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Rooftop Garden at Chum

The CHUM rooftop gardens are the hidden jewels of the largest public health care construction project in North America. Following nearly a decade of multidisciplinary planning, intense collaborative design and delicate construction, five of the six planned gardens were finally inaugurated in 2017, just in time for the mega-hospital’s long-awaited opening.

The Centre Hospitalier de l’Université de Montréal (more commonly referred to as CHUM), is actually comprised of multiple buildings, spanning across urban blocks. Within its impressive scale and complexity, generous openings create a series of strategically located rooftop terraces. These terraces are not only bright gardens, but they also allow much needed outdoor access and breathtaking views of the cityscape.

 

Each rooftop was imagined as a large-scale horizontal landscape painting, transforming images through various graphic manipulations and dithering. Each terrace celebrates a different plant species used extensively in traditional medicine, as inspired by Brother Marie-Victorin’s renowned herbarium.

Marie-Victorin was a noted botanist and illustrious Université de Montréal professor. His “Flore laurentienne” is a botanical record of all species indigenous to southern Quebec, and was the first such record to be compiled. For example, the largest CHUM rooftop depicts the leaves of the White Willow (Salix alba), whose bark was used to extract salicin, an organic compound used long before it was involved in the development of common aspirin (cetylsalicylic acid).

These outdoor spaces contribute to the CHUM’s cultural identity through surprising landscape compositions. The rooftops help reflect both the institution’s rich medical heritage, but also its position at the forefront of care innovation, education and research.

In essence, the project consists of elegant surface treatments mixing green roof and white roof technologies. The result is a hybrid rooftop, showcasing an extensive green roof system, interwoven with a pedestrian system whose interface is embroidered with custom-shaped paving slabs. Above all, the gardens offer a luminous, intriguing and poetic use for the massive hospital’s fifth façade.

Objectives / Social + Environmental impacts:

• Counter main heat-island effects by increasing vegetation cover and reducing solar radiation.
• Ensure overall safety and respect all healthcare building related requirements.
• Support the hospital’s goals and missions by providing health and wellbeing benefits for all patients, visitors and health workers.
• Improve overall patient quality of life and enhance the healing process.
• Provide physical and visual access to sunlight, natural materials and fresh air.
• Frame and multiply vistas to the city and its landmarks, offer diverse vantage points.
• Enhance the CHUM’s institutional and cultural identity.

Design challenges / innovations:

• Achieve the solar reflectance index (SRI) of typical white roof membranes, but with accessible and durable materials (a custom concrete mix was developed).
• Provide innovative design solutions to safety and code regulations, including fire ratings and wind uplift considerations.
• Install vegetated roof system that is irrigation-free and tolerant of various extreme growing conditions. The selected sedum mats were grown specifically for the project’s unique situation and were assembled following project-specific installation details.
• Adapt design to areas located above intensive clinical functions by replacing the vegetated areas with dark colored slate aggregates.

Specifications:

• An extensive green roof system, interwoven with a pedestrian system whose interface is embroidered with custom shaped paving slabs.

Materials:

• Class “A” Fire resistant assembly and materials, including the following components:
• Custom precast concrete slabs with a SRI of 78 minimum, but ensuring visual comfort (low glare)
• Slabs are 75mm x 897x597mm, including multiple compound shapes, built using special adjustable molds
• Certain slabs are inscribed with plant data / information
• Green roof system components (including drainage mat, filter fabric, etc.)
• Custom-grown drought-tolerant and wind-resistant sedum carpets, including a diversity of species.
• 75mm to 250mm depth of lightweight, ultra-absorbent rooftop specialty planting soil (soil surface is continuous under concrete slabs to ensure maximum soil volume and allow optimal root development)
• Dark colored slate aggregate

Fabrication / building:

The rooftop garden building process was completed over multiple building seasons, in coordination with the hospital’s complex construction schedule. All materials (vegetation, planting soil, concrete slabs) were prepared for assembly and were delivered to site via hospital freight elevators or nearby tower cranes.

Architects: Cannon Design and NEUF Architects
Project location: CHUM
1051, Sanguinet Street
Montreal (Quebec) H2X 3E4
CANADA
Design year: 2010-2015
Year Built: 2017

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