WoodWorks CaseStudy CLT Milestone in Montana Cross Laminated Timber Makes its Mark with The Long Hall It happened so quickly that most design and construction professionals probably missed it. But when the first commercial building project in the U.S. constructed with cross laminated timber (CLT) was completed in 2011, it opened the door to new opportunities for the entire building industry. The Long Hall in Whitefish, Montana epitomizes many of the benefits of CLT construction—speed of installation, environmental and aesthetic benefits of wood, and energy efficiency. The two-story wood structure took just five days to erect, and gave the owner a sustainable, energy-efficient building.Earn one AIA/CES CEH (HSW) by reading this document andtaking a short online quiz. For details and learning objectives,visit the Online Training Library at woodworks.org.WoodWorks is an approved AIA provider. woodworks.org
Converting from CMU The Long Hall is a mixed-use, urban infillproject designed to replace an unsightly60-year-old Quonset hut in downtownWhitefish, Montana. The new 4,863-square-foot structure provides business and retailspace on the first floor, and the second flooris occupied by a martial arts studio. Originally designed with concrete masonryunits (CMU), the building designer, DatumDesign Drafting, worked with InnovativeTimber Systems (ITS) and Darryl Byle, PE, ofDSB Engineering & Consulting to convert thestructure to CLT. “Together, we convincedthe client that CLT would be a cost-effectivealternative to CMU while delivering a high-performance building, more sustainably andwith a better design aesthetic,” said Byle. “Theclient had no particular affinity for concrete andalso had time constraints. We were confidentthat CLT would provide the perfect solution.” Byle said the top three benefits of using CLTfor The Long Hall were speed, aesthetics andthermal performance. “With CLT, the entiretwo-story structure took just five days to install.We went from slab to occupancy in threemonths. And the owner loves the interior arts studio through the fall,” he explained. “By and shipped directly from the manufacturerfeel and renewability of the resource. He raising the building structure in just five days, he to the job site, where they can be quicklyalso wanted a high-performing structure; the was able to open the studio for the fall season.” and efficiently lifted into place. “By modelingenergy efficiency of the CLT system made this the entire structure in 3-D and meeting witha good choice.” Planning Ahead vendors and subcontractors well in advance, The resulting Type VB structure was built we defined the design challenges and resolvedto 2009 International Building Code (IBC) Because local code officials and issues dynamically,” said Byle.requirements. The building consists of 38 glulam subcontractors were not familiar with CLT,beams along with 13,000 square feet of CLT Byle said it was critical to plan ahead. “I worked as a building official myself, Pre-assembled Wallsfor the walls, second floor, roof, clerestory,partitions and arches. so I understood their concerns about being Because of shipping constraints from Europe, first to use a new product,” he said. “That’s CLT panel size was limited to 7 feet 4 inchesCost Competitive why I began talking with our local building in width and 39 feet in length, said Byle. “This department more than six months in advance; meant the wall panels could not stack full- Overall cost of the entire project was to make sure they were comfortable with it. story height as is often the case with otherapproximately $145 per square foot, $60 of The project became a real team effort; we all pre-manufactured CLT wall assemblies. Afterwhich was attributable to the installed cost of wanted to do this right so the building officials reviewing the pros and cons of vertical versusthe CLT and glulam. were there asking questions and educating horizontal stacking, we determined that it Because CLT had not been used for a themselves but also keeping an eye out for us.” would be more effective to assemble the wallscommercial building in the U.S., one of the first Preplanning was also critical because CLT as vertical elements in a standard platformthings Byle and his team verified was its cost for The Long Hall was sourced from Europe framing configuration.”competitiveness. Pete McCrone, a Quantity (although there are now several North American The Long Hall had less than 30 inches ofSurveyor with ITS, compared CMU and CLT suppliers). CLT panels are manufactured for spacing between it and adjacent buildings.across approximately 30 project elements. The specific applications, so are prefabricated Because this left virtually no room for on-siteanalysis favored CLT, in construction, contractors pre-assembled thepart because the exposed main vertical CLT walls in four- and five-panelwood structural shell could elements at a nearby site. They glued andserve both as interior wall screwed the splines and then transported theand ceiling finish. The pre-assembled wall panels to the job site (theCLT system also required largest were 30 x 11 feet) using an A-frame on aless time on site for low-boy trailer.erection, which reduced By pre-assembling the vertical panelsconstruction costs. and lifting them into place via crane, the Initial estimates put the contractor minimized on-site installation time.cost difference between Panels arrived from the manufacturer withCLT and CMU close to pre-slung lift webbing, which also helpedeven, but Byle said time construction move quickly and efficiently. Thevalue of the finished CLT manufacturer used CNC equipment tobuilding tipped the scales precisely pre-cut beam pockets and openingsin favor of CLT. “Originally, for windows and doors at the factory.the owner was going tohave to close his martial
engineer designed a flexible glulam beam base plate using a tongue and groove connection at the base of the CLT wall. Anchor bolts connect the plate to the foundation at locations offset from panel attachment points, providing a flexible connection able to take the prescribed seismic loads. Thermal Performance CLT’s thermal performance was an attractive benefit for The Long Hall’s owner. Because CLT is a solid wood panel, it provides thermal mass. Wood is also a good natural insulator. And, since CLT panels can be manufactured using CNC equipment to precise tolerances, panel joints fit tight, which further improves energy efficiency. To help illustrate this benefit, Byle contacted a Montana Department of Environmental Quality (DEQ) official, who conducted a blower door test on the structure for educational purposes with an Energy Systems class. “They don’t normally do these tests for commercialApproved as a One-hour CLT Met Other Design Challenges buildings,” he said, “but the results reflected aRated Assembly The design and construction team used CLT very airtight system. Energy code maximum is four air changes per hour, and two is considered While The Long Hall was designed as a to overcome a number of other challenges. For tight for an energy-efficient home. This CLTType VB structure, fire protection was still a example, the site’s soils got softer as they went system measured just 1.5 air changes per hour,consideration in terms of getting CLT accepted deeper, so the foundation had to stay shallow. which is excellent.”for use. Since the structure was sited within five Since CLT weighs less than CMU, they were Byle said they taped panel joints and beamfeet of the property line, the north and south able to use a smaller foundation. Heavier CMU ends before installing mineral wool insulationexterior walls were required to be one-hour fire- would have also increased footing size and slab boards on the exterior of the structure. “Thisrated, and the entire building was sprinklered. connection requirements, so additional cost fast, simple installation helps us maintain a Byle met with building officials to resolve savings were realized by using CLT. vapor-open, breathable structure.”concerns about fire safety. In order to meet the In order to optimize available floor space anddesign objective to feature exposed CLT on the internal space configuration, the structure was designed to free-span the 25-foot-wide lot. Pre-planning Paid Offinterior, they needed approval of the CLT systemas a stand-alone, one-hour rated assembly. Byle They incorporated CLT wall panels as out-of- The significance of being involved with theused data on fire design from sources such as plane bending elements to provide sufficient first commercial CLT installation in the U.S.the National Design Specification® (NDS®) for stiffness for the transverse lateral loads on the was not lost on Byle. “I learned that I am goingWood Construction and experimental CLT fire structure. Each panel/column/beam assembly to love using CLT,” he said. “The owner hadtest data from manufacturers and independent acts as a modified moment frame to absorb never heard of CLT before this project, but hesources1 to show CLT panels could be expected lateral forces and distribute them to the loves wood; CLT allows him to have a high-to perform well in a fire event. foundation. performance structure that looks good. He Additionally, Byle negotiated to reduce the Because CLT has high stiffness, the design had considered using CMU and metal, and wasrequired overall thickness of the wall assembly had to accommodate vertical motion along hesitant about being first to use somethingby taking advantage of the longitudinal walls. In order to do that, the new, but he is thrilled with theCLT’s unique structural end result.”characteristics. Because Byle knew that breaking groundCLT is only exposed on one with CLT would be a challenge, butside, it can easily withstand cites careful planning as key to theirthe code-prescribed one- success. “Getting early buy-in fromhour burn. Further, the the code officials was a definiteundamaged portion will still advantage,” he said.transfer loads bi-directionally He added that early designaround the compromised completion was probably thearea. Working with the most important thing he learned.local code official, Byle “Having the design finalized wellestablished a reasonable in advance of construction helpedfire event dimension and us pre-emptively identify anddesigned the structure to solve problems,” said Byle. “Pre-deal with that localized planning with our CLT supplier andstructural compromise (an subcontractors also paid off. As aapproach that is conceptually result, we finished the project onsimilar to disproportionate time and on budget. I look forwardcollapse regulations used in to more success with CLT.”the United Kingdom).