Green roofs are vegetated areas installed as an addition to a conventional rooftop. Key components of a green roof are high quality waterproofing and root barrier, a drainage layer, filter cloth, a mineral-growing medium and plants. Root barriers are essential as they ensure that roots do not penetrate the roof membrane. While typical green roof plants do not have aggressive rooting, root barriers are installed as a precaution should any weed species sprout.

In 2009, Toronto became the first city in North America to pass a bylaw requiring all new construction with more than 2,000 square meters to incorporate a green roof. This law was primarily intended to reduce the strain on the city’s aging sewer system because studies have found green roofs can retain 60 to 100 percent of incoming rainfall depending on their substrate depth. A green roof also helps to naturally cool and freshen the air on hot summer days, reducing electricity demand. Some even provide space for recreation and food production.

A recent vacation to Vancouver, British Columbia included a tour of this beautiful city. The green roofs were breathtaking to observe. The largest green roof in Canada covers the Vancouver Convention Center. (See photo by author). The roof features more than 400,000 native plants and grasses that provide insulation and habitat for pollinators.

Green roofs are one of the most visible and easily recognizable design features on a building. Aside from adding visual appeal, green roofs offer a number of potential social, economic and environmental sustainability benefits. A vegetated roof attracts birds and bees, and the soil becomes a habitat for small insects.

The "heat island effect" is an urban phenomenon, wherein the temperature in a city is a few degrees higher than its surrounding area. Heat islands occur when materials in asphalt and concrete absorb solar radiation and re-radiate it as heat into the surrounding area. Cities can be one to three degrees Celsius warmer in the daytime and up to twelve degrees Celsius warmer at night. Heat islands can have an adverse effect on air quality. Green roofs help beat the heat by using the sun’s energy to conduct photosynthesis and cool the air through evaporative cooling.

Green roofs assist in keeping the interior of the building cooler during hot summer months as well. They provide a buffer between hot and cold extremes. On hot summer days, the surface temperature of a green roof can be cooler than the air temperature, whereas the surface of a conventional rooftop can be up to fifty degrees Celsius warmer than the air temperature.

From the point of view of human health and sustainability, the aesthetic qualities of green roofs have a positive effect on people’s psyche. Research shows that access to views of nature is associated with improving a person’s health, boosting productivity and reducing absenteeism in offices and other workplaces. Green rooftops offer apartment residents a place to plant gardens. They can also serve as community gardens for local food production.

By capturing and storing rainwater in their soil, green roofs can help reduce the rate and quantity of storm water outflow. Storm water volumes are reduced and flow rates diminished by slowing down the water via soil percolation.

A green roof is advantageous for the environment. It has the potential to improve employee productivity. The aesthetic appeal of commercial green roof systems increases the value of the property and the marketability of the building as a whole. Furthermore, the construction and maintenance of green roofs provide business opportunities for roofing contractors, plant producers, landscape designers and contractors, and other green industry members while addressing the issues of environmental stewardship. You are encouraged to observe a local green roof located on a storage shed at the Adams County Ag Center located at 670 Old Harrisburg Road, Gettysburg. Hopefully in the near future, our towns and cities in Adams County, Pennsylvania and throughout America will have green roofs enhancing their skylines.