Since 2009 the City of Toronto has required commercial and industrial new buildings to have green roofs. France recently adopted a law requiring new commercial and industrial buildings to have at least partial green roofs and solar panels. This kind of policy direction helps to move the climate change response incrementally forward. As more and more buildings comply with these laws, the detailed refinements in response will begin to emerge.

In the US, many buildings are adopting green roofs as part of a sustainability strategy, but the response is scattered, and financing is an issue in many areas.  The standards and initiatives vary tremendously among the 50 states.

Here is a summary of the benefits of green roofs compiled by the Union of Concerned Scientists

Benefits of Green Roofs

There are so many benefits to green roofs. Here are just a few:

1. Adding natural beauty and major aesthetic improvement to buildings, which in turn increases the investment opportunity.
2. Helping contribute to landfill diversion by prolonging the life of waterproofing membranes, using recycled materials, and prolonging the service of heating, ventilation, and HVAC systems through decreased use.
3. Green roofs assist with storm water management because water is stored by the substrate, then taken up by plants, and thus returned to the atmosphere through transpiration and evaporation. They also retain rainwater and moderate the temperature of the water and act as natural filters for the water that does run off. They delay the time at which runoff occurs, which results in decreased stress on sewer systems during peak periods.
4. The plants on green roofs do a great job of capturing airborne pollutants and other atmospheric deposition. They can also filter noxious gasses.
5. They open up new areas for community gardens, commercial and recreational space in busy cities where this space is generally quite limited.

Combining green roofs with solar installations on rooftops has been tested and shown to be mutually beneficial.  See the installations at Scalo Solar, for example. Here the Sunscape rooftop in Crafton PA, acts as a “showroom” for various configurations of solar arrays and technologies, including several versions of green roof installations. The various arrangements are fully instrumented and monitored to compare efficiency and effectiveness. The data stream is available to university students in Pittsburgh for research.