A group of PAYETTE people recently traveled to New Hampshire to learn more about sustainable forestry and its ramifications for the architecture industry. We are increasingly paying attention to embodied carbon – the carbon emissions associated with building materials. Bio-based materials like wood show tremendous potential to reduce and even offset the embodied carbon footprint of buildings, particularly when used in large quantities. Mass timber is one example. A building’s structure represents 40-60% of the footprint of a building. Substituting mass timber in place of steel and concrete can make a significant impact. Within PAYETTE, projects are leveraging the embodied carbon reductions from bio-based materials in different ways. Among others, the Land’s Sake Farm (nearing construction completion) is framed with heavy timber. The UMass Amherst Sustainable Engineering Laboratory (at the end of Schematic Design) is pursuing a steel-timber hybrid structure, and most of the team joined the tour to learn more.
Our action-filled day touched on the full arc of wood production, led by University of New Hampshire foresters Andrew Fast and Steven Roberge. We began with a rapid-fire lecture on Forestry 101, then witnessed the UNH educational sawmill in operation. We walked through actively managed, recently logged UNH forest land, then toured the 90 Arboretum Building, a recently completed mass timber office building. Andrew and Steven from UNH and Ricky McLain from WoodWorks were wonderful guides who touched on many different scales of forestry and timber – from global supply chains to firewall detailing.
As architects, it can be hard to tell what impact our design decisions have on ecosystems. Over the course of the day, we learned about the intricacies of the second- and third-order impacts of our material specifications. Across scales, we gained a better understanding of both constraints and opportunities around sustainable forestry.
In contrast to other parts of the country, most New England’s forests are owned by small landowners, who engage in a wide range of different forestry practices – from active to passive, with focuses including timber harvesting, ecological conservation or carbon sequestration. Within a single stand of trees, multiple objectives might be layered together, tuned by a forester to the landowner’s objectives and the health, age and structure of the forest. Mature, older-growth forests have higher levels of carbon storage (the total amount of carbon stored in the ecosystem), while younger, growing forests might have higher levels of carbon sequestration (the rate of carbon being pulled out of the atmosphere and stored in biogenic material).
Much of New England benefits from a biodiverse patchwork of various types and ages of forest due to the diversity of landownership and forestry objectives. Even if one landowner chooses to aggressively log their property, adjacent landowners might avoid logging entirely. The variety of management approaches buffers the impact of any individual but can also make for an unreliable timber supply. Some of us were surprised to realize the extent of private ownership of natural resources in New Hampshire. For example, property owners own all the plants on their property, but the state owns all the animals. Who knew?!
One of the constraints on wood production is the presence of sawmills in a region. New sawmills are multimillion dollar capital expenses for lumber companies, making new mills rare, and only built when sustained, long-term growth in the lumber market is forecast. Short-term fluctuations in wood demand or prices (i.e. lumber price spikes during the pandemic) are not always enough to increase the number of sawmills in operation. Operational sawmills have a fixed production cap dictated by the size and speed of their equipment. Even when more timber is harvested in a particular season, the sawmills cannot mill any faster – but if harvests drop significantly, mills may shutter and take a long time to reopen.
Another constraint for mass timber specifically is the scarcity of Cross Laminated Timber (CLT) presses – there are only a handful in North America. Each press and the CLT it makes must be tested and certified in accordance with the PRG-320 standard, governing the properties of CLT. The UNH Department of Natural Resources and the Environment is working to expand the availability of locally harvested, locally milled CLT in New England, using locally abundant species like Hemlock in contrast with the dominant use of pine and fir in other regions). Currently, local wood needs to be sent to other parts of the county, like the Southeast or Mountain West, to be processed on a certified CLT mill, before being returned to New England as a finished product. If the UNH initiative is successful, we might one day see a robust regional economy with harvesting, milling and construction of mass timber buildings.
Despite the abundance of interest in and publicity around mass timber – it is massive after all! – we learned that it represents only a small fraction of the wood products market – dwarfed by hardware store staples like 2x lumber and plywood. And architectural wood products are only a portion of the wood that is harvested in the logging process. Only the long, straight portions of mature tree trunks can be effectively milled into useful lumber. Smaller branches, curved trunks, and other “irregular” pieces are sent instead to a pulp mill to be turned into paper-related products. The remaining pieces (thin branches and uppermost portions of the tree) are either left to decompose in the forest or burned for fuel. There is some controversy as to whether this burning is carbon neutral or carbon-emitting.
At the 90 Arboretum building, we saw mass timber in action – glulam columns and beams, CLT decks and shear walls. The wood surfaces were beautifully machined – smooth faces with precut penetrations for connections and services. The dense texture of many small strips of wood gave a richness and consistency to the space. Black Spruce was used for the timber members, supplied out of Quebec. While the UNH forestry team worked to source local hemlock CLT for the project, it was ultimately too expensive for the client – highlighting some of the difficulties with starting up a regional mass timber industry.
So, what can we do as designers with this knowledge of wood and forestry? For one, there is a great deal of nuance in the carbon accounting of forests, sequestration and biogenic emissions. Starting life cycle assessments early and often can help us understand the benefits of using wood in place of non-biogenic materials before it becomes cost prohibitive to pivot the design. To the extent that we can, learning about where wood is being milled, sourced, harvested and processed, helps us understand the local, regional or international impacts of a material spec. We can begin to understand the ways labor and environmental regulations impact the cost, but also ethics and ecology of different materials and different products of the same material. We are constrained by the market for building products while also having significant ability to influence what buildings are made of.
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