The Ontario Secondary School Teachers’ Federation (OSSTF) Headquarters and Multi-Tenant Commercial Building
Moriyama Teshima Architects
The Ontario Secondary School Teachers’ Federation (OSSTF) Headquarters and Multi-Tenant Commercial Building is a progressive 3-storey, 124,000SF mass timber project that uses net-zero strategies, and will seamlessly integrate commercial opportunities with the relocation and revitalization of the OSSTF’s office centre in Toronto. The building is intended to house the headquarters of the OSSTF and represents all the educators, educational assistants, psychologists, speech-language pathologists, social workers, and many other education professionals in the secondary school system in Ontario, as well as additional tenants. All design decisions were rigorously assessed for long-term value, health and wellness of employees, and operational savings.
Overlooking the Don Valley ravine landscape, the building is a highly sustainable, financially viable, and innovative new workplace that is on target for LEED Platinum certification and high-energy performance levels at 67 kWhr/m2/year. Designed to the highest environmental standards, the facility is built on a foundation of social, environmental, and financial sustainability.
Despite perceived premiums for a mass timber structure, after thorough analysis, the OSSTF went forward with a mass timber LEED Platinum solution that also invested in naturalized restoration of the ravine edge. Constructed out of cross laminated timber (CLT) floor slabs and glue laminated timber (GLT) beams and columns, structural components have been sourced nationally where possible, and demonstrate a robust, honest, yet innovative application of natural materials. The mass timber structure of the building uses a 9m x 9m grid of glulam columns, beams, and purlins with a CLT infill panel for the general floor system. This is an optimal grid for office layouts and was chosen for its optimization of the timber volume.
This highly efficient facility will ensure the OSSTF functions as a hub that continues to support public education in the province, provide healthy workplace environments for its staff and visitors, and responsibly meet the organization’s goals of financial resiliency.
The new Multi-Tenant Commercial Building is spatially divided to house the OSSTF Headquarters as well as two floors of leasable tenant space. Joined by a central atrium, the building will offer abundant outside views, light, openness, and numerous opportunities for spontaneous interactions between the OSSTF staff and tenants. Furthermore, shareable spaces on the ground floor include the lobby, café, and ground floor terrace, and features a multipurpose, convertible Event Space; this space will be shared not only by the building occupants, but by outside groups, providing opportunities for engagement with the wider community.
The architecture is inspired by WELL and Passive House design standards and promotes health and wellness at every level: generous structural bays provide optimal sizes for offices and corridors, maximizing the amount natural daylight to reach the interiors; a ‘Fresh Air Strategy’ ensures air moves through the building at a regular rate using building automation systems; large overhangs reduce solar heat gain and control glare; geothermal heating, a rainwater harvesting system for toilet flushing and irrigation, green roof, rooftop solar PV panels, and automated daylight dimming controls further contribute to significant energy savings. The LEED Platinum design achieves significant reductions in energy consumption and a reduction of greenhouse gas emissions. The building systems are comprised of geothermal heat exchange, passive natural ventilation system used together with a decoupled active mechanical system, and energy generation from the rooftop photo voltaic array. The key player in the building performance is the façade that contributes most significantly to the environment and experience for the building occupants.
Natural daylighting has been maximized thanks to generous structural bays; building automation systems move fresh air through the building; large overhangs reduce solar heat gain and control glare; geothermal heating, a rainwater harvesting system for toilet flushing and irrigation, green roof, rooftop solar PV panels, and automated daylight dimming controls further contribute to significant energy savings. These strategies have resulted in the reduction of greenhouse gas emissions by 84%, the reduction of thermal energy consumption by 60%, and a total energy reduction of 63%.
Analysis of the embodied carbon of OSSTF’s design revealed that while the overall carbon performance of the building was admirable, the construction of the shading device with a steel substructure worked at cross purposes with the timber and contained a significant carbon footprint. While the overall project achieves ambitious targets and commits to renewable resources and significant energy reductions, the modelling and analysis teaches us that we can continually improve as we turn our attention to embodied carbon reductions in the selection of materials and in construction.
The Don Valley ravine edge on which the building sits will also undergo intensive restoration and stabilization through naturalization and water balance strategies. Low Impact Development (LID) measures will control the major overland storm water flow route through the site and into the ravine. The design prioritizes democratic access to light and view as well as access to outdoor space and communal connection to the ravine. The exposed timber environment, beyond the commitment to renewable, carbon sequestering construction, creates an enveloping connection to nature in the daily life of the employees.