Straw-bale construction is an unlikely byproduct of the invention of mechanical baling, which took place in the 1850s, and some of the first buildings that utilized bales of hay for insulation are still standing.
The 1990s saw a natural building boom in the southwest that gave rise to what Graham calls the second generation of straw-bale houses, which amounted to both a reinvention and revival of the style, as little of the development of the first generation was carried over. As straw-bale construction has spread since then, it has found common ground with the passivhaus movement, changing not only to accommodate new climates, but also rising energy and sustainability standards.
As Graham observes in a post for Green Building Advisor, new ideas for straw-bale construction have emerged in response to builders' demands for higher levels of insulation. Mark Hoberecht of Harvestbuild in Columbia Station, Ohio, pioneered a technique in which straw-bale construction was combined with cellulose-insulated wood-framed walls, while others focused on developing preassembled straw-bale panels. These panels have specific design features for connections and airtightness geared toward superinsulation, and they are constructed in controlled environments, thereby lowering the risk that moisture levels will induce rot in the straw, a common problem.
New Frameworks adopted and developed Hoberecht's techniques after early conversations with him in 2012. After using a kickstarter project to analyze their work, they began to understand that second generation straw-bale construction wouldn't provide the desired energy conservation returns. Rethinking their system, they examined Hoberecht's idea of adding a load-bearing wood frame to the outside of a straw-bale wall, thereby harnessing many of the advantages of stud frame structures.
The addition of a stud frame eliminates and streamlines several of the steps traditionally required for straw-bale construction. The exterior coat of plaster can be eliminated, as the straw bales are inherently protected from the weather by siding attached to the structural frame. An 18" pony wall typically used to keep straw bales off the ground and protected from moisture is also eliminated from the design, as the bales can be installed all the way to the interior finish floor. The frame provides numerous places to secure bales, more so than in timber-frame structures, and also facilitates easier installation of doors and windows. Traditional processes of squaring bales and stuffing cracks are also eliminated, as interior strapping allows the bale strings to be cut, letting them expand into place. The structural frame also facilitates greater flexibility for builders, allowing for conventional siding and exterior air barriers. Third generation hybrid walls also make straw-bale houses candidates for passivhaus certification, allowing builders to add cellulose insulation, which helps the structure meet increasing standards for superinsulated buildings.
After examining their new design, it was clear to New Frameworks that they were dealing with an entirely new generation of straw-bale construction. Graham admits that he can hardly consider going back to second generation techniques, after achieving a blower door test result of 0.84 ach50 on a 1,200-square-foot addition, in a project where they were aiming for 1.5 ach50.
The hybridization of straw-bale construction with a stud frame has so far allowed New Frameworks to reap the benefits of both building designs in several successful projects, representing an evolution that unites both modern and traditional styles.