For our purposes, a carbontransect is a conceptual tool, serving as a means of visualization and, perhaps, as a metaphor. We used it recently to describe to students and teachers the technical processes and environmental impacts embodied in the production of a new building we were designing for their school.

The transect we chose to draw for them, which constitutes the subject of this case study, originates roughly 60 years earlier in northern Quebec below St. James Bay, where genetic material of the species Picea mariana germinated and sprouted as seedlings in the peaty soils of eastern Canada’s boreal forest. There, in the cold climate and short growing season of the subarctic, black spruce trees began the photosynthetic process of material formation, slowly but steadily laying on woody mass by absorbing a mix of atmospheric CO₂, water, and solar radiation to produce the particularly dense and strong cellulose carbohydrate that would ultimately become the primary structure of the new arts and sciences center at the Common Ground High School in New Haven, Connecticut.

Having now steered the studio component of a large design-build program for over a decade and having wrangled an array of resources, institutional partners, and an ever more diverse group of graduate students with different academic interests and professional goals, I have come to believe that its pedagogical value lies not just in the technical execution of a design, nor in the examination and implementation of a set of materials, means, and methods. Instead, I recognize the potential of a design-build program as an interdisciplinary research and design platform from which any student, even those with less technological interest and inclination, can reach out to explore and address, through a range of disciplinary approaches, any number of concerns implicit in a building project.

It has often been observed that wood is one of the oldest materials in our building culture, but it is also notable that—for well over a century, as the processing and construction technologies of steel and concrete (the two other primary classes of structural material) were revolutionized and then continuously refined—the use of wood and timber has been stuck in a kind of construction limbo, relegated to the limited scale of the craftsman's workshop or, worse, to the relatively light structural demands, but significant environmental destructiveness, of low-rise, suburban sprawl.

The supply is potentially infinite, and where extraction is wellmanaged, the landscapes that are its source will naturally and rapidly regenerate, providing critical environmental services such as well-oxygenated air, filtered potable water, and an array of marketable consumer products, all while protecting diverse biological habitats and sequestering significant amounts of atmo - spheric carbon. The energies required for its processing are low compared to other common structural materials. Residues left over from the material extraction process can be left as a kind of nutritive feedstock for future production, contributing either to increasingly compressed layers of carbon-rich soil or to a sustainable exchange of aerobic decay and carbon uptake. Similarly, processing waste serves as fuel for the manufacture of building products.

If it weren't so patently obvious that I've just described wood, forests, and photosynthesis, this passage might read like an elevator pitch for a geo-engineering start-up or a book jacket for an eco-utopian novel.

Using a readily available lifecycle assessment tool and building modeling software, this study compares the carbon emissions of low- and high-density housing morphologies and weighs the lifecycle embodied energy costs against the operational energy benefits of increasing thermal performance in the building envelopes of each housing type. The assessment shows that in spite of increasing energy demands embedded in the materially and technically intensive construction of high performance assemblies, the adoption of these techniques in both the house and multi-unit apartment dramatically reduces lifetime GHG emissions. However, the initial toll of building high performance houses—measured in emissions and extrapolated as construction costs—is burdensome to the environment and homeowner alike. As an alternative, high performance apartments can be built at a carbon and dollar cost only marginally higher than that of conventionally-constructed multi-unit dwellings, with a per-unit lifetime GHG footprint that is one quarter of that of a standard house. The economic and land-use efficiencies of enhanced construction assemblies deployed in dense urban residential development create a multiplier effect in potential GHG reduction; a critical factor for contemporary environmental planning and policy.