After a fire ravaged the Grenfell tower block in Western London last June, killing 72 and leaving hundreds homeless, an in-depth investigation was launched into the cause of the fire and why it spread so rapidly. After fire specialists BRE Global pointed the finger at the combustible cladding used in the tower’s most recent renovation, England acted to implement a ban on combustible cladding in new structures—a ban that includes timber. The original Clifford Wearden and Associates–designed tower was built in 1974 with passive fire prevention in mind. However, a 2016 renovation (reportedly to beautify the housing block to improve the views from the wealthier neighborhoods to the south and east) clad the concrete building in combustible polyethylene-cored aluminum panels. Alleged incompetence on the part of the contractors also created a “chimney effect” wherein flames were able to travel upwards through the gap between the structure and flammable panels. These revelations led the UK’s Ministry of Housing, Communities and Local Government to declare a ban on combustible external cladding for new buildings over 59 feet tall and those that contain housing. Hospitals, dorms, schools, and residential towers would all be affected. The ban goes into effect on December 21, a full 17 months after the fire. The ban, which would also affect retrofits, effectively limits the materials that can be used as exterior cladding to steel, stone, glass, and others with a European fire rating of Class A1 or A2. After the final terms of the ban were revealed, the Architects’ Journal reported that London’s Waugh Thistleton Architects, of cross-laminated timber (CLT) proponents, spoke out against the restriction of timber in high rises. Other than slowing the research and development of engineered timber, the ban would disallow the use of a low-carbon cladding alternative. On the other hand, the Royal Institute of British Architects (RIBA), has seemingly embraced the ban. Adrian Dobson, RIBA director of professional services, released the following statement shortly after the ban was first announced: “It is good news that the Government has acted on the RIBA’s recommendations to ban combustible cladding on high-rise residential buildings over 18m. The ban needs to be accompanied by clear guidance and effective enforcement to promote fire safety and leave no room for cutting corners. “However, toxic smoke inhalation from the burning cladding very likely contributed to the disproportionately high loss of life at the Grenfell Tower disaster. Permitting all products classified as A2 does not place any limits on toxic smoke production and flaming particles/droplets. In our view, this is not an adequate response to the tragic loss of life and might still put the public and the Fire and Rescue authorities at unnecessary risk.”
Posts tagged with "cross-laminated timber":
Thanks to a recent addendum to Oregon’s building code, the state is the first in the country to allow timber buildings to rise higher than six stories without special consideration. Portland has become something of a hotbed for timber innovation as of late. Carbon12, PATH Architecture’s eight-story glulam and cross-laminated timber (CLT) tower with a steel core, recently became the country’s tallest timber building and was set to be surpassed by LEVER Architecture’s 12-story Framework. Alas, that project was put on hold due to mounting financial difficulties last month, but it seems the precedent that the project achieved in securing a building permit from the State of Oregon and City of Portland will live on. The timber allowance comes courtesy of Oregon’s statewide alternate method (SAM), a state-specific program that allows for alternate building techniques to be used after an advisory council has approved the “technical and scientific facts of the proposed alternate method.” The allowance comes after the International Code Council (ICC)–the nonprofit group that Oregon models its building codes after–established the ICC Ad Hoc Committee on Tall Wood Buildings in 2015 to explore the benefits and challenges of using timber in tall buildings. A Committee Action Hearing was held in April of this year, where the Ad Hoc Committee, made up of code experts, stakeholders, and industry members presented their findings. All 14 of the committee’s suggestions were adopted, introducing standards and best practices for fireproofing, the load-bearing potential of CLT and heavy timber, water resistance, sealing, seismic ratings, and more. Three new building classifications were introduced as a result: Type IV A, timber buildings permitted up to 18 stories and 270 feet tall, Type IV B, timber buildings with a maximum height of 12 stories and 180 feet, and Type IV C, which is permitted to rise nine stories and 85 feet tall at maximum. The shortest of the timber typologies is allowed to use exposed structural timber as an interior finish, whereas the tallest, type A, must enclose all exposed surfaces and include a three-hour fire-resistance rating for the structural elements. “We congratulate the State of Oregon on becoming the first state to provide building code recognition for construction of tall, mass timber buildings,” said American Wood Council President & CEO Robert Glowinski in a statement. “Mass timber is a new category of wood products that will revolutionize how America builds and we’ve seen interest in it continue to grow over the last several years. This action by the Codes Division Administrator helps code officials in Oregon by making provisions consistent throughout the state. In adopting this new method, Oregon has also recognized the significant environmental benefits that accrue from greater wood product use.”
Disappointing news has come out of the woodwork this week: plans for the tallest timber building in North America have been shelved. Framework, a 12-story structure planned for downtown Portland, Oregon, designed by LEVER Architecture, was set to begin construction after receiving a building permit and a $6 million investment from the City of Portland to include 60 units of affordable housing. The developer, project^, said that inflation, escalating construction costs, and fluctuations in the tax credit market are to blame for the sudden hold. Despite massive investment, the project still had not met it’s $29 million fundraising goal as of Monday. The tower was on track to break records as the largest single use of Cross-Laminated Timber (CLT) in the U.S., and would have set an example for possibilities in timber structures. It would surpass the already-built Carbon12, an eight-story, mass timber building also in Portland. The research and planning that went into crafting the design for Framework were considered by many to be revolutionary in the field. Anyeley Hallova, a developer with the project, acknowledged the extensive work and collaboration the Framework team has undertaken with both private entities and public agencies since the design process began in 2014. “Although beset with market challenges beyond our control, we are very proud of Framework’s achievements and the new standards we’ve established for the use of CLT in the U.S.,” Hallova said in a statement. The project was also expected to be a building block for the revival of the state’s rural timber industry. Recent political attention has surfaced on the topic as Oregon senators Ron Wyden and Jeff Merkley pushed for a half a million dollar grant last week to be awarded to Oregon State University to study the durability of CLT. The team behind Framework was also able to advance research through a $1.5 million award which it won in the 2015 U.S. Tall Wood Building Prize Competition, sponsored by the U.S. Department of Agriculture.
Yale University and Gray Organschi Architecture have designed and built a self-sufficient tiny house for UN Environment and UN Habitat, and the building is on display in UN Plaza in Midtown Manhattan until August 11. The Ecological Living Module contains 215 square feet of occupiable interior space and carves out another 16 square feet for a rear mechanical closet. The unit uses passive lighting and moisture collection, structural cross-laminated timber (CLT), food-growing green walls, and sun-tracking solar panels to shrink both the building’s embodied energy and resource needs. According to UN Environment, housing construction worldwide uses 40 percent of all resources produced every year and accounts for one-third of greenhouse gas emissions (not to mention the conflicts being fought over rapidly dwindling materials like sand). The module was commissioned just in time for the United Nations High-level Political Forum on Sustainable Development, to illustrate the idea that sustainable urbanization can only be accomplished if buildings minimize their contribution to climate change. The Yale Center for Ecosystems in Architecture and Gray Organschi worked together to design and install the module in only four weeks. The building was fabricated partially in New Haven and partially in Brooklyn and assembled on the UN campus amidst heavy security and tight construction restrictions. In order to balance maximum sun exposure with thermal comfort, the module was designed with New York’s specific micro-climate in mind. The dramatically-sloped building is clad in dark cedar planks and is home to two cascading “farm walls”, one on either side, and Gray Organschi claims that in New York the home can produce over 260 servings of vegetables. Plants were used inside as well in the loft area, and a living wall in the upper loft area purifies air for the inhabitants. “Structure was used as finish,” explains Gray Organschi founding principle Alan Organschi. The same pale CLT used to support the building was left exposed inside to create all of the finished surfaces, from countertops to stairs. The timber was sourced from the northeastern U.S. and sequestered more carbon than the effort used to harvest it. The team optimized daylighting in the building by carving strategic cuts into the back and roof. An Integrated Concentrating Solar Facade was installed to both reduce the amount of incoming sunlight and harvest solar power; an array of tiny panels track the sun’s movement and focus light on the minimally-sized solar receivers. The team wanted to build a system that could be assembled with the least amount of effort, and that would use the minimal amount of toxic materials to create. After August 11, the Ecological Living Module will be partially disassembled and brought to San Francisco; the structure was built narrow enough to be towed by truck. After that, the module will be flown out for demonstration in Quito, Ecuador, and then Nairobi, Kenya.
Unicorn design/build company Katerra is continuing its impressive expansion from start-up to $3 billion tech-and-construction giant with the recent acquisition of Vancouver’s Michael Green Architecture (MGA). The Canadian architecture studio is known for pushing the boundaries of timber construction (including some of the largest mass timber buildings in the U.S.), and Katerra reportedly wants to use their expertise to bring down construction costs as well as better understand the material. The key to Katerra’s success lies in its vertically integrated business model; the company moves its projects through a single pipeline and handles everything from design, to engineering, to construction, using prefabricated modules to standardize the process. With $1.3 billion in projects under various stages of development–many of which are already framed with mass timber–the company is constantly searching for ways to optimize its production. Before acquiring MGA, Katerra was already hard at work building out their 250,000-square-foot cross-laminated timber (CLT) panel factory in Spokane, Washington. MGA had been an early adopter in the mass timber construction game, and the firm, jointly based in Portland, Oregon, as well as British Columbia, has continued to push timber towers taller. Joining Katerra, was for the 25-person studio, a natural progression according to founder Michael Green. It also happens to align the weight and financing of a major Silicon Valley player behind the studio. “Two values convinced me to join with Katerra,” Green told Vancouver magazine, “addressing our impact on the climate and making good architecture affordable. This acquisition gives us the opportunity to address both of those issues at scale.” Through the use of mass customization (using a kit of parts to design distinct buildings instead of a “one size fits all” modular approach) and mass timber, Katerra is hoping to lower its construction costs by up to 30 percent. While land prices are typically the largest slice of the development cost pie, Katerra is bringing down both its material as well as labor costs. But the choice was about more than that, according to Katerra's head of architecture, Craig Curtis. In order for the company to continue expanding, it would need to bring aboard more design talent, and MGA has had experience with timber buildings of all scales. On MGA's side, Katerra won't be fully consuming their practice, and the firm will still handle a stable of its own projects independently.
Timber construction continues its march to mass market feasibility following a series of live blast tests on full-scale cross-laminated timber (CLT) structures. Through a series of tests conducted at the Tyndall Air Force Base in Florida, the WoodWorks Wood Products Council and U.S. Army are putting together guidelines for framing buildings with CLT. As Engineering News–Record reports, the idea to test CLT for its blast resistance properties arose after developer and construction company Lendlease entered into an agreement to build hotels on army bases across the U.S. As Lendlease chose to frame some of their hotels with CLT to save on time and construction costs, they were told that CLT wasn’t explicitly mentioned in the Unified Facilities Criteria, the building code for the U.S. Army. This meant that the material would have to pass a battery of durability and security hardening-related tests before it could be applied in any real-world structures. While the Army allowed the construction of Lendlease’s first CTL hotel, the Redstone Arsenal in Alabama, any future timber-framed buildings would require full-scale testing on a physical mockup before it could be approved. Lendlease reached out to WoodWorks Wood Products Council, who arranged the seven blast tests, Karagozian & Case Inc. (KCI), who developed and followed through on both phases of the testing, the Air Force Civil Engineer Center, and the University of Maine. The tests were carried out in two phases–the first in late 2016, and second at the end of last year. Lendlease built the testing structures, each of which were exposed to successively larger blasts over a period of seven tests; two of the mock buildings were 27 feet tall with two-foot-tall parapets and window cutouts at 12 feet, and the third was 23 feet tall, with two-foot-tall parapets and window cutouts at 10 feet. Both “buildings” had 15-square-foot footprints. After exposing the structures to 32 pounds, 67 pounds, and 199 pounds of TNT (with 610 pounds used for the last test), KCI concluded that for blast exposure, CLT was equivalent to the standard steel-studded wall. Because CLT panels contain multiple laminated layers, the remaining wood provides additional strength at the point of rupture. The load from the blast is also more evenly distributed owing to the panel’s support on all four sides, allowing the force to be evenly distributed towards the joints. The U.S. Army Protective Design Center (PDC) has already released their report on the 2016 tests and will follow it up with their analysis of the second round of testing this June.
Is wood dangerous? It’s one of the oldest, most sustainable building materials (if harvested correctly) and recent advances in cross-laminated timber (CLT) have made it possible to build taller, multifamily timber buildings, but local building codes are just beginning to catch up. Sure, any Girl Scout knows that you can’t start a fire without it, but it’s generally considered kosher: CLT boosters say that if contractors know how to work with the material, timber is just as safe as steel. Despite their widespread use, concrete industry groups strenuously object to the use of “combustible materials” in construction. One industry group has launched an email campaign to ostensibly make members of the AEC industry aware of (non–fire-treated) wood’s shortcomings. These emails are part of an ongoing battle between the wood, concrete and steel industries, a conflict which seems to have escalated in concert with the growing popularity of CLT and the introduction of the timber innovation act, which would provide government support to the development of mass timber technology. With ominous subject lines like “Georgia Bill Would Leave Savannah Exposed to Hurricane Threat” and “Flames Quickly Consume Combustible Denver Apartment Complex Under Construction,” the emails seem to sow doubt about the durability and safety of timber buildings. The five-story, 84-unit Denver building detailed in the latter missive was under construction when it was engulfed by fire. “Combustible materials have no place in mid-rise housing projects, regardless of whether they’re under construction or fully operational,” said Kevin Lawlor, spokesperson for Build with Strength, which initiated the campaign, in the email. “These buildings are effectively tinderboxes on steroids, and when a fire breaks out, they’re incredibly difficult to extinguish.” Build with Strength is a partnership convened by the National Ready Mixed Concrete Association. As their names suggest, both groups are unabashedly pro-noncombustible materials, concrete and steel included. Reached by phone, Lawlor said Build with Strength doesn’t have a beef with wood—it just wants to fulfill its mission of educating the AEC industry on the benefits of ready-mixed concrete and its use in low- to mid-rise buildings. Its members include architects, engineers, steel and concrete interests, political leaders, and even religious organizations. “It’s not a materials fight,” Lawlor said. “The goal is to promote safer construction in three- to seven-story buildings. The notices are not specifically designed to go out and attack any particular industry.”
Sixty-three trees, 67 cross-laminated timber (CLT) panels, and 12 days—that’s what it took for Seattle-based atelierjones to erect the firm’s 1,500-square-foot CLTHouse, one of the first all-CLT residences constructed in the United States. The three-sided home is built on a leftover 2,500-square-foot triangular lot in Seattle’s Elliot Bay neighborhood on the shores of Lake Washington, where architect Susan Jones launched her research house experiment back in 2015. The house’s blackened, shou-sugi-ban treated exterior panels contrast with the blonde, white-washed, and daylit-spaces within the home, which emanate from a three-level circulation core containing a staircase, wet walls, and concealed utilities. The rustic home is inspired by the Northwest’s ubiquitous log cabins and features exposed wood paneling inside and out in homage to this building type. The approach, according to Jones, seeks to project a sense of “living with nature in the city” and provides a productive example of the smaller-scale capabilities of emerging CLT technologies. The house is punctured by triangular, gable-shaped windows that infuse it with daylight. Combined with the gypsum, plastic-laminate, stainless steel, and quartz-lined interior surfaces, it provides an “immersive, visceral, and natural experience,” according to the architect. Constructed using CNC-milled, rapidly renewable, and sustainably harvested CSFI-certified spruce, pine, and fir panels made by Structurlam, the building is crafted to inspire a sense of naturalistic escape and relaxation. The home’s exposed knotty pine aesthetic is reflected in a pair of stylized second-floor screened window walls that mark a triangular notch carved into the structure. Here, two pairs of sliding glass doors along the ground floor open the dual-lobed plan to the outdoors. Dining and living room spaces swing around this interior corner, where on one side, a thin plywood partition separates the dining and kitchen spaces from one another. Behind the kitchen sits a short hallway that connects the building’s backdoor entrance—located below a cantilevered bedroom suite—with the stair core. On the floor above, a trio of bedrooms, two bathrooms, and a reading nook cap off the home’s living areas while a rooftop deck overlooks the entire neighborhood from a wooden perch. The pilot house was developed as a research prototype and required extra municipal approvals to account for building codes that had not yet incorporated mass timber structural systems. Though crafted from sustainable materials from the start, atelierjones went one step further and planted 800 trees in conjunction with the project to act as an additional carbon sink. The result, according to Jones, is simply “hypernatural.”
The University of Toronto is teaming up with Vancouver-based practice Patkau Architects and Toronto’s MacLennan Jaunkalns Miller Architects (MJMA) to build a 14-story timber and concrete tower, the tallest in North America. Cross-laminated timber (CLT) is taking on the role of structural core and envelope, with the only concrete portion being the existing foundation. According to Shane O'Neill of Patkau Architects, the new tower will “utilize conventional glulam timber floor slabs, in addition to glulam timber columns, beams, and cross-bracing members.” The entire CLT structure is wrapped in multi-angled glazed glass, with a series of skylights and tilted planes providing natural light to atriums and stairwells below. The tower will be built atop the University of Toronto’s Goldring Center, which was designed by Patkau Architects and MJMA in 2014 to support the mass of a significant structure atop it. According to the University of Toronto News, the tower was originally going to be built of steel and concrete. However, wood building incentives provided by Ontario’s Mass Timber Institute and the environmentally friendly qualities of timber construction convinced the school and the designers to opt for the natural material. The structure joins the growing list of timber towers and academic buildings cropping up globally, ranging from London’s 121-unit Dalston Lane to the University of Idaho’s under-construction basketball arena. Currently, Patkau Architects and MJMA are wrapping up the design phase, with the goal of beginning construction in late 2019.
Catalog homes could soon be seeing a resurgence, as London-based startup Cube Haus has enlisted several big-name English architects to design modular, off-the-shelf homes for design lovers on a budget. Adjaye Associates, Skene Catling de la Pena, Carl Turner Architects, and furniture designer Faye Toogood have all signed on to design high-density housing that will infill “awkward” sites throughout London. London homeowners have the option to subdivide their property and build on the unused portions, resulting in awkwardly shaped plots. Cube Haus claims that its modular designs can be scaled to fit these unorthodox lots and infill areas naturally and that their homes will cost 10 to 15 percent less than a conventional model because of their off-site manufacturing. Each home will be framed from solid sheets of cross-laminated timber and moved into place at the construction site, then clad in sustainable materials. Cube Haus is also offering up its designs for consumers building in more traditional lots as well. Adjaye Associates is no stranger to residential housing in London, and their rectangular Cube Haus design closely resembles Adjaye’s 2007 Sunken House in Hackney. Excavated gardens in the home’s yard plays a central role in this scheme, as do tall windows and ample natural light. Everything else about the timber-clad home’s layout is up to the landowner, and all of the rooms have been designed for a plug-and-play approach. Carl Turner has brought two schemes to the table. The first is a two-story house with a flat courtyard area on the roof, which splits the upper level into two pitched volumes. Cube Haus notes that the pitch of the roof can be adjusted, rotated, or flattened out according to the client’s whims. The second model is single-story slab pierced with a square courtyard, with the home’s programming arranged around this space. Consumers have the choice of cladding their homes in opaque glass, zinc, charred timber, or dark brick. Skene Catling de la Peña engineered their scheme as a “building within a building,” designing a masonry-clad central column that serves as a fireplace, staircase, hot water heater, and storage space around which the rest of the rooms are organized. Homeowners have several options for how they can clad the shaft, from tile to marble–or it can be left undecorated, exposing the precast concrete structure below. The homes themselves will be malleable to the irregular sites, linked through their spacious rooms and ubiquitous views of the main column. Faye Toogood has offered up a simple scheme in two material palettes; one light and one dark. A central garden placed between two pitched peaks breaks up the rectilinear massing of the house, creating a form suitable for both the urban environment as well as the countryside. Cube Haus is the child of entrepreneurs Philip Bueno de Mesquita (himself an owner of an Adjaye-designed home in London) and Paul Tully. The company is already building, with two sites in Forest Gate, London under construction and others in pre-planning throughout the city. Cube Haus hopes that its three-bedroom homes will sell for anywhere from $880,000 to approximately $1 million.
Thanks to a two-year, $250,000 Wood Innovations Grant from the United States Forest Service, and with further support from the National Hardwood Lumber Association, Indiana Hardwood Lumberman’s Association, and the Indiana Department of Natural Resources, IKD is currently working on an advancement that may completely change the cross-laminated timber (CLT) market. Currently, CLT is made primarily of softwoods, which have the advantage of being fast growing and inexpensive. IKD believes the future of CLT should also include hardwood, and now it just might. As a proof of concept, IKD has constructed a large installation, which stands as the first hardwood CLT structure in the United States. The project was built with an experimental CLT material made from low-value hardwood-sawn logs for Exhibit Columbus, the new architectural exhibition in the modernist mecca of Columbus, Indiana. A reference to the conversation pit in the Eero Saarinen–designed Miller House, the IKD’s Conversation Plinth is a multilevel occupiable installation in the plaza in front of the I.M. Pei–designed Cleo Rogers Memorial Library. The motivations behind using hardwood are two-fold. Currently, over 50 percent of the 80 million cubic feet of hardwood harvested in Indiana each year is used for low-value industrial products. By integrating this wood into the higher-value CLT, it raises the value of what is already Indiana’s largest cash crop. And from the perspective of designers and engineers, hardwood CLT provides the possibility of a more fire-resistant panel and a form-factor advantage. “We are currently exploring a number of applications that could have larger scale building applications,” IKD partner Yugon Kim said. “Since hardwood has superior mechanical properties, we believe we can achieve a panel that could be thinner to meet the same structural capacity of an equivalent softwood CLT panel.” The Conversation Plinth is not simply an exhibition piece for IKD. It is a test of the hardwood CLT the firm developed with SmartLam, the first CLT manufacturer in the United States. Over the months, the project will be subjected to the varied and sometimes-extreme weather of south-central Indiana, providing firsthand data that IKD and SmartLam can use to advance their research on the material. From the beating sun of late summer through the sleet, snow, and ice of winter, the project will be monitored for durability as well as aesthetic and structural changes. “We are closely observing the mixed-species panels and seeing how they react in the extreme temperature and moisture fluctuations so that we can continue to refine the species mix within the panel, the adhesion process, and the finish application and approach,” Kim explained. “It is really interesting to see how differently hardwood moves from softwood when the moisture content varies, and we are looking deeper at the fiber structures and unique characters of species themselves as well to create a superior CLT panel.” The project continues much of the timber research IKD has been doing, including its design for the Timber City at the National Building Museum in Washington, D.C., and work on timber modular waste units, a timber version of CMU made from timber waste that has won numerous awards. Resources Project Lead and Designer IKD CLT Fabrication SmartLam Timber Engineering Bensonwood Phase One Hardwood Testing Material Supplier Pike Lumber Company Phase Two Conversation Plinth Hardwood Material Supplier Koetter Woodworking General Contractor Taylor Brothers Construction Co. Softwood Material Supplier And Fabricator Sauter Timber
If the steady stream of newly announced mass wood projects is any indication, mass timber building technologies are poised to take the American construction and design industries by storm over the next few years. As products like cross-laminated timber (CLT), nail-laminated timber (NLT), glue-laminated timber (glulam), and dowel-laminated timber (DLT) begin to make their way into widespread use, designers, engineers, and builders alike are searching for the best—and sometimes, most extreme—applications for mass timber technologies. But rather than reinvent the wheel, American designers can look to experienced mass timber designers in Europe and Canada for key lessons as they begin to test the limits of these materials in the United States. European and Canadian architects and researchers have long been at the forefront of mass timber design, starting with early experiments in the 1970s. By the 1990s, researchers like Julius K. Natterer at the Federal Institute of Technology in Lausanne, Switzerland, were developing initial CLT prototypes. Natterer’s work has been buttressed by that of many others, including research performed at the Norwegian Institute of Wood Technology under Thomas Orskaug and experiments conducted at the Technical University of Munich under Stefan Winter. One key lesson European timber projects teach is that when it comes to structural systems, weight matters. On average, mass timber assemblies weigh between one-third and one-fifth as much as concrete structures, despite equivalent structural capacities. As a result, mass timber buildings are much lighter than concrete ones, a positive for building in tricky urban situations, for example—where underground rail yards, subway tunnels, and municipal utilities place limits on how heavy and tall buildings can be. London-based Waugh Thistleton Architects (WTA), for example, recently completed work on Dalston Lane, a 121-unit CLT midrise complex located above a tunnel serving the Eurostar train line in the city’s Hackney neighborhood. For the project, the architects worked with timber-engineering specialists Ramboll to develop a stepped tower cluster rising between five and ten stories tall. CLT panels are used for the external, party, and core walls of the building, as well as the stairs and the building’s floors. The variegated massing is due directly to the architect’s use of CLT construction, which resulted in a lighter building that allowed the designers to build taller without more extensive foundations. The resulting building, with its staggered massing, better maximizes daylight infiltration into apartment units. The added height allowed the architects to add 50 more units to the project than originally permitted, a testament to just how light CLT can be. Andrew Waugh of WTA said, “Timber buildings are just simpler, cheaper, and nicer [than concrete ones]. High-density urban housing should be built using mass timber.” Lighter mass timber buildings also perform better in seismic zones. Since the lighter buildings carry less inertia, the potential for catastrophic swaying goes down. The strategy was applied this year with the Brock Commons tower, an 18-story, 400-bed college dormitory designed by Vancouver-based Acton Ostry Architects for the University of British Columbia Point Grey campus. The tower is made up of a hybrid structural system that includes CLT floor slabs, glulam columns, steel connectors, and dual concrete cores. The concrete cores anchor the light mass wood structure in place, helping to counteract seismic and wind-generated forces. The 173-foot-tall structure is currently considered the tallest mass timber building in the world, and the construction is particularly multifaceted, utilizing a specifically fabricated set of interdependent building materials and finishes to meet structural and fire-safety regulations. The Brock Commons tower’s hybrid structural system brings to light another valuable lesson: that above certain heights—ten to twelve stories—the lightness of mass timber construction becomes a liability with regard to wind loads. The lack of physical mass at the highest parts of a prototypical timber tower results in increased deflection from wind loads. Ola Jonsson, partner architect at Swedish architecture firm C.F. Møller, recommended architects “go back to thinking about construction when designing mass timber structures,” as a way of rethinking approaches to dealing with difficult-to-manage structural conditions. He added, “It’s so early [in the adoption of mass timber technologies] that few really know how to do it well.” The architect said that with certain tall timber tower projects the office is working on, designers had to develop new massing strategies to limit wind loads. Jonsson continued, “Many engineers lack experience in mass timber, so architects have to become central figures in construction and design during this early phase of adoption.” The firm is currently developing over ten mass timber projects, an emerging body of work that came out of earlier mass timber competition entries developed by C.F. Møller that took the world by storm. C.F. Møller recently entered into a partnership with HSB Stockholm—Sweden’s largest housing association—to design a series of new mass timber housing towers, including the 34-story Västerbroplan tower designed with concrete cores and wraparound terraces. The tower’s columns and beams will consist of a blend of CLT and solid timber. The building’s terraces will come with integrated exterior curtains and will be fully enclosed by a steel superstructure containing glass panels. The tip of the building is designed to dematerialize as it steps back along two facades, creating a series of exposed terraces and planted areas. Like Brock Commons, Västerbroplan tower features a hybrid structural system that is “resource-effective,” according to Jonsson, meaning both lightweight and rigid. The firm is also at work on a 20-story bundled housing tower called Hagastaden for HSB Stockholm, this one designed as part of a new quarter of the city that will contain mixed uses and generous pedestrian areas. The tower features varied floor heights designed to accommodate divergent uses like student flats, penthouse apartments, and typical family-occupied units. Aside from the firm’s multiple mass timber projects, C.F. Møller is working as part of an interdisciplinary research team that is developing new strategies around mass timber towers rising 20 stories or more. The group—backed by SP Technical Research Institute of Sweden, Växjö Municipality, and Linnaeus University, among others—will investigate mass timber construction from a fire-safety, life cycle, and construction technology perspective. Regarding the research project, Jonsson explained, "Massive wood constructions give urban planners, architects, and designers great possibilities to develop innovative and sustainable architecture,” adding, "but a broader knowledge and more practical experience in the industry is needed." Another paradigm-shifting impact mass timber construction has had on European building methods relates directly to the construction process. Because mass timber elements are factory-produced to order, the relationship between engineer, builder, and architect is extremely integrated. Cory Scrivner, mass timber specialist with Canadian mass timber manufacturer Structurlam, said, “For us, it’s all about the 3-D model. [Digital modeling and coordination] are all done before we go into production in the factory: Everything has already been approved by the architect, engineer, and our team.” Scrivner explained further that the intense coordination was necessary, as “we are designing a building made from components that are accurate within one to two millimeters of the digital model.” The designers behind Brock Commons utilized Structurlam as the mass timber manufacturer for the project. The advanced level of project coordination and off-site fabrication meant that project was finished roughly four months ahead of schedule, with a time-lapse video on a project website showing construction crews erecting upward of two floors per day. The first story for the project was built from cast-in-place concrete, while the remaining 17 stories are built in mass wood. The structural system utilizes glulam columns, steel connectors, and a two-way spanning CLT flat-slab. The design creates a floor beam–free structure that could be erected start-to-finish in nine and a half weeks. The rapid-fire construction time line, however, comes at the expense of longer planning and design phases prior to any work boots hitting the job site, as the teams must become absolutely synced prior to fabrication. Waugh of WTA explained that often with timber buildings, the firm asks its clients to “give us more time now [in the planning stages of construction] and we’ll save you even more time on the back end.” Waugh added, “The better programmed the construction process, the faster and more accurately the buildings come out.” Waugh said that after erecting several mass timber structures, the firm had “gotten so much better at it” than when they first started. One area of improvement has been material usage, which decreased with each project as the structural capabilities of mass timber have been further explored, tested, and certified. The Dalston Station project mentioned earlier, for example, utilized about two-thirds as much timber as the firm’s first mass timber project erected a decade ago. Part of the reason for the improvements, Waugh and Jonsson agreed, results from designers’ greater awareness of and comfort with the construction process. “To design well in mass timber, you need an architect who wants to understand that the nature of [the architect] is one of a ‘master builder’ as well as one of a ‘master designer,’” Waugh explained. Since mass timber construction methodologies are based on kit-of-parts assembly systems of mass-produced panel types and structural elements, there has been increased interest among European and Canadian firms in building high-density mass timber housing. These experiments have positive implications for the many American cities burdened with housing shortages and long project-approval times. Waugh explained that WTA’s focus rests on expanding the abundance of available housing through mass timber construction. He said, “We design everything in our office now as if it was a mass timber project. Concrete projects are becoming more and more rare.” Several projects in the works, like Shigeru Ban’s recently proposed 19-story Terrace House in Vancouver, Michael Green Architecture’s 35-story Baobab building in Paris, and PLP Architecture’s 80-story addition to the Barbican housing estate in London, point toward a wider adoption of tall and supertall mass timber housing towers. With faster construction times and fabrication that can occur in tandem with permitting, mass timber has the potential to help cities add housing rapidly, safely, and efficiently. Waugh added, “Humanity is becoming more urban, so the principal job of an architect in the 21st century is to develop high-density urban housing. In an era of climate change, it behooves you [as a designer] to reduce the amount of carbon emitted. Again, for us, mass timber is a way to do that.”