Instead of a traditional cool roof — or in tandem with one — many facilities are installing green roofs, especially now that modular systems have been developed that have helped reduce installation costs. With modular systems, soil and plant media are pre-planted offsite in 100 percent recycled plastic modules, which are then laid out on the roof.

Green roofs can offer many of the same benefits as cool roofs, including helping to reduce air conditioning and heating costs. However, they can also provide a facility other benefits as well, such as:

• Conserving energy by moderating the temperature of the roof throughout the year.
• Reducing stormwater runoff volume and peak flow rates after rainfall events.
• Restoring the ecological and aesthetic value of urban open space.
• Helping quiet the upper floors of a facility.
• Releasing oxygen into the air and absorbing pollution and carbon dioxide.
• Protecting conventional roofing systems, typically doubling the service life of the existing roof membrane.

Soil and plant media can be pre-planted offsite in 100 percent recycled plastic modules, which are then laid out on the roof. (Photo courtesy of GreenGrid.)

The Big Picture

When it comes to evaluating the overall benefits of green roofs, it’s crucial to understand the urban heat island effect, whereby darker building materials, including roofs that lack vegetation, add about 6 to 8 degrees of heat in major metropolitan areas. This elevated temperature impacts all facilities in these core areas, requiring them all to consume more energy in the summer months. Additionally, studies indicate that as the temperature rises, air quality decreases, increasing the likelihood of smog-related respiratory problems.

Cool roofs as well as green roofs help mitigate the urban heat island effect in cities located in both warm and cool climates. A Toronto study found that if cool or green roofs were widely adopted, the city could save more than $10 million annually in energy costs. And on a national level, these savings could approach $750 million annually.

Viewed on a broader scale, the ability of green roofs and cool roofs on a collective basis to lower heat island temperatures during the summer lowers energy costs for all building owners as it reduces energy needs. CR