Waterproofing Green Roofs

Sourced from Waterproof! Magazine

Vegetated or green roofs are not a new concept. The Hanging Gardens of Babylon, built thousands of years ago, is one famous example. This show of rooftop greenery was so spectacular that it qualified as one of the “seven wonders of the ancient world,” along with the pyramids of Egypt and the Parthenon in Greece.

Green roofs today can be just as impressive, and they’re gaining in popularity. Thanks to modern materials, they’re easier to install. State-of-the-art waterproofing and leak detection technology mean vegetated roof assemblies can provide decades of hassle-free service.

Green roofs can be installed on a wide range of structures. A few, located atop sprawling parking garages and industrial facilities, cover acres and acres. Others are installed on apartments and residences to provide space to relax, play, or grow vegetables. 
The vast majority of green roofs are installed for more practical reasons. Vegetated roof systems are a proven solution to nagging urban problems such as stormwater runoff, energy consumption, smog, the heat island effect, and other issues.

Chicago was an early proponent of green roofing, and has more acres of planted rooftops than any other city. Other metro areas also promote these systems. Portland, Oregon, specifically recommends green roofs as a rainwater management solutions, along with Washington, D.C., New York City and Philadelphia. San Francisco recently passed a green roof bill mandating living roofs on most new construction. The legislation, effective Jan. 1, 2017, requires new roofs to incorporate solar panels or living roofs on a minimum of 15% to 30% of total roof square footage on projects. If the green roofs work as well as expected, it’s likely that other metropolitan areas will follow suit.

It’s difficult to describe a “typical green roof assembly” as the phrase encompasses everything from fields of native grass to tree-lined walkways. Climate, roof size, building type, acceptable roof loads, and so forth all influence green roof design. Yet the basic components remain the same.

According to Greg Raymond, the North American manager for Sopema’s vegetated roofing systems, “Waterproofing membranes are the most important component of the vegetated roof. Not only must waterproofing membranes prevent water from entering the building from the outside, but they must also be capable of resisting mechanical damage from tools and the penetration of plant roots. In addition, these materials should be capable of lasting many years without repair or replacement, as the roof garden will need to be deconstructed to perform any repairs.”

Other critical components include water retention and drainage systems, insulation, a root barrier, lightweight growing media, and the plants themselves. Raymond says, “These systems can be installed either as fully built-out systems or as lightweight, interlocking modular trays that reduce the installation time and offer pre-grown vegetated options.”

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