The city of Toronto approved a by-law in May 2009 mandating green roofs on residential and industrial buildings. There is criticism from Green Roofs for Healthy Cities that the new laws are not stringent enough, since they will only apply to residential building that are a minimum of six stories high. By 31 January 2011, industrial buildings were required to render 10% or of their roofs green. Toronto City Hall's Podium roof was renovated to include a rooftop garden, the largest publicly accessible roof in the city. The green roof was opened to the public in June 2010. Many green roofs in Canada also use sustainable Rainwater harvesting practices.