MiraDRAIN 9000 - 4' x 50' Roll

Case Study 1: Revamping Toronto’s Nathan Phillips Square

Every year more than 1.5 million visitors pour into events and activities in Toronto’s Nathan Phillips Square. The square was designed by the world-famous Finnish architect Viljo Revel and opened in 1965 and has since served as the city’s premier public space and civic gathering place. Visitors can enjoy concerts, art exhibitions, dance and music performances, farmer’s market, and skating under the arches.

Unfortunately, due to an increase in population, and the increased number of tourists visiting the square, some of the structures have fallen into disrepair and some closed permanently.

The city of Toronto realized it was time to perform renovations in order to get the square in great condition to meet the needs of the residents, tourists, and even allow for more events and special events.

As part of the project to revitalize the square, a design competition was held by the city and the design from the team led by Shore Tilbe Irwin & Partners, Inc and Plant Architect Inc was chosen from more than 48 entries. One of the key components of the design is a garden roof for the City Hall Podium Roof utilizing a waterproofing system from Carlisle Coatings & Waterproofing Inc (CCW).

Toronto had an interest for a long time in the use of green roofs. In 2004, they started a study to understand the environmental benefits of green roofs which led the city council to embrace a Green Roof by-law in 2009. Toronto became the first city in North America to enact a by-law that went into effect as of January 21, 2010. The by-law required that all new developments, both commercial and residential, above 2,000 square meters have green roofs over a certain percentage of the available roof space.

The concept of using roofs to grow plants actually dates back thousands of years with the discovery of roof gardens as early back as the fourth century in Mesopotamia. Outside of being aesthetically appealing, roof gardens help to control stormwater runoff and contribute to a reduction in the urban heat-island effect. One of the most important debates for a roof garden is to ensure the roofing material that lies beneath the plants is capable of withstanding time while offering waterproofing protection for the building.

Bob Ashby, the architectural consultant at Shore Tilbe Irwin & Partners, Inc., knows how important the roofing system below the garden is which is why he recommended a hot-applied system. Ashby believes that out of all the materials available for consultants to choose to keep water out of a structure, rubber is by far the best choice. He said that millions of square feet of a successfully waterproofed project are all the endorsement a product needs.

Flynn Canada Ltd was hired to install the new garden roof on Toronto’s City Hall. According to Terry McGlade, Manager of Flynn Canada, Gardens in the Sky, the social interaction is just as important as improvements to air quality, reduction of the heat island, and the money saved for the building’s energy performance.

They started the project by removing the existing pavers and stored them for future use by the City. Jim Guzik of Flynn Canada said the podium roof was only one phase of the project, they wanted to obtain a LEED® Gold certification for the finished project so they tried to salvage as much as possible from the system that had been already in place. The crew recycled a part of the old insulation and the existing 30-year old rubberized asphalt waterproofing membrane was left in place then power washed and cleaned using a Carlisle-approved cleaner. They installed a two-millimeter layer of CCW-500R hot applied rubberized asphalt membrane followed by Carlisle Coatings & Waterproofing’s reinforcing fabric and applied a final three-millimeter layer of CCW-500R.

According to Guzik, for this installation, the CCW-500R hot-applied system was the only way to go. Throughout the years, there had been two other waterproofing systems installed. Removing them would have been very disruptive to the building tenants and very laborious work. The 500R was the perfect choice to use over the existing membrane as it bonds firmly to just about any sound surface. He said the use of the 711-90 reinforced flashing made quick work of the details.

After the membrane was in place they installed Carlisle’s 1 ⁄8-inch horizontal protection board then the high-density extruded polystyrene insulation.

CCW MiraDRAIN® 9000 drainage board was placed over the insulation in preparation for the garden roof. The MiraDRAIN permits for good drainage of water and offers a woven monofilament fabric that can withstand high abrasion from overburden such as from a roof garden. The garden roof was installed using a tray system and covers approximately 35,000 square feet of the 120,000 square foot roof.

After being closed for a number of years, the podium roof of Toronto’s City Hall was reopened as a public garden on May 19, 2010. Mayor David Miller, architects, school children, and a band announced the new green roof officially open.

Along with the garden tray system, the podium roof offers walkways, a courtyard, terraces, and benches. There is one very large planter on the south end of the roof houses, three Kentucky Coffee trees, which provide visual interest and a shady spot for visitors to rest and relax. The new garden roof offers a refreshing habitat for Toronto’s residents and visitors. It also serves as an educational opportunity for the city to teach others that it’s possible to reside in a dense urban area and still minimize the environmental impact on the planet.