Are Green Roofs Renewable Resources or Nonrenewable Resources?

Green roofs are rooftops covered with grass, vegetables, fruit trees or other vegetation. They provide benefits through insulation, cooling, noise reduction, pollution mitigation and any useful crops which they produce. Green roofs are neither a renewable nor nonrenewable resource because they are not a "resource," per se.

Renewable vs. nonrenewable

• The terms renewable and nonrenewable resource refer to the timescale by which naturally occurring resources are replenished. A nonrenewable resource would be oil because it takes millions of years to make more oil. Wind power is a renewable resource. Timber is partially renewable, because forests can be replanted, but it is partially nonrenewable because this takes a long time and depletes soil, which is relatively nonrenewable. The question about green roofs is whether or not they are sustainable.

Sustainability

• Green roofs may require inputs of fertilizer. Depending on the fertilizer, this may be a nonsustainable input, because many fertilizers are produced using fossil fuels. Overall, however, green roofs make a building more sustainable because they reduce both heating and cooling costs and create arable spaces on which useful crops can be grown. These benefits outweigh any negative environmental consequences of fertilizer use.

Benefits

• Green roofs cool a building through evaporative cooling and can reduce the need for air conditioning by 50 to 90 percent. They also insulate a building and reduce heating costs in winter, as well as reducing storm water runoff, cooling the surrounding area and filtering pollutants out of the air and water.