The single most important benefit of building with wood is contributing to climate stability. New techniques of mass timber construction allow the use of wood in almost every setting where steel and concrete dominate today, and replacing steel and concrete with sustainable, renewable wood construction can provide climate benefits as large as those from solar and wind power. When those benefits on the construction side are linked with Exemplary Forestry approaches to growing and harvesting trees, the climate benefits multiply.
Concrete and Steel vs. Wood
Concrete and steel are produced by heating materials mined from the earth to greater than 2500 degrees Fahrenheit. Today that heat is achieved by burning fossil fuels, usually coal, and production of steel and concrete for construction makes up fully a tenth of the world’s carbon emissions. Wood by contrast is produced by trees using the sun’s energy to combine carbon dioxide and water into carbohydrates. The contrast could not be stronger:
- Wood is a renewable material; we will never run out of it, and we don’t have to mine the earth to obtain it. Over the last sixty years, global use of steel has quintupled, and use of concrete has increased 13-fold, but use of wood has not even doubled. This represents an unsustainable reliance on non-renewable materials.
- While wood is growing toward harvest it actively reduces global warming. Trees remove carbon dioxide from the atmosphere, and that carbon dioxide remains trapped in the wood after harvest and in long-lived wood products for decades to centuries.
- Implementing even more sustainable and climate friendly techniques for wood production, generally requires only advances in knowledge and changes in the financial incentives offered landowners. Implementation can happen immediately, and the trees already growing will respond immediately, in line with the urgency of the climate crisis. Experimental techniques for less polluting steel and concrete production require years more research and proof of concept, followed by retooling of factories that were designed to last for decades, at substantial expense.
Today we have an alternative available for much steel and concrete usage. We can use mass timber to construct tall wood buildings, mid-rise housing and offices, parking garages and even bridges. By doing this we avoid the emissions associated with the production of steel and concrete; this is the first of four climate benefits from mass timber construction.
Mass Timber and Sustainable Forestry
Not all mass timber offers the same climate benefits. Wood derived from forests that are also accumulating carbon provides the greatest climate benefits, as harvest does not reduce the amount of carbon stored in living trees. Achieving this requires a balance of harvest and growth, and techniques to increase the rate of forest growth allow society more flexibility. These techniques were developed as part of the development of forest science over the last 125 years. Over the last 75 years, New England Forestry Foundation has applied forest science principles to our lands here in New England. We practice them today on more than 38,000 acres, and have recently codified them as our Exemplary Forestry Standards. Exemplary Forestry provides guidance about how to manage forests in New England for wildlife, other forest values, and carbon storage, while ensuring high rates of growth and production of high-quality forest products.
NEFF advocates for a circular bioeconomy approach that derives the wood for mass timber construction from sustainably managed forests that continue to store carbon at high levels to produce the greatest climate benefits. By linking new wood construction to sourcing standards that support Exemplary Forestry, we can derive a second climate benefit from mass timber construction.
Exemplary Forestry also allows foresters to manage forests to transition to new structures and assemblages of tree species that will maintain resilience in the face of climate disruptions—like increases in frequency and intensity of wildfire, increases in insect outbreaks, and increases in damaging wind and ice storms.
The transitions of the coming century demand not only renewable energy, but renewable raw materials; Exemplary Forestry or equivalent approaches are key.
Mass Timber Buildings as Carbon Storage
With growing urbanization, the idea of the urban footprint has become common. This represents the idea that a city relies on less urbanized areas for its food, water, energy and materials, and implies that as a city grows it can become unsustainable. Mass timber opens a new way to think about cities. Instead of viewing them as consumers of resources, the city can become a repository, a place where we build carbon storage over time, creating climate-protecting storage of carbon to replace the deep storage of fossil fuels under the earth. The city becomes not a consumer, but an integral part of the system.
Mass timber buildings store carbon in their walls, floors, roofs and beams for as long as the building is standing and sometimes for decades or even centuries afterwards. The amount of carbon stored is not trivial. The mass timber Brock Commons dormitory at the University of British Columbia stores the equivalent of 1,753 metric tons of carbon dioxide in its structure. Applying similar techniques to the 350,000 multifamily units built in the United States annually might allow the storage of an additional 5 million metric tons of carbon dioxide per year in residential buildings alone (most single-family residences are already built from wood).
Impact of Mass Timber Buildings on Urban Development and Traffic
Currently around many transit hubs, new apartment buildings are limited to five or six stories. This is because building codes allow traditional wooden stud construction only up to five stories, or six if there’s a concrete and steel first floor. Steel and concrete construction is generally only cost-effective for residences above 12 stories. Mass timber construction’s fourth and final climate benefit could come by helping us to capture space above the sixth floor. Mass timber is highly cost effective from six to 12 stories.
With taller buildings around transit hubs a variety of climate and social benefits become possible. First, some residents won’t need vehicles to commute; this reduces auto emissions and traffic congestion. It can also help improve social equity as having a reliable car is no longer the price of admission to jobs that require commuting. Second, less sprawling residential development on the fringes of the metropolitan area will be needed. This reduces loss of forest for housing, directly preserving forests’ future sequestration abilities and the carbon stored in them today. A more compact form of development also means shorter average commutes to jobs, shops, doctor’s offices, and other services, improving quality of life, reducing traffic, and again improving social equity. And less traffic congestion even for daily tasks again reduces transportation emissions. Less traffic congestion also makes for safer streets for children and pets, and makes bus routes quicker, improving public acceptance of mass transit.
With metro Boston needing 185,000 new housing units by 2030, and other New England cities facing similar crunches, these benefits are consequential.