Starting at the [roof] top for urban clean energy and health

Urban heat island depiction

Whether it's the idea of growing one's own food in the midst of the current economic downturn or the gaining popularity of buying 'green' and 'local' - urban gardens and green roofs, particular those planted on rooftops in dense urban areas - have rapidly grown in popularity over the past year.  Done right, these projects have the potential to benefit both local urban environments and our global environment in numerous ways.  Here's a collection of recent stories in the media on these urban rooftop gardens:

A plethora of environmental, social, and economic benefits of urban rooftop gardens exist and are spelled out quite thoroughly in Kaid Benfield's earlier blog post here.  What has me so excited about rooftop gardens and green roofs in general are the enormous potential benefits these projects provide in saving energy and reducing global warming pollution.  Two energy saving benefits I want to highlight in particular are reducing the urban 'heat island' and increasing building thermal performance.

Reducing the urban 'heat island'

Energy Secretary Stephen Chu recently quipped, the world should try to have "white roofs everywhere",  citing that the reflectivity of white roofs versus dark-colored roofs could potentially reduce electricity use (in urban environments) for air conditioning by as much as 15 percent.  The picture below depicts the physical processes that lead to the urban heat island problem.


Unfortunately, this form massive-scale "geo-engineering" to slap white paint on roofs does not come cheaply.  A study done for NYC in 2002, titled, "New York City Regional Heat Island Initiative: Mitigating New York City's Heat Island with Urban Forestry, Living Roofs, and Light Surfaces" showed through high resolution satellite imagery that NYC could indeed reduce its city-wide air conditioning load.  It also showed that given the three option of planting trees, 'green' living roofs, and light surfaces (white paint), the planting of trees and 'green' living roofs came out as far more cost effective in providing a long-term solution to the urban heat island problem.

Increasing building thermal performance

Published studies have shown green roofs to be effective at increasing a building's thermal performance, particularly in the summer in keeping cool air inside.  Available studies can be found here, here, and here.

When you consider the twin issues of increasing electricity costs and higher carbon emissions, rooftop gardens and green roofs show to be a great option in fighting global warming and improving the health and environment of our cities.