Nathan Phillips Square Podium Roof Garden 

Toronto, Ontario

Photo Credit: Steven Evans

CASE STUDY

Initial Research by: Jiaqi Yi

Continued Research by: Nicole Brekelmans

Edited by: Samantha Miller

Case study compiled in 2019

 

 

Project: Nathan Phillips Square Podium Roof Garden

Type of Urban StrategyGreen Cities 

Type of ProjectGreen Roof 

LocationToronto, Ontario 

Date Designed/Planned: 2007

Construction Completed:  2010

Designer: Plant Architect Inc.

 

Nathan Phillips Square Podium Roof Garden is on top of Toronto’s City Hall in downtown Toronto, at 100 Queen Street West. The roof can be accessed from the ramp on the east side of Nathan Phillips Square, and from behind City Hall by taking the stairs near the intersection of Elizabeth and Hagerman street. From concrete to living garden, the podium roof is now a public green roof garden. As an attractive destination in the heart of the city, people can enjoy unique views of downtown from the roof garden with new gardens, courtyards, terraces, furniture and walkways.

Moreover, the project serves as the flagship green roof project for the City of Toronto, catalyzing Toronto’s Green Roofs Strategy – Making Green Roofs Happen (February 2006), which is to demonstrate leadership by installing green roofs on City-owned facilities.

 

CONTEXT


Nathan Phillips Square Podium Roof Garden is on the Toronto’s City Hall in downtown Toronto, at 100 Queen Street West (PLANT Architecture Inc, n.d.). The roof can be accessed from the ramp on the east side of Nathan Phillips Square, and from behind City Hall by taking the stairs near the intersection of Elizabeth and Hagerman street (PLANT Architecture Inc, n.d.). From concrete to living garden, the podium roof is now a public green roof garden (PLANT Architecture Inc, n.d.). As an attractive destination in the heart of the city, people can enjoy unique views of downtown from the roof garden with new gardens, courtyards, terraces, furniture, and walkways (PLANT Architecture Inc, n.d.).

In 1965, the City Hall was originally devised by the Finnish architect Viljo Revell, as a space for gathering, ceremony, and where the public can closely view the tower’s fine architectural detail. A giant sculptural ramp was built to connect the roof and Nathan Phillips Square (PLANT Architecture Inc, n.d.). However, the roof space was viewed as a grim and paved void and failed to achieve the original potential of Revell’s design, remaining closed to the public for over a decade (PLANT Architecture Inc, n.d.).

As an important part of the Nathan Phillips Square Revitalization, the green roof project was launched to reintroduce the public space as a more functional and environmentally sustainable community meeting place (PLANT Architecture Inc, n.d.).




SITE ANALYSIS


The podium roof was devised as a ceremonial space, connected by the east ramp for cars to drop off visiting dignitaries at the “front door” of the Council Chamber (Heritage Issues Report, 2005). But, this function was phased out with time. The podium roof garden aims to integrate the upper-level space with the elevated walkway system, respecting the complicated heritage status and reopening it to the public as a truly engaging 21st century space (Heritage Issues Report, 2005).

The roof garden re-integrates the City Hall with the Nathan Phillips Square and serves as a unique viewing point where people can enjoy the urban landscape in the heart of the city (Heritage Issues Report, 2005). As the biggest public green roof garden in Toronto, it not only provides people with a social and green space but establishes a strong connection between the people of Toronto and the City Hall (Heritage Issues Report, 2005).




PROJECT BACKGROUND AND HISTORY


In 1957, the City of Toronto launched an international design competition for its new City Hall and civic square. Competitors were encouraged to create an “atmosphere” suggesting government, democracy, and community (Heritage Issues Report, 2005). In 1958, Finnish architect Viljo Revell won the competition (Heritage Issues Report, 2005). He described a podium whose roof forms an upper plaza overlooking the square. In 1970, consultant John B. Parkin pointed out that “the roof of the podium stands in virtual isolation…it would be folly to connect certain elements of the City Hall complex without dealing with the whole problem of design and functionality.” However, nothing came out of the correspondence (Heritage Issues Report, 2005). In 1972, the Committee on Parks, Recreation and City Property decided to investigate the possibility of providing structures on the Podium Roof, such as a licensed outdoor café (Heritage Issues Report, 2005). In 1991, Toronto City Hall was designated for architectural and historical reasons under the Provisions of the Ontario Heritage Act (Heritage Issues Report, 2005). The heritage attributes described in the designation by-law in terms of the Podium Roof are: “the podium roof and ceremonial ramp leading to it from Nathan Phillip Square”; “the ceremonial ramp leading from the east side of Nathan Phillips Square to the podium roof” (Heritage Issues Report, 2005). Competitors should respect the heritage attributes and demonstrate any proposed alteration which may affect the heritage attributes but would not compromise the integrity of the original design (Heritage Issues Report, 2005).

In 2006, the design competition of Nathan Phillips Square Revitalization was launched (Green Roofs – Nathan Phillips Square, 2019). PLANT Architect Inc. and Shore Tilbe Irwin + Partners won this competition (Green Roofs – Nathan Phillips Square, 2019). The Nathan Phillips Square green roof was constructed with the LiveRoof brand hybrid modular green roof system which contains a combination of 6″ deep LiveRoof® Deep System Modules and 4” deep LiveRoof® Standard Modules with multiple plant mixes in the design (Green Roofs – Nathan Phillips Square, 2019). During the summer of 2009, the project was grown at the LiveRoof Ontario nursery and then installed on September 1, 2009 (Green Roofs – Nathan Phillips Square, 2019). In early November 2009, the installation of the green roof was completed. The podium roof garden was completed and opened to the public in late May 2010 (Green Roofs – Nathan Phillips Square, 2019).




GOAL OF THE PROJECT


• Creates a new public space in downtown Toronto

• Connect the podium roof with the Nathan Phillips Square

• Improves Toronto’s green spaces

• Creates habitat for insects and birds in the downtown

• As part of the site-wide stormwater management system,

reduces stormwater runoff

• Improves thermal and sound insulation at City Hall

• Improves air quality and reduces the building’s contribution to

the urban heat island effects

• Increases the lifespan of City Hall’s roof membrane by reducing

thermal contraction and expansion

(Podium Green Roof, n.d.)




DESIGN, DEVELOPMENT, AND DECISION MAKING PROCESS


Phase 1 of the design selected a diversity of plant species, grown regionally based on their seasonal colour and ability to withstand difficult rooftop conditions (Podium Green Roof, n.d.). Phase 2 of the project planted a pre-vegetated, modular green roof system that is essentially trays of vegetation in a growing medium, which have been grown off-site and seamlessly installed on the rooftop (Podium Green Roof, n.d.). Phase 3 assembled pre-planted trays on the finished roof assembly with the plants already established, making for a “finished” looking roof from day one. The units were designed for rapid assembly, shortening installation time (Podium Green Roof, n.d.). The last phase removed the top portion of each tray exposing two to four inches of soil, allowing the plants to spread roots between trays, making a unified field of plants, and tying together the entire system (Podium Green Roof, n.d.).




ROLE OF DESIGNERS


PLANT Architect Inc. was inspired by Paul Klee’s Polyphony (1932) and proposed a planting plan which features a complex mosaic of 23 sedum species inter-planted with 42 species of grasses and perennials; the colors ranging from yellows and oranges at the sunny southwest to purples and reds at the shady northeast (Christopher, 2011). The progression of plant and blossom colours follows the progressive circuit and ensures something new is blooming in different parts of the garden from April to October, marking the seasonal change (Christopher, 2011). The shade structures track the movement of the sun in a day and their shadows align with benches at specified hours from 10am-2pm (Christopher, 2011). The plants will shift and move from the abstract geometry to a more Fauvist set of drifts as the years pass, although the initial garden layout is rigid (Christopher, 2011).




CITATIONS


1. Uffelen, Chris van. Green City Spaces : Urban Landscape Architecture 1st edition. Salenstein: Braun, 2013. 2. "Nathan Phillips Square Podium Roof Garden PLANT Architect Inc." World. Accessed February 13, 2019. https://www.world-architects.com/en/plant-architect-inc-toronto/project/nathan-phillips-square-podium-roof-garden. 3. Torontoist. "Winner Announced in Nathan Phillips Square Design Competition." Torontoist. March 09, 2007. Accessed March 13, 2019. https://torontoist.com/2007/03/and_the_winner/. 4. "NATHAN PHILLIPS SQUARE DESIGN COMPETITION FINDINGS Heritage Issues Report." October 24, 2005. Accessed February 20, 2019. http://ville.montreal.qc.ca/pls/portal/docs/PAGE/CONSEIL_PATRIMOINE_MTL_FR/MEDIA/DOCUMENTS/(2)NATHANPHILLIPSS_HERITAGE_ISSUES_05.10.24.PDF. 5. "NATHAN PHILLIPS SQUARE TORONTO CITY HALL PODIUM GREEN ROOF" 11 September 2019. Accessed February 20, 2019. https://www.greenroofs.com/projects/nathan-phillips-square-toronto-city-hall-podium-green-roof/ 6. "Podium Green Roof." Accessed February 28, 2019. https://www.toronto.ca/services-payments/venues-facilities-bookings/booking-city-facilities/city-squares/nathan-phillips-square/podium-green-roof/. 7. "Nathan Phillips Square." Wikipedia. March 05, 2019. Accessed February 13, 2019. https://en.wikipedia.org/wiki/Nathan_Phillips_Square. 8. Henry, Christopher. "NPS Podium Roof Garden / PLANT Architect & Perkins Will Canada." ArchDaily. July 06, 2011. Accessed March 2, 2019. https://www.archdaily.com/147547/nps-podium-roof-garden-plant-architect. 9. "The Green Podium Roof at Toronto City Hall." Accessed March 5, 2019. https://www.toronto.ca/wp-content/uploads/2017/11/910f-Toronto-City-Halls-Podium-Green-Roof-route-map.pdf. 10. "December 2011/January 2012 - Nathan Phillips Square Wins 2011 Award of Excellence." InfraStructures. Accessed March 7, 2019. http://www.infrastructures.com/0112/green.htm.




PROGRAMMED ELEMENTS


• The design consists of four key components: a central courtyard;

new plantings; trees and a terrace; furniture and shade.

• The central courtyard is a multi-use event space for exhibitions,

gatherings, and civic activities

• With the changing seasons, the colour palette of plants shifts to

please visitors and viewers

• A new tree planter is proposed to be at the front of the roof

with shade and seating on the new terrace. As a gathering

space, moveable furniture and future food kiosk are proposed.

• Benches and other seating with shade structures in key

locations track the movement of the sun

(Toronto – City – Halls, n.d.)




PROJECT IMPACT


The project achieves the original intention of the roof to connect the main square, as a place for the ceremony and offer people chances to get close the fine detail of the building (Infrastructures, 2011). It brings new potential to the building and space by offering a garden respite from the harsh concrete downtown environment with places for intimacy and lingering, for lunch breaks, evening strolls, and art installations (Infrastructures, 2011). Technically, the project is a success as a sustainable design experiment, contributing to energy efficiency, roof membrane longevity, sound insulation, filtration, stormwater management, and habitat creation (Infrastructures, 2011). Moreover, the project serves as the flagship green roof project for the City of Toronto, catalyzing Toronto’s Green Roofs Strategy – Making Green Roofs Happen (February 2006), which is to demonstrate leadership by installing green roofs on city-owned facilities (Infrastructures, 2011).




MAINTENANCE AND MANAGEMENT


Individual trays must be lifted off the membrane, then repairs are completed, and then the plants are put back in place, with little disruption to the plants themselves (Podium Green Roof, n.d.).




FUNDING


The cost of the Nathan Phillips Square Revitalization is $40 million (Torontoist, 2007).

$16 million was provided by City Council while the remaining $24 million was from private sector donors. However, its final cost is expected to tally up to $60 million since the construction work frequently lags, compared to the original plan (Torontoist, 2007).




THE CHALLENGE


The podium roof stood in virtual isolation which failed to connect certain elements of the City Hall complex without dealing with the whole problem of design and functionality (Heritage Issues Report, 2005).

As another challenge, the raised walkway between City Hall podium roof and Holiday Inn provided little value unless the West Colonnade surrounding the Nathan Phillips Square was extended to connect the podium roof and stairs provided therein as part of the existing structure and rather than an appendage thereof (Heritage Issues Report, 2005).




GENESIS OF PROJECT


The Nathan Phillips Square project was a masterpiece by Finnish architect Viljo Revell. The square was designed originally to integrate with the City Hall and featured an expansive paved plaza framed by an elevated walkway on three sides (Heritage Issues Report, 2005). A sinuous ramp was designed to connect the podium roof (Heritage Issues Report, 2005). However, over the decades, many of these elements were undermined with compromising clarity and functionality by ad hoc interventions (Heritage Issues Report, 2005).

In 2007, the revitalization project in order to address increasingly ambitious programming and deferred maintenance items was launched. As the first step of Nathan Phillips Square Revitalization, the podium roof garden project was proposed to provide people with a ceremonial, gathering and walking public space (Wikipedia, 2019).





 

EDITOR

 

Samantha Miller

Nicole Brekelmans

Zoe Goldman

Desiree Theriault

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