Ryan DeDonato, BCT; Kayla Baker, NRC; Clayton Sibley, BCT
From the street, homes across the United States appear aesthetically diverse. Some homes are one-story while others are two-stories. Certain homes display an old-world colonial style while others are modernistic. However, if you stripped these homes of their facades every home would be grouped into three different categories: wood framed homes, steel framed homes, and concrete homes. Why are houses built of different materials? The two fundamental reasons that determine the building material of a home are tradition and geography.
A large majority of residential buildings in the United States are built of wood because of tradition and geography. From the time the United States was settled by the first colonists in the seventeenth century, homes were built from wood because it was readily available and easy to harvest. These European colonists chose to build with wood because this was the material most commonly used in their home country. Furthermore, wood was suitable for the mild New England climate. In fact, wood is a suitable building material for much of the continental United States, from the dry, cold climate of the Northern Midwest to the humid continental climate of the Northeast to the humid subtropical climate of the Southeast (Allen & Thallon, 2011).
To this day, wood continues to be the main building material of residential buildings. When asked about why most homes are framed with wood instead of steel, residential framing contractor Brian Basoli says:
Homes across the country, and especially in New England, are framed with wood because that is how homes are traditionally built. Wood has proven to work well for framing houses for hundreds of years. [Framing with wood] is familiar to contractors and builders. Using steel to frames homes is still relatively new, and [steel] is more difficult to work with. I would rather frame a house with wood than steel because we know it works. (personal communication, November 9, 2013)
However, in certain regions of the United States, namely the subtropical area of the Southeast, a large number of residential buildings are being built with steel and concrete. In his 2001 article, Ward states that over 140,000 concrete homes were constructed in the US, primarily in Florida, during 2001. In fact, the construction of concrete homes increased from about 3% in the mid-1990s to almost 11.1% in 2008, or about one out of every nine homes built (Portland Cement Association1, 2013) Additionally, about 3 to 6 percent of new homes in the United States use steel framing (Perkins, 2000).
The increase in steel and concrete homes is the result of the misconception that wood is not suitable for the subtropical climate of the Southeastern United States. Perkins (2000) and Ward (2001), like all advocates of concrete and steel residential construction, argue that steel and concrete are strong, durable, and resistant to rot and termites, whereas wood does not possess these characteristics. However, wood does in fact possess these physical properties and Perkins (2000) and Ward (2001) further fail to mention the significant environmental impacts of steel and concrete.
With regard to embodied energy, carbon sequestration, and air emissions, steel and concrete are more harmful to the environment than wood. Our buildings account for 40% of energy usage in the United States (Allen & Thallon, 2011). When the energy required to harvest and manufacture steel, concrete, and wood are taken into consideration, that 40% energy usage percentage increases (Allen & Thallon, 2011). According to the United States Environmental Protection Agency (n.d.), our energy usage directly relates to greenhouse gas emissions that contribute to climate change. We believe the use of wood in-place of steel and concrete can reduce carbon emissions and slow climate change. As a result, a campaign to educate and convince contractors in the Southeast is needed to reverse the growing trend of steel and concrete residential construction so that all new homes are built with wood.
Why does Energy Matter?
One way to assess the environmental impact of different materials is to measure their embodied energy. As defined by the Canadian Wood Council (n.d.), embodied energy “represents the energy consumed in the acquisition of raw materials, their processing, manufacturing, transportation to the site and construction” (p.3). When looking at the embodied energy of wood, concrete, and steel building materials, wood has a lower embodied energy. In a study conducted by the Canadian Wood Council (n.d.), researchers found that steel and concrete use 26% and 57% more energy than wood, respectively (p. 10). According to Norgate, Jahanshahi, and Rankin (2007), the process for manufacturing steel includes mining raw ore, which requires the use of large amounts of fossil fuel to fuel trucks and equipment. The raw ore must be melted in a blast furnace, which requires further fossil fuel input. As outlined by Huntzinger, and Eatmon (2009), every step of the concrete manufacturing process, from raw material quarrying to shipping, requires the input of some form of energy, whether it be coal, fuel oil, or natural gas.
Why is wood’s embodied energy so low compared to steel and concrete? In his Forest Products Journal article, Bob Falk (2009) states, the energy required to grow trees comes directly from the sun and “over half the energy consumed in manufacturing wood products in the United States is from biomass, … which is typically produced from tree bark, saw dust, and by-products of [paper] pulping …” (p.7). The embodied energy and environmental impact of wood is drastically reduced because most of the energy to grow and manufacture wood products comes from the sun and other renewable fuel sources.
Wood Cleans Our Air
Manufacturing non-wood products is energy intensive and produces substantial emissions. Because wood can be substituted for more fossil fuel-intensive products, the reduction of carbon emissions is even larger than the benefit of carbon sequestration in wood products (Gustavsson and Sathre, 2011). In their 1994 article, Buchanan and Honey calculated the CO2 emissions released during the production of building materials. When wood-framed buildings were compared to steel or reinforced concrete versions of the same buildings they found that the wood buildings released less CO2 emissions (Buchanan and Honey, 1994).
A study by Börjesson and Gustavsson (2000) compared wood framed and concrete framed multi-story buildings and found that concrete construction used 60-80% more energy for the production of materials than wood construction. There has been significant research concluding that displacing fossil fuel-intensive building materials with wood could play the most substantive role in mitigating climate change (Borjesson and Gustavsson 2000; Buchanan and Levine 1999; Lippke et al. 2004; Lippke and Edmonds 2006; Perez-Garcia et al. 2005; Sathre 2007).
In addition to emitting less greenhouse gases than steel and concrete, wood also has the ability to sequester carbon from the atmosphere through photosynthesis. They also release CO2 during respiration and decay. Carbon dioxide is the most prevalent greenhouse gas produced by human activities. In 2000, it accounted for 72 percent of human-related greenhouse gas emissions (Malmsheimer et al., 2008). Approximately 150 million tonnes of carbon are sequestered by forests annually in the U.S., the equivalent of 10 percent of total carbon emissions nationally (Falk, 2009). Harvesting trees in older tree stands may be important in restoring a forest’s ability to sequester carbon. Young trees have a higher rate of carbon sequestration than mature trees. As the forest ages, trees release more carbon through respiration and decay than the amount that is taken up in photosynthesis (Malmsheimer et al., 2008).
Managing forests through active harvest for lumber production can increase the ability of the forest to sequester carbon. These harvested trees can be sawn into lumber for use in residential home building. Although harvesting will initially release carbon by disturbing the soil and removing organic matter, the tree’s carbon will remain stored permanently (Malmsheimer et al., 2008). When wood is harvested and used its carbon is transferred from the forest to the products; therefore, trees sawn into lumber for building sequester carbon for the life of the building (usually decades).
The high carbon sequestration levels of managed forests provide the most benefits for climate change mitigation relative to unmanaged forests. Over time, harvested forests delay wood-decay CO2 emissions from wood products, which further increase climate change mitigation benefits. A vast area of the United States is forested – 33 percent – so even small increases in carbon sequestration abilities will add up to very substantial quantities (Malmsheimer et al., 2008). Further, commercial forests, which tend to utilize short, intensive rotations, can sequester significant carbon if the wood products are long lived (Perez-Garcia et al. 2005).
Several studies have shown that managed forests sequester more carbon and have fewer air emissions than unmanaged forests. Eriksson et al. (2007) found that overall CO2 emissions were lower when forests were managed more intensively to produce timber for use as construction material. Life-cycle analyses have also revealed that when wood products are used in construction they store more carbon and use less fossil energy than steel, concrete, brick, or vinyl (Lippke et al., 2004). Malmsheimer et al. (2008) gave the main reasons for this:
1) managed forests consist of younger trees that have higher rates of net carbon uptake; 2) managed forests are a source of wood products that continue to store carbon (in use or in landfills) … 3) the use of wood products substitutes for use of alternative materials, such as steel, brick, concrete, aluminum, and plastic, all of which are based on nonrenewable resources that require much more energy in manufacture; 4) managed forests have lower greenhouse gas emissions resulting from wildfires, insect depredations, and land conversion … (p. 152).
The Economic Benefits of Wood
One concern with wood displacing steel and concrete residential construction is the potential job loss for steel and concrete workers. However, any jobs lost to steel and concrete will be replaced by wood. According to the Portland Cement Association (2013), wood frame homes can be built with the same amount of workers as steel and concrete homes. As a result, there is no net loss of jobs in the local economy.
First, building with wood has economic benefits. Wood frame homes are built faster. In a study conducted by the National Association of Homebuilders (NAHB) Research Center, one framing crew, experienced in both wood and concrete homebuilding, constructed two similar 1,100 square foot homes. One home was built from wood and the second was built of concrete using a common concrete system, flat wall plank insulated panel concrete forms. The wood frame home took a total of 60.70 labor hours while the concrete home required 96.91 total labor hours. The concrete home took 60% longer to build than the wood home (Portland Cement Association2, 2013). Likewise, it is faster to frame with wood than steel. One of our authors, Ryan DeDonato, knowns this from personal experince because he worked doing residential framing. On one project, the company Ryan worked for framed a basement using steel. What should have taken their crew six hours, took them about ten hours to complete. It should also be mentioned that their crew had experience with steel framing. Because wood frame homes are faster to construct, more homes can be built and workers are kept busy which results in economic benefits.
Additionally, wood frame homes are cheaper than concrete residential buildings. In the same study conducted by the NAHB Research Center, the total labor cost of the wood frame home was $1,730. On the other hand, the total labor cost of the concrete home was $2,838. Furthermore, the above grade wall material cost for the wood frame home was only $1,249 while the cost for the concrete house was $3,148 (Portland Cement Association2, 2013). It is clear that wood frame homes are cheaper and more affordable for homeowners. In turn, affordable housing produces economic benefits such as creating construction-related jobs and stimulating the local economy by attracting new employees and employers to the area (Wardrip, Williams & Hague, 2011).
Wood can Handle the Job
Steel and concrete supporters argue wood is not strong enough to withstand hurricanes and resist moisture related decay and insect damage; as a result, wood homes are not suitable for the Southeast (Ward, 2001). However, this opinion is untrue. Wood framed homes can withstand hurricanes, decay and insects.The best way to ensure the proper strength of wood and prevent moisture related decay and insect damage is to build homes correctly. It is a simple solution, and a solution that is expected when homes are built. However, homes are not always built correctly either because of human error or ignorance.
Moisture control is the most important obstacle to manage. If moisture is controlled through proper design and construction, then decay and insect damage can be prevented because mold and insects require moisture. The Wood Handbook: Wood as an Engineering Material (2010) states, “serious [wood] decay problems are almost always a sign of faulty design or construction” (p. 14-7). One, construction practice to prevent decay and insect damage is to use pressure-treated wood. Pressure-treated wood is chemically treated and injected with oils or water-borne salts to make the wood decay and insect resistant. The chemical treatment lasts for the life of the wood. Another construction practice to prevent decay and insect damage is to protect wood with weather barriers or moisture-resistant membranes. Every house has a weather barrier or moisture-resistant membrane that protects the home from water entering the structure. If the membrane is installed correctly, the wood frame will be protected from moisture and prevent decay and insect damage. A third, and simple, construction practice to manage water is to control water run-off with gutters, drains and vegetation. A final practice, which is often done incorrectly, is providing ventilation and air circulation to allow wet wood to dry (Allen & Thallon, 2011).
Furthermore, advocates of steel and concrete argue wood is not as strong and cannot withstand hurricanes. On the contrary, when comparing wood and steel, Allen and Thallon (2011) state, “wood is comparable to steel on a strength-per-unit-weight basis” (p.86). In addition, when comparing the allowable tensile strength of wood and concrete, wood has an allowable tensile strength of 700 psi (pounds per square inch) while concrete has an allowable tensile strength of 0 psi. When comparing the allowable compressive strength of wood and concrete, wood has an allowable compressive strength of 1,100 psi while concrete is only slightly better with an allowable compressive strength of 1,350 psi (Allen & Thallon, 2011, Figure 4.21). Also, according to the Forest Products Society (2011), wood engineered products, such as glulams and parallel strand lumber, provide another wood option because they are designed to be stronger in bending and compression than wood lumber. Therefore, the strength of wood allows wood-framed homes to withstand hurricanes.
In fact, the Florida building code shows how wood-framed homes can resist hurricane force winds (Allen & Thallon, 2011). Homes are often destroyed by hurricanes because windows or doors fail, resulting in the pressurization of a home and causing walls to collapse. Even concrete houses are destroyed by the same window and door failures (Ayscue, 1996). Clearly, the strength of wood is not the reason why wood framed homes are destroyed by hurricanes. Despite the facts proving wood is able to withstand the Southeastern environment, contractors still promote steel and concrete homes.
Spread the Word that Wood is Good
As we argued, all new residential construction should use wood rather than steel or concrete. Steel and concrete use in residential construction in a national problem. Steel and concrete homes are being built across the country, even in New England. However, this problem is centered in the Southeast which is where we focus our proposal on.
The difficulty is convincing contractors, architects, developers, building inspectors, and environmental advocacy groups, especially in the Southeast, that wood should be used in residential construction. Wood industry members should inform these skeptical groups of wood’s lower environmental impacts compared to concrete and steel. Sadly, most members of the Southeastern construction industry will not change their methods solely based on the environmental benefits of wood. Wood industry members must also dispel the myths that wood cannot be used in the Southeast because it is not strong enough to withstand hurricanes, moisture, and insects.
In order to convince residential construction industry members to use wood, wood industry members should attend the annual Southeast Building Conference (SEBC) to address the concerns of contractors, architects, developers, building inspectors, and environmental advocacy groups. According to the Southeast Building Conference (2013), the SEBC is the largest building industry trade show in the South that attracts thousands of builders, contractors, and other members of the construction industry from the Southeast. Facts and scientific evidence are the only ways to convince residential construction industry members in the Southeast that wood is more environmentally friendly than steel and concrete and can be used successfully in the Southeast. Nationally recognized residential construction and wood industry members are the most credible sources of such information. These groups are the ones who can convince resistant Southeastern residential construction members.
The National Association of Home Builders, one of the largest design and construction trade associations comprised of contractors, designers, material manufacturers, and realtors, along with the International Code Council (ICC), a group of architects, builders, and building code officials who write building codes, should lead the campaign to inform Southeastern residential construction members at the SEBC (Allen & Thallon, 2011). In support of the wood campaign, groups such as the American Wood Council (AWC) and APA- The Engineered Wood Association can inform steel and concrete advocates of the lower environmental impact of wood and support their claim with scientific data. The AWC and APA can also address the concerns that wood is not strong or durable enough to withstand the moisture, hurricanes, or termites of the Southeast with scientific data and real world experiences. Additionally, the Certified Forest Products Council and the Forest Products Society can attest that the wood harvested in the United States and used by the wood industry has a minimum environmental impact and utilizes careful forest management practices. Moreover, local groups such as the Southeastern Lumber Manufacturers Association and the Southern Forest Products Association and further verify that these claims are accurate. Finally, to end the misconception that wood cannot be used in the Southeast, it is important for contractors from the Southeast who have built homes using wood to speak with the steel and concrete advocates to prove that wood can in fact be used successfully in the Southeast.
However, even if contractors from the Southeast are convinced to use wood because of its lower environmental impact compared to steel and concrete, and recognize wood can be used successfully in the Southeast, the only definitive way to get all new residential buildings to be built with wood is to change the law. Together with the help of the ICC and residential construction and wood industry members from across the country and the Southeast, local contractors, designers, architects, building inspectors, and environmental advocacy groups can change local building codes to allow all new homes to be built with wood as the primary building material.
Wood can Help Save the World
The evidence is clear; wood can and should be used in all new residential construction. Energy usage is important to us now, and will be more-so in the future. Our built environment uses massive amounts of energy; 40% of U.S. energy is used by our buildings (Allen & Thallon, 2011). Our energy usage is harmful to the environment and this problem will only worsen as time goes on if changes are not made today. This energy usage produces immense amounts of carbon dioxide and greenhouse gases. Carbon dioxide and greenhouse gas emissions directly relates to climate change which has a far-reaching effects on us and the world we live in. There are many things we can do as a society to reduce energy usage and carbon emissions. One solution that is proven to reduce energy usage and carbon emissions is to build homes with wood in place of concrete and steel.
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