Evolving Building Codes and the Wood Revolution  

There is a quiet revolution taking place within the design community. After a prolonged emphasis on concrete and steel for buildings other than homes, design professionals are using wood to great effect in a growing number of non-residential and multi-family building types—in applications that range from traditional to innovative, even iconic. Some are driven by wood's cost effectiveness¹ while others cite its versatility or low carbon footprint,² but their collective path has been made possible by building codes that increasingly recognize wood's structural and performance capabilities, and the continued evolution of wood building systems and techniques.

When the International Building Code (IBC) was introduced in 2000, it consolidated three regional model building codes into one uniform code that has since been adopted by most jurisdictions. It increased the possibilities for wood construction by (among other things) recognizing additional fire protection techniques, consolidating the maximum allowable areas and heights from the three legacy codes into one (thus increasing what's allowable in some jurisdictions), and allowing the use of wood in a wider range of building types. In subsequent versions of the IBC, even more opportunities have been created where additional fire protection features are used.

Even so, the pioneering nature of building design is such that there are always architects and engineers seeking to push beyond the conventional, and it is common for project teams to require—and be granted—variances for designs not covered in the code that can nonetheless be justified on a case-by-case basis.

This CEU will examine the use of wood both within the current IBC and through building projects that have further pushed the boundaries of wood design and construction.

CASE STUDY Pushing the Boundaries of Wood Design

Photo by Nic Lehoux; courtesy of Bing Thom Architects Project: Arena Stage at the Mead Center for American Theater Location: Washington, D.C. Architect: Bing Thom Architects Structural Engineer: Fast+Epp Structural Engineers Specialty Timber Façade Design- Builder: StructureCraft Builders Inc. Size: 200,000 square feet Completion Date: 2010 When Arena Stage at the Mead Center for American Theater reopened in 2010, it was the first modern building of its size to use heavy timber components in the United States capital. It was also the first project in the U.S. to use a hybrid wood and glass enclosure to envelop two existing structures. The design includes 18 parallel strand lumber (PSL) columns around the perimeter of the glass façade, each measuring 45 to 63 feet tall and supporting steel roof trusses, which cantilever beyond the envelope to create an overhang that runs around the structure. Designed to brace the façade against wind loads and to carry roof loads up to 400,000 pounds, the columns have no internal steel support. Local code authorities were skeptical about allowing wood and about fire safety in particular, so the design team presented an in-depth fire report along with the results of a smoke study undertaken by a code consultant. “Through computer modeling, we showed that effects of a fire on the structure would be minimal, and there would be plenty of time for safe building evacuation,” says Julien Fagnan, associate and project manager for Fast+Epp Structural Engineers. The design team also did a char analysis, and showed District of Columbia code officials how char actually protects the interior of the wood. While charring would leave a column of reduced size, calculations showed that, because the column was sized mainly for deflection, it already had additional strength capacity.

Fire Protection

Large Beams, Cross Laminated Timber Perform Better in Fire

Some wood products, such as the large beams used in heavy timber construction and cross laminated timber (CLT), may perform better in a fire situation than noncombustible materials. Because they are thick and solid, these products char at a slow and predictable rate. This char protects the wood from further degradation, helping to maintain the building’s structural integrity and reducing its fuel contribution to the fire, which in turn lessens the fire’s heat and flame propagation.4 Section 602.4 of the 2009 IBC has prescriptive provisions for wood members which meet the definition of heavy timber. Recent fire resistance testing conducted by the American Wood Council confirmed that CLT exterior walls exceed the requirements for heavy timber construction. Photo courtesy of FPInnovations

Building codes require all building systems to perform to the same level of safety regardless of material used, and wood-frame construction has a long history of fire-safe performance.³ In fact, the IBC allows larger wood structures in a greater range of building types than designers may think possible.

Using tabular allowable areas as a starting point, the IBC allows designers to increase the floor area and building height of wood-frame structures with the addition of sprinkler systems, fire walls, augmented exiting, fire-resistive materials and open perimeter spaces.

For example, it permits low-rise, two-story business and mercantile buildings of wood construction to be unlimited in area if they have a fire sprinkler system and 60 feet of fire separation distance from property lines. Residential wood buildings with sprinklers and exterior walls made from fire-retardant-treated wood (FRTW) can be up to five stories tall and have additional “levels” when mezzanines are included. Under the 2009 IBC, mezzanines are permitted to be 33 percent of the floor area below and considered part of that story, though local jurisdictions may allow a greater percentage. The code also permits the use of wood for many features in buildings required to be of a noncombustible construction type, often even whole roof structures.

Under the IBC, designers can use fire walls to separate a building into smaller fire areas when additional size is needed and sprinklers either aren't an option or they don't afford the necessary increases for the use and site characteristics of the building. In a Type V building, fire walls are permitted to be wood-frame construction, allowing designers to divide the structure into separate buildings for purposes of size, each subject to its own height and area limits.

In addition to the sprinkler and open frontage trade-offs, a designer's options also include fire-resistance rating the entire structure, using fire-retardant-treated wood in the exterior walls, and heavy timber construction:

Rated assemblies consist of specific wall/floor/ceiling component combinations that are used to prevent the spread of fire for a specific time period—typically one or two hours.⁵ Assembly ratings are normally established through standardized tests that approximate actual fire conditions. The standard for measuring fire resistance of building assemblies is ASTM Test Method E-119, Standard Test Methods for Fire Tests of Building Construction and Materials. For exposed beams and columns of heavy timber dimensions, the IBC also permits fire resistance to be established by methods of calculation. Chapter 7 of the IBC references Chapter 16 of the National Design Specification® (NDS®) for Wood Construction for designing exposed wood members for a specific fire resistance. In this way, buildings can take advantage of the larger areas and heights of rated construction types. FRTW, covered under IBC Section 2303.2, can be used in roof assemblies of Types I and II construction—construction types which are otherwise required to be noncombustible. Fire-retardant treatment limits flame spread and prevents progressive combustion over time. Heavy timber roofs without fire-retardant treatment are also permitted in all construction types except Type 1A.

Heavy timber construction combines the beauty of exposed wood with the strength and fire resistance of heavy timbers.⁶ Modern versions include sawn stress-grade lumber, tongue and groove decking, and glued laminated (glulam) timber. Under the code, fire resistance is achieved by using wood structural members of specified minimum size and wood floors and roofs of specified minimum thickness and composition; by providing the required degree of fire resistance in exterior and interior walls; by avoiding concealed spaces; and by using approved fastenings, construction details and adhesives for structural members. Heavy timber construction is classified as Type IV—a special class that recognizes the inherent fire resistance of large timber and its ability to retain structural integrity in fire situations. Since large wood members char when exposed to fire, surface char insulates the member so it can continue to support its load, increasing the amount of time before the member fails.

CASE STUDY Designing for Fire Protection

Rendering courtesy of Cline Design Associates, Pa. Project: Gallery at Cameron Village Location: Raleigh, N.C. Architect: Cline Design Associates, Pa. Engineer: SCA Consulting Engineers Size: Five stories, 550,000 square feet Completion Date: Fall 2013 Slated for completion next fall, this mixed-use project includes five stories of wood-frame construction over a concrete podium deck. Designed as Type IIIA construction, the wood portion will include fire-retardant-treated structural wood products on the exterior, plated wood floor and roof trusses, and a mix of plywood and/or fire-retardant-treated oriented strand board (OSB) sheathing. Designers achieved a 2-hour rating on exterior walls using double layers of fiberglass mat gypsum sheathing over FRT wood studs and a double layer of Type X gypsum wall board on the interior supported by 6x9 PSL beams rated for 180 minutes. Using this unusual approach, the wood trusses are supported by PSL at the 2-hour bearing exterior walls. By engineering the building with holdowns that eliminated shear on the exterior walls, while also using interior shear walls, designers were not required to use plywood on the exterior. The project team utilized the potential for wood in the code to the fullest, by designing a one-story above-grade concrete podium for retail and leasing, and three subterranean levels that are separate from the Type III wood structure above, as allowed by section 509 of the 2009 IBC. Adding a fire wall allowed them to split the structure into two separate buildings for code purposes and therefore take advantage of the maximum building height for each as they step down the sloped site. The higher building is two levels above the lower building, and this vertical offset allowed both buildings to stay under the maximum height allowed in Type III wood-frame construction.

 

Wood is Allowed in Noncombustible Construction

Although perhaps counter-intuitive, the IBC allows the use of wood in “noncombustible” buildings and construction types that require noncombustible exterior walls. • Type I and II construction require noncombustible materials, but Section 603.1 of the IBC allows use of FRT W for a number of applications; it also lists other typically non-structural uses of wood permitted in these buildings. • While Type III construction requires noncombustible materials for exterior walls, Section 602.3 allows FRT W in wall assemblies with a 2-hour rating or less. • Type IV (heavy timber) construction includes noncombustible materials for exterior walls and timber for interior framing; Section 602.3 also allows FRT W for exterior wall assemblies with a 2-hour rating or less. • Table 601 permits heavy timber roof structures in all construction types except Type 1A.

Seismic Performance

Years of research and building code development have proven that wood-frame and hybrid structures can meet or exceed the most demanding earthquake design requirements.⁷

Forces generated in an earthquake are proportional to the structure's weight and wood is substantially lighter than other common building materials.⁸ The fact that wood buildings tend to have numerous nail connections means they also have more load paths, and less chance the structure will collapse should some connections fail. This is also why they have inherent ductility, with multiple load paths to dissipate energy when faced with the sudden loads of a seismic event.

The correct design of elements such as frames, shear walls, diaphragms and their connections to each other is of utmost importance as earthquake forces “search out” the weak links between structural members. Where there is serious damage or collapse, research shows it is often the result of connection failure.

Demonstrating wood's performance in a seismic event, an assessment of the damage to California schools in the 1994 Northridge earthquake was summarized as follows:

“Considering the sheer number of schools affected by the earthquake, it is reasonable to conclude that, for the most part, these facilities do very well. Most of the very widespread damage that caused school closure was either non-structural, or structural but repairable and not life threatening. This type of good performance is generally expected because much of the school construction is of low rise, wood-frame design, which is very resistant to damage regardless of the date of construction.”⁹

In 2002, the California Dept. of Government Services completed a legislated inventory and earthquake worthiness assessment of schools. School buildings that were constructed of steel, concrete, reinforced masonry or mixed systems designed between 1933 and July 1, 1979 were required to be evaluated. Older wood-frame schools were exempted on the basis that “wood-frame buildings are known to perform well in earthquakes.”¹⁰

CASE STUDY Designing for Seismic Forces

Photo courtesy of Thorson Baker & Associates Project: Hyatt Place El Segundo Location: El Segundo, Calif. Architect: Braun & Steidl Architects Engineer: Thorson Baker & Associates Size: 83,900 square feet Completion Date: December 2012 Seismic forces presented the greatest engineering challenge for this Hyatt Place hotel in California, which includes five stories of wood-frame construction. To accommodate the large windows that are typical of the Hyatt prototype, the exterior walls are designed as segmental shear walls so the force is transferred around the window. Because the ground floor includes large meeting rooms where walls are taller and fewer, designers used eccentric inverted V-braces and moment frames with unique reduced-beam sections where the beam is weakened on purpose. Developed in the 1990s based on lessons learned from previous earthquakes, this technique allows the weak spot to fail slowly if the building exceeds the design loads during a seismic event, thus preventing the moment connection from brittle failure. The placement of shear walls also required some ingenuity. “Like most hotels, the Hyatt Place El Segundo is long and narrow, so seismic weight in the long direction is a challenge,” says Donald Schehl, PE, LEED AP, of Thorson Baker & Associates, Inc. “Given the number of large windows, we had to use pretty well every inch of exterior wall and every inch of corridor. The panel edge fasteners on the plywood sheathing were spaced 2 inches on center (o.c.) on each side of the walls on the lower levels.” Photo courtesy of Ingraham/DeJesse Associates Above: Continuous rod holdown system in the Telegraph Apartments. Rendering courtesy of Rolnizky Architect Project: Telegraph Apartments Location: Berkeley, Calif. Architect: Rolnizky Architects Engineer: Ingraham/DeJesse Associates Size: 37,885 residential square feet Completion Date: 2013 Located close to the Hayward Fault in an area with extremely high seismic forces, the Telegraph Apartments includes four stories of wood-frame construction over a one-story post tensioned concrete podium—and an exterior façade that’s almost entirely glass. In general, seismic forces pose a particular challenge for the bottom floor of a four-story multifamily wood-frame building because the length of the required solid shear wall often means minimizing the exterior glazing—which is programmatically challenging with narrow, deep living units. To meet these challenges, the design team used the rigid diaphragm analysis approach, which allowed long interior corridor shear walls to transfer a larger percentage of the seismic load than is typically the case. A combination of dimension lumber and engineered wood products, including 2x/3x framing, OSB sheathing on the floors, walls and roof, and a continuous rod holdown system at the ends of the shear walls provided an efficient design that allowed the framing to proceed in a standard manner. The engineering firm is currently using this design for structures with up to five stories of wood-frame construction.

Wind Resistance

In addition to superior seismic performance, wood buildings can be designed to effectively resist high winds. Wood's elastic limit and ultimate strength are higher when loads are applied for a short time, which tends to be the case in high wind events. When structural panels such as plywood or OSB are properly attached to lumber framing and used to form diaphragms and shear walls, they also form some of the most solid and stable roof, floor and wall systems available.¹¹

However, in order for the diaphragms and shear walls to be effective, all of the related components—including framing, structural panel sheathing and inter-element fastening details—must be designed and installed correctly.

For the structural system to work as intended, the roof diaphragm must be able to transfer lateral loads to the shear walls and the shear walls themselves must transfer these loads to the foundation. The success of the entire system is only as good as the quality and quantity of the connections. Therefore, the key to constructing a building that can resist lateral loads is understanding how forces are transferred and how to design and install proper connections.

In hurricanes, the loss of roofing materials and sheathing is the leading cause of structural failure in wood-frame buildings. The most common reasons behind these failures are improper connection detailing between structural systems and inadequate fastening of sheathing to supporting members. Most local building codes require a minimum of 33 fasteners for a standard 4×8 panel installed over roof supports 24 inches o.c. Fasteners, such as 8d common nails (2.5 inches x 0.131 inch) or other code-approved options, should be placed a maximum of 6 inches o.c. along panel edges and 12 inches o.c. at intermediate supports. Following Hurricane Andrew in Florida, damage assessment teams found roof sheathing panels with as few as four fasteners. Once the roof sheathing has been pulled off its framing, the load path is interrupted and the diaphragm ceases to function.

Sound Transmissions and Acoustics

The IBC requires multi-family residential buildings to have a minimum Sound Transmission Class (STC) rating of 50 and a minimum Impact Insulation Class (IIC) rating of 50 for partitions and floor/ceiling assemblies between adjacent dwelling units or between dwelling units and adjacent public areas. Acoustical problems arise when sound transmits through the structure or when reverberation occurs via hard reflective surfaces.

Wood-frame construction is particularly efficient in residential buildings where sound insulation is required. Attaching gypsum board to walls and ceilings using resilient metal channels significantly reduces sound transmission, as does placing glass-fiber or rock-fiber insulation within wood-frame floor and wall assemblies. Wood-frame construction does not present the impact noise transmission issues commonly noted with concrete construction.¹²

That said, the design of any functional and safe building is difficult if not impossible without considering acoustics, and wood has a proven record in this regard. Wood is not as acoustically lively as other surfaces and can offer acoustically absorptive qualities, hence its widespread use in performance and musical venues. At the Arena Stage at the Mead Center for American Theater, for example, a small theater called “The Cradle” posed a challenge because of the sound reflections caused by its oval shape. In response, Bing Thom Architects developed a wood slat wall system made from poplar, designed to look like a basket weave, which could absorb and disperse sound.

CASE STUDY Designing for Acoustics

Project: Duke School Location: Durham, N.C. Architect: DT W Architects & Planners/Fielding Nair International Engineer: GKC Associates Size: 79,204 square feet Completion Date: 2009 When DTW Architects & Planners and Fielding Nair International signed on to design Duke School, they faced the same challenge school boards and design teams face across the country: how to balance cost and functionality objectives while creating an enriching space that inspires learning. “To create a positive learning environment, we used exposed wood as the main design element,” says DT W’s Robert Sotolongo, AIA , LEED AP. Glulam columns, girders, purlins and arches comprise the main structural frames, while exposed tongue-andgroove wood roof decking is used as a design element. However, no building design is without its challenges and the desire for large, open rooms dominated by exposed wood decking meant consideration to acoustics. “At first we planned to use dropped acoustical ceilings in select areas, but the owner loved the wood so much we changed our minds,” says Sotolongo. “We put down carpet and suspended ceiling baffles in select areas. We also constructed wall panels—essentially wood framing with batt insulation covered with fabric—which turned out to be a cost-effective solution.” Photo by Jerry Markatos; courtesy of DTW Architects & Planners

The Evolution of Wood Construction

Growing recognition of wood's benefits continues to increase its appeal in specific building types, while new products and technologies expand the possibilities for how and where wood is used.

Mid-rise/multi-family—Mid-rise buildings are typically Type V construction, which allows the use of untreated wood throughout, or Type III, which allows wood roof and floor systems as well as interior wood-frame walls. (FRTW is required for exterior wood-frame walls in Type III buildings.)

Many developers and design teams default to wood for mid-rise buildings up to four stories because it's the most economical choice; however, with five-story wood buildings (and potentially higher) permitted in the IBC, there has been a marked interest among those who see taller wood buildings as a way to achieve greater density at lower cost. Podium structures in particular, which include multiple stories of residential wood-frame construction over a podium deck, are common among design professionals seeking to incorporate parking, retail or restaurants into their designs.

CASE STUDY Beyond Five Stories with the IBC

Photo courtesy of Togawa Smith Martin, Inc. Project: Union Square Condominiums Location: San Diego, Calif. Architect: Togawa Smith Martin, Inc. Engineer: Edmond Babayan and Associates Size: 263 condominium units Completion Date: 2005 Architects for the Union Square condominium project in San Diego made use of code provisions to increase the height of the project by adding two levels for residential use. First, utilizing IBC Section 505, designers added a mezzanine, which increased the number of wood-frame levels to six. Second, since the project was not located in a retail neighborhood, the Type IA concrete level at grade was designed to incorporate residential “stoop units,” each with access to the street. The building was thus able to achieve seven levels of residential use with a density of 143 units per acre.

Schools—The IBC has well-established parameters for wood-frame schools, which is good news for school districts trying to accommodate increasing enrollment on a limited budget. However, many who turn to wood-frame construction for its cost effectiveness find that wood also offers other advantages—such as speed of construction, design versatility and the ability to meet green building goals. Increasingly, research is also supporting the idea that exposed wood in a room promotes the well-being of occupants, reduces stress and creates a positive environment for learning.

For example, a study¹³ at the University of British Columbia and FPInnovations found that the presence of visual wood surfaces in a room lowered activation of the sympathetic nervous system (SNS) in an office environment. The SNS is responsible for physiological stress responses in humans such as increased blood pressure and heart rate while inhibiting the parasympathetic system responsible for digestion, recovery and repair functions. Study author David Fell says research on wood and schools is underway, but the results of the office study apply to any interior environment. “The stress-reducing effects we found for wood in office environments are in theory transferable to any building type as these are innate reactions to natural materials.”

At the 322,500-square-foot El Dorado High School in Arkansas, designers used exposed wood and natural light to create an environment that would motivate students to stay in school. “We used exposed wood products in structural systems and in elements such as doors, millwork and trim to provide a unique architectural aesthetic that helps to naturally soften and warm the spaces,” says project architect Blakely C. Dunn, AIA, NCARB and principal of CADM Architecture, Inc. From a code perspective, this project is noteworthy because it was one of the first schools in Arkansas to make extensive use of wood following a change in school board policy that had previously prohibited wood in school construction. In 2008, recognition of wood's safety and performance attributes led the Arkansas School Board to modify its School Facilities Manual to reflect the IBC. It is also noteworthy from a cost perspective. Originally designed in steel and masonry, the school was changed to wood-frame construction for budget reasons—a move that saved the school board $2.7 million.

At the 322,500-square-foot El Dorado High School in Arkansas, the use of exposed wood and natural light creates a welcoming environment. Photo by WI Bell; courtesy of WoodWorks

 

Mass timber—Since the invention of modern day plywood in the early 1900s, a succession of engineered wood products have offered increasing strength and stability, expanding the options for (among other things) taller walls and longer unsupported spans in wood buildings.

In the latest development, mass timber products such as glulam, laminated veneer lumber, laminated strand lumber and now cross laminated timber (CLT) are inciting much discussion (and press) around the safety, feasibility and economics of constructing high-rise wood buildings.

Sometimes referred to as “plywood on steroids,” CLT typically consists of three, five or seven layers of solid dimensional lumber, kiln-dried and layered perpendicular to one another and then glued to create full-depth solid wood, wall and floor panels up to 12 feet by 60 feet. This cross lamination provides exceptional strength, stability and rigidity, allowing CLT to be used as a low-carbon alternative to concrete and steel in many applications. Benefits of CLT also include quick installation, minimal on-site waste, light weight and (as a result) reduced foundation requirements, thermal performance, and design versatility.

In Europe, there are examples of eight- and nine-story CLT buildings, and a 10-story CLT building has just been completed in Australia. In the U.S., recent changes to the IBC place CLT of a certain thickness within Type IV construction. Fire-resistance testing has confirmed that it performs at least as well as heavy timber while providing for even greater fire resistance by eliminating concealed spaces in wall and floor assemblies of traditional dimensions.¹⁴

In May 2012, APA published ANSI/APA PRG 320-2011 Standard for Performance-Rated Cross-Laminated Timber, an American National Standard that provides requirements and test methods for qualification and quality assurance of CLT. CLT products manufactured to the standard will be recognized as code-compliant in the 2015 iteration of the IBC.

CASE STUDY Designing with New Materials

Photo courtesy of StructurLam Products Ltd.; rendering courtesy of Promega Project: Promega GMP Facility Location: Fitchburg, Wis. Building design: Uihlein-Wilson Architects; EwingCole; Archemy Consulting CLT Engineer: Equilibrium Consulting Inc. Size: 260,000 square feet Completion Date: October 2012 Building codes are flexible enough to accommodate new materials and it’s common for building projects to require—and be granted—variances for designs not in the code that can be justified on a case-by-case basis. Such was the case for the new Promega biotechnology production facility, which features an innovative mix of glulam and CLT. Building department approval was achieved through use of the newly completed ANSI/APA PRG 320-2011 Standard for Performance-Rated Cross-Laminated Timber. “The design team discussed the standard with building officials early in the process,” says Kris Spickler of StructurLam Products Ltd. “Engineering information was then submitted under the “alternate designs” section of the code. IBC Section 104.11 states that ‘An alternative material, design or method of construction shall be approved where the building official finds that the proposed design is satisfactory and complies with the intent of the provisions of the code.’ Local building officials accepted both the AN SI/APA standard and the design.” Most of the new Promega facility will be dedicated to manufacturing with committed (fixed) production lines and flexible manufacturing areas. It will also feature a customer experience center for employees and guests that will include spaces for training, laboratory demonstrations, conferences, an exercise and fitness center, and dining.

 

Green Building Codes, Standards and Rating Systems

In addition to requirements designed to ensure safety and structural performance, there are a growing number of codes, standards and rating systems that seek to minimize a building's environmental impact.

The most recent example is the International Green Construction Code (IgCC), released in March 2012. Adopted by eight jurisdictions so far, it is the latest phase in an evolution that's included two American National Standards (covering residential and non-residential construction), the California Green Building Standards Code (CALGreen), and ASHRAE 189.1, a code-intended commercial green building standard published by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) in cooperation with the Illuminating Engineering Society of North America (IES) and US Green Building Council.

The IgCC covers subject areas typically found in any green building effort, including site, materials, energy, water, and indoor environment. Although a voluntary code that some jurisdictions have adopted to provide guidance regarding public or publicly funded buildings, it includes 'mandatory' provisions within all subject areas as well as recommended provisions and electives. It is potentially applicable to almost every commercial building project, including additions and repairs.

In terms of material use, the IgCC's key mandatory requirement is that at least 55 percent of materials (based on mass, volume or cost) be used, recycled, bio-based, and/or indigenous in any combination. However, this rule need not be met when a whole building life cycle assessment (LCA) is performed.¹⁵

LCA is a scientific approach to evaluation that considers the impact of materials over their entire life cycle, from extraction or harvest through manufacturing, transportation, installation, use, maintenance and disposal or recycling. When integrated into green building codes, standards and rating systems, LCA encourages design professionals to compare different building designs based on their true environmental impacts and to make informed choices about the materials they use. It replaces the prescriptive approach to material selection that's been common until now, which assumes that certain prescribed practices—such specifying products with recycled content—are better for the environment regardless of the product's manufacturing process or disposal. LCA studies consistently show that wood is better for the environment than steel or concrete in terms of embodied energy, air and water pollution, and greenhouse gas emissions.¹⁶

In the U.S., LCA is included in the Green Globes rating system and the American National Standard based on Green Globes, ANSI/GBI 01-2010: Green Building Assessment Protocol for Commercial Buildings, as well as the ICC 700 National Green Building Standard. It's part of both CALGreen and ASHRAE 189.1, and is included as a pilot credit in the Leadership in Energy and Environmental Design (LEED) rating system. Although LCA isn't mandatory in the IgCC, elimination of the “55 percent requirement” is a powerful incentive for its use.

Wood: The Sensible Revolution

Today's building codes recognize wood's safety and structural performance capabilities and allow its use in a wide range of building applications, from the light duty repetitive framing common in small structures to the larger and heavier framing systems used to build mid-rise/multi-story buildings, schools and arenas. This hasn't been lost on design professionals seeking to have it all—cost effectiveness, functionality, design flexibility, beauty and environmental performance—who, through their collective projects, are leading a revolution toward the greater use of wood in non-residential and multi-family buildings.

Wood and Carbon Footprint

Using wood can significantly reduce the carbon footprint of a building project. As trees grow, they absorb carbon dioxide (CO2) from the atmosphere, release the oxygen (O2), and incorporate the carbon into their wood, leaves or needles, roots and surrounding soil. One of three things then happens: • When the trees get older, they start to decay and slowly release the stored carbon. • The forest succumbs to wildfire insects or disease and releases the carbon quickly. • The trees are harvested and manufactured into products, which continue to store much of the carbon. In the case of wood buildings, the carbon is kept out of the atmosphere for the lifetime of the structure, longer if the wood is reclaimed at the end of the building’s service life and manufactured into other products. In all of these cases, the cycle begins again as the forest regenerates and young seedlings once again begin absorbing CO2.17 To illustrate the impact of just one project, El Dorado High School in Arkansas used 153,140 cubic feet of lumber, panels and engineered wood. These products store an estimated 3,660 metric tons of carbon dioxide equivalent (CO2e), while the use of wood instead of fossil fuel-intensive materials means that another 7,780 metric tons of CO2e emissions were avoided during manufacturing. According to the U.S. EPA Greenhouse Gas Equivalencies Calculator, this is equivalent to the annual emissions from 2,100 cars or the energy to operate an average home for 970 years.18

 

ENDNOTES
1	reThink Wood
2	Carbon 101: Understanding the Carbon Cycle and the Forest- Carbon Debate, Dovetail Partners Inc.
3	American Wood Council offers a number of publications related to the fire design of wood buildings for code acceptance
4	Calculating the Fire Resistance of Exposed Wood Members, American Wood Council
5	Fire Rated Wood Floor and Wall Assemblies, American Wood Council
6	Design of Fire-Resistive Exposed Wood Members, American Wood Council
7	ANSI/AF&PA SDPWS-2005 – Special Design Provisions for Wind and Seismic Standard with Commentary, American Wood Council; Design Concepts for Building in High Wind and Seismic Zones, APA
8	American Wood Council
9	The January 17, 1994 Northridge, CA Earthquake An EQE Summary Report, March 1994
10	Seismic Safety Inventory of California Public Schools, California Department of Government Services, 2002
11	ANSI/AF&PA SDPWS-2005 – Special Design Provisions for Wind and Seismic standard with Commentary, American Wood Council; Design Concepts for Building in High Wind and Seismic Zones, APA
12	Fire Resistance and Sound Transmission in Wood-Frame Residential Buildings
13	Wood and Human Health, FPInnovations
14	American Wood Council
15	More information on the International Green Construction Code is available from Dovetail Partners, Inc.
16	Life Cycle Environmental Performance of Renewable Building Materials in the Context of Building Construction, Consortium for Research on Renewable Industrial Materials, Phase I 2005, Phase II 2010; A Synthesis of Research on Wood Products and Greenhouse Gas Impacts, Sarthre, R. and J. O’Connor, 2010, FPInnovations; Wooden building products in comparative LCA: A literature review, Werner, F. and Richter, K., 2007, International Journal of Life Cycle Assessment, 12(7): 470-479
17	Carbon 101: Understanding the Carbon Cycle and the Forest Carbon Debate, Dovetail Partners, Inc., 2012
18	El Dorado High School Students Get the ‘Wow’ They Deserve, US WoodWorks, 2012

The reThink Wood initiative is a coalition of interests representing North America's wood products industry and related stakeholders. The coalition shares a passion for wood and the forests they come from. Innovative new technologies and building systems have enabled longer wood spans, taller walls, and higher buildings, and continue to expand the possibilities for wood use in construction. www.rethinkwood.com