Three new stations in the Toronto Transit Commission Line 1 Extension employed inverted roof membrane assemblies to achieve cool roof and longevity requirements. Unlike most inverted roof membrane assemblies, these roofs are not flat, nor high atop a building out of public view. At each location the roof is a key design feature utilizing curves in multiple directions to create the architect’s vision. The performance and longevity of each roof system was a top priority to meet Toronto Green Standards at each station.
Architects and roofing contractors agree the longevity of the inverted roof membrane assembly is determined by protecting the membrane from UV exposure and thermal cycles. Increasing membrane life expectancy is achieved by adding layers of material above the membrane. In the most basic assembly, the layers above the membrane may be insulation, filter fabric, and ballast. For a vegetated roof, the layers may be insulation, drainage space, root barrier, filter fabric, and a planting medium.