Cities from Los Angeles to Boston are mandating zero-carbon footprints for new public buildings. New York is even setting carbon limits on the private sector. Concurrently, designers and manufacturers alike are seeking alternative materials to create buildings and structures for which After Architecture founders Katie MacDonald, Assoc. AIA, and Kyle Schumann have coined the term “ecology-positive.”
The Knoxville, Tenn.–duo has set its sights on a byproduct of sustainable forestry and ecological restoration: invasive plants. In North America, efforts to remove or contain invasive plant species and rehabilitate native ecosystems are often ad hoc, relying on volunteer labor and limited funding. What constitutes an invasive species varies by region. In most cases, they comprise plants that are capable of creating imbalances in local food webs, crowding out indigenous species and reducing overall biodiversity. They also can exacerbate soil erosion, reduce groundwater recharge, and diminish habitat for local wildlife.
By developing architectural uses for nonnative species and timber thinnings—specimens that are strategically removed as part of forest management—MacDonald and Schumann believe the building industry can wean off carbon-intensive materials, such as concrete, steel, and aluminum, while creating mutually beneficial supply chains.
Learning about and working with invasive species may also help architects shed their tendency to rely on standardized commercial building products, MacDonald says. As design researcher and consultant Oliver J. Curtis writes in “Nominal Versus Actual: A History of the 2×4” (Harvard Design Magazine, No. 45), prior to industrialization in the United States, “trees were felled, skidded, sized, and made to order for carpenters. Sizing tolerances varied, thus leaving final measurements to site construction. Trees were grown and used locally.”
The emergence of the railroad allowed for transcontinental shipping, driving the desire for smaller, lightweight, kiln-dried lumber, such as the common 2×4, to reduce shipping costs. In response to what Curtis describes as the building industry’s “obsessive concern for material efficiency,” he suggests that architects should “return to a species-based synthesis of growth, harvest, usage, and aesthetics.”
After Architecture is pursuing such a synthesis, which it terms “bioagency,” and which Schumann describes as “a collaboration between the designer and the embodied intelligence of the biological material.” Bioagency moves beyond biomimicry, which tends to replicate natural forms and processes through mechanical or passive means. “Standardized materials have so much waste and energy embedded in their production,” MacDonald says. “We’re interested in the alignment of natural form that occurs in plant material and customized form for architectural applications, the idea that there might be a relationship between natural irregularity and a desired irregularity.”
Last fall, MacDonald and Schumann led a University of Tennessee, Knoxville studio that explored the use of regional invasive species as building material. Working with experts to identify the most widespread and destructive nonnative species, their students developed fabrication techniques and structural systems that take advantage of the plants’ behavioral, chemical, and aesthetic properties—or what Schumann refers to as their “embodied intelligence.”
For their project Branching Inventory, UT students Tyler Sanford, Assoc. AIA, and Kevin Saslawsky harvested and 3D-scanned the fallen branches of Bradford pear trees, a nonnative ornamental species whose weak forks make them prone to abruptly shedding their limbs. After organizing the branches by size and shape with custom computational tools, they developed a lattice-like architectural system. “Natural branch curvature is matched to the curves of the designed model,” the students note in their project statement, “and thicker, stronger branches are located near the base of the assembly.” Steel knife plates connect the small-diameter members of the 9-foot-tall, 25-foot-wide assembly, which the students erected on campus.
Rony Feghaly, Yegi Rahbari, and Courtney St. John augmented bamboo to create Reflex, a responsive sculpture installed along a busy walkway on the UT campus. First, they made kerf cuts into 7- to 12-foot-tall bamboo poles, rendering them flexible. Then, they anchored the poles into concrete footings, arranged them by height, and wired them together. When a sensor detects people moving nearby, a motor winds the wire, bending the poles in succession and creating an ephemeral arcade.
MacDonald and Schumann are planning to construct Homegrown, a 17-foot-tall, 13-foot-square pavilion constructed entirely using panels made of fibers from kudzu and bamboo plants. (The project is postponed due to the COVID-19 pandemic.) The panels take advantage of the natural mechanical performance and light weight of the plants’ fibers. From the outside, the surfaces look flat, angular, and solid. From the inside, the panels’ porosity is revealed along with their organic curves, molded with the help of a reusable pneumatic forming system.
Pavilions and small-scale installations cannot disrupt building supply chains alone, but they can have an outsize impact on public awareness. In Hawaii, for instance, invasive albizia trees are now sought after as a building material thanks to a recent demonstration project.
Albizia trees were introduced to the Hawaiian Islands in 1917 as a part of reforestation efforts. But the trees soon outcompeted slower-growing native trees and altered the forest’s soil chemistry, further disadvantaging native species. Like Bradford pear trees, albizia are also prone to shedding branches without warning, leading many people to assume that the wood was weak and had little commercial value.
In 2016, Joey Valenti, then a doctoral student at the University of Hawaii at Mānoa School of Architecture, created the Albizia Project, a supply chain that seeks to reduce the island’s housing costs and to fund future forest restoration. He designed and built Lika, a 400-square-foot, all-albizia affordable housing prototype. Completed on campus in 2018, the arched structure, whose design was inspired by Polynesian dwellings, uses glue-laminated albizia members as structure.
Today, demand for albizia wood, once left to rot in the forest or along roadsides, has outstripped supply. “Whatever has reached the sawmills is gone,” Valenti says. “It’s used in projects.”
Valenti himself is also in demand, both as a designer and a fabricator. For the new headquarters of Hawaii’s Elemental Excelerator business incubator, Valenti worked with Dean Sakamoto Architects to design and fabricate an undulating, albizia wave ceiling. More than 500 board feet of albizia was CNC-milled into a series of 11-foot-long fins, forming a rippling, woven pattern. For the local nonprofit Purple Mai‘a, Valenti is using albizia for interior screens and the frames of modern Shoji doors. Other designers in Hawaii have begun specifying albizia too. “This is just the beginning of an emerging market,” Valenti says.
Still, albizia and other invasive tree species are far from displacing Douglas fir and Southern yellow pine as common building materials. Establishing a supply chain is a logistical, economical, and bureaucratic challenge, requiring the alignment of public agencies and industries such as forestry, shipping, and construction. Alongside his work on the Albizia Project, Valenti is coordinator of the Hawaii Wood Utilization Team, formed in 2018 after the state received a $250,000 Wood Innovations Grant from the U.S. Forest Service to further develop the market for local timber.
The team is planning to construct Kōke‘e ADU, a 400-square-foot accessory dwelling unit built from nonnative trees—in this case, eucalyptus and loblolly pine planted for erosion control on Kauai in the 1960s and 1970s. The ADU is an experiment in what Valenti calls “forest-to-frame,” or using invasive or unwanted woods for every part of a structural system. But without an existing logging industry on the island, necessary infrastructure is limited.
The Kōke‘e Timber Management Area, located on the west side of Kauai, currently contains 1,760 acres—and 3.25 million net cubic feet—of nonnative eucalyptus and pine forest, enough to build 1,200 houses. Harvesting the trees is a priority for Hawaii’s Department of Land and Natural Resources, which wants to encourage native species and reduce the risk of wildfire. But roads near Kōke‘e are narrow and ill-suited to harvesting operations, and only a handful of companies on the island are capable of logging and milling the wood.
Furthermore, Hawaii has no one to grade the lumber. Local building codes require that wood products be visually or mechanically graded to ensure quality; without a grade, lumber milled at Kōke‘e wouldn’t be permitted for building projects. (The ADU is considered a demonstration project.) Similar challenges exist for bringing albizia to market as a structural material.
These challenges are not insurmountable, says Amelia Baxter, CEO of WholeTrees in Madison, Wis. The company, which Baxter co-founded with Roald Gundersen, AIA, in 2007, provides unmilled timbers culled from managed forests for structural use. According to the company, whole timbers are 50% stronger in tension and bending than a dimensional piece of lumber with an equivalent cross-section that was milled from the same tree. Whole timbers also have a smaller carbon footprint.
“Whole timbers are the original mass timber,” Baxter says. Standard mass timber products such as CLT, she adds, typically require a “predictable, non-variable tree, meaning monocropped agriculture, so it still points to a paradigm of mining an agricultural resource.”
The small- to medium-diameter trees that Whole Trees sources come from forest thinnings, which not only maximize the growth of the remaining trees, thus increasing profits for landowners, but also enhance biodiversity and wildlife habitat and may reduce the likelihood of wildfires. WholeTrees has coordinated with public agencies, like the Wisconsin Department of Natural Resources, but more often works with private forest owners. The company uses its 3D scanning technology to inventory trees slated for removal on project sites, choreographing their reuse with local sawmills, and maintains an online database of its inventory, as well as a CAD library full of beams, columns, trusses, assemblies, and connections in order to simplify the specification process.
The company also employs a Timber Products Inspection–certified grader, who visually inspects the wood in its manufacturing yards, where WholeTrees peels, sands, and finishes the wood with a nontoxic sealant. For timber fabricated out of state, the company contracts with a TPI grader near the project site. Baxter is working toward getting her products machine-stress-rated, which is how glulam and dimensional lumber is graded. She says mechanical rating is both more efficient and more accurate.
Because WholeTrees’ timbers are minimally processed, their embodied energy is low and innate strength preserved. In a way, it’s bioagency in action. Baxter expects the demand for whole timbers to grow with design tools such as the Embodied Carbon in Construction Calculator. “If architects have a database directing them to the cleanest, greenest materials,” she says, “that’s free advertisement for carbon-neutral or -negative materials like regional timber thinnings.”
And yet the history of the 2×4—and of most building materials—is a reminder that market dominance results from myriad factors. A cost-competitive, reliable supply chain of building materials from invasive or unwanted woods will require the close coordination of product suppliers, forest owners, industry associations, regulatory agencies, contractors, and design professionals.
But it can happen. The principals of After Architecture point to mass timber as the result of exactly that level of coordination, especially in the Pacific Northwest, but also in states like Arkansas, where building codes have been updated and new manufacturing facilities seem to spring up overnight.
“It’s exciting to see the alignment between government, industry, and design professions in promoting and developing a space in which mass timber construction is viable,” MacDonald says. “That’s a precedent for the type of work that we’re doing.”
The Invasive Supply Chain
Looking ahead, the best-case scenario for these symbiotic supply chains differs depending on the material. For business models that rely on byproducts of sustainable forest management, such as that of WholeTrees, developing a long-term supply chain makes sense because raw material will be available as long as economic and environmental incentives to manage forests through thinning exist.
Building a supply chain for an invasive species is more difficult: Some conservationists worry that creating a market for an invasive species might lead to its cultivation. One potential solution is to design temporality into the supply chain. In Hawaii, for instance, some forestry experts are working with product suppliers to develop a succession plan for transitioning to other unwanted tree species.
In any case, using invasive species in construction will require close coordination among agencies that oversee natural resources, utilize technology to monitor local ground conditions, and facilitate material selection. Most of all, it will take continued work and creative thinking. Buildings can be net-positive for planetary health and biodiversity, but only if the environmental footprint of architectural materials is part of the equation.
This article has been updated since first publication to clarify that the carbon footprint of whole timbers as compared to conventional nominal lumber is smaller, but not to the extent originally published. We regret the error. The story has also been updated to clarify that the strength of whole timbers is 50% stronger in tension and bending than a piece of milled lumber with a equivalent cross-section.