Tall Timber Student Housing

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Building tall with mass timber is becoming increasingly more feasible as strides are made to innovate within the tall timber space. The Tall Timber Student Housing project at the British Columbia Institute of Technology (BCIT) in Burnaby, British Columbia, is the first of the next generation of point-supported CLT structures and represents a significant advancement in tall, hybrid, mass timber construction.

This 12-story structure at BCIT builds upon the previous success of the 18-story UBC Tallwood Building at Brock Commons in Vancouver, British Columbia, that, when completed in 2017, was recognized as the tallest mass timber hybrid building in the world, reaching over 173 feet.

Featuring a single story of concrete at grade, which supports 11 stories comprised of mass timber floors, the BCIT Tall Timber Tower will bring 470 single occupancy studio and single-bedroom units to the campus. Not only does the hybrid structure answer the call for much needed affordable student housing, it also underlines BCIT’s sustainability goals with the use of mass timber and prefabrication.

Each mass timber level features flat, two-way spanning Hem-Fir cross-laminated timber (CLT) floor plates, point-supported on steel columns. The application of 11 feet, 6 inches-wide CLT panels provided by Kalesnikoff Mass Timber, with a maximum length of 43 feet, 7 inches, incorporates five layers of 2x lumber and utilizes machine stressed lumber in the strong direction to maximize spans, while considering punching shear behavior at column locations.

Punching shear in CLT, like punching shear in concrete slabs, is caused by high concentrated loads, such as at column supports. When high concentrated loads are applied to the face of the CLT panel, laminations are susceptible to "roll" against each other and may cause rolling shear failure. Therefore, considerations were made to detail column-to-column connections with 16-inch square wide top plates on each column at every level to distribute these loads and avoid accumulated loading perpendicular to grain. These direct force transfers are essential to the point-supported CLT system.

The CLT panels are designed to achieve a 2-hour fire resistance rating. This includes one hour of effective encapsulation by way of two layers of 5/8-inch-thick Type X gypsum board layers at the underside, and one hour of char in the wood panel. The 2-inch concrete topping provides full encapsulation to the top side of the CLT panel.

The large-format prefabricated facade panels used on the project, Flynn’s Speedwall system, are comprised of insulated metal panels supported on an aluminum chassis with pre-installed windows. Attachment of these panels to the main structure were designed with consideration to limit deflection in the CLT panels. Gravity connections for the facade panels are located at the column grid lines, where deflection is minimal.

The project incorporates several significant advances in mass timber construction:
Point-Supported CLT System: The two-way flat slab system without beams allows for unobstructed service distribution and reduced structural depths, enabling tighter floor-to-floor heights.

Wide format CLT Panels: The 11 feet, 6 inches wide CLT panels align with partition walls, such that columns are concealed within walls and suites are acoustically separated for optimal acoustic performance.

Testing and Validation: Results from testing, completed at Fast + Epp’s own Concept Lab and in conjunction with the University of Northern British Columbia, validated the point-supported and punching shear reinforcing design approaches for CLT, an approach not currently in the building code. Testing also confirmed the use of Hem-Fir CLT as a point-supported system, a species historically limited in similar applications due to Hemlock’s tendency to hold moisture in “pockets,” resulting in a required, uneven drying process. Kalesnikoff’s long-standing experience in drying Hem-Fir mitigated risk of this concern.

Steel Lateral Resisting System: The steel lateral resisting system, designed in self-stabilizing configurations at egress cores, limits the need for temporary shoring during construction. The braced frames were prefabricated in 5- and 6-story lifts to maximize shop welding and allow cores to top out before CLT installation.

The construction of the BCIT Tall Timber Tower was a collaborative effort involving architects, engineers, and contractors. Early coordination and construction modeling were crucial in accelerating construction timelines, resulting in the building being completed months ahead of schedule if such planning had not been in place.

Construction began late 2022, and the concrete podium was completed by early 2024. Prefabricated components like CLT panels, facades, and steel cores sped up the process, with quick installation of steel braced frames reducing trade overlap. Hem-Fir CLT panels were selected in substitution for Spruce Pine Fir (SPF), keeping product delivery on track despite site delays.

By mid-2024, the mass timber floors were being installed two floors below alongside the prefabricated cladding systems. This method enclosed the tower quickly, reducing weather exposure. The structure topped out late summer and was fully enclosed by early fall 2024, significantly faster than conventional building timelines due to the efficiencies of using mass timber.

The construction schedule was meticulously planned to optimize efficiency:

CLT Installation Cycle: Starting at Level 3, CLT was installed every 2 weeks. Week 1 involved laying down the floor plate, and Week 2 focused on installing steel HSS columns for the next floor's support.

Facade Enclosure: By Week 2 of CLT installation for Level 4, a floor two levels below was already being enclosed with the facade.

Drywall Encapsulation: From Week 2 of CLT installation for Level 6, a floor four levels below was being encapsulated with drywall. This schedule repeated for each subsequent floor.

Moisture Mitigation: A moisture mitigation program was implemented by removing water from panels daily, providing drainage solutions and coverage, and monitoring moisture levels. A vapor-permeable membrane allowed panels to dry naturally, and splines were taped immediately after installation.

Prefabrication and an efficient layout reduced crane sharing, contributing to the efficient construction schedule.

Choosing a mass timber structural system from the start helped meet sustainability goals. CLT floors make up 15% of the building's mass, including finishes, and their carbon sequestration lowers the project's overall embodied carbon. Moreover, this project was supplied by a vertically integrated mass timber supplier, who sustainably manages its own reforestation. The use of a high-performance cladding system further enhances the building's energy efficiency.
This project shows point-supported CLT systems offer a cost-competitive alternative to traditional concrete, particularly for multi-unit residential buildings. The insights gained are shaping future mass timber designs, promoting sustainable and efficient construction practices.

The BCIT Tall Timber Student Housing tower is more than just a building; it’s a symbol of what is possible with innovative engineering and sustainable construction practices. Projects like this play a crucial role in shaping the future of the construction industry as the demand for environmentally friendly building solutions grow. ■