Using Wood for Sustainable Design + Construction

Using Wood for Sustainable Design + Construction
   
Wood is a historic, classic, and durable building material that has leant longevity, aesthetics, and a natural flair to buildings for thousands of years. And while wood has long been considered an environmentally friendly resource, more and more focus is being placed on the recycling and renewability aspects of wood products, as

well as the use of certified forest land.

More than 200 million acres of forestland in the U.S. alone are certified as sustainable and responsibly managed, attributable to four main forest certification programs active in North America:
• The Forest Stewardship Council— an international organization which requires chain-of-custody documentation and product labeling. The FSC sanctions the work of third-party certifiers, such as the Rainforest Alliance’s SmartWood program and Scientific Certification System’s Green Cross label.
• The Sustainable Forestry Initiative (SFI)—a certification program developed by the American Forest and Paper Association.
• The American Tree Farm System—a certification program primarily targeted at small, non-industrial forest landowners.
• The Sustainable Forest Management Program—a certification program developed by the Canadian Standard Association (CSA).

Validating assurance of legality and sustainability for the

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FSC, SFI, and CSA programs, a recent study released by the United Kingdom’s Department for Environment, Food and Rural Affairs reported that all four of these systems adequately ensured that certified forests met U.K. government requirements. 

Reclaimed wood. Beyond certification, another growing green building trend is the use of reclaimed and “rediscovered” wood. According to the Rainforest Alliance, sources of this material include:
• Demolition projects for antiquated buildings.
• Dead, fallen, diseased, or nuisance trees from urban/suburban properties.
• Orchards where unproductive trees are cut for replacement.
• Fallen trees carefully reclaimed from rivers and lakes.
• Usable wood safely reclaimed from demolition landfills.
• Wood by-products from secondary manufacturers.

At a practical level, using environmentally certified and reclaimed lumber can, in some cases, save significant construction dollars, in addition to offering a green marketing advantage, according to the Natural Resources Defense Council (NRDC) handbook, Efficient Wood Use in Residential Construction.

Another attraction of reclaimed wood materials is purely aesthetic. “Recovered wood’s beauty is unsurpassed,” says Deb Alden, editorial staff member for home improvement expert Bob Vila. “Left to age among the elements, whether in the baking sun, the close, dry conditions of an abandoned factory, or preserved in the cold depths by underwater silicates, these woods are transformed by the natural aging process.”

Wood alternatives. Yet another green trend is the increasing

popularity of engineered wood products and rapidly renewable wood alternatives, such as bamboo. In general, engineered wood—whether plywood, medium-density fiberboard, or prefabricated I-joists, boards, and beams—is a more efficient use of wood and relies less on large-diameter, old-growth deciduous trees. In addition, some engineered wood products outperform wood in terms of resistance to cracking, shrinkage, and warping, as well as offering a high degree of strength.

On the other side of the coin, the use of imported wood and rare hardwoods, despite their attractiveness and elegance, is often criticized for originating from non-certified, poorly managed forests, primarily in less well-developed tropical countries. “Forests in these areas may simply be cut down for agriculture, ranching, or even fuel by poor people who see no other options,” states Liza Murphy, forest products marketing associate with the Rainforest Alliance in New York City.

Although certification programs have begun including more imported and rare wood species, the effort hasn’t kept pace with the rapidly increasing quantities of tropical hardwood lumber and hardwood flooring being imported into the U.S. According to the American Institute of Architects’ Environmental Resource Guide, 42 million acres of tropical forest were cleared in 1990, an increase of 40% from 1980 levels. The AIA predicts that all tropical forests could be depleted by the middle of the 21st century.  

Toxicity. Other environmental concerns for wood-related products relate to health issues concerning toxic finishes. Although awareness has increased in recent years, leading to a surge in materials and finishes low in volatile organic compounds (VOCs) and free of aromatic solvents, heavy metals, or suspected cancer-causing chemicals, Building Teams must be armed with the relevant information before specifying. VOCs and their by-products can cause eye and skin irritation, lung and breathing problems, headaches, nausea, muscle weakness, and liver and kidney damage, according to the American Lung Association. In addition, VOCs released into the atmosphere can combine with each other and with other substances to create ground-level ozone.
Public awareness and health policy have spurred on the development of alternative wood finishes, namely water-based coatings that contain no VOCs and closely resemble traditional wood coatings in appearance.

Structural systems
Wood brings many environmental benefits—and some noteworthy drawbacks—to the construction of buildings, whether for the structural system, the building exterior and fenestration, or the interior flooring and finished carpentry. From an environmental point of view, one of the biggest arguments in favor of wood is that it takes significantly less energy to produce, compared to concrete, steel, cement, or glass (see below, “Life Cycle Analysis: The Environmental Proof of Wood”). In addition, untreated wood is completely biodegradable and 100% renewable, with strong insulation properties.

On the production side, lumber mills make extremely efficient use of wood through engineered lumber solutions, culled wood programs, and scrap recovery, which essentially make use of the entire tree.

The versatility and abundance of wood has led to its dominance in low-rise construction, particularly for residential, hospitality, and retail uses. It can easily be shaped, sanded, repaired, replaced, stained, or painted. 

When it comes to expansions, wood framing is extraordinarily malleable and forgiving, whereas other materials, such as concrete and steel, may require demolition and high-energy means for retrofitting, which often carry considerable expense.

On the other hand, wood does have some limitations with regard to structural capacity. “Wood is simply not as strong as steel or concrete, and therefore is definitely less efficient and ultimately costs more when long spans are called for,” says Duo Dickinson, an architect in Madison, Conn. However, the Structural Board Association, Markham, Ont., which represents manufacturers of oriented-strand board (OSB), counters that, pound for pound, wood is stronger than steel because it has a more favorable strength-to-weight ratio. Even so, says Dickinson, recycled and pre-engineered wood products will not work for every project application: “Once a certain load capacity is reached, they simply don’t have the strength or structural efficiency of their steel or concrete counterparts.”

Wood vs. light-gauge steel. Architects and engineers are quick to point out, however, that hybrid wood products offer several significant benefits over solid wood timber and wood frame construction. For example, says Dickinson, engineered wood members lend themselves to more predictable, regular, and accurate structural calculations. Once installed, the products are more dimensionally stable, meaning that tolerances and margins of error are greatly reduced.

Dickinson maintains that wood is very competitive with light-gauge steel framing and that heavy timber actually requires less fireproofing than true light-gauge steel. Also, the Natural Resources Defense Council points out that light-gauge steel studs require considerable energy in manufacture, and that the thermal performance of steel-framed homes has typically been poor.

This leads to two sustainability concerns: 1) embodied energy related to initial production, and 2) the energy efficiency of installed systems. Traditional detailing of light-gauge steel as a component of structural wall assemblies raises other performance questions, says Jennifer Duthie, National Wood Works technical coordinator with the Canadian Wood Council: “In steel-stud wall construction, the cavity in the wall space cannot be insulated, and a designer has to account for the loss of usable floor space since the steel stud wall is a hollow cavity. With wood-framed wall systems, you have structural capacity, insulation, and acoustic properties, as well as aesthetic beauty.”

In terms of cost, Kenneth Bland, P.E., building codes senior director with the American Wood Council, says, “Wood has always been a cost-effective alternative to conventional commercial construction materials. Recent hikes in steel prices make wood more affordable than ever.” The National Association of Home Builders recently disagreed, stating in a technical report that light-gauge steel framing “is gaining a foothold on wood’s long-standing dominance in residential framing.” Among the reasons given in the NAHB report: “The price and consistency of lumber grow less reliable,” leading some homebuilders to take a cue from commercial builders who have developed fast ways to produce steel-framed products. The NAHB report concludes that, “with its lightweight and stress-resistant frame, steel lends itself to the rigors of the road.”

Wood cladding and sheathing
As a building cladding material, wood products enjoy a good reputation for field performance as well as overall environmental profile. The Canadian Wood Council’s Duthie notes that for cladding and sheathing applications, wood is available in many forms and can fit into many different building types and styles of design, in addition to being incorporated into high-performance envelope assemblies, such as rainscreens. The American Wood Council’s Bland states, “Wood products provide unmatched structural resistance to wind and seismic loads and act as air-infiltration barriers.”

Architect Dickinson applauds the choice of wood as a cladding material for its malleability and adaptability to field conditions. On the other hand, he says, “In terms of its downside, it is simply not as strong as steel. And even with pressure treatment and the use of substantial overhangs and other architectural protections, treated wood will tend to degrade over time unless kept fairly aggressively coated with something which shunts ultraviolet and water exposure.”

On this point, envelope experts at Building Science Consulting, Westford, Mass., strongly advise that wood cladding and sheathing be primed/sealed against rainwater on all six surfaces.

In terms of ease of installation, several new cladding and sheathing products have contractor-friendly features. One example is a sheathing panel, available in 4 x 8-foot sheets of oriented-strand board (OSB) and plywood in various thicknesses, with pre-printed gridlines to facilitate measuring, marking, cutting, and fastening.
Engineered wood. Because it can be produced from small-diameter or low-grade tree species, OSB has yet another side benefit: its efficient use of forest resources, which is one reason why, according to Duthie, OSB is one of the two most common panel products for sheathing, along with plywood.

“In terms of performance, engineered wood products actually improve upon many of the inherent structural advantages of wood,” adds Jack Merry, industry communications director for APA–The Engineered Wood Association. “Cross-laminated plywood and OSB distribute along-the-grain strength of wood in both panel axes. OSB eliminates knots and knotholes. And glulam beams and wood I-joists can carry greater loads over longer spans than is possible with natural solid sawn wood of the same size.”

According to American Wood Council’s Bland, “Engineered wood products such as glulam and laminated veneer lumber (LVL) combine high strength with flexible design characteristics. These properties allow architects to design spaces with long, open spans, but still incorporate the beauty of wood.”

Here, according to the APA’s Merry, are some of the advantages offered by engineered wood products:
• Ready availability.
• Strength and stiffness properties.
• Cost-competitiveness relative to other products.
• Scheduling and speed of construction.
• Long-term performance and durability.
• Aesthetics of exposed woods and veneers, such as with exposed glulam beams.
• Conduciveness to fire- and noise-rated construction systems.
• Natural insulating properties.
• Environmental merits.

Another important benefit of wood sheathing is in the detailing of seismically rated and resistant structures. An analysis of earthquake damage in California and Japan cited by the Structural Board Association revealed that panel-sheathed wood frame structures fared better than masonry and concrete buildings.

Dickinson notes that wood-based sheathing and cladding are more malleable and forgiving than, say, concrete board and gypsum panels, so much so that he calls these materials “site-condition friendly.” On the other hand, he says, all wood products require complete encapsulation from the elements to protect their integrity. “Medium-density fiberboard (MDF), fiberboard, and plywood are excellent materials, as long as they are adequately protected from sun and rain,” he concludes.

This is not to imply that wood sheathing will always be the designer or contractor’s first choice, note construction experts. Gypsum board is also readily available, easy to repair, fire resistant, inexpensive, and versatile. In addition, some manufacturers are producing gypsum-board panels that feature water-repellent face and back paper, as well as water-resistant core materials. Concrete board, another option, offers a more uniform surface condition than wood products, which can be important in specific construction projects.

Wood flooring
When deciding between flooring options, wood is well known for its aesthetic appeal and durability. “Wood is warm underfoot, works well with radiant floor heating systems, and is easier on the joints of the people who inhabit the space,” says the Canadian Wood Council’s Duthie. “It looks fantastic and has longevity.” Wood floors can be rejuvenated with sanding and refinishing, which only needs to be done every 10 to 15 years or so, depending on usage. And at the end of its long life, a wood floor is completely biodegradable.

Market studies also confirm the appeal and popularity of parquet, plank, and other wood flooring choices. A recent national survey sponsored by the National Wood Flooring Association found that 90% of real estate agents report houses with wood floors sell faster and for higher prices than houses without any exposed wood flooring.

Building scientists also point out that wood floors help building occupants avoid common problems associated with carpeting, such as dust, bacteria, and toxins. Of course, careful attention must be paid to the wood’s finish to ensure that low-VOC emitting products are used; fortunately, there is now a large and growing supply of low-VOC wood finishes, in response to greater demand from homeowners, tenants, and building owners. Dickinson, as well as major flooring contractors, contends that high-end, water-based coatings actually offer better protection than their toxic counterparts. 

Wood flooring alternatives. Increasingly, Building Teams are specifying floors made of bamboo and eucalyptus, which grow quickly and often provide a finish comparable to more expensive (and slower-growing) trees, such as oak. Yet while bamboo and eucalyptus grow quickly and so are rapidly renewable, sustainable-design advocates are split on whether bamboo and eucalyptus are always truly environmentally preferable to wood.

“Obviously, bamboo and eucalyptus grow much more quickly than softwood and hardwood flooring,” says architect Dickinson. “However, these species need to be shipped from great distances to get to where we build. You have to take the big picture of where did the carbon footprint start and end.” Dickinson is also a little wary of bamboo’s performance characteristics: “Bamboo seems to be extremely tough, but vertical-grain quarter-sawn standard hardwood floors are extremely durable at a relatively modest cost.”

Another option which is growing in popularity is recycled wood flooring made from salvaged chestnut, hickory, cherry, or oak boards. Remilled trees and wood, sometimes made from reclaimed timber discovered at the bottom of lakes and rivers from long-defunct logging operations, are another possibility. Because this type of recycled or reclaimed wood typically comes from old-growth forests, the National Association of Home Builders maintains that it is usually harder, denser, and more attractive than much new wood flooring.

Wood doors and windows
Aesthetics drive the use of wood for doors and windows in commercial, institutional, and multifamily construction projects. According to the Window & Door Manufacturers Association, Des Plaines, Ill., a trade association representing over 145 U.S. and Canadian manufacturers and suppliers of windows and doors, wood is “highly versatile due to its botanical structure, composition, and properties. As a material, it has high strength in relation to its weight, high heat- and electrical-insulating properties, and desirable acoustical properties. In addition, wood imparts a feeling of warmth not possessed by other materials, such as metals or plastics.”

But even within the wood family, a number of choices need to be sorted through. For example, regarding door selection, the highest-quality, most expensive choice is a 100% wood door with solid-wood frames and sashes, says Andrew P. Kandels, a St. Paul-based contractor. Such doors obtained from a high-quality manufacturer will resist most major shifting and expanding, he says, “although in wood, this is always a risk. They will need to be kept up annually or there will be problems with the finish, but these doors can always be sanded and refinished down the road.” The major disadvantage of solid wood doors, according to Kandels: price, with wood doors running as much as 10 times or more the cost of a steel door.

Solid-core wood doors are more economical, but do not last as long and require more maintenance. “Thin laminates or plywoods usually can be sanded and refinished only a minimum number of times,” says Kandels. “The coverings will absorb moisture, many times from the inside, behind the protective clear-coat finish, and they will peel or bubble out. Fading is always going to be a problem.”

Although engineered wood is also viable choice, one interesting option is a newer product, a steel/wood hybrid. Manufactured as a solid wood door on the interior, it can be stained to match the furniture, trim, or other furnishings. The exterior is made of steel, the better to protect the door from the elements.

A relatively new material for windows and doors is fiberglass. “It’s very low maintenance, resists denting and scratching, and is very strong and secure,” says Kandels. “Another benefit is that unlike wood and steel, it doesn’t need to be finished to be considered low maintenance. Fiberglass, even when left unfinished, will last for years without fear of mold, deterioration, or rust.” As far as sustainable attributes go, ASTM testing shows that fiberglass composite windows and doors are durable, have high R-values, and have only a small amount of embodied energy as compared to aluminum and vinyl.

Whether all-wood or solid-core doors are an ecologically sound choice depends on where the lumber is sourced and the U-factor, or total heat-transfer coefficient, of the door assembly. [According to the Web site Windows for High Performance Commercial Buildings (http://www.commercialwindows.umn.edu/index.php), the U-factor (or U-value) is the standard way to quantify insulating value and indicates the rate of heat flow through a window or door. The U-factor is the total heat transfer coefficient of the window or door system and represents the heat flow per hour (in Btus per hour or watts) through each square foot (or square meter) of window for a 1°F (1°C) temperature difference between the indoor and outdoor air temperature. The smaller the U-factor of a material, the lower the rate of heat flow.] Still, if specified and maintained carefully, wood doors may be a greener choice than aluminum or steel doors and frames.

Wood window specification. As compared to metals and vinyl, wood windows tend to perform well in green building assessments. For example, a February 2006 U.S. Green Building Council report on life cycle costing, “Assessment of the Technical Basis for a PVC-Related Materials Credit for LEED,” showed that the worst environmental impact for a window choice was an aluminum window frame. Other studies by U.S. and British groups show that wood windows outshine their vinyl counterparts in terms of green manufacture, energy efficiency, and overall environmental impact.

Wood windows also contribute to LEED certification points, including one prerequisite and up to 25 total points out of the 69 in the LEED for New Construction (LEED-NC) system.

Finished carpentry
Because wood is so popular when it comes to finished carpentry, such as paneling, trim, bookcases, countertops and reception consoles, it has continued to be a choice interior building material. The growing emergence of alternatives such as bamboo, eucalyptus, and composite wood panels—and even faux wood finishes—is giving Building Teams even more options to choose from.

For example, in terms of renewability, some bamboo species can grow up to four feet in one day. Bamboo re-grows from the same roots, without replanting. Bamboo is being processed and marketed by a growing number of manufacturers as an attractive and viable carpentry alternative to traditional hardwood.

Similarly, a renewable wood material made from eucalyptus is now being offered as hardwood lumber, plywood, and veneer. With its “tropical” aesthetic qualities and strong grain and color, this product has been found to work well with applications such as cabinetry, furniture, and millwork.

Another reason to consider such newer offerings is the decreasing quality of traditional hardwood species, says Dickinson. “There are fewer old-growth trees that are harvestable, and the trees that are being harvested as plantation-grown have gotten such an enormous softness and span between their growth rings that they move way too much.” However, this does not mean that designers necessarily should select thermoplastic and fiberglass architectural trim over wood, says Dickinson. “Plastic trim has real problems as well,” she notes. “It is not totally stable and it does move. In terms of making something that can be fair, flush, and adaptive, wood is still the best choice.”

Fine finishes. As with wood flooring products, non-toxic applications for finished carpentry are preferred by all sustainable building guides and programs. Thanks to the considerable research and development that has gone into water-based coatings, their performance properties now rival those of other solvent-based coatings.

Another type of finish is faux-wood, which attempts to mimic the appearance of real wood by coating other materials. While faux-wood finishes are an option for designers, many architects and contractors remain skeptical of their value. “Anything that is a painted-on application or a simulative system, such as photographs of wood underneath layers of plastic with laminates, simply does not have the basic gist of why you want to use wood in the first place—the visual depth and sustainability that you would get from a natural wood application,” says architect Duo Dickinson.

Other environmental issues
No discussion of wood materials and sustainability would be complete without mention of construction site recycling. Although such a practice may require initial effort and expense, the benefits of instituting on-site separation and recycling programs are becoming increasingly important.

“Besides environmental benefits, recycling can have economic benefits for one’s business,” says Kimberly Cochran, an environmental engineer with the U.S. Environmental Protection Agency’s Office of Solid Waste. “Some recyclers charge less money to accept materials that can be recycled, especially if they are separated from other materials. Additionally, recycling or using material on site can reduce material hauling and disposal costs.”

In the context of climate change and green awareness, businesses that recycle or make an extra effort to use recycled products may enhance their public image. Similarly, Cochran suggests, “The increased national interest in constructing green buildings is likely to generate more interest in recycling construction and demolition materials.”

The key to any construction waste recycling operation is training construction crews to separate materials. Following the separation of waste, all clean, untreated wood can be re-milled, chipped, or ground. Wood scraps can be processed into feedstock for engineered particle board, boiler fuel, animal bedding, mulch, and compost. Recovered lumber can also be re-milled into flooring.

With less construction waste going into landfills, the burden on landfill loading and operation can be decreased, and the possibility of soil and water pollution caused by chemically treated wood may also be reduced, according to the Sourcebook for Green and Sustainable Building.

Conclusion: sustainability and wood
Although wood has a few drawbacks, most of its qualities are quite positive, making it a widely used and attractive green building material, from the building’s structure all the way to the interior finishes. With a growing availability and interest in renewable sources and engineered wood products, the application of wood is continuing to expand.

When environmental impact is a key consideration in the selection of materials, ecological concerns about protecting the world’s forests from excessive consumption may raise questions about the source and treatment of wood-based building materials. On the plus side, wood is renewable, requires less energy than most materials to process into finished products, and is low in toxicity and completely biodegradable. In many building assemblies, it enhances thermal performance, interior acoustics, and fire resistance.

The key is to use this resource wisely. Choose certified wood where possible, as well as composite and engineered wood materials salvaged from everyday lumber production. Where possible, use reclaimed and “discovered” wood rather than imported, exotic hardwoods from unregulated sources and markets. Last, minimize waste on the jobsite and in design detailing.

Whether it’s wood’s warm, aesthetic beauty, ecological friendliness, low energy production, durability, or longevity, this natural material is bound to play a prominent role in the green building and construction industry.

About the authors
C.C. Sullivan is a communications consultant and author specializing in architecture and construction. Barbara Horwitz-Bennett is a writer and contributor to construction industry publications.

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Reed Business Information is a Registered Provider with the American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non-AIA members are available on request.
       This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.