Cross Laminated Timber Over Other Building Materials in Terms of Speed and Efficiency of Construction, Design Performance Environmental Flexibility, and Other Factors

CONTINUING EDUCATION 1 arn 0.1 ICC CEU E bjectives O

CONTINUING EDUCATION

Describe the characteristics of cross Describe the characteristics of cross and its use in a laminated timber (CLT) range of building types. Discuss the advantages of cross laminated timber over other building materials in terms of speed and efficiency of construction, design performance environmental flexibility, and other factors. buildings can Recognize how U.S. CLT building under current be approved codes and how this will change under the 2015 International Building Code. Use technical guidance available in the U.S. U.S. the in available guidance technical Use related Handbook Timber Cross-laminated design, structural as such issues key to resistance. fire and vibration, connectors,

Examine the use of CLT in three innovative innovative three in CLT of use the Examine in the building projects but very different U.S., Canada and Australia.  5. To receive credit, you are required to read the entire article and pass the test. Go to www.awc.org for complete text and to take the test for free. Learning be should you article, this reading After to: able 1. 2. 3. 4. , a product a , ANSI/APA PRG PRG ANSI/APA It offers It the structural 1 InternationalBuilding Code InNorth America, is relatively CLT 320-2012 Standard Performance-Rated for 320-2012 Cross-LaminatedTimber standardthat details manufacturing andperformance requirements for qualificationand quality assurance. Thankscodechanges, recently to approved is also CLT scheduled includedbe to inthe 2015 (IBC).Inthe meantime, handful a of innovativedesigners already have built new but quickly but new gaining momentum. Last the American year, National Standards Association approved simplicity needed cost-effective for projects, as well as benefits such as design versatility, rapid installation, reduced waste, lighter weight (compared to concrete), and energy efficiency. construction to new heights, the most recent example which of is the Forté, a 10-story apartment CLT building in Australia. By Layne Evans ross laminated timber is (CLT) an engineered wood building system designed to complement light- and heavy-timber

CLT hasCLT been popular in Europe C Sponsored by reThink Wood, American Council, reThink Wood, by Sponsored Wood and | FPInnovations Cross Laminated Timber Taking wood buildings to the next level Photo courtesy of Lend Lease framing options. Part a new of product category known as massive “mass”) (or timber, it is made from several layers of lumber board, stacked crosswise (usually 90at degree angles) and glued together theiron wide faces. This cross lamination provides dimensional stability, strength and rigidity, which is what makes a CLT viable alternative to concrete, masonry and steel in many applications. can It be used an for entire building, as both the lateral and vertical load resisting system, select for or elements such as the roof, floors walls. or than more for 20 years, with extensive research and a documented track record supporting its widespread use. Internationally, it has propelled wood CROSS LAMINATED TIMBER

U.S. CLT HANDBOOK

The U.S. CLT Handbook is a peer reviewed technical resource developed by research organization FPInnovations in cooperation with the American Wood Council, USDA Forest Products Laboratory, APA, U.S. WoodWorks and a team of more than 40 national and international experts. It includes detailed information that can be used for the design and construction of CLT systems under the “alternate design” path (or similar concept) that is typical in building codes. It can be downloaded free of charge from the website www.masstimber.com, and hard copies can be obtained from the American Wood Council (www.awc.org).

CLT structures in the U.S. and Canada, use of CLT in a project, such as structural Design flexibility. CLT can be used for having had them approved under their design, connections and fire performance, an entire building or any combination of local building code as an alternative as well as resources available to those wall, floor/ceiling and roof applications. building system. In the IBC, the applicable seeking additional detail. Through Its light weight and other characteristics section is 104.1.1, which states that “An examples of existing buildings in North make it highly adaptable to different types alternative material, design or method of America and around the world, it will of projects, designs and site conditions construction shall be approved where the also illustrate the design flexibility and like soft soils or tight proximity to building official finds that the proposed adaptability of this unique wood product. neighboring buildings. CLT elements can design is satisfactory and complies with also be combined with other building the intent of the provisions of the code.” Why CLT? materials, enabling flexibility in design, This course will consider the Designers choose wood for a variety style and finish architecture. When field characteristics of CLT that make it not of reasons—including aesthetics, modifications are needed, one of the only a viable option, but an ideal choice cost effectiveness and environmental advantages of CLT over materials such as for many building types. Based on the performance—many of which are the precast concrete is that changes can be U.S. Cross-laminated Timber Handbook2 same for CLT. However, CLT also builds made on site with simple tools, pending it will focus on technical information on these advantages with several of its approval by the engineer of record. necessary to engineers considering the own. This section provides a high-level Three examples of CLT’s design

Photo courtesy of Karakusevic Carson Architects overview of these benefits, and is followed Photo courtesy of Martin Tessler, courtesy of Perkins+Will by a closer look at issues of particular importance to structural engineers.

Speed and efficiency of installation. CLT panels are manufactured for specific applications. They are prefabricated, complete with pre-cut openings for doors, windows, stairs, service channels and ducts, and shipped directly from the manufacturer to the job site, where they can be quickly and efficiently Designers of the five-story Earth lifted into place. This can shave months Sciences Building at the University of off the construction schedule. Many British Columbia used CLT for the roof manufacturers ship panels with pre- and exterior canopies. installed lifting straps; contractors Photo courtesy of Lend Lease then use cranes to lift panels into place. Because panels are designed for specific end-use applications, they are often delivered and erected using a “just-in- time” construction method, making CLT ideal for projects with limited on-site storage capacity. When Bridport House (see image) in London was constructed in 2011, it was the largest contemporary timber- CLT’s relative light weight made it ideal built apartment block in the world. In addition to its structural characteristics, for the five- and eight-story Bridport The CLT construction was completed CLT’s aesthetic benefits are highlighted in House, located over a large storm in 12 weeks, by four skilled laborers Forté suites with exposed balcony ceilings sewer in London’s Hackney Borough. and one supervisor.3 and interior walls.

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Photo courtesy of IVALSA flexibility are discussed in case studies degradation. In addition, later in this course: CLT offers increased EDUCATION CONTINUING The Crossroads, a 52,000-square-foot compartmentalization if client and staff reception area owned by used for interior walls. Fire the Promega Corporation, is part of a protection is covered in more 300,000-square-foot Good Manufacturing detail later in this course. Practices (GMP) facility, which is a highly regulated and specialized building Seismic performance. used for manufacturing medical device Because of their dimensional products. The Crossroads has a fairly stability and rigidity, CLT complex footprint, forming a sinuous panels create an effective S-curve which wraps around one corner lateral load resisting system. of the larger facility. The design team Since it is a system of chose to use wood for the two-story, open multiple, small connectors, area. Structurally, they were challenged CLT also offers good to use a material that would perform well ductile behavior and energy for the long-span deck needed to cover the dissipation. Researchers curved roof. CLT provided the solution. have conducted extensive The Earth Sciences Building (ESB) seismic testing on CLT and at the University of British Columbia is found panels to perform comprised of two five-story wings—a exceptionally well with laboratory wing made from conventional no residual deformation, reinforced concrete and the North Wing, particularly in multi-story a new LEED Gold building with offices applications. and lecture halls, which utilizes wood as In Japan, for example, a the main structural element. The North seven-story CLT building Wing features an innovative combination was tested on the world’s of mass timber systems, including CLT largest shake table. Even roof and exterior canopies, composite when subjected to severe laminated strand lumber/concrete floors, earthquake simulation and glued laminated timber (glulam) Tested in Japan on the world’s largest shake table, (magnitude of 7.2 and heavy timber braced frames. The two wings this CLT building survived 14 consecutive seismic acceleration of 0.8 to 1.2 are connected by an atrium, also made events with almost no damage. g), the structure showed no from solid wood panel and glulam post- residual deformation after and-beam construction. masonry and steel building types. Even the test. The maximum inter-story drift Forté (see cover image) is the first CLT without accounting for the advantages was 1.5 inches and the maximum lateral building in Australia and currently the of faster construction time and lower deformation at the top of the building 4 world’s tallest timber apartment building. foundation costs (because of CLT’s was just 11.3 inches. The building The walls and floors form a honeycomb- light weight), CLT was found to be cost survived 14 consecutive seismic events like load-bearing frame, with floor spans competitive for mid-rise residential and with almost no damage—which, in reaching up to 19 feet (6 meters) and pro- non-residential, low-rise educational, addition to demonstrating the safety of viding a repetitive load path for vertical and low-rise commercial, and one-story CLT buildings, illustrates their promise lateral resistance. Lend Lease, which was industrial buildings.5 CLT is particularly in the context of “resilient” design. A both the developer and project architect, cost effective in large, regularly shaped growing trend within the sustainability cites a number of reasons for choosing structures and in situations where movement, resilient design places an CLT, including the ability to manufacture fabrication is repetitive. emphasis on making efficient use of materials to precise tolerances off site and Manufacturers work closely with the resources while creating buildings that fast installation. Installing 10 stories of CLT design team to develop estimates based on last because they are less vulnerable to took five skilled laborers just 10 weeks— factors such as the thickness, grade and events such as earthquakes. which Lend Lease estimates is a 30 percent size of the panels, size of the job (large savings over the same structure in concrete. jobs tend to cost less per square foot as Thermal performance and energy tooling, set-up and delivery costs are efficiency. Thermal conductivity is a Cost competitiveness. Light wood- distributed), number of openings needed, measure of the rate of heat flow through frame construction is still the most type of fasteners, and other project- one unit of thickness of a material economical wood system for low-rise specific factors. subjected to a temperature gradient. projects. However, CLT is competitive The thermal conductivity of common when compared to other materials in a Fire protection. CLT’s thick cross- structural wood is much less than the variety of building types. In a 2010 study section provides valuable fire resistance conductivity of metals with which wood by FPInnovations, researchers compared because panels char slowly. Once formed, is often mated in construction. It is the cost of CLT versus certain concrete, char protects the wood from further about two to four times that of common

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Control (CNC) equipment to precise CASE STUDY tolerances, panel joints fit more tightly, EARTH SCIENCES resulting in better energy efficiency for the structure. Because the panels are solid, BUILDING, UNIVERSITY there is little potential for airflow through OF BRITISH COLUMBIA the system. As a result, an extremely tight building envelope can be achieved.

Owner: University of British Columbia Environmental performance. Location: Vancouver, BC (Canada) Manufactured using wood from Architect: Perkins+Will Canada sustainably managed forests, CLT Engineer: Equilibrium Consulting provides a number of environmental Completed: 2012 benefits in addition to energy efficiency. Under one roof, the University of Wood grows naturally and is British Columbia’s new Earth Sciences renewable. Life cycle assessment (LCA) Building combines five stories, four studies also show that wood outperforms steel and concrete in terms of embodied science departments, and two distinct Photo by KK Law, courtesy of naturallywood.com structural systems. The South Wing energy, air pollution and water pollution, is a conventional reinforced concrete The panels span between glulam and LCA studies are underway on CLT laboratory building. The North Wing, post and beam frames, which run specifically. Wood also has a lighter which consists of academic teaching across the building width on a 21-foot carbon footprint because wood products and research spaces, lecture halls (6.4-meter) grid. The panels were continue to store carbon absorbed by and offices, uses wood as the primary simply secured to the glulam beams the trees while growing, and wood using self-tapping lag screws, which manufacturing requires less energy and structural material, as does the 8 connecting atrium. made for fast and reliable installation. results in less greenhouse gas emissions. The new generation of self-tapping Carbon storage is an important With its innovative combination of screws commonly used in solid wood attribute of wood structural materials, the ESB exemplifies not construction was originally developed components, which typically stay in only the design flexibility inherent to in Europe, but examples are now place over long periods. With CLT, CLT, but its value as a complement to readily available in North America the stored carbon mass of the wood is other materials. CLT is featured in the from a number of suppliers and in a significant. For example, calculations roof and generous exterior canopy variety of types and sizes. done for The Crossroads estimated structure surrounding the building. the total potential carbon benefit of The structure is supported by glulam In addition to being technically the wood used just in the CLT portion columns and beams, and floors are innovative, the use of mass timber of the building at 692 metric tons of products supported the environmental made from an innovative composite of CO2 (equivalent), which compares to laminated strand lumber and concrete. goals of the University and design keeping 132 cars of the road for a year, team. “The project boasts a low or providing total energy to operate a One of the largest applications of embodied energy profile and home for 59 years. CLT to date, the North Wing also sequesters carbon dioxide, thereby Depending on the manufacturer demonstrated CLT’s advantages mitigating the impact of climate and other factors, the wood used in in terms of speed of construction. change,” says Jana Foit, ESB’s Project North American CLT products may According to the manufacturer, roof Architect and Higher Education be a factor in LEED certification or panels were placed on the building at a Practice Leader of Perkins+Will’s other green building rating systems, for rate of one every 15 minutes. Vancouver office. example when the wood comes from certified forests or from forests killed by insulating material. For example, the panels have lower U-values; they are mountain pine beetles. conductivity of structural softwood better insulators and therefore require lumber at 12 percent moisture content less insulation. Resource efficiency. CLT contributes is in the range of 0.7 to 1.0 Btu×in/ The commonly used R-value for wood to efficient use of the resource in (h×ft^2×oF compared with 1,500 for is 1.25 per inch of thickness. So a 7-inch- several ways. One of the advantages aluminum, 310 for steel, 6 for concrete, thick CLT panel would have an R-value of CLT is that it can make use of 7 for glass, 5 for plaster, and 0.25 for of 8.75. Softwood in general has about smaller-dimension material that might 6 mineral wool. one-third the thermal insulating ability not otherwise be used in structural Since CLT is a solid wood panel, it of a comparable thickness of fiberglass applications. Also, since CLT panels also provides thermal mass. But the key batt insulation, but about 10 times that of are manufactured specifically for each measures of CLT’s thermal performance concrete and masonry, and 400 times that project, there is almost no job site waste, are U-value (coefficient of heat transfer) of solid steel.7 and manufacturers can re-use any and R-value (insulating ability). Both In addition, since CLT panels can be fabrication scraps for stairs and other are related to panel thickness. Thicker manufactured using Computer Numeric architectural elements, or as biofuel.

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Photo courtesy of U.S. WoodWorks Photo by Martin Tessler, courtesy of Perkins+Will A CLT building may require more total wood than a light-frame building, but EARTH SCIENCES EDUCATION CONTINUING when compared to steel or concrete BUILDING in applications where all three are potentially applicable, advantages such The expansive 12,378-square-foot as renewability, carbon off-sets, low (1,150-square-meter) canopy of the embodied energy and operational energy Earth Sciences Building appears as efficiency make CLT an environmentally a pristinely flat timber plate which preferable choice. emerges from the building and cantilevers past a glulam colon- CLT BASICS nade, giving the appearance that As recently as 2011, CLT panels had the entire canopy is made from to be shipped from manufacturers in a single, giant piece of CLT. The Europe, but there are now a number of illusion is achieved by locating all manufacturers and distributors working supporting beams on top and hang- in North America.12 ing the panels from the underside CLT manufacturers typically work with self-tapping screws, effectively closely with the project design team, creating an upside-down structure. Estimated carbon benefits of offering technical support and material The 32-square-foot (3-square-meter) the Earth Sciences Building. efficiency advice throughout the process. double cantilever corners are strate- Estimated by the Wood Carbon An engineer of record (EOR) is required gically reinforced with hidden steel Calculator for Buildings elements located on top or in the (www.woodworks.org), based on for a CLT project. However, the CLT research by Sarthre, R. and J. O’Connor, manufacturer often acts similarly to a panel joints. 2010, A Synthesis of Research on Wood truss or component manufacturer in that Products and Greenhouse Gas Impacts, they have staff engineers and technicians FPInnovations. Note: CO2 on this chart that provide shop drawings and calcula- refers to CO2 equivalent. tions to meet the EOR’s specifications. On most projects, there is continuing interac- In terms of overall resource use, the tion and support from the manufacturer distinction between light-frame and to optimize the CLT system. “heavy” construction is important. CLT Panel sizes vary by manufacturer; was developed not as a replacement typical widths are 2 feet (0.6 meters), for light-frame construction, but as 4 feet (1.2 meters), 8 feet (2.4 meters) a low-carbon alternative to “heavy” and 10 feet (3 meters). Length can construction materials such as concrete be up to 60 feet (18 meters) or more, and steel in building applications and the thickness can be up to 20 where light-frame construction is inches (50.8 centimeters), though the less appropriate—in taller buildings, current maximum available in North certainly, but also others, such as an America is 16 inches (40.6 centimeters). polyurethane (PUR) structural adhesives industrial warehouse with 40-foot walls Transportation is most likely the variable with exceptional moisture performance. that need to withstand the impacts of that will limit the CLT panel size, not the Adhesives must be qualified in accordance heavy machinery, or a Class A office manufacturing capabilities. with ANSI/APA PRG 320 for bonding building where few partition walls and North American manufacturers use strength, moisture durability, elevated minimal floor vibrations are desired. formaldehyde-free interior/exterior temperature performance, and heat durability. Boards are face-glued and then pressed, planed or sanded into panels. WILL CLT LEAD TO FOREST RESOURCE DEPLETION? Using CNC precision machinery, the Extensive research has been done to is no. Stringent sustainable forest panels can be custom fabricated to create ensure that CLT will not create a chal- management practices in the U.S. and openings, compound angles and unique lenge to the sustainability of North Canada restrict harvesting levels, while features requiring complex geometry to American forests. The basic ques- maintaining other forest values such as meet specific end-use applications. tion was asked: if designers begin to biodiversity and wildlife habitat.9 In the Manufacturers in North America may replace construction materials typically U.S., less than 2 percent of the stand- use different species or mixes of species used in commercial buildings with mass ing tree inventory is harvested each in their CLT products. Typical species timber products such as CLT, will we year while net tree growth is close to 3 are discussed in the ANSI/APA PRG-320 create an unsustainable trend leading percent.10 In Canada, less than 0.2 per- standard. to forest resource depletion? Based on cent of the forest resource is harvested In general, however, designers don’t analysis of market projections and for- annually and all forests on public land select a particular species, but instead est growth-removal ratios, the answer must be successfully regenerated.11 specify the required performance based on the application (floor, wall, roof, etc.)

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Photo by Uihlein/Wilson Architects CASE STUDY THE CROSSROADS

Owner: Promega Corporation Location: Madison, WI Architects: Uihlein/Wilson Architects, Inc. / EwingCole Engineer: EwingCole Environmental Consulting: Archemy Consulting CLT Engineer: Equilibrium Consulting Inc. Completed: 2013

The project team for The Crossroads evaluated several types of structural systems during the initial design phase. “There was no particular assumption in terms of what the structural material needed to be,” says David Rousseau from Archemy Consulting, design consultant for Promega. “I think we may have even initially assumed it would be a steel structure Aitor Sanchez-Prado, structural engineer and since that’s what we were using for the GMP portion of the principal for EwingCole, said, “CLT provided us project.” with a solution that met all of our architectural and engineer- ing goals. Architecturally speaking, our decision to use CLT Cross laminated timber came up because it’s an innovative for the roof of The Crossroads allowed us to leave the interior material and the team knew it wanted to create a unique ceiling surfaces exposed, which certainly enhanced the glulam space, but it also served the design in key ways. “Together beam and column superstructure. From an engineering point with glulam, it was a natural fit for the warm aesthetic we of view, the CLT panels gave us the ability to increase deck wanted to create,” says Rousseau. “Plus, we wanted to have a spans while supporting heavily loaded areas due to snow high quality, exposed roof deck with long spans and minimum drifts. In addition, the CLT panels allowed us to design an on-site construction complexity. CLT met the criteria.” overhang of three feet while maintaining a slim profile.”

and request the appropriate grade of CLT. and number of layers varies by application condition. Also, because smaller- There are two routes manufacturers can and manufacturer.13 dimension lumber can be used, the take to achieve a specific stress grade— CLT’s dimensional stability is rooted moisture content tends to be consistent prescriptive and performance. “Layup” in its manufacture and is the result of two throughout the product. is the term for the arrangement of the basic factors: The nature of cross lamination is timbers that make up a CLT panel. With The lumber itself has an average also a major contributor. Wood expands the prescriptive route, a lamination moisture content (MC) of about 12%, and contracts five to ten times more size, species and grade-specific layup which is relatively dry. Dryer lumber tangential to the grain than parallel to combination has been tested and is means less overall shrinkage when the grain. The alternating orientation of known to have certain structural design the lumber acclimates to the service layers in CLT has the effect of restricting properties. With the performance route, Photo courtesy of FPInnovations any alternative layup can be used if it is proven by the manufacturer to qualify as meeting the CLT grade requirements. This approach is taken with other engineered wood products such as wood structural panels. With either route, the grade of the CLT will be third-party certified ensuring the stated design values. CLT panels are usually manufactured with an odd number of layers, which creates a direction of greater strength for a specific application (floor, roof or wall). Although panels have strength capacity in both directions like a plate element, the direction parallel to the grain of the outside laminations is typically the stronger axis (i.e., major strength CLT panels direction). Exact lamination thickness

6 CROSS LAMINATED TIMBER overall expansion and contraction of the accommodate MEP. For floor and roof CLT elements, key panel in both directions. Create a drop ceiling to conceal the characteristics that must be taken into EDUCATION CONTINUING The exact weight of CLT is dependent MEP. account are the following: on the density of the species used and Gap the CLT panels to accommodate Out-of-plane bending strength, thickness of the panel (for values, see the plumbing and mechanical and add a thin shear strength, and stiffness National Design Specification® (NDS®) faux panel on the face. Short-term and long-term behavior: for Wood Construction), but may be Create a non-structural built-up - Instantaneous deflection estimated at about 35-36 pounds per cubic floor on top of the CLT floor deck to - Long-term deflection (creep foot. Manufacturers provide detailed accommodate plumbing and mechanical, deformation) information for their product offerings. similar to the approach with heavy  - Long-term strength for permanent Structural design is discussed in the timber. loading next section, but in general there are a When the CLT is covered, there are Vibration performance of floors number of simple details that can be two basic approaches: Compression perpendicular to used to establish roof/wall, wall/floor, Rout and bore the panel to take the grain issues (bearing) and inter-story connections in CLT electrical conduit, plumbing pipes and Fire performance assemblies, to connect CLT panels to other mechanical chases. This can be done on Sound insulation wood-based elements, or to connect CLT site with traditional carpentry tools or in Exposure to elements panels to concrete or steel for a hybrid the factory using CNC technology, but the assembly. The type of hardware depends latter would require more coordination For wall elements, key characteristics on the assemblies to be connected, on the and would increase the cost of the that must be taken into account at the panel configuration, and on the type of product. design stage include: structural system used in the building. Fur the wall out to accommodate Load-bearing capacity (critical Some of the more common lateral load MEP. This is likely to be the more criterion) transfer connectors include metal ‘L’ common method in North America based Out-of-plane shear and bending brackets for shear or traditional strap on building practices and need to satisfy strength hold-downs used for overturning. sound insulation requirements. Fire performance Proprietary self-tapping screws or Local MEP codes may have an impact Sound insulation a variety of commodity nails can be on the options available. In addition, note Exposure to elements used to connect panels in plane or at that “concealed spaces” are not allowed intersections. Ease of installation along in Type IV (heavy timber) construction, The U.S. CLT Handbook discusses these with high lateral and withdrawal capacity which is where CLT is being added under and many other issues such as proposed make self-tapping screws especially the IBC. analytical design methods, research and popular because they can take combined conclusions about lateral design of CLT axial and lateral loads. STRUCTURAL DESIGN buildings, enclosure design, environmental CNC technology is also driving the CONSIDERATIONS performance, etc. This section on structural development of new and innovative CLT panels are typically used as load-car- considerations will focus on two key areas: fastening systems. For example, glued-in rying plate elements in structural systems connections and floor vibration. The rods can be used for connections under such as walls, floors and roofs. Lumber following section will summarize important high longitudinal and transverse loads, in the outer layers of CLT panels used as information about fire resistance. and epoxied shear connectors can be used walls are normally oriented up and down, to create composite floors with structural parallel to gravity loads, to maximize the Connections and Construction of concrete over CLT. wall’s vertical load capacity. Likewise, for CLT Structures Detailed guidelines on how to design floor and roof systems, the outer layers Connections in timber construction, structural elements using CLT are run parallel to the longer span direction. including those built with CLT, play included in the U.S. CLT Handbook.

CLT and Mechanical/Electrical/ CLT AND THE INTERNATIONAL BUILDING CODE Plumbing In the next version of the IBC, recently approved changes are scheduled to streamline When the CLT is exposed on the interior, the acceptance of CLT buildings. The 2015 IBC will recognize CLT products when these are some of the ways MEP is being they are manufactured according to the product standard. In addition, CLT walls addressed: and floors will be permitted in all types of combustible construction, including Type Fur out a wainscoting on the lower IV buildings. Type IV wall provisions require the exterior side (only) of exterior CLT half of the wall to accommodate electrical walls to be protected by fire retardant treated wood sheathing, gypsum sheathing, outlets and plumbing pipes. or a noncombustible material; however, there are other requirements for the exterior Run the conduit, pipes and chases wall, floors, roof, etc. Floors are required to be 4-inch (10.16-centimeter) nominal on the face of the CLT and use them as minimum thickness and roofs a minimum of 3-inch (7.16-centimeter) nominal. While exposed architectural elements. this code change will not go into effect officially until the 2015 IBC is adopted by a jurisdiction, the information could be used to simplify an alternative methods Add stick-framed partition walls argument under current codes. For more information, see the American Wood on the interior of the structure to Council website at www.awc.org.

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CASE STUDY Forté is the first residential building in Australia to achieve a ‘5 Star Green Star As Built’ rating, which is similar to LEED FORTÉ Platinum. “The construction industry is one of the worst in the world for polluting,” says Daryl Patterson, Head of Operational Owner: Lend Lease Excellence and Development for Lend Lease. “If we want to do Location: Melbourne, Australia Photo by Lend Lease something about this, we have Architect: Lend Lease Design to challenge the materials Engineer: Lend Lease Design and we’re building with. Among the Robert Bird Group other things, we need to place Completion: 2012 a greater focus on embodied carbon in addition to opera- Numbers tell a powerful story when tional energy efficiency.” it comes to Forté. It’s Australia’s first As it turned out, the use CLT building and the first 10-story of CLT helped Lend Lease CLT building anywhere. Research and achieve its objective of “as development was a three year pro- close to a net zero carbon cess, followed by a year of design and building as possible.” Be- 10 months of construction from site tween the carbon seques- preparation to completed building. tered in the wood itself and the greenhouse gas emissions Although Lend Lease cites benefits avoided by not using steel such as speed of installation and or concrete, Forté kept ap- lightweight materials (a particular proximately 1,450 metric tons advantage given the site’s poor soil of carbon dioxide (equivalent) conditions), the three-year invest- out of the atmosphere. It also ment in R&D had more to do with the set the stage for additional company’s desire to demonstrate that carbon savings in future CLT sustainability can be cost effective in developments.14 a large commercial development.

CLT AND ENVIRONMENTAL PRODUCT atmosphere while the trees were growing) is greater than their DECLARATIONS cradle to gate carbon emissions. Increasing interest in EPDs reflects a growing demand for Environmental Product Declarations (EPDs) are a means of present- sustainability in every aspect of a building’s design, construction ing environmental information in a standardized way, independent- and operation, and the recognition that this cannot be evaluated ly verified by a third party. A common part of decision making else- without transparent, verifiable data. Their growing use will allow where in the world, they are relatively new to the U.S., produced designers to compare products in the same category in a much mainly by large manufacturers or industries committed to being more transparent and meaningful way than is otherwise possible. leaders in environmental performance, and used by a relatively small number of design practitioners with the same objective. The information contained in EPDs is quantifiable and verifi- able—but it is not the final word, by any means. EPDs are Governed by international standards (ISO 14025, ISO 21930 complementary to other third-party independent certifica- and others), EPDs are based on life cycle assessment, which tions such Energy Star labels and forest certification pro- is a rigorous study of inputs and outputs over a product’s grams (for example, Forest Stewardship Council, Sustainable lifetime and the associated environmental impacts of those Forestry Initiative, and Programme for the Endorsement of flows to and from nature. Forest Certification). EPDs remain only one of many reporting mechanisms, and product certification continues to serve im- EPDs are currently available for two CLT products manufac- portant functions. Products have other impacts besides those tured in North America.15 Prepared by research organization covered by EPDs, involving human and social values such as FPInnovations, both consider all aspects of production from cradle fair practices, biodiversity, and many others. to gate—i.e., from the extraction of raw materials through final production of the CLT. They provide life cycle data on primary In the case of wood products, for instance, sustainably manag- energy use as well as impact categories such as global warming ing forests with future generations in mind, conserving biodiver- potential, smog potential and ozone depletion potential. In terms sity, and protecting other values related to forests have great of carbon footprint, the EPDs conclude that both products have worth and complement the parameters measured in an EPD. To- a negative carbon balance leaving the mill gate, which means the gether, EPDs and forest certification provide a more complete amount of carbon sequestered in the wood (absorbed from the picture of the environmental attributes of a forest product.

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Photo courtesy of Uihlein/Wilson Architects an important role in maintaining the integrity of the timber structure and in EDUCATION CONTINUING providing strength, stiffness, stability and ductility. Consequently, they require thorough attention of the designers. Traditional and innovative connection systems have been used in CLT assemblies in Europe and North America. Common With virtually no square types of connections in CLT assemblies angles in the structure, include: in-plane panel-to-panel (floors, beam-to-column walls and roofs), out-of-plane panel connections created intersections, and panel-to-foundation. a challenge. To avoid Basic panel-to-panel connection can the need for more than be established through single or double a hundred different configurations, the team exterior splines made with engineered designed a steel pin wood products, single or double interior connector which allowed splines, or half-lapped joints. Metal most joints throughout brackets, hold-downs and plates are the project to have used to transfer forces at the wall-to- elegant and typical floor/roof interfaces and in wall-to- connections. wall intersections. Innovative types of connection systems can also be used Design values for proprietary fasteners that current minimum geometric which lead to enhanced performance or and information on their approved use requirements given in the NDS for dowels, quicker assembly. are available in Evaluation Reports or the screws and nails in solid timber or glulam Mechanical fasteners may be dowel- manufacturer’s literature. could be applicable to CLT. However, type (e.g., nails, screws, glulam rivets, Researchers in Europe have developed designers need to be cautious about this as dowels, bolts) or bearing-type (e.g., split design procedures for traditional further verification is needed, considering rings, shear plates). connections in CLT. These include the specific features of individual panel CLT connections should adhere to the dowels, wood screws, and nails, which types. Brittle failure modes, which have NDS just like other wood connections. are commonly used in Europe for not yet been investigated, also need to be The NDS has specific provisions for designing CLT assemblies. Empirically- taken into account. commodity fasteners, which can be based equations were developed for the The Connections chapter in the U.S. found in Appendix K - L. It does not yet calculation of characteristic embedment CLT Handbook is mainly focused on include information on how to apply its properties of each type of fastener (i.e., connecting CLT to CLT. However, since dowel bearing equations regarding grain dowels, screws, nails), depending on all buildings are considered to be mixed direction to CLT. However, the existing the location with respect to the plane of construction to a certain extent, the NDS design provisions can be applied the panel (perpendicular to or on edge). scope covers hybrid construction, where with some modification, assuming that Those equations were verified with testing traditional wood-based systems (e.g., light the CLT dowel bearing strength is based and results seem to correspond well with frame, glulam, etc.) or materials such as 16 on the species-specific gravity of the ply in calculated predictions. concrete or steel are mixed with CLT to the shear-plane and the loading direction Yield mode equations were adopted resist vertical and lateral loads. relative to the grain angle of the ply in for the design using CLT fastener the shear-plane. A reduction in effective embedment strength equations. Empirical Vibration Performance of Floors thickness is also taken for the plies equations have also been developed Studies at FPInnovations found that bare running perpendicular-to-grain if the ply for the calculation of the withdrawal CLT floor systems differ from traditional in the shear-plain is parallel-to-grain. resistance of the various types of fasteners lightweight wood joisted floors with Self-tapping screws will likely be the in CLT based on hundreds of tests. Based typical mass around 4 pounds per square most common connector used in CLT on limited exploratory validation tests foot (20 kilograms per square meter) and construction. These are proprietary conducted at FPInnovations using self- fundamental natural frequency above 15 connectors and design values and tapping screws on European CLT, the Hz, and heavy concrete slab floors with requirements would be specified by the proposed embedment equations seem to a mass above 40 pounds per square foot manufacturer. The manufacturer will provide reasonable predictions of both the (200 kilograms per square meter) and be responsible for providing lateral and lateral and withdrawal capacity based on fundamental natural frequency below 9 withdrawal connection values and any the Canadian timber design provisions.17 Hz. Based on FPInnovations’ test results, information needed to explain how to More work is needed, however, to validate bare CLT floors were found to have mass apply provisions of the NDS (e.g., dowel the proposed equations using North varying from approximately 6 pounds bearing strength adjustments, dowel American made CLT and different types per square foot (30 kilograms per square bending strengths of the self-tapping of fasteners. meter) to 30 pounds per square foot (150 screws, and specific application of the Due to the reinforcing effect of kilograms per square meter), and a funda- NDS yield equations). cross-lamination in CLT, it is speculated mental natural frequency above 9 Hz. Due

9 CROSS LAMINATED TIMBER

Photo courtesy of FPInnovations this approach, the success in avoiding excessive vibrations in CLT floors relies mostly on the designer’s judgment. Besides, static deflection criteria can only be used as an indirect control method because they ignore the influence of mass characteristics of the floors. Therefore, a new design methodology is needed Thick timber members slowly char to determine the vibration controlled at a predictable rate, spans for CLT floors. A proposed design so CLT panels can methodology for controlling vibrations of maintain significant CLT floors under normal walking is given structural capacity in Chapter 7 of the U.S. CLT Handbook. forn a extended durationf o time when CLT AND FIRE RESISTANCE exposedo t fire. Structural integrity and fire contain- ment capability of building assemblies to these special properties, the standard Some CLT manufacturers have can be assessed by conducting full-scale vibration controlled design methods for recommended that deflection under a fire-resistance tests in accordance with lightweight and heavy floors may not be uniformly distributed load (UDL) be ASTM E119 standard test methods. Fire applicable for CLT bare floors. used to control floor vibration. Using resistance is defined as the ability of a

CLT AND CURRENT CODES

While CLT has been used in Europe for years, it is still finishes to more closely meet the standard required in a non- relatively new to North America. Fortunately, U.S. building combustible building. Further, taking advantage of the highly codes are flexible enough to accommodate new materials. compartmentalized nature of the wing, a fire risk analysis was Promega’s design team for The Crossroads earned local presented to show that the risk of fire growth and spread building department approval by using ANSI/APA PRG would inherently be limited by the many separate, individual 320-2011 standard. The design team discussed the standard offices and rooms. To address concerns, the wood structure with building officials early in the process, and submitted was engineered to account for the charring of the wood engineering information under the ‘alternate designs’ section members for the required fire-resistance period so that the of the IBC. resistance provided by the reduced cross section (unburned portion) of the wood members would continue to resist the “The building was designed per the 2009 IBC with State gravity loads expected during the fire. of Wisconsin amendments,” says structural engineer Aitor Sanchez-Prado. “The basic criteria for the project consisted A key component in the fire safety design of the heavy timber of minimum roof snow loads of 30 psf with a maximum snow element, which is traditionally not explicitly addressed by drift load of 132 psf. The structure was designed for basic the building code, was the fire performance of the steel wind speeds of 90 mph and seismic design category B. These connections. The minimum fire resistive properties of steel loads, together with diaphragm chord and tie forces, set connectors were considered critical since the loss of the the design criteria that the custom-made CLT panels were load-bearing capacity of the structure at the early stage of required to meet.” a fire would be significant if the steel connectors failed. To ensure the connectors would continue to transfer loads in the In the Earth Sciences Building, under the prescribed fire safety heavy timber wood-frame system during a fully-developed requirements for the British Columbia Building Code (BCBC), fire, concealed connections were specified. Where there were having the academic wing built entirely of heavy timber or other exposed steel elements that were part of the wood wood-frame construction was not permitted. In order to structure’s load path, appropriate ‘passive’ fire protection, in allow for the use of wood as the main structural element, a the form of an intumescent coating, was also specified. fire hazard assessment was carried out and documented in a Building Code Alternative Solution, which was peer-reviewed ICC-ES has not yet published any reports for CLT products as part of the building permit approval process. or their connections; however, there are several APA Product Reports (e.g., PR-L306) that provide third-party testing and The assessment essentially looked at how the wood may be accepted under IBC Section 104.11.1. Moreover, the construction might perform in fire. The Earth Sciences research and testing data provided in the U.S. CLT Handbook Building was designed with an automatic sprinkler system, can also be provided as an alternate means approach under and a fire retardant coating was applied where necessary to that section. At least one manufacturer to date also has alter the surface burning characteristics of the wood interior testing data available on a series of CLT connectors.

10 CROSS LAMINATED TIMBER material or their assemblies to prevent or CLT panels have the potential to provide The fire resistance calculation retard the passage of excessive heat, hot excellent fire resistance comparable to the methodology outlined in Chapter 8 EDUCATION CONTINUING gases or flames under conditions of fire. typical Type IV exterior wall assemblies of also accounts for altered performance A fire-resistance rating is defined as the non-combustible construction. Due to the characteristics of a laminated product period of time a building element, compo- inherent nature of thick timber members like CLT. In addition to the fire-resistance nent or assembly maintains the ability to to slowly char at a predictable rate, CLT calculation method of CLT assemblies, this confine a fire (separating function), and/ panels can maintain significant structural chapter provides requirements related to or continues to perform a given structural capacity for an extended duration of time fire safety in buildings, namely with regard function. More specifically, a standard when exposed to fire. to the types of construction prescribed fire-resistance test entails three failure/ac- Adhesives can also have an effect on fire in the IBC, fire-resistance requirements, ceptance criteria: performance, but standards exist to prevent connection detailing, interior finishes, Structural resistance: the assembly that from playing a significant role in the through-penetrations and exterior walls. must support the applied load for the overall product performance and to ensure duration of the test. appropriate adhesive performance under PROVEN PERFORMANCE, NEW Integrity: the assembly must prevent heat and fire. The ANSI/APA product OPPORTUNITY the passage of flam e or gases hot enough standard established for CLT requires CLT’s strength, structural performance to ignite a cotton pad. that, in the U.S., adhesives used in the and cost-competitiveness are expanding Insulation: the assembly must manufacturing of CLT shall meet similar opportunities for the use of wood in a prevent the temperature rise on the requirements as structural glued laminated wider range of buildings. Available in unexposed surface from being greater timber used in dry service conditions (the North America and increasingly accepted than 325°F (180°C) at any location, or equilibrium moisture content of wood is under building codes, it provides a flexible, an average of 250°F (140°C) measured at less than 16 percent). Also, adhesives shall sustainable and efficient alternative to a number of locations, above the initial be evaluated for heat performance. concrete and steel for many applications. ■ temperature. The time at which the assembly can no longer satisfy any one of these three criteria defines its fire-resistance rating. ENDNOTES 11. The State of Canada’s Forests AWC conducted a successful ASTM Report, 2012, Natural Resources Canada, E119 fire resistance test on a CLT wall 1. http://designbuildsource.com.au/ http://cfs.nrcan.gc.ca/pubwarehouse/ at NGC Testing Services in Buffalo, melbourne-launches-the-worlds-tallest- pdfs/34055.pdf NY. The wall, consisting of a 5-ply CLT timber-building 12. A list of current manufacturers (approximately 6-7/8 inches thick), was 2. http://www.masstimber.com/ can be found at http://www.masstimber. covered on each side with a single layer of products/cross-laminated-timber-clt/ com/contacts-and-resources/ 5/8-inch Type X gypsum wallboard. The handbook maufacturers wall was loaded to the maximum load 3. http://woodworks.org/wp-content/ 13. FPInnovations http://www. attainable by the NGC Testing Service uploads/IS-CLT.pdf; forintek.ca/public/Eng/E5-Pub_ equipment. The 10×10 foot test specimen http://www.storaenso.com/products/wood- Software/5a.fact_sheets.html lasted three hours, five minutes, and 57 products/success-stories/bridport/Pages/ 14. Calculated by Lend Lease and seconds (03:05:57)—well beyond the two- default.aspx presented at the U.S. CLT Symposium, hour goal.18 4. As of September, 2013 http://www.slideshare.net/rethinkwood/ Industry has taken an analytical 5. Cross Laminated Timber: A Primer, daryl-pattersonforte-architectural-design approach to CLT, rather than the route of Crespell, P., S. Gagnon, FPInnovations, 15. U.S. CLT Handbook, Chapter 1 prescriptive fire-rated assemblies. This is 2010 16. Uibel, T., and H.J. Blass. 2006. because CLT assemblies, and in particular 6. American Wood Council, http:// Load carrying capacity of joints with floors, will most likely never be loaded to www.awc.org/helpoutreach/faq/ dowel type fasteners in solid wood panels. their full design capacities, but instead be FAQfiles/Conductivity.html Paper presented at the 39th meeting of designed based on serviceability (vibration 7. Thermal Performance of Light- the Working Commission W18 – Timber and/or deflection). Therefore, it would Frame Assemblies, Canadian Wood Structures, International Council for be overdesigning to evaluate based on Council Research and Innovation in Building a prescriptive fire-rated assembly. This 8. Werner, F. and Richter, K. 2007. and Construction, Florence, Italy, also allows more flexibility in wall and Wooden building products in comparative August 2006. floor assembly designs. The approach LCA: A literature review. International 17. Mohammad, M., and W. Munoz. taken was to test CLT under different Journal of Life Cycle Assessment, 12(7): 2011. Connections in cross-laminated load ratios, including full design loads, in 470-479 timber buildings. In CLT Handbook, ed. order to validate the proposed calculation 9. U.S. CLT Handbook, Chapter 11 S. Gagnon and C. Pirvu. Chapter 5. method(s). Fire resistance calculation 10. State of America’s Forests, 2007, Québec, QC: FPInnovations. methods will be included in the next Society of American Foresters, http:// 18. http://www.awc.org/Code- version of the NDS and are explained in safnet.org/publications/americanforests/ Officials/2012-IBC-Challenges/NGC- Chapter 8 of the U.S. CLT Handbook. StateOfAmericasForests.pdf CLT-Report.pdf Results of full-scale fire tests show that

11 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 it comes 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

American Wood Council is the leading developer of engineering data, technology, and standards on structural wood products in the U.S. These tools are used widely by design professionals, building officials, and manufacturers of traditional and engineered wood products to ensure the safe and efficient design and use of wood structural components. www.awc.org

FPInnovations is among the world’s largest private, not-for-profit forest research centers. It helps the Canadian forest industry develop innovative solutions based on the unique attributes of forest resources, with a focus on sustainable development and taking full advantage of the industry’s substantial scientific, technological and commercial capital. www.fpinnovations.ca