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Grain Elevation

Wood’s natural and technical virtues give it a new edge

“What is this building made of?” This is the first question I ask my architecture students about the opening image in their first undergraduate building construction course. They are looking at a modest historic building that sits in a meadow surrounded by trees. It has the features of a typical New England home: white clapboards, doors, and windows; black shutters; and faded-to-gray roof shingles.

One student raises her hand. “Wood?”

“Correct!” I reply. Her reward is another question. “Why did the builders choose wood?” Now almost all the students are eager to respond. “Wood is easy to work with.” “Wood can be used for all parts of the house: structure, siding, roof.” “The wood probably came from the trees on the site.” “Wood is a warm material; it’s natural.” In less than a minute, the students are beginning to analyze wood’s material properties, its range of uses, its detailed construction, and their psychological responses to it.

Only then do I tell them that we are looking at the front façade of the Shaker Meeting House at Sabbathday Lake, Maine, built in 1794. I use this image because it is a familiar architecture with profound material, religious, and environmental implications. With a little encouragement, these students discover for themselves the integrated natural, cultural, and technical virtues of wood.

It might seem curious to start a course on building construction in the 21st century with a wood building from the 18th century, but wood construction is by no means an obsolete technology. Quite the contrary: wood is now at the leading edge of contemporary practice. The natural qualities of wood have satisfied the needs of different building cultures throughout history and across the globe because of its availability, workability, and versatility.

These very same qualities are even more relevant in our age of building for high performance and low environmental impact. Wood is even at the forefront of new thinking for tall buildings — a domain, until recently, reserved for steel and concrete. Architect Michael Green of British Columbia calls these new timber buildings “Tall Wood.” He contends that such buildings could possibly be built up to 30 stories while sequestering more carbon than they use for their production. Increasingly, wood is answering the questions of the architectural vanguard.

The current focus on wood is understandable when we consider its inherent sustainable attributes. For example, wood is the only truly renewable building material. It is grown and harvested, and can be used for building with relatively little processing. It captures carbon in the building process instead of producing more of it.

Because it is relatively lightweight, transportation energy is reduced and so, too, is the size of the foundation. Wood buildings are easy to alter, so they are adaptable and equally easy to deconstruct. At the end of the life of a building, wood is reusable or biodegradable. Wood, therefore, has the lowest embodied energy for the full life cycle of a building of all the other major construction types, including masonry, concrete, and steel.

Wood also has remarkable technical qualities. Structurally, it is excellent in both tension and compression, and has the same or better strength per weight than steel. Although combustible, wood can also perform better than steel in a fire. Because of its mass, wood can absorb significant amounts of heat energy before catching fire. If wood does ignite, the outer layer of char protects the inner mass of wood and preserves its structural integrity. Wood is also very durable when properly protected from deleterious effects of water and fire. Case in point: The timber Hōryū-ji Temple in Ikaruga, Japan, is more than 1,300 years old.

Equally captivating as these performative criteria is the strong psychological affinity we have for wood. Its idiosyncratic patterns remind us of its natural origins. A room of wood seems to embrace us with its warm color of reflected light. Sounds in a wood room are rich and mellow. The soft texture of wood is vulnerable to our interaction with it, recording the passage of time with scratches and scrapes.

Culturally, wood has paralleled the great changes in how we build. In America, all wood buildings before the Industrial Revolution were either heavy timber frame construction or a solid timber construction such as log cabins. Both construction types required a relatively high level of craft to produce them. But the explosive growth of 19th-century cities created the need to quickly build more dwellings at the urban periphery.

As masonry structures began to dominate the urban core of cities such as Boston and Chicago, the first-ring suburbs were being built with a new form of wood construction: the balloon frame. This lightweight construction type displaced the hand-hewed heavy timbers with standardized wood studs and joists produced from industrialized manufacturing processes. Additionally, the construction of balloon frame buildings no longer required fine skills or sophisticated tools. Instead, a small crew with a hammer and a saw could build a multifamily house for low cost in a short period of time. This democratized building construction by making it more accessible to the immigrating masses. The balloon frame and its subsequent variation, the platform frame, were agents of one of the great cultural shifts in urban America: rapidly expanding cities of wooden homes. As early skyscrapers defined the city center of commerce, wood framing created the fabric for the city’s expanding population.

In the 20th century, wood technology continued to evolve to become the source for significant material innovation. Multiple forms of “engineered lumber” were developed to create materials that are stronger and more stable than solid wood. For example, compressed-particle lumber types use rapid-growth soft woods and timber-industry byproducts in ways that optimize the qualities of wood while minimizing the quantity of material. Other types are plywood and laminated beams that adhere wood pieces together to form finished lumber in any shape. Also, mass timber panels are set in place, much like precast concrete panels, for use as vertical load-bearing walls and spanning floors, which saves both construction time and overall costs.

Innovations in engineered lumber construction are gaining momentum in the 21st century. Architect Green calls wood “the most technologically advanced building material.” At the molecular scale, the interwoven longitudinal plus radial cell pattern that gives wood its strength could be imitated for the next generation of smart building materials. At the urban scale, buildings of timber have already been built up to 10 stories tall. If Green’s prediction for Tall Wood proves valid, then we could be entering the next phase in the continued evolution of wood construction, one that could transform how we build and settle our cities. Imagine a city of wooden skyscrapers: structures grown, not manufactured; and capturing carbon, not creating more. New research and innovation is transforming wood once again to be at the vanguard of building technology. The virtues of wood that appealed to early Americans are now meeting global demands for more sustainable, higher-performing building materials.

What will your next building be made of?