The building sector currently accounts for roughly a third of global emissions. Building and climate scientists have determined that, as a sector, we need to be carbon neutral by 2050 if we have any shot of keeping global temperatures in check. Buildings are responsible for emissions in two general categories - first, through resource extraction, transport and construction and then again through energy use - mostly heating, cooling and lighting - over the course of the building's operational life. While both phases of the building’s life cycle are important, given the urgency of reducing emissions in the near term, mitigating the carbon impact of our construction phase is increasingly critical.

Since the industrial revolution and the availability of cheap fossil fuel energy, the building industry has been overwhelmingly organized around high strength, rapid-assembly materials regardless of the often-significant environmental impacts and carbon emissions associated with those material selections.

At one end of the spectrum are manufactured materials such as steel, concrete and aluminum that are extremely energy and carbon intensive to extract, manufacture and transport. At the other, are building materials ‘manufactured’ by the natural process of photosynthesis and biologic growth. Powered by solar energy, living plants and trees pull CO2 out of the atmosphere, fix the carbon atoms into their fibers of plants, and release the oxygen atoms back into the air. This process cleans and regenerates our atmosphere, making this planet habitable for all of us that breathe.

Uninterrupted, most of that carbon in plant material is cycled back into the atmosphere when the plants die and decompose. As our building sector requires immense quantities of physical material, it provides a tremendous opportunity to intercept this natural carbon cycle, and sequester the carbon locked in the plant fibers for many decades as walls and other useful building materials. While trees, and the wood they produce, are an obvious and important aspect of this conversation - there are strategies using other plant fibers - particularly straw (the dried stalks of agricultural grain crops) that can significantly amplify the emission reduction potential of our building sector, even turning buildings carbon negative - meaning they sequester more carbon over their life than was required to build and operate them. A very promising proposition indeed!

If you’re reading this in a house, or small 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 stick-framed construction–a decision of profound consequence, but 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 stick-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 stick-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, which are 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 aesthetically-pleasing, 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.

Finally, and problematically, the basic arrangement of spaced-apart studs of stick-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.

Conventional stick-framed construction in the United States is a dirty and expensive business. 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.

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. The edible grains are harvested and the dry, woody cellulose-fiber stalks are left standing. These stalks, that we call “straw”, are a byproduct of the harvest and a waste problem for farmers. Traditionally straw is burned or left to decompose in the fields; both processes release the crop’s carbon back into the atmosphere. Repurposing this woody agricultural waste product into a building material presents a tremendous opportunity to sequester vast quantities of carbon each season. Straw can store approximately 60 times more carbon than would be required to grow, bale and transport it to building sites. For every pound of carbon locked up in a bale used for building materials, 3.67 pounds of CO2 are prevented from entering the atmosphere (one carbon atom binds with two oxygen atoms to create carbon dioxide, which is 3.67 times heavier than a single carbon atom).

Rather than burning or 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. This simple and low-tech system has been used for over a century in the Midwestern plains where trees were scarce and lumber was hard to come by. Furthermore, if the farm operates with regenerative agricultural practices–sequestering additional carbon below ground and building healthy topsoil–the climate and environmental benefits compound into a transformative ecosystem connecting our food and construction sectors.

Bale walls can replace (or at least reduce) a number of the conventional stick- framed building systems, including the stick-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. Straw is plentiful and local, driving very low raw material costs and embodied energy. 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 each year.

Beyond the environmental benefits and advantages for 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 when you walk into a bale home. The acoustics are extraordinary, a sense of quiet rarely found in today’s world is immediately apparent upon entry. And, so long as it is appropriately finished, a bale structure actually smells good, the lingering chemical odor of synthetic finishes and paints is replaced by the cool and earthy smell of plaster and weathered rock.

After being in a bale home over the course of a day and night, another key characteristic is experienced: one of exceptional insulation and thermal mass. Straw 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 limitation of the studs themselves). A bale wall, on the other hand, can 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. The result is a very stable interior home temperature, even in environments with significant temperature swings 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. With a relatively minor investment in on-site renewable energy and storage systems, a well designed straw bale home can achieve the holy grail of carbon negative design and construction.

A series of questions typically arise when considering building with straw: Won't it fall down? Won’t it burn? Won’t it rot? Won’t it be a haven for rodents? The simple answer to all of these questions is, thankfully, “no.”

Structurally, there are a range of options for carrying snow, wind and seismic loads that exceed the already conserative requirements of our modern building codes. Bale walls are assembled in one of two general categories. The first, load-bearing bale walls, in which the bales themselves carry the weight of the roof. In this system, the bales are stacked like bricks until the wall reaches its full height, at which point the builders cap the wall with a wooden beam and run steel rods down to the foundation (on both sides of the wall) and the bales are compressed and stabilized. The second category is what we call post and beam infill, wherein the building structure is carried by a framework of posts and beams and the bales are infilled between the posts to create enclosure. With both wall systems, the surfaces of the bale walls are 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. This is primarily because a bale wall does not contain the open cavities of a stick-framed wall which, when penetrated by fire, act as flues - sucking fire along the wooden studs and up into the roof structure. And it is also the 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 stick-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, etc. - 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 stick-framed construction.

In the same way stick-framed walls can take the form of virtually any architectural style and context, bale construction is similarly adaptable. We’ve recently been involved in the design of 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 goal with the project is to demonstrate a 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. 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.

Straw bale 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 straw bale, as they are simple, large rectangular buildings that often require highly insulated walls.

So why isn’t straw bale construction more prevalent? There are a number of reasons. First, it is only recently that 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 stick-framed building). This translates to less interior space for the same overall building footprint - a real challenge when working with limited site areas. Finally, a major reason straw bale construction hasn’t become more mainstream is that there are few owners, architects, and builders familiar with the system. As a result, each project requires a great deal of education for all the parties involved, offsetting the potential cost and schedule benefits straw bale construction can offer. However, given the extremely low cost of straw as a raw material and the simplicity of the construction systems, straw bale has the potential to become very cost competitive. As more projects are built and published, communities of builders and suppliers will inevitably develop, refine and scale the supporting construction systems and expertise.

If we judge the merits of a system holistically on its economic, environmental or health metrics, it becomes abundantly clear how absurd it is that we, collectively, continue to destroy 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, when instead we could be using a local agricultural waste product that retains a huge amount of carbon out of our atmosphere, rely on fewer polluting industries, create economic benefits for our farmers and produce higher quality buildings at a competitive 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 developments in the code and regulatory environment, seemingly everyone’s stated emission-reduction goals and a crop of new, beautiful projects being built, there’s reason to be hopeful that public interest and the unstoppable forces of the market will soon be driving change for all of us.

There are a number of excellent resources to learn more about straw bale construction, here’s a few to get you started:

California Straw Bale Association with links to professionals, code information and the invaluable handbook for anyone designing or building with straw, Straw Bale Building Details

Strawbale.com is and excellent online resource for a wealth of information and videos on how this all works. 

The Eco Building Network and Bruce King’s excellent book, The New Carbon Architecture.