The steepest green roof in Ontario - roof pitch up to 50°

The new LiUNA Local 183 union building in Vaughan

The new LiUNA Local 183 union building in Vaughan is the headquarters of the largest construction local union in North America and stands out as an architecturally distinctive structure. This striking complex is enveloped on all sides by approximately 11,700 m² of green roofs – an integral element of its LEED sustainability certification ambitions. The vegetated surfaces extend to roof slopes of up to 50°, making LiUNA the site of Ontario’s steepest sloped green roof. Usable outdoor spaces on flat roof areas and courtyards above the underground garage encourage outdoor interaction and engagement. Four specialized ZinCo system build-ups were used to precisely meet the requirements of the various green roof types implemented across the project.

LiUNA Local 183 is one of ten local unions in Ontario and part of the Labourers’ International Union of North America (LiUNA), which represents over 600,000 members across Canada and the United States. The new headquarters was officially opened in October 2024 with great pride and celebration. Designed by Diamond Schmitt Architects, the complex includes a six-storey office tower and a connected three-storey wing that leads into a large multi-use event hall.

More than just an administrative hub, the building also functions as a training centre and venue for union member events. A doctor’s office, pharmacy, financial services, and recreational facilities are located within the lower floors. Rooftop walkways and spacious courtyards offer inviting meeting places in the open air. The green roofs, aside from their aesthetic appeal, shield the waterproofing membrane by moderating temperatures – cooling in summer and insulating in winter – thereby reducing the building’s energy demand. In addition, they provide stormwater retention, improve the microclimate through evaporation, and filter dust and pollutants. All of these benefits contribute significantly to the application for LEED Silver certification in the Building Design and Construction (BD+C) category.

Long lifespan

Protecting the roof waterproofing is key to extending its lifespan. At LiUNA, a double-layer bituminous membrane was installed. In geometrically complex areas – such as where steep roof sections converge at hip angles – liquid-applied polymethyl methacrylate (PMMA) was used for a perfect seal. Thanks to the inverted roof design, the waterproofing layer lies beneath the ZinCo Root Barrier WSF 40 and a thermal insulation layer of XPS hard foam, either 150 mm or 175 mm thick. All layers above the insulation had to remain permeable; hence, the installation began with the permeable “Separation Sheet TGV 21.”

The specific ZinCo system build-up used varied according to the roof area and vegetation type. Across the board, green roofs enhance thermal performance and minimize temperature fluctuations, which significantly extends the waterproofing’s lifespan.

Steepest green roof up to 50°

The LiUNA building not only hosts Ontario’s steepest green roof but also features Canada’s largest installation of the ZinCo Georaster® system – covering 3,600 m². The “Steep Pitched Green Roof” build-up is typically suited for slopes up to 35°, providing critical shear and erosion control. However, roof pitches on the event hall reach up to 50°, necessitating enhanced reinforcement through a network of shear barriers.

In this case, shear barriers were spaced every 60 cm horizontally and every 4.25 m vertically. Perforated aluminium edging profiles were mounted atop the barriers to form a stabilizing line, ensuring safe water runoff. These were secured using ZinCo’s “Shear Fix LF 600” brackets, each rated for loads up to 600 kg.

In addition to the physical barriers, the Georaster® system itself is engineered to prevent slippage. Made from recycled HD-PE, the interlocking 54 × 54 cm elements (10 cm high) form a rigid grid with ample root space. Robust root growth further helps stabilize the system and reduce erosion.

Greened slopes—up to 25°

For moderately sloped areas (up to 25°), the “Pitched Green Roof” build-up with ZinCo’s Floraset® FS 75 was applied over 1,700 m². These EPS foam drainage elements, 75 mm high, create a stable matrix that transfers shear forces to the roof structure. Their design allows for effective substrate interlocking. Approximately 10 cm of extensive green roof substrate was used here, consistent with the steep roof areas.

To ensure rapid and effective vegetation coverage, pre-cultivated 8 m long sedum mats were installed. These mats, delivered in rolls, provide immediate erosion protection. Dripline irrigation systems support healthy plant establishment and ongoing vitality.

Quick installation on flat roof areas

For an additional 3,500 m² of flat roof on the event hall, the “Sedum Carpet” build-up using ZinCo’s Fixodrain® XD 20 was installed. These drainage and water storage rolls are made from recycled polyolefin and feature interlocking studs for seamless installation. With a pre-attached filter sheet, they facilitate a quick and efficient build. A 10 cm layer of substrate was blown onto the surface, followed by the swift rollout of pre-cultivated sedum mats.

Roof terraces with diverse vegetation

Walkways and rooftop terraces—located atop the event hall, the three-storey office wing, and in the courtyards – utilize the “Roof Garden” build-up with ZinCo’s Floradrain® FD 40-E. This system supports 1,900 m² of intensive green roof and 1,000 m² of pedestrian walkways. Floradrain’s dual-sided design includes water retention cells on top and a drainage channel system underneath for excess water.

After installing the system filter and intensive green roof substrate, native perennials and grasses were planted over 6,000 in total. These included woolly yarrow (Achillea tomentosa), lady’s leek (Allium cernuum), aster (Aster laevis), lanceleaf coreopsis (Coreopsis lanceolata), great blanket flower (Gaillardia aristata), blazing star (Liatris cylindracea subspicata), black-eyed Susan (Rudbeckia hirta), and prairie dropseed (Sporobolus heterolepis).

To prevent waterlogging on walkway surfaces, Floradrain® FD 40-E is installed upside down and filled with chippings for stability. Large pavers are then laid atop this base.

A milestone in sustainable architecture

The LiUNA Local 183 building sets a new benchmark for sustainable, climate-responsive architecture in urban spaces. It is a vivid demonstration of the potential of green roofing at scale. These biodiverse rooftop landscapes offer not only visual appeal but critical environmental functions, such as stormwater retention and microclimate regulation. This forward-thinking architecture meets its social responsibility by creating greener, more livable spaces – showing what’s possible when sustainability is built into every layer.

Author: Heidrun Eckert, Business Unit Manager ZinCo GmbH

Site board

Construction project: LiUNA! Local 183 – Headquarters, Vaughan, ON L4H 5H9, Canada

Client: LiUNA Local 183, Vaughan, ON L4H 5H9, Canada

Construction year: 2023–2024

Roof area: approx. 11,700 m²  

Green roof build-up:    ZinCo system build-ups: 
“Steep Pitched Green Roof” with Georaster®
“Pitched Green Roof” with Floraset® FS 75
“Sedum Carpet” with Fixodrain® XD 20
“Roof Garden” with Floradrain® FD-E

Architect: Diamond Schmitt Architects, Toronto, ON M5V 1R7, Canada

Landscape architect: PMA Landscape Architects Ltd., Toronto, ON M6P 2K6, Canada

Contractor: Skygrid Construction Inc., Mississauga, ON L4W 0A9, Canada

Roof installation: Flynn Group of Companies, Missisauga, ON L4V 1K2, Canada

Green roof installation: UCC Group Inc., Toronto, ON M9W 5R, Canada

System supplier: ZinCo Canada Inc., Carlisle, ON L0R 1H0, Canada

System manufacturer: ZinCo GmbH, 72622 Nuertingen, Germany