The Carbon Vaults Project
Delaying the decomposition of woody biomass is one of the crucial ways the Carbon Containment Lab works toward containing carbon at scale. An exciting new idea to increase that delay has sparked the imagination of the lab members since its founding. An idea that has long captured the lab's imagination, using architectural design to slow wood decay, took shape as a full pilot study: the Carbon Vaults Project, developed by Professor Jana VanderGoot.
Wood preservation has long been a tradition in architecture. Architects have been thinking of ways to raise the wood off the ground to prevent its decay for decades. In the CC Lab, specifically, using carbon vaults for carbon storage was first imagined in 2021. Our call-to-action was clear: The United States Forest Service (USFS) is approved to thin 70 million acres of overstocked forests as wildfire treatment by 2032, which produce slash piles. These piles may decay or catch on fire, releasing a lot of carbon.
Covering and protecting these slash piles is a strategy that serves both fire mitigation and carbon storage, particularly across the American West, where wildfire risk is most severe. We explored several structural approaches to achieve this.
Earth berms
Our initial solution idea as the lab was constructing a basic “earth berm” structure using mass timber and plaster to cover the slash piles. This storage method would be an effective short-term solution to store carbon, for a relatively low cost of $10-15k. However, the team soon started to realize that these wood vaults not only can be helpful for fire mitigation purposes, but they can also provide much-needed temporary storage for waste wood as a potential fuel source for future bioenergy facilities with carbon capture and storage (BECCS).
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Mine reclamation
The idea that followed was storing the wood for a longer period of time, for at least a few decades in a very accessible way, at which point direct air capture technologies would be abundant enough so that this stored wood could be used in the biofuel industry and eventually in other carbon containment projects such as chemical weathering or TrapRock.
One way to achieve this long-term storage is through wood burial in reclaimed mines, which can offer storage for more than a century. Since EPA requires by law that the mining companies reclaim unused mines, we saw potential in this type of wood carbon storage. However, mine reclamation projects typically cost around $3-5 million and require accounting for the transportation carbon footprint to carry the wood biomass to the mine. Therefore, the team is performing site suitability studies to determine which mines are close to lumber facilities, as part of the Carbon Vaults Project.
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Mass timber sheds
The third and perhaps the most cost-efficient and easy-to-scale carbon vault technology also determined the focus of Summer 2022 for the carbon vaults team: designing small wood mass timber sheds, using a special construction design technology called Dowel Laminated Timber (DLT). The timber shed design offers many advantages, for example, it can store carbon for around 10-50 years for a cost of around $10-15k. The DLT design also makes the sheds very durable and resistant to fire, since DLT has a 2-3 hour fire rating; due to the char layer that develops on top of the wood layer when it catches on fire.
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Early prototyping explored two innovative panel designs built on this technology: Cross-stacked Residual-DLT and Braced Residual-DLT. Both incorporate "residual," or small-wood, material thinned from forests as small-diameter trees, storm- or beetle-damaged wood, or the byproduct of sawing logs for dimensional lumber, turning wood that would otherwise be wasted into a structural material and exemplifying a circular economy approach to design. The diagonal and cross-stacked layering in these designs also make them more structurally stable than standard single-layer DLT panels, offering greater resistance to wind and seismic activity. We've also explored an ash-cob plaster layer, made from waste incinerator ash and clay-soil, to further improve fire resistance.
As Professor VanderGoot describes it, the near-term goal is ensuring each vault type gets a pilot project to generate useful data, while the long-term aim is to scale these design strategies for wood carbon containment nationally, encouraging other groups to adopt and build on them. This work continues through on-site prototyping with stakeholder partners, testing the economics, labor requirements, and structural performance of DLT sheds, above-ground berms with a variety of fireproof coverings, and below-ground burial vaults across a range of environments.
Carbon Vaults in the Lab
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