
Wood’s popularity as a construction material has surged due to its impressive carbon sequestration capacity. Wood is about half carbon by weight, allowing the material to perform significantly better than others—such as concrete and steel—from a carbon emissions perspective. The realization of wood’s massive carbon storage capacity has encouraged much of the recent proliferation of new timber structures.
However, we cannot rely on the amount of carbon in wood alone to meet environmental targets without considering the material’s life cycle. Wood only acts as an effective carbon bank if it does not rot, burn, or otherwise deteriorate. Although some eventual fates of timber construction—such as fire—may occur without our intention, other ends are inherently avoidable.
For example, it may surprise some to know how much wood ends up in landfills. According to to National Waste Associates, wood is the second-most prevalent component of construction and demolition (C&D) waste after concrete. “But unlike concrete and steel, which have relatively high recycling rates (98% and 82% respectively), lots of C&D derived wood waste goes straight into the dumpster and then to landfill,” the organization claims. Such a high quantity of discarded material, which will readily decay and return its carbon to the atmosphere, will undo much of the good intent of using wood in the first place. And few design teams are likely accounting for this future carbon release in new projects.
One reason so much viable new lumber is discarded is the labor and expense required to repurpose it, such as by removing nails or staples. Oakland, CA-based Urban Machine intends to solve this problem with an innovative material reclamation process powered by artificial intelligence and robots. Dimensional lumber is fed into the device, which uses computer vision to evaluate the material and employs robot armatures to pick out bulk fasteners from all sides. A final review confirms the material’s readiness for new construction.
Significantly, the Urban Machine is an inherently local solution. The rentable apparatus resides on a job site as an ongoing wood reclamation solution, enabling typically unwanted lumber to be reused on the same project or saved for other construction needs. The technology can accommodate heavy timber, glulam, and dimensional lumber from 2x4 to 6x18 in size.
The Vibrant Cities Lab has developed a comprehensive resource plan for managing urban forests and improving socioeconomic and environmental outcomes. Founded by American Forests, the USDA Forest Service, and the National Association of Regional Councils, the lab offers an Urban Forestry Toolkit as a holistic green infrastructure management roadmap.
One of the organization’s publications is the Urban Wood Reuse Action Guide, which promotes alternative futures for waste stream-bound material. The guide advocates for deconstruction over demolition. When dismantling a structure, deconstruction allows the careful identification and salvaging of reusable materials, adding jobs and generating another source of revenue—as opposed to the relatively hasty and indiscriminate process of demolition.
The Vibrant Cities Lab also looks beyond buildings for reclaimed wood. “Approximately 17 percent of municipal waste nationwide is from some form of wood,” claims American Forests. Municipal sources are distinct from C&D waste and thus represent an additional reclamation opportunity. Another potential resource is wood harvested from urban tree pruning—equivalent to almost 30 percent of the yearly hardwood consumption in the U.S.
As Frederick, Maryland-based InventWood demonstrates, reclaimed wood can also be significantly transformed as a material. The company is developing several emerging wood technologies, including wood honeycomb, transparent wood, and insulating wood, all made via sophisticated chemical and mechanical processing methods.
The manufacturer’s flagship product, MettleWood, aims to do nothing less than replace most steel and concrete in construction. InventWood removes the lignin present in wood’s cell walls and subjects the remaining material to extreme compression, creating a substance that is 50% stronger, 80 percent lighter, and less expensive than steel. MettleWood also exhibits a Class A fire rating, which the company claims is a first for a 100% wood product. Furthermore, MettleWood can be produced from “almost any wood including abundant, fast-growing, and even invasive wood species.”
If the impressive technology is scalable and without excessive embodied energy, it would represent the ultimate example of upcycling: the ability to transform a common, frequently under-appreciated substance into a super material capable of dramatically increasing the environmental performance of the built environment. This is precisely the kind of aspiration we should adopt for waste. How can this untapped resource surpass, not simply emulate, common virgin materials?
Read more:The latest from columnist Blaine Brownell, FAIA, includes a review of: Building the Future with Snow | Reimagining Grandeur | The rise of phygital spaces | the potential of STFE | an interview with Pritzker prize-winning architect Riken Yamamoto, a review of 3D-Printed Nanocellulose Materials, a roundup on sustainable manufacturers in Egypt, a review of the Grand Egyptian Museum, a look into Cairo's informal settlements, a profile on textile designer and weaver Suzanne Tick, and he also looks at emerging carbon capture and storage technologies, and the blue economy.
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