and rain; for this we wrap the exterior plywood with layers of synthetic fabrics, engineered to be both water resistant and breathable. These fabrics alone, however, are not durable nor sightly, so we cover them with any variety of siding materials and paints - often more wood, synthetic cement boards, stucco or vinyl products.

On the interior side of the wall, we cover the studs and insulation with finish panels - often gypsum wallboard (sheetrock) and coat that with layers of plaster and paint. Depending on the climate you’re building in, we’ll often need to add a plastic sheet within the wall to prevent water vapor from moving through the wall (driven by differences in humidity and temperature on either side of the wall) and condensing on a cold surface where it can become liquid water and, through mold and rot, wreak havoc on the wood construction.

And finally, the basic arrangement of spaced-apart sticks of wood framed construction is particularly well suited to burn. To mitigate the inherent fire risk, many of the materials used in the assembly must be treated with chemical fire retardants. These treatments, along with myriad chemicals used in the manufacturing and finishing of our building materials off-gas toxic vapors and harmful contaminants into the indoor air, in some instances for years after the building is constructed.

Beginning with the studs themselves, each layer of the wall assembly is the product of numerous polluting industries and complex global supply chains, beginning with extraction and ending with a specialty subcontractor installing the materials themselves in the building - each step adding significant economic, health and environmental costs.

It took root in North America during the colonial period, when natural resources - particularly timber - were considered infinite. Forests were cleared, making way for settlement and agriculture. The lumber was used to build homes, cities, ships and railroads. The indigenous communities that had lived for millenia among the vast North American forests were displaced and systematically eradicated. To the homesteaders and early industrialists, the forests were for the taking, a wilderness to be conquered and tamed, and a tremendous opportunity for enrichment.

Despite a recent awakening to the brutality of this shameful history and our much deeper and clearer understanding of the critical ecological value of the world’s forest ecosystems -- supporting biodiversity, oxygen production and immense carbon sequestration -- not much has changed. Our 17th century model of wood framed construction largely perpetuates today as the industry standard, driving an insatiable demand for lumber, which in turn, results in the ongoing devastation of the North American forests. Today the clearing of the forests is strategically out of sight for most of the population. Logging operations are typically in semi-remote valleys, tucked out of view from most towns and highways, though a quick tour on Google Earth, beginning in southern Oregon up through British Columbia makes clear the dreadful state of the great western forests. That checkerboard pattern of lighter-green and brown are the scars of clear-cuts and the sickly remnants of one of the greatest ecosystems on the planet.

Some advocates for the timber industry have argued that logging and replanting forests is actually a climate solution, claiming young, fast growing trees absorb more carbon dioxide from the air than mature trees in an older forest. This argument -- that logging is somehow good for the environment -- has since been completely debunked. Beyond the obvious devastating impacts to the living systems of a mature forest, when a forest is cleared, huge quantities of sequestered carbon are immediately released through the ripping-up of the carbon-rich top soil and duff, the stripping and rotting or burning of slash (branches, stumps and other woody debris) and the destruction of the understory vegetation. Additional soil carbon is then released in the seasons that follow as rain and wind erode the barren landscape left behind. And while it is true that the replanted young trees are highly effective at absorbing carbon, their small size and relatively low ‘leaf count’ - mean that they have a much lower capacity to extract and carbon than their ancient predecessors. Multiple studies since 2008 have researched over 400 species of trees around the world and found that the older, larger trees absorb carbon at a lower rate per leaf than a young tree, but because they are so many times larger, with exponentially more leaves, the older forests are significantly more effective carbon sinks that the younger forests.

Compounding the disastrous effects of clear cutting, these younger, denser second or third generation forests are fueling the catastrophic fires we now experience every year in the American west. Native forests did not sprout at one time, from a freshly cleared landscape but instead evolved over centuries, reaching a state of equilibrium with the natural cycles of weather and fire. Through so-called ‘forest management’ - today’s forests are far less biodiverse, often overcrowded with trees of the same age and species, selected and planted by industry based on lumber value. This results in forests with severely diminished natural resilience and resistance to fire, pests and drought. When combined with hotter temperatures and persistent drought, today's wildfires are hotter and more violent, often destroying the entire forest, including centuries-old trees that had survived dozens of prior fires. Millions of acres of forests are so intensely burned, some historical species may never come back, degrading the landscape and setting it down the path of desertification - first to scrub land and eventually desert.

Wood will always have an important role in our construction industry. Wood is, no doubt, a miraculous material; it is atmospheric carbon dioxide magically converted by a living tree into a tough, cellulose tissue. Through the incredible process of photosynthesis and wood-making, the trees also release oxygen, cleaning and regenerating our planet’s atmosphere, making it habitable for all of us that rely on oxygen.

In the same way that a tree uses photosynthesis to create the cellulose fibers of a 2x4, millions of acres of grain crops across the United States grow each season, pulling carbon dioxide out of the atmosphere and fixing it into their stems, leaves and roots. The edible grains are harvested and dry, woody cellulose-fiber stalks are left standing in the fields. These stalks - we call straw -- are a byproduct of the harvest and a waste problem for the farmers. Traditionally straw would be burned or left to decompose on the fields - both processes that release the crop’s stored carbon back into the atmosphere. Repurposing this woody agricultural waste product into a building material, and thereby reducing the demand for lumber, presents a tremendous opportunity for improvement over today's conventional construction systems.

Rather than disposing of the straw, a farmer can cut and bundle it into dense, rectangular bales. They can then sell the bales to builders, creating an additional revenue stream for the farm. The builders can then stack the bales like oversized bricks and create walls. As a bale wall reaches its full height, the builders anchor the top of the wall down to the foundation with steel rods, and plaster both sides of the walls for a finished surface. This shockingly simple and low-tech system has been used for over a century in the mid-western plains where trees were scarce and lumber was hard to come by.

Bale walls replace a number of the conventional wood-framed building systems, including the wood framing, the insulation, the exterior plywood, and the building wraps and siding. On the interior face of the wall, because the bales are encased in a finish plaster, the builders have no need for sheetrock, paint or other interior finishes, thereby significantly improving the indoor air quality of the finished building. And from a supply chain perspective, straw is plentiful and local - driving very low raw material costs and embodied carbon. In the construction industry a five hundred mile radius is considered local, and there are very few parts of the United States that are more than five hundred miles from a straw-producing farm. Each year there are roughly one million new home starts in the United States. For a sense of scale, only 5% of the domestic straw production would yield a sufficient supply of bales for one million 2,000 square foot homes a year.

By simplifying the system and eliminating multiple layers of a conventional stick framed wall, a straw bale project can achieve cost and time savings in addition to the immense reductions in the carbon footprint and environmental impact of the industries required to create a building’s walls.

And beyond the environmental benefits and advantages for the builders, the resulting homes perform far better than conventional stick framed buildings in several ways. Most noticeably, due to their thick, plastered walls a palpable sense of gravity and permanence is immediately experienced as you walk into a bale home. The acoustics are extraordinary - a sense of quiet rarely found in today’s world is immediately apparent upon walking inside. And, so long as it is thoughtfully finished and furnished, a bale structure actually smells good - the lingering chemical odor of synthetic finishes and paints is replaced by the cool smell of plaster with hints of earth and weathered rock.

And after being a bale home over the course of a day and night, another key characteristic is experienced - one of exceptional insulation and thermal mass. The bale walls are thick and monolithic, as opposed to thin, stud-framed walls. In a conventional wall, each stud acts as a thermal conductor, interrupting the plane of the insulation and bridging the indoor and outdoor temperatures. The insulation capacity of a wall is measured in thermal resistance, or “R Value.” A conventional 2x6 framed wall stuffed with R-21 insulation, archives only a total wall R-value of R-13 (the insulation value reduced by the thermal bridging of the studs). A bale wall, on the other hand, can easily achieve R-33 or better. Additionally, because of the thickness and mass of the bale assembly, the walls themselves are very thermally stable - meaning it requires a lot of energy and time to change the temperature of the wall material. This results in a very stable interior temperature of the home even if the outdoor temperature swings significantly from day to night. This increased insulation value and modulating thermal mass translates to huge energy savings, both in hot and cold climates, creating yet another tremendous advantage of the system in contributing as a climate solution.

Three questions typically arise when considering building with straw (perhaps due to the unfortunate introduction to home building many of us were given as children with the story of the three little pigs….) a house of straw - wont it fall down? Won’t it burn? Won’t it rot or be a haven for mice? The simple answer to all of these questions is, of course, no.

Structurally, there are a range of options for carrying snow, wind and seismic loads that exceed the already conservative requirements of our modern building codes. Many of these options use the bales as the primary load bearing assembly of the building. By stacking them like bricks, capping the wall with a wooden beam and then running steel rods from the beam down to the foundation (on both sides of the wall) the straw is compressed and stabilized. The surfaces of the bale walls are then wrapped in a metal mesh and coated in an inch or more of plaster. The completed assembly provides both the strength to carry the roof and is rigid enough to resist even the highest seismic and wind loads found in the United States. This monolithic assembly, encased in noncombustible plaster, is ultra fire resistant - primarily because it does contain the open cavities of a stud-framed wall. These open spaces, when penetrated by fire, act as flues - sucking fire along the wooden studs and up into the roof structure. And it is also this dense, monolithic aspect of the bale walls that discourages mice and rodents - because there are no cavities in the walls for them to travel through and nest, the walls are more resistant to rodents than a conventional stick framed building.

Just as any wood framed building must be well designed and built to prevent damage from moisture - either liquid water or vapor in the form of humidity - water can similarly damage a bale structure if poorly designed. Both wood and straw, at the microscopic level are composed of cellulose fibers. When left unprotected from moisture for extended periods of time, these fibers can host mold and fungus and begin to decompose. However with prudent design techniques - large roof overhangs, gutters, flashings and the like - it is fairly straightforward to protect the bale walls from excessive liquid water. Humidity is also easily managed through the use of permeable plaster mixes that allow the transmission of water vapor through the walls. The walls naturally ‘breathe’ in any climate found in the United States, other than those with extended seasons of high humidity (70% - 80%+ RH) as you might find in the southeast. For those environments, there are a number of alternative building systems that are more suitable than bale or wood framed construction.

There are a number of reasons. First, because it is only recently that the building codes used in the United States have recognized it as an acceptable, prescriptive construction system. In California, for example, beginning with the 2019 code cycle, local building jurisdictions are now mandated to adopt the new Straw Bale building code, paving the way for streamlined permitting. Second, the bale walls are thick - between fifteen and twenty five inches, compared to five to eight inch thick walls of a wood framed building. This translates to less interior space for the same overall building footprint - a real challenge when working with limited site areas. And finally, a major reason it hasn’t become more mainstream, is because there are few owners, architects, and builders yet familiar with the system meaning each project still requires a great deal of education for all the parties involved. However, as more projects are built and published, it's likely that market conditions alone will begin to favor strawbale based solely on its potential economic competitiveness. Furthermore, if we judge the merits of a system on its economic, environmental or health metrics, it becomes abundantly clear how absurd it is that we, collectively, continue to destroy critical ecosystems far from our building sites, rely on complex networks of polluting, extractive global supply chains to build homes that don’t perform very well, perpetuating the harm that was set in motion centuries ago - when instead we could be using a local agricultural waste product, rely on fewer specialty trades, create economic benefits for our farmers and produce higher quality buildings at a lower cost.

Like so many problems with our modern economy, we’re held back by narrow-minded, short term thinking and immense economic and industrial inertia. Fortunately, these changes can happen incrementally - on a project by project basis by thoughtful owners, architects and builders willing to break from irrational conventions. And progress is underway, between progress in the code and regulatory environment, Biden’s recent commitment to stop deforestation, seemingly everyone’s stated emission-reduction goals and a crop of new, beautiful projects being built, I’m confident that public interest and the unstoppable forces of the market will soon be driving this change for all of us.

In the same way wood framed walls can take the form of virtually any architectural style and context, bale construction is similarly adaptable. We’re currently designing several bale buildings across the aesthetic spectrum. One project is a simple, understated home in a rather unremarkable 1950’s California suburb, the design - single story with a basic gable roof - is intended to seamlessly merge with the neighborhood, indistinguishable from the housing stock surrounding it. Our goals with the project are to demonstrate this better way to build ordinary housing for everyday Americans.

Just up the coast, in one of the most expensive neighborhoods in the nation, we’re in the early stages of design of a spectacular contemporary Montecito hilltop residence, nestled into the mountainside and overlooking the Pacific coast and Channel Islands beyond. And far from the sea, another project is taking shape in the mountains of the Eastern Sierra as a family ski lodge with traditional gable forms and large expanses of glass. Finally, we're also working with our local school district on a simple classroom building, where the thick walls and deep window sills blend seamlessly with the hundred year old Spanish Revival campus and, hopefully paves the way for better K-12 buildings - a sector plagued by cheap, lowest common denominator buildings.

Straw bales construction is, in the end, simply an alternate wall system and is suitable for a range of styles and low-rise building types - excellent for homes, churches, small commercial and multifamily buildings. Industrial warehouses, typically built from carbon-intensive concrete or steel are perfectly suited to strawbale, as they are simple, large rectangular buildings that often require highly insulated walls.