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Awareness, perceptions and willingness to adopt Cross-Laminated Timber by the architecture community in the United States

Cross-Laminated Timber is an engineered wood-based product, developed in Europe in the early 1990s. Cross-Laminated Timber is made of multiple layers of wood boards, which are oriented perpendicular to the adjacent layers. Cross Laminated Timber is a
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  Awareness, perceptions and willingness to adopt Cross-LaminatedTimber by the architecture community in the United States Maria Fernanda Laguarda Mallo * , Omar Espinoza University of Minnesota, United States a r t i c l e i n f o  Article history: Received 25 July 2014Received in revised form20 January 2015Accepted 30 January 2015Available online 10 February 2015 Keywords: Cross-Laminated Timber (CLT)Massive timberMarket potentialSustainable buildingsAwareness levelArchitecture community a b s t r a c t Cross-Laminated Timber is an engineered wood-based product, developed in Europe in the early 1990s.Cross-Laminated Timber is made of multiple layers of wood boards, which are oriented perpendicular tothe adjacent layers. Cross Laminated Timber is a promising construction technology that represents anopportunity to use low-value timber from small diameter and insect-infested forest resources, for a highvalue-added application, which contributes to better use our forest resources. While Cross-LaminatedTimber has been successful in Europe and is making its way into the Canadian and Australian mar-kets, it has not yet been widely adopted in the United States. Research has proven that the rate of diffusion is dependent on potential adopters' perceptions of the product attributes, thus the study of perceptions play an important role in understanding and analyzing the adoption potential of a newproduct or technology. This document presents the results from research conducted to assess the marketpotential and barriers to the adoption of Cross-Laminated Timber in the United States, through theanalysis of level of awareness, perceptions, and willingness to adopt Cross-Laminated Timber by theUnited States architecture community.Results from a nation-wide survey of United States architecture  fi rms show that the level of awarenessabout Cross-Laminated Timber in the United States is low. The main perceived bene fi ts of Cross-Laminated Timber are a favorable environmental and structural performance, and outstandingaesthetic properties. Major perceived disadvantages are high maintenance costs and  fi re performance.The most important barriers to the successful adoption of Cross-Laminated Timber according to surveyparticipants are building code compatibility issues, initial cost, and the lack of Cross-Laminated Timberavailability in the United States market. Most respondents were uncertain when asked about theirwillingness to adopt Cross-Laminated Timber in the near future; although willingness to adopt wasfound to be positively correlated with familiarity with the system. From these results, we conclude thatthe success of Cross-Laminated Timber-based construction in the United States will depend in great parton the information about the material's bene fi ts reaching the target audience. ©  2015 Elsevier Ltd. All rights reserved. 1. Introduction Wood has been the preferred building material for millenniadue to its affordability, abundance, and weight-to-strength ratio.However, despite its many advantages, the use of wood as abuilding material is not free from challenges. Wood properties arenot homogeneous, and vary widely depending on species, cellulararrangement, moisture content, and location of the treeand withinthe same tree (Forest Products Lab, 2010). Furthermore, due to theanisotropic nature of wood, its properties change with direction(e.g., longitudinal vs. radial direction) (Hoadley, 2000). In part toaddress wood's inherent variability and utilize the material moreef  fi ciently, Engineered Wood Products (EWPs) were developed.Examples of successful EWPs are Oriented Strand Board (OSB)panels, Medium Density Fiberboard (MDF), and glued laminatedtimber (Glulam). These products are manufactured to achieve tar-geted engineering properties, such as high strength, enhanceddurability, and consistency. EWPs also help make a more ef  fi cientuse of low-value and small-diameter trees (Forest Products Lab,2010; Woodall, 2011; McKeever, 1997; APA, 2013). The develop-ment and improvement of adhesion technologies, mechanicalconnections, and grading technology have resulted in EWPs that *  Corresponding author. 320 Kaufert Laboratory, 2004 Folwell Ave., St. Paul, MN,United States. E-mail address: (M.F. Laguarda Mallo). Contents lists available at ScienceDirect  Journal of Cleaner Production journal homepage: ©  2015 Elsevier Ltd. All rights reserved.  Journal of Cleaner Production 94 (2015) 198 e 210  greatly extend the possibilities for wood-based construction(Canadian Wood Council, 2010).One of the most recent innovations in EWPs is the developmentofCrossLaminatedTimber(CLT)panels.Thesepanels(also referredto as  “ X-Lam, ” “ Massive Timber ”  or  “ Cross-Lam ” ) are con fi guredsimilarly to plywood, with boards that are glued side by side in asingle layer and then glued to another layer of boards placed atright angles with the adjacent layers (Fig.1). This cross-laminationis intendedtoimproverigidity, stability, andmechanicalproperties(Evans, 2013). A list of literature on CLT's main attributes is pre-sented in Table 1.CLT is a new construction technology that srcinated in Europe,and has been very successful in that market since its introductiontwo decades ago (Lehmann, 2012). CLT production in the continentrose from 25,000 m 3 in 1996 to 340,000 m 3 in 2010 (Crespell andGagnon, 2010). CLT has been used for a wide range of applica-tions in Europe, including single and multi-family residentialbuildings, educational institutions, and of  fi ce buildings. While CLT-basedconstructionhasexperiencedrapidmarketgrowthinEuropeand more recently in the Australian and Canadian markets, in theUnited States this system has not been adopted beyond a fewdemonstrationprojects. Interest about CLT is growingin the UnitedStates in the wood products and construction industries, as well asthe architecture community (Evans, 2013). Abundant informationhas been generated about the technical aspects of CLT and severalU.S. Department of Agriculture grants have been awarded toinvestigateCLT(Gagnon,2011;Mohammadetal., 2012;APA, 2013).However, one area that has received little consideration is CLT'smarket potential, particularly the elements that play an importantrole in a new product's adoption: the awareness, perceptions andwillingness to adopt the new construction system by the likelyadopters (e.g., the architectural community). In this context, thegoal of this study was to estimate the level of awareness about CLTamong architectural  fi rms, learn the perceptions about the envi-ronmental,structural andeconomicperformanceof CLT, andassessthewillingnesstoadopt CLTbytheU.S.architecturecommunity. Asthe following section demonstrates, this is important informationto assess the potential for successful implementation of CLT in thecountry. 1.1. Product adoption The successful introduction of a new product in the marketcarries signi fi cant economic risk for a company and relies signi fi -cantly in two consumer processes: the adoption process and thediffusion process (Armstrong and Kotler, 2013). A number of au-thors have addressed the process of product adoption (Harvey,1979); and several models have been proposed. Koebel et al.(2004) for example, proposed the following  fi ve-stage adoptionprocess for products: (a) awareness; (b) interest; (c) evaluation; (d)trial; and (e) adoption of the product.  Awareness  refers to the moment when consumers  fi rst becomeaware of the new product's existence and develop preliminaryperceptions of the product attributes. This step greatly depends oncommunication and education (King, 1996). Once potential con-sumers are aware of the new product, the second step is theestablishment of an  interest   in the product. During this stage, theconsumer  seeks  information and details about the new product(Armstrong and Kotler, 2013). In the next step, consumers  evaluate the product's perceived bene fi ts and drawbacks, and assess if it  fi tstheir wants and needs. A positive evaluationwould lead tothe nextstep,aproduct trial .Duringthetrialperiod,theproductistestedona limited basis and further evaluated. Finally, the  adoption  of theproduct, the  fi nal step, is likely to occur if the trial period wassuccessful (King, 1996) According to Gayle (2009), during or after this  fi nal stage, the consumer often becomes a strong promoter forthe innovation in the community, which is essential to furthertransmit the knowledge about the product to potential newadopters.Typically, the adoption of a new product occurs in phases, and adifferent type of consumer is prevalent in each phase. According toLindquist and Sirgy (2003) adopters can be categorized into  fi vegroups on the basis of the stage of the lifecycle inwhich theyadoptthe new product.  Innovators  are usually the  fi rst individuals to trynew products. The next type of consumer are the  early adopters ,which are the most in fl uential group, because they tend to havemore favorable attitudes towards new ideas and are seen as themarket leaders and trend setters. According to Rogers (1983),among early adopters are opinion leaders, who have an importantrole in transmitting information about the new product to otherpotential users. Their in fl uence can signi fi cantly determine thesuccess or failure of a new product in the market (King, 1996).Therefore, effectively directing the efforts towards the earlyadoptersisperceivedasacriticalstepinlaunchingasuccessfulnewproduct. After the earlyadopters come the  early majority , whotendto be more careful in their decisions than innovators and earlyadopters. The  late majority  group is typically composed of thosemainstream consumers that adopt a new product only when it hasbeen steadily established in the market. Finally,  laggards  are thoseconsumers that resist new product adoption until it is soon to bereplaced by a new product (Armstrong and Kotler, 2013).Speci fi cally,theforestproductssectoristypicallyseenasmatureand conservative towards change and the adoption of new prod-ucts. However, over the past decades the wood products industryhas been facing increasing pressure from non-wood productssubstitutes. In this sense, innovation is seen by Hansen (2010) as acompetitive advantage that can propel the wood industry. Ac-cording to Shrapnel (2014) the Engineering Wood Products sectorhas developed a strong presence in the U.S. thanks to the adoptionof laminated veneer lumber (LVL), strand lumber (LSL), and I-beams, which represent 35% of the material used for  fl oor bearersandjoists.Theincreasingacceptanceofstructuralengineeredwoodproducts, as well as the rapid growth in consumption, are just acouple of reasons that are driving new product development (Qiet al., 2010). In this context CLT has a favorable potential as a newinnovative product in the U.S. market, which could add to thecompetitiveness of the wood products industry. Therefore theemphasis of this study was placed on evaluating process of inno-vation adoption related to CLT from the consumer's point of view.Since the development of CLT in the U.S. is considered in the em-bryonicstage(Evans,2013),itisimperativetofocusresearcheffortsin the fi rst stages of new product adoption, namely: awareness and Fig. 1.  Schematic view of CLT's layered con fi guration. M.F. Laguarda Mallo, O. Espinoza / Journal of Cleaner Production 94 (2015) 198 e  210  199  interest. Understanding potential adopter's knowledge, percep-tions and attributes in fl uencing the decision to adopt a product isvital. Consequently, information about the level of awareness, howpeople perceived CLTattributes and their willingness to adopt it inthe future, is essential to assess the potential for successfulimplementation of CLT in the country. 2. Background e research on CLTcharacteristics as a building material Thefollowingsectionsummarizestheresultsofresearchstudiesconducted over the past decade. Topics covered include the envi-ronmental, structural, design,  fi re, seismic and thermal perfor-mance of the system. Table 1, which appears at the end of thissection summarizes the most relevant  fi ndings on each topic,which have been examined by a number of research projects.  2.1. Environmental performance The environmental bene fi ts of wood as a building material havebeen studied by multiple authors. There is wide consensus thatwhenforestsaresustainablymanaged,woodiscarbon-neutral,andacts as a repository of carbon, either as growing stock or as avalue-added product (Oneil and Lippke, 2010). Trees convert carbon di-oxide (CO 2 ) to biomass as a result of the process of photosynthesis,effectivelystoring carbon (Lehmann andHamilton,2011),aprocessknown as carbon sequestration. It is roughly estimated that onecubic meter of wood stores around 1.10 tonnes of CO 2  (Puettmannand Wilson, 2005; Puettmann and Wilson, 2005).The environmental qualities of wood as building material havebeen contrasted with other materials, such as steel and concrete(Robertson et al., 2012; Chen, 2012; John et al., 2009; Hammondand Jones, 2008). Robertson et al. (2012) conducted a Life-Cycle Analysis (LCA) study comparing two  fi ve-story of  fi ce buildings,onebuiltinconcreteandanotherwithCLT,andconcludedthatoverthe building life-cycle, the wood-based alternative consumed 15%less energy compared to concrete. Chen (2012) calculated theoperational energy (de fi ned as the amount of energy that isrequired by a building to satisfy the demands for HVAC systems(heating, ventilation and air conditioning, lighting, appliances) of a fi ve-story of  fi ce building in CLT and another in concrete andconcluded that CLT buildings have a 10% lower operational energydemands, adding that further reduction are possible throughimproved technology and design optimization. The results from acomparative study of two mid-rise of  fi ce buildings conducted by John et al. (2009) indicated that CLT has a favorable environmentalperformance, in all impact categories (ozone depletion, globalwarming potential, eutrophication), compared to a comparablebuilding built with concrete. The same study also concluded thatthecarbonsequestrationpotentialassociatedwithCLTwouldallowthe building to operate for the  fi rst 12 years with no net CO 2 emissions. Research conducted by Hammond and Jones (2008) inthe United Kingdom showed that a concrete and steel six-storybuilding contains around the same amounts of embodied CO 2 (1984tonnes) while theequivalentCLTbuilding hasless than ahalf thatamount(727tonnes).Howeverifcarbonsequestrationistakenintoaccount,theCLTbuildingturnsouttobecarbon-negative,withavalueofapproximately  2314tonsofembodiedCO 2 (Atlee,2011).For this reason, massive timber construction systems, such as CLT,offer the opportunity to turn buildings into  “ carbon sinks ”  (Salazarand Meil, 2009; Wang et al., 2013).CLT is also especially suited for incorporation of underutilizedand low-quality timber. Due to insuf  fi cient demand and lack of resources to manage U.S. forests, the prevalence of small-diametertimber is growing (Perkins, 2006). Also, decades of   fi resuppression and high-grading led to an over-abundance of small-diameter timber of low quality and value. Studies have suggestedthat small-diameter logs can yield high quality material, whenprocessed with the proper equipment and methods (LeVan-Greenand Livingston, 2003; Lowell and Green, 2001). The U.S. forestresource is also subject to stress due to insect infestation, such asthe mountain pine beetle, the gypsy moth, the southern pinebeetle, the spruce budworm, and several others (Alvarez, 2007).However, neither the fungus nor the beetle eat the wood struc-ture, and the resulting stain does not cause decay problems(Forintek, 2003). Tests on properties of timber from MPB-killedtrees show that there is no signi fi cant reduction in stiffness andbreaking strength performance (Uyema, 2012). Consensus existsthat traditional markets cannot absorb all the low quality timberin existence. Since CLT is made of small components assembledand glued together, the quality of individual pieces is not as criticalas with other timber-based building components. Increased de-mand from growing use of newly developed markets, such asCross-Laminated Timber (CLT) presents the opportunity to use thislower value, yet mechanically unaffected material at economicallyattractive prices to pay for increased forest management costs.New high value-added uses, such as CLT, are of critical importanceto support proper forest management and to enhance the eco-nomic wellbeing of rural communities that rely on forest productsindustries.  2.2. Installation simplicity and cost competitiveness CLT is a system based on large format, light-weight panels thatvary in size from manufacturer to manufacturer. Typical widths aretwo, four, eight, and ten feet; panel length can be up to sixty feet ormore, and thickness can be up to 20 inches. Using fewer but largerelements implies greater construction simplicity (Waugh, 2010).According to Kirkegaard (2012), CLT makes possible a new way of building structures, shifting the design from  “ frames ”  to  “ plates ” .CLT's installation simplicity is governed mainly by the connec-tions used during construction. Panels are assembled using me-chanical fastening systems, such as self-drilling threaded screws(Evans, 2013). Gavric (2012) established that these screws enable the creation of structurally stable constructions with effectiveresponse to both vertical and horizontal forces. Concealed metalplates and dowels can also be used as connections. Research con-ducted in Canada by FPInnovations (2013) concluded that this typeoffasteningsystemprovidesconsiderableadvantagesoverexposedplates and brackets, especially when it comes to  fi re resistance,since they are protected by surrounding wood.One of the most attractive features of CLT as a building systemrelates to the speed in which CLT buildings can be erected, in greatpart due to its prefabricated nature. This allows for high precision(openings in the panels are cut using a CNC machine), fastercompletion, increased safety, less disruption to the surroundings,and less waste generation on site (Evans, 2013; FPInnovations,2013). Several case studies highlight the rapid on-site construc-tion that may be as short as three to four days per story(WoodWorks, 2013), compared to twenty eight days per story fortypical concrete construction 1 (Wilson and Kosmatka, 2011). Con-struction may take as little as three to four months for buildings of up to nine stories, less than half the time compared to traditionalconstruction methods, such as concrete (Lehmann and Hamilton,2011). Patterson (2013) compared two ten-story residential 1 Concrete needs to be cured for at least 28 days before 90% of the material's  fi nalstrength is reached and the formwork for the next  fl oor can be placed (Wilson andKosmatka, 2011). M.F. Laguarda Mallo, O. Espinoza / Journal of Cleaner Production 94 (2015) 198 e  210 200  buildings,oneinCLTandanotherinconcrete,andconcludedthatinsome cases a reduction of eleven to twelve months in constructiontime could be achieved by choosing the former.  2.3. Structural performance CLTelements are built with layers orthogonal to each other, in awaysimilartoplywood.Withthiscon fi guration,adjacentlayersactas reinforcement of the whole panel, adding to dimensional sta-bilityand allowing panels to span and carryload in bothdirections,similar to a concrete slab (Turner, 2010; Van de Kuilen et al., 2011).Several experimental tests on CLT elements, in particular thoseconducted by Steiger et al. (2008) and Steiger and Gülzow (2010), concluded that those characteristics allow CLT panels to be used asload-bearing plates and shear panels, in contrast to other woodengineered products. Cross lamination also enhances dimensionalstability, as individual layers constrain the expansion andcontraction of the adjacent layers (Evans, 2013).Several studies have placed especial attention in the structuralperformance of CLT, especially in respect to bending and shearstrength, stiffness and de fl ection. Stiffness of CLT panels is evalu-ated by testing panels following product standards such as theEuropeanStandardsEN13353(DIN,2003),EN13986(DIN,2005a), and EN 789 (DIN, 2005b). In North America the requirements andtestmethodsforquali fi cationandqualityassuranceofCLTpanelsiscovered by the recently published American Standard forPerformance-rated Cross-Laminated Timber (ANSI/APA PRG 320)(APA, 2013).According to Fountain (2012), CLT's strength-to-weight rela-tionship has expanded the opportunities for the use of wood in awider range of buildings, especially as a viable alternative to steeland concrete in mid to high-rise building construction. There areseveral examples of CLT used in tall buildings, with prominentexamples such as the Stadthaus, an 8-storey residential buildingin London (KLH, 2013), and the Forte Building, a 10-storey resi-dential building in Melbourne, Australia (Lend Lease, 2013). Arecent report by the architecture and engineering  fi rm Skidmore,Owings and Merrill proposed a 42-storey CLT-concrete hybridbuilding in Chicago, called Timber Tower Research Project (SOM,2013).  2.4. Design  fl exibility According to some authors, the structural characteristics of CLTallow for great architectural freedom during the design process,allowing different building con fi gurations of openings (number,size and location) and providing  fl exibility in organizing spaceswithout compromising the structural integrity of the structure(Kwan, 2013; Kirkegaard, 2012). CLT also allows covering longspans without intermediate supports; something that would betoo complex or impossible to attain using wood in traditionalways. For example a CLT panel with 7 layers (9 inch thickness) canbe used to cover spans of up to 25 feet (Malczyk, 2011). Somevariations of traditional CLT panels, such as  “ folded ”  and  “ cassette ” fl oors have improved the performance of   fl oor structures bydecreasing the weight of the elements, allowing covering up to 65feet-long spans (Fountain, 2012). Silva et al. (2013) has evaluated special applications of wall-structures working as deep beams thatcan help solve long spans without intermediate supports. A studyconducted by Jaksch et al. (2012) evaluated the use of CLT ele-ments to achieve folded geometries, which they de fi ned as theintersection of two planar surfaces on a speci fi c angle. The studyconcluded that the use of CLT was not only viable, but also rep-resents a new type of wooden architectural language based onlarger planar surfaces.  2.5. Fire performance Several research studies have focused on CLT's performanceunder  fi re situations, given the common perception that woodbuildings perform poorly in these situations (Frangi et al., 2009;FPInnovations, 2013). Authors of these studies state that woodenstructural elements of large sections such as CLT panels havedesirable  fi re resistance properties, mainly because of wood'sparticularcharring properties. Accordingtothe ForestProducts Lab(2010), a char depth of 1.5 inches at 1 h is generally expected forstructural wood members. Correspondingly, experiments per-formed by Friquin et al. (2010), in which several CLT panels wereevaluated under different  fi re conditions, observed that woodformed a char layer that protected non-charred wood from furtherthermal degradation and mass loss. This behavior allows thestructural element to maintain its strength and dimensional sta-bility without collapsing in an abrupt way, potentially providingtime for the evacuation of occupants from the building.The American Wood Council conducted an ASTM E119 experi-mental  fi re resistance test 2 on a series of three CLT walls at an in-dependent fi re testing facility in Buffalo, New York(AWC, 2012). Allwallsampleslastedmorethana180minbeforecollapsing,whichissigni fi cantlylongerthan therequiredtimeof90 minsetforTypeIV (heavytimber)constructionintheInternationalBuildingCode(IBC,2012). Further research conducted by Frangi et al. (2009) on a full- scale 3-story building showed that providing tighter connectionsbetween panels can limit the spreading of smoke and  fi re, limitingthe damage to a room. The results from another full-scale  fi re test(Evans, 2013) concluded that CLT panels have the potential toprovide  fi re resistance comparable to the typical exterior wall as-semblies of non-combustible construction.  2.6. Seismic performance It has been proposed by several authors that CLT-based con-structions perform well under lateral forces and also possessductilitydue toitsmultiple,small connections(Winteretal., 2010).In one remarkable experiment, the Trees and Timber ResearchInstitute of Italy tested a full-scale seven story CLT building on theworld's largest shake table in Japan (Popovski et al., 2010). Evenwhen subject to a severe earthquake simulation (magnitude of 7.2in the Richter scale), the structure showed no permanent defor-mation, with a maximum inter-story drifts of 1.5 inches andmaximumlateral deformationof 12inches after thetest(measuredlaterally at the highest point of the 82-feet building). The re-searchers concluded that the damage to the structure was  “ negli-gible ” . In a similar experiment, Hristovski et al. (2012) conducted afull-scale shake table test for a CLT building prototype, to verify thecomputationalmodeltheydevelopedtopredictthebehaviorofCLT joints under seismic forces. The results showed that fasteningsystemshelpdissipatetheseismicenergy,whichisfavorableunderseismic conditions.  2.7. Thermal performance One of the measurements used to describe the thermal perfor-mance of a material is  thermal conductivity , de fi ned as  “ the rate of heatthat fl owsthroughoneunitofthicknessofthematerialsubjectto a temperature gradient ”  (Staube and Burnett, 2005). Thermalconductivity is typically measured in Btu    in/(h    ft 2    F). Thelower the thermal conductivity the less heat the material is able to 2 The test is intended to evaluate the duration for which wood structures contain fi re without diminishing their structural integrity. M.F. Laguarda Mallo, O. Espinoza / Journal of Cleaner Production 94 (2015) 198 e  210  201  transfer, which in turn means that the material has better insu-lating properties. The thermal conductivity of wood is much lowerthan that of metals and it is about two to four times the thermalconductivity of mineral wool, a material commonly used for ther-mal insulation (Staube and Burnett, 2005). For example, the con-ductivity of softwood lumber is about 0.7 e 1.0 Btu    in/(h  ft 2   F), compared with 310 for steel, 6 for concrete, and 0.25for mineral wool.Another factor that affects the thermal performance of an en-velope is thermal mass of the materials used. Since CLT is a solidwood panel, it also provides thermal mass (Cambiaso andPietrasanta, 2014), thus CLT panels both in the building enclosureand in interior  fl oors and walls act as a thermal mass that storesheat during the day and releases it at night. This property canreduce heating and cooling loads, shifting the time of peak loads,and lowering overall building energy use ( Jowett, 2011; Muller,2010). The R-value is another measure used to describe a con-struction material's thermal performance (Staube and Burnett,2005). It is a measure of thermal resistance or insulating ability.Thismeansthat materialswithhigherR-valuesarepreferablesincethey have higher insulating ability. For wood, the R-value isapproximately 1.25 ft 2   F  hr/Btu (Staube and Burnett, 2005). Astudy conducted by Jowett (2011) determined that a 7 inch-thickCLT panel has an R-value of approximately 8 ft 2    F    hr/Btu.For comparison, a concrete wall of similar thickness has an R-valueof 1.35 ft 2   F hr/Btu.Similarly to thermal conductivity,  “ air tightness ”  of a building isanimportantcharacteristic forthebuilding's thermalperformance,because air in fi ltration can have a signi fi cant effect in the indoorclimate (Mardookhy et al., 2013). According to Staube and Burnett (2005), making a building envelope air-tight can help preventsome problems caused by condensation of humid air from theoutside or cold and warm air penetrating or leaking (depending onthe season) from the construction. The International Energy Con-servation Code (IECC, 2012) includes rigorous requirements for airleakage through the building envelope to reduce energy con-sumption during winter (heating loads) and summer (coolingloads). Regarding this topic, in their study on thermal performanceof CLT structures, Skogstad et al. (2011). Concluded the mainadvantage of CLT is that it offers the possibility of creating an air-tight construction, due to the large panels, which also makepossible using a reduced number of elements and joints throughwhich air could in fi ltrate or leak.From the literature, it was found that there is an abundance of information on the technology of building with CLT. However, onearea that has received limited attention has been the market  Table 1 Summary of research projects on CLT's performance as a building material.Attribute Study ReferenceEnvironmentalperformance andsustainability- CLT has the capacity to store carbon in large quantities over a long period of time, offeringthe opportunity to turn buildings into  ‘ carbon sinks ’ (Lehmann, 2012)- CLT panels can be reused which further lowers the environmental footprint of the buildings (FPInnovations, 2013)- The use of CLT allows for a reduction of the use of fossil fuel during manufacturing of the panels (FPInnovations, 2013)- CLT buildings have less than a half the amount of embodied CO 2  compared to concrete or steel (Hammond and Jones, 2008)- Heavy Timber offers negative net total GWP when compared with concrete or steel ( John et al., 2009)- CLT buildings have a lower operational energy demand (Chen, 2012)- CLT building offer lower environmental impact and allow to save 18% of non-renewable energy,compared to concrete buildings(Robertson et al., 2012)Installation simplicityand cost competitiveness- Concealed metal plates provide a good performance under  fi re situations (FPInnovations, 2013)- CLT buildings allow for greater construction simplicity than a traditional wood-frame solution,due to having fewer but larger elements(Waugh, 2010)- Construction per  fl oor could take up to 4 days, compared to 21 days if concrete was used (WoodWorks, 2013)- CLT shifts the design from  “ frame ”  to  “ plates ”  (Kirkegaard, 2012)- CLT enables the reduction of construction time up to 30%, which signi fi cantly reducesthe costs associated with on-site labor(Silva et al., 2013)- Self-drilling threaded screws are employed for the creation of a structurally stable constructionable to resist vertical and horizontal forces(Stora Enso, n.d.)Structural performance - Thecombination ofCLT andconcretecould allowdesignerstohavebuildingsas highas150m tall (Van de Kuilen et al., 2011)- Each CLT element constitutes a stable structure by itself that is able to resist forces in twodirections(Popovski et al., 2010)- Shear strength and stiffness in CLT was identi fi ed as key issues in the performance of CLT (FPInnovations, 2013)- Cross-laminated nature of CLT allows panels to perform well as load-bearing plates and shearpanels(Steiger and Gülzow, 2010)- CLT represents a viable alternative to steel and concrete for mid and high-rise buildingconstruction(Fountain, 2012)- Stiffness properties of CLT panels depend on the homogenization of the individual layers (Steiger et al., 2008)Design  fl exibility - CLT allows the creation of buildings with  “ folded ”  geometries (Meyer, n.d.)- 9 inch thick CLT panels allow to cover spans up 25 feet, similar to those covered by concrete slabs (Malczyk, 2011)- Wall-structures working as deep beams, and columns can be used to cover long spans withoutintermediate supports(Silva et al., 2013)-  “ Cassette ”  and  “ folded ”  fl oor allow to cover larger spans of up to 65 feet (Fountain, 2012)Fire performance - Tightness between panels can prevent smoke and  fi re to spread, limiting the damage to speci fi careas(Frangi et al., 2009)- CLT wall samples tested lasted more than hundred 80 min before collapsing (AWC, 2012)Seismic performance - CLT structures showed no permanent deformation after being tested in an earthquake simulator (Popovski and Karacabeyli, 2012)- CLTsystemsofferstrengthandductility,whichhelpsthepanelsperformwellunderseismicforces (Winter et al., 2010)- Fastening systems help dissipate the seismic energy (Hristovski et al., 2012)- Connection layout and design has a strong in fl uence on the overall behavior of the structure (Pei et al., 2012)Thermal performance - A 7 inch thick CLT panel would have an R-value of approximately 8 ft 2  F hr/Btu ( Jowett, 2011)- CLT offers the possibility of creating a tight construction with less air leakage, thus improving thethermal performance of the building(Skogstad et al., 2011)- The massive nature of CLT offers a good amount of thermal inertia, essential in energy ef  fi cientbuilding construction(Cambiaso and Pietrasanta, 2014) M.F. Laguarda Mallo, O. Espinoza / Journal of Cleaner Production 94 (2015) 198 e  210 202
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