American Hardwoods Rediscovered

Life cycle thinkers are drawn to the sustainable qualities of hardwoods.


By The Hardwood Council

Versatile, durable and high-touch, American hardwoods have been serving builders, architects, cabinetmakers and homeowners for centuries. Nontoxic and natural, hardwoods bring desirable physical properties, eco-effectiveness and a warm aesthetic to floors, furniture, cabinetry and millwork. They embody sustainability better than many of the newly synthesized materials meant to imitate them.

Explains materials scientist Andrew Dent, "The whole point of a composite is putting two dissimilar materials together ... basically the perfect composite material is wood. It has the right combination of strengthening fibers and gluey binders to put it all together." He adds, "Wood being so wonderfully reusable in very different forms—and wonderfully sustainable—unfortunately the thing they try to replace it with is probably one of the least sustainable materials you're ever going to come across."

This leads architect Huston Eubank, of Rocky Mountain Institute to suggest, "How about looking at old materials and finding new ways to use them? Let's look at some old solutions before we feel the need to invent some piece of rocket science that takes the entire power output of the Columbia River to manufacture."

Few solutions are older, simpler or more sustainably available than wood; and rarely are people drawn so instinctively to a material. Architect John Connell observes, "The thing about the natural materials, and not just the woods, but also stone, fabrics and fibers—things that have been around since the dawn of time—is that we have an association with them that is probably more profound than we realize. All of our senses evolved to enable us to survive in the natural world. I'm finding people are having an increased hunger for traditional materials."

For many, the need for sustainability is just as paramount.

In the U.S., hardwood growth annually outpaces harvesting by almost two to one—the very definition of sustainability. The hardwood volume in American forests increases by 10.2 billion cubic feet each year, while annual removals total only 6 billion cubic feet, according to

the U.S. Forest Service. As a result, over the last 50 years, the inventory of hardwoods in U.S. forests has grown by more than 90 percent.

Amid low-cost global sourcing; the proliferation of synthetic and exotic materials; and concern with greenness, architects' and designers' time, budgets and resources are stretched thin. Making sustainable decisions and choices can be more complicated than ever before.

How can design practitioners decide thoughtfully where American hardwoods are the most environmentally preferable choice and use them most sustainably?

To make effective specifying decisions, it's important to understand what hardwoods are and how to compare them with alternative materials, both natural and manufactured.

The term "hardwood" applies to angiosperms—trees with leaves rather than needles. Hardwoods produce fruits or nuts in the summer, shed their leaves in the fall and go dormant in the winter. Among the hundreds of hardwood species growing in the U.S. are: Alder, Ash, Aspen, Basswood, Beech, Birch, Cherry, Cottonwood, Cypress, Elm, Gum, Hackberry, Hard Maple, Hickory/Pecan, Pacific Coast Maple, Poplar, Red Oak, Sassafras, Soft Maple, Sycamore, Walnut, White Oak, Willow. (For detailed profiles of each, see Species Guide at

Any of the commercially available hardwoods listed here can be used for cabinets, furniture, mouldings and other millwork—it's simply a question of aesthetics and availability. For reasons of fashion, custom or convention, many of them are unexplored or underused despite their commercial availability.

American hardwoods exhibit rich diversity in color and grain, so they're are most often specified where visual appeal is important. Hardwoods contrast with the "softwoods," or gymnosperms— cone-bearing trees with needles including fir, pine, redwood and spruce most often used in construction.

In general, hardwoods are denser and harder than softwoods, although actual resistance to pressure and wear in both groups varies from species to species. For this reason, not every American hardwood is suitable for flooring.

Sources of U.S. Hardwood Sustainability
U.S. hardwood forests cover 269 million acres—land equal to all of Georgia, Illinois, Indiana, New York, North and South Carolina, Ohio, Pennsylvania, West Virginia—and half of Virginia. Most hardwood forests are in the eastern U.S., with more hardwood tree species than any other temperate-zone hardwood forests on the planet. The reason: each species thrives under a unique set of conditions. Variations of soil, nutrients, moisture, warmth, sunlight and shade favor different woods in different regions, or even on different sides of the same hill.

The U. S. Forest Service estimates that 73 percent of these hardwood forested acres are privately owned. The forest industry owns another 11 percent, and 16 percent is held by federal, state and local governments. The private owners number around 7 million individuals and families, and most hold an average of 50 acres. Often, this hardwood forestland ownership goes back several generations, as does the practice of sustainable forestry.

Hardwood trees in American forests have a natural life span of 60-80 years. At maturity, they decay, blow down or topple from natural causes. Hardwood forestry mimics nature by employing single- or small-group tree harvesting. Trained hardwood foresters select mature trees for removal, careful to maintain the total forest. Selection harvesting promotes growth by giving younger trees a greater share of sunlight, water and nutrients.

Domestic hardwood forests replenish themselves on their own natural timetable—and without human intervention, just as they have for millions of years. Hardwood forest renewal happens without the postharvest replanting required for softwoods. "Volunteer" hardwood trees sprout naturally from seeds, tree stumps and roots. With a healthy diversity in species and stages of growth, sprouts, seedlings, saplings and mature trees grow side-by-side.

Hardwoods In The Global Economy
harvesting in U.S. forests is subject to federal, state and local laws and regulations that protect water and wildlife. In contrast, many of the hundreds of hardwood species that grow in the world's tropical forests are subjects of special concern because of illegal and unsustainable harvesting and its effects on wild habitats.

A well-understood concept like fire resistance has generated whole libraries full of codes, specifications, ratings and technical data, with its own specialized vocabulary. Yet fire resistance involves only a few variables. Sustainability is vastly more complex. Global sourcing is a tangle, and product information is imperfect and often incomplete.

Tight budgets, brisk timelines, and other trade-offs creep into every project: few materials choices are ever cut-and-dried. Decision-making tools, including LEED (Leadership in Energy and Environmental Design) and LCA (life cycle assessment), are evolving, but the question remains: Can sustainability be quantified and standardized?

The answer: up to a point.

Tradeoffs and Tie-Breakers
In the real world, architects and designers rely on such labor-saving shortcuts as certification systems, rating standards and assessment techniques.

  • Certification Systems
    Industry groups and third-party organizations have introduced various forest-products certification programs highlighting best practices and chain-of-custody documentation. They include the Forest Stewardship Council (FSC); Sustainable Forestry Initiative (SFI) and American Tree Farm programs.

    They offer at-a-glance reassurance that a product offers some level of sustainable merit. However, not all sustainable products take part in the certification process; and certifications can become outdated as products change. Not all that's sustainable is certified: some products meet certification standards but have not been tested and certified.

    American hardwood sources are a case in point. Most U.S. forests are in the hands of private individuals and families; and although their record of sustainable management spans 50 years, most do not participate in the fee-based, third-party certification programs established in the 1990s. In fact, only about 5 percent of the hardwood forestland in the U.S. is certified under any system.

    LEED (Leadership in Energy and Environmental Design): Although not intended as a product-evaluation tool, it often is used as a checklist by professionals in a hurry. Yet, LEED is a work in progress and leans heavily on certain certification systems and a limited range of products. Architects and designers can be tempted to focus on racking up LEED points, rather than on integrated design. LEED-certified architect Jill Kowalski of EwingCole notes, "If you get too hung up in the credits, you don't take advantage of the whole system. That's how LEED is meant to be used. If you're not used to integrated design, you may work line-by-line instead of big-picture. You almost have to put the LEED checklist aside for a minute. Do integrated design, though, and LEED will be automatic."

    Life cycle assessment traces every input and output of every step in the production, use and disposal of a product: extraction and processing of raw materials, manufacturing, transportation and distribution, use or reuse, and recycling, waste management and disposal. While detailed—and useful—LCA data exists for some products, the limits of this information are many. It's unlikely that LCAs using exactly the same terms and statistical tools would have been performed for two materials that a specifier is trying to compare. Sustainability concerns range from energy conservation, recycling and indoor air quality to impact on indigenous peoples. Comparing two potential material alternatives—and defending the eventual choice—can mean evaluating a mixed bag of characteristics. How, for instance, to weigh the positive impact of high recycled content against the negative impact of high embodied energy?

On the job and in a crunch, what rules of thumb can help in making defensibly sustainable decisions? Although full-scale life cycle assessment may be unrealistic, "life cycle thinking" is a practical route to sensitive materials selection. It's a common sense framework for evaluating alternatives and is tailored exactly to a specific project. Life cycle questions have no simple answers: there's no substitute for critical thinking and common sense. When it comes to evaluating materials or products, it can be useful to ask:

  1. Is the material a natural resource that is renewing sustainably? If it's a composite, how sustainable are the components, and the resins that hold them together?
  2. Is supply abundant, accessible and readily available?
  3. Is it durable and long-lasting, and is its service life measured in life year, decades or more?
  4. If recycled content is appealing, how much energy does it take to convert the original material into the new synthetic?
  5. If recyclability is a factor, how much energy will it take to separate the material's components at the end of its useful life? Is a credible collection and disassembly infrastructure in place?
  6. If the material is an exotic or tropical crop, is an upswing in demand disturbing wild habitats?

When the material of choice is American hardwoods, why use a sustainable resource in an unsustainable way? As Aldo Leopold pointed out nearly 80 years ago, forest conservation requires not only "intelligent production of lumber," but it also "depends in part on intelligent consumption."

Leopold—one of the last century's most powerful voices for conservation— was a forester and issued this challenge in a 1928 issue of American Forest magazine, in an article titled "The Home Builder Conserves:"

"Take our universal insistence on clear hardwoods for furniture and interior woodwork. A sound knot is absolutely taboo on the face of a drawer or a baseboard or a window casing. Consider that the greater part of our enormous hardwood waste occurs in the process of trimming out knots. Is it too much to hope that fashion may some day lift the ban against sound knots in places where they may enhance the beauty of the wood and do not injure strength?"

There's more character-marked wood than clear wood in a mature tree. Clear wood represents only the most recent chapters of its life, and becomes the highest-grade, highest-cost, lumber. Environmentally sensitive specification means making decisions to use the resource fully. Environmentally inspired designs embrace the knots, color variations and distinctive signatures of natural materials precisely because they are not mass-produced and artificially uniform. Indeed, they express the tree's entire history.

Another approach might be to serve sustainability, aesthetics and economy by not using high-grade, clear lumber for concealed portions of furniture, cabinetry or a built-in.

    At least 95 percent of all hardwood lumber produced in the United States is flat-sawn to produce the greatest amount of useable lumber from each tree at the lowest cost. If dimensional stability is a concern, it's important to know that flat-sawn products perform just as well when they are handled and stored properly on the job site.

    The key precaution: plan to get the materials to the job site after it's climate-controlled, but several days before installation. That allows time for their moisture content to balance out with the conditions that will prevail after installation.

    Multiple native hardwood species—and staining techniques—can be juxtaposed for dramatic contrast or subtle effects. Combinations with other materials also offer wide possibilities. "We've also been using hardwoods for windows, particularly where we're wrapping windows, with copper," says architect Peter Bohlin. "We've used maple or cherry for the basic wood frame that's visible on the inside, and ... a copper sheathing on the outside, particularly where we're at high altitudes ... that is quite a sustainable strategy."

    It also is a strategy that taps into the profound affinity with natural materials. "When I go into a place that's been built with a lot of natural materials, and has been there a long time, and used by a lot of people, the atmosphere in there is palpably rich … you can sense it in your bones," says architect John Connell.

    As Huston Eubank, architect and secretary of the World Green Building Council notes, "What are the things we need to make us really comfortable? One is a strong connection with nature. Touching a piece of wood is a whole different experience from touching a steel desktop." Eubank concludes, "Nature makes things that are far more durable than anything man's learned how to make. There are huge lessons to learn."