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Boston Society of Architects

Renew Feature

Seeing the forest for the building

Wood is reframing the narrative about sourcing, supply chains, and carbon neutrality

RENEW Jan-March 2020

Wood Hero 03

In Japan’s Mie Prefecture, the Ise Grand Shrine complex is intimately related to the sacred Japanese cypress forest, the source of their material. Rebuilt every 20 years, this architecture links building and forest in ways that synchronize tree growth cycles and the passing of intergenerational techniques. The Shinto shrine complex—at once perpetually new and perpetually ancient—offers architects some insight into contemporary timber building.

The Ise Grand Shrine has been torn down and rebuilt every 20 years for the past millennium.
N yotarou, Wikimedia Commons

Recent mass timber buildings are objectively neither good nor bad in ecological terms. Through their respective building processes, they might alternately cultivate life in healthy forests or obliterate a forest ecosystem. Mass timber buildings may be either a carbon sink or a source of carbon emissions. The latter in both cases most likely originates from architects who see mass timber as a substitute for steel or concrete construction. With this substitution mentality, the core problems of how architects conceive construction persist: Too often they continue to think of a building as a composed, constructed object rather than a composition of intricate planetary processes and cycles.

The upside of recent timber building interest is that some architects are beginning to unlearn what modernity trained architects to forget: that building is inherently terrestrial—that to understand building is to understand the range of ecological, social, and political relations that engender building. The Ise shrine complex has long illustrated that for us. In this regard, some architects are beginning to understand the profound—but obvious—fact that timber buildings come from forests. To know timber building is to know forest building as well.

Take, for instance, the different forests in New England and Quebec. The boreal forests of Quebec are predominantly black spruce stands, often held in very large ownership tracts, all in the resource extraction-intensive context of the Canadian economy. This singular species, its socioeconomic context, and its specific material properties all suit the production of cross-laminated timber panels quite well.

By contrast, New England presents a very different forest, one characterized by a mix of hardwood species, along with a changing coniferous mix. Much of this forest is held by a plethora of landowners who own small parcels of land and often subscribe to a misguiding conversation ethic in which trees are never cut, even at the price of forest health, biodiversity, water quality, and resilience. In the New England context, cross-laminated timber panels are not at all obvious as a forest product. Timber components, made in small and varied facilities from a diverse mix of species and harvesting practices, suit the New England forest. Canadian and New England forests have their own characteristics; neither is better than the other, but each has its own inherent potential.

Today the ultimate merits, or burdens, of timber building will come to bear not only on the design of a particular building alone but also on that building’s contributions to forest building. For instance, in aesthetic terms, if it comes to light that a conventionally beautiful mass timber building is the result of vulgar forestry practices and material geographies, then it instantly begins to appear less aesthetically and architecturally satisfying. If a mass timber building’s shallow claims on carbon neutrality only serve to mask ill-considered and carbon-emission-intensive transportation, production, and forestry dynamics, then the merits of its architecture are ultimately in doubt. (Consider that the trees on a fully loaded logging truck contain a finite amount of sequestered carbon. That truck can drive only so far before it has emitted as much carbon as that locked in the logs it is transporting. And all that occurs before the logs are pushed through an emission-laden timber processing and fabrication process, and before that timber is transported once again to a construction site.)

New England forest map.
David Kennedy, Jacob Mans, and Benjamin Peek, Harvard GSD MDes thesis, 2016

To adequately consider mass timber building today is to rethink the systems and boundaries of conventional construction: that is, what we include when we think about building. This prompt regarding system boundaries is not about instilling a stubborn localism; it’s about knowing the whole construction ecology of any contemporary building. To build with mass timber is a territorial proposition as much as it is a proposition for a particular client on a particular site.

It is also a unique molecular proposition. Timber used in construction has a unique set of material properties. Its cellular solid composition allows it to absorb heat and moisture unlike other materials. This is partly why, colloquially, we think of wood as a “warm” material. There is science behind that perception. Imagine blocks of wood and steel in front of you that are the same temperature. After touching each, you would remark that the steel feels colder and the wood, warmer, even though they are the same physical temperature. The wood has a lower thermal effusivity, which quantifies the propensity of a material to lose or absorb heat relative to another material, in this example, through your fingertips. You lose more heat to the steel, hence the difference in thermal perception. Accordingly, an all-wood building will have a very different thermal experience than that of other materials. Perhaps timber buildings should thus have a different energy code: In the winter, a wood building can be quantitatively cooler in air temperature yet feel warmer than a building surfaced with other materials.

Designing timber buildings based on the unique molecular properties of timber has further implications. Engineer Salmaan Craig is in the midst of refining an approach to uninsulated solid timber buildings that meets, or beats, current energy-code standards. In Craig’s approach, calibrated holes in a solid timber wall turn the wall into a heat exchanger. Interior heat moving through the solid timber heats incoming ventilation air. The approach eliminates not only insulation but also mechanical heat exchangers. Absolving a building of the carbon-intensive, randomly sourced layers of construction and mechanical systems goes a long way toward positive environmental impacts. Much like the unique properties of a forest, timber building today also involves deep forays into material properties.

Diagram outlining wood thermal variables attached to effusivity.
David Kennedy, Jacob Mans, and Benjamin Peek, Harvard GSD MDes thesis, 2016

From the molecular to the territorial, architects and engineers are beginning to reengage the fundamental terrestrial character of building. With timber building, they are beginning to see the forest for the building. They are also beginning to peer into novel molecular architectures as they pioneer a new paradigm of carbon-positive building.

This is not the result of switching building materials. It is the result of a shift in how designers think about construction at a range of scales, through a variety of intrinsic processes. It is a result of thinking through the construction ecology of building, not with the aim of minimizing environmental impacts but of maximizing the good that design can achieve, through the inherently terrestrial act of building.

For another look at how materials are being used, you may want to look at our exhibition, DURABLE: Sustainable Material Ecologies, Assemblies, and Cultures.