Rick is a Cleveland-area architect who writes extensively about local architecture, landmarks, attractions, and sustainable development.
A 'Growing' Building Material
A House of Straw?
Sure, you’ve heard the tale of the three little pigs, and how one of them decided to build his house of straw. But did you ever think that you might someday build a house of straw yourself? And be practicing sustainable architecture at the same time? Let this architect explain how and why it's done.
As the struggle for sustainability surges across the United States, innovators, designers and builders are pursuing the use of what has often in the past been considered merely a waste product — agricultural fiber. America’s farming sector annually produces prodigious quantities of rice and wheat straw, as well as other plant fibers, that can be incorporated into structural insulated panels for use as siding and sheathing in a variety of applications. As a recycled ‘waste’ product, agricultural fiber can provide panels that compete very effectively on price with other traditional construction materials, such as wood, metal and concrete. Such ‘agri-fiber’ panels can also provide an additional supplementary income stream for the nation’s farmers.
Recycling Agricultural Materials
Agri-fiber panels (most often referred to in the industry as compressed agricultural fiber, or CAF, panels) can be used just about anywhere traditional wood, plywood or particle-board sheathing or decking would otherwise be used. Due to the particular strength characteristics of agricultural fiber, however, CAF panels are usually quite a bit thicker than traditional sheathing, ranging from about 4-1/2” to 8” thick, depending on the strength and span required.
Like precast concrete panels, therefore, CAF panels are specifically engineered in advance for their particular use, location and loading. They are typically shaped or formed to the exact configuration needed, including having required openings for doors, windows, etc., cut into the panels. Since CAF panels are fully fabricated in a shop prior to being shipped to a construction site, they contribute nothing to site construction waste and thence landfills, making them even more environmentally attractive.
Making CAF Panels
The fabrication of CAF panels begins with the collection of the source agricultural fiber. Plant straw must first have its moisture content adjusted through short-term storage in a controlled environment. It is then cleaned of insects, debris and dirt, before being sorted by condition and strand length. Natural additives make the raw product both mold- and pest-resistant.
The plant material is then guided to mold forms, where compression and heat are applied to initiate the molding process. As panels are formed, regularly spaced channels are bored within the panels to serve as electrical wiring conduit chases in the eventual in-place panels. Heavy-duty paper is laminated to CAF panel faces as a finish. The final step in the fabrication process is the creation of what is essentially a wooden box to hold the CAF panel. A shallow pan is constructed, consisting of a perimeter ‘profile’ beam of laminated wood, and a pan bottom, of oriented strand board (OSB). The CAF panels are glued into the pan, before a closing lid of OSB is glued then nailed in place, sealing the entire assembly.
After compression for setting and curing, the wooden box surrounding the CAF core acts as container, handling frame, stiffener, strengthener and field-attachment zone for the final panel. Panel openings are cut into panels after curing. Typically, panels are provided with a mortised keyway along panel edges to allow panels to be ‘chained’ together via field attachment.
Advantages of CAF Panels
Construction of structures employing CAF panels offers a number of advantages over traditional construction methods. CAF panels are structural insulated panels (SIPs), and, as such, require little or no exterior wall framing. They therefore allow for much more rapid enclosure of structures, resulting in significant time and labor savings. With no intermediate framing members to create less-insulated ‘gaps’ in a building’s thermal envelope, CAF panels also contribute to a much ‘tighter’ building for heat loss and gain. This leads directly to energy savings for building heating and cooling systems.
A CAF panel building is also tighter with regard to noise; panels have a very high rating for minimizing sound transmission. Furthermore, CAF panels offer a more fire-resistive core than foam-insulated walls. The panel fabrication process has been refined to reduce or eliminate any harmful product emissions or out-gassing over a panel’s service life. Finally, the use of compressed straw cores not only removes that straw from its traditional waste stream, but also reduces the amount of dimensional lumber typically required by traditional construction methods. As a result, CAF panels can actually show a negative carbon footprint.