The Ontario Secondary School Teachers’ Federation (OSSTF) Headquarters and Multi-Tenant Commercial Building

Moriyama Teshima Architects

Short description

The Ontario Secondary School Teachers’ Federation (OSSTF) Headquarters and Multi-Tenant Commercial Building is a progressive 3-storey, 124,000 SF fully exposed mass timber project that uses net-zero strategies, and seamlessly integrates commercial opportunities with the relocation and revitalization of the OSSTF’s offices in Toronto. The building houses the headquarters of the OSSTF—an organization that represents all education professionals in the secondary school system in Ontario, as well as additional tenants. Joined by a central atrium, the building offers abundant outside views, light, openness, and numerous opportunities for spontaneous interactions between the OSSTF staff and tenants. Furthermore, shareable spaces include the lobby, café, and ground floor terrace, as well as a multipurpose, convertible Event Space that is shared not only by the building occupants, but by outside groups, providing opportunities for engagement with the wider community. 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.

Aside from the many obvious benefits of utilizing mass timber throughout a large-scale structural system, such as efficiency and performance, construction speed and efficiency, or sustainability and environmental benefits, wood contributes to the structural solution of OSSTF by providing versatility in its design. 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 underground parking, ensuring no transfer beams are necessary.

A unique detail of the mass timber design in OSSTF is the central atrium skylight structure, the focal point of the building constructed in a diagrid pattern. As this project was to be as financially sustainable as it was environmentally sustainable, the design team was deliberate in choosing where to deviate from the regular, economical, rectilinear grid system. This led them to do something special in the atrium, the shared central space where OSSTF employees and building tenants alike come together to work, socialize, and gather. The diagrid’s expression is of an overhead canopy of trees, evoking the feeling of being in a forest while reflecting the site’s character within the Don Valley. The mass timber system consists of diagonally oriented beams that form a lattice-like design, resulting in diamond-shaped cavities that open to the sky above causing unique shadows to cascade down into the heart of the facility.

Every design decision was led through the lens of OSSTF’s values, propelled by the vision of creating a facility made from a renewable resource that sequesters carbon from the atmosphere and is harvested from Canadian-owned industries under sustainable regulations. This has resulted in a building design that is warm, welcoming, inclusive workplace that is thoughtfully connected to the natural beauty of its surroundings.

The architecture, inspired by WELL and Passive House design standards, prioritizes health and wellness at every level. Generous structural bays optimize the depth of offices and corridors, maximizing natural daylight throughout the interiors. A ‘Fresh Air Strategy’ ensures consistent air movement throughout the building via smart automation systems. Large overhangs minimize solar heat gain and control glare, while geothermal heating, a rainwater harvesting system for toilet flushing and irrigation, green roofs, rooftop solar PV panels, and automated daylight dimming controls further enhance energy savings. Achieving LEED Platinum status, the design significantly reduces energy consumption and greenhouse gas emissions. The building incorporates geothermal heat exchange, a passive natural ventilation system paired with an active mechanical system, and energy generation from the rooftop photovoltaic array. The façade plays a crucial role in enhancing building performance, significantly improving both the environment and the occupant experience.

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%. This highly efficient facility ensures that the OSSTF functions as a hub that continually supports public education in the province, provides healthy workplace environments for its staff and visitors, and responsibly meets the organization’s goals of financial resiliency.

The building is an efficient compact form, with a well-insulated envelope that is comprised of a CLT backup panel rain screen assembly protected by a metal cladding system. The overall energy modelling revealed that the key energy drivers for the project were plug loads and lighting loads. This was critical to the design process and resulted in the following envelope decisions:

• Atrium design with a glazed skylight for daylighting deep into the building.
• Atrium design with operable vents and fan assistance to function as a solar chimney for natural ventilation design.
• Operable windows throughout.
• 50% window to wall ratio to maximize daylight harvesting.
• Shading on 3 façades to mitigate heat gain—depth of shade varies based on sun exposure.

The Don Valley ravine edge on which the building sits went through 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 views 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.