France recently made headlines around the world when lawmakers passed a mandate for all new commercial roofs to either be covered with solar panels or green plants. And France isn't the first country to make this happen: Toronto, Canada passed a law in 2009 to require a portion of all commercial roofs to have greenery. The question is, how does green roofing help companies?
How Plants Help With the Bottom Line
Why plants? There are both cost-saving and environmental benefits to planting things on roofs, as it turns out. And commercial roofs are more likely to be flat—easier to plant—and large enough to make a difference, as compared to residential roofs. Still, the proof is in the cost savings of installing a green roof. Here are some of the reasons a building owner might want one:
- Protects underlying materials like waterproofing membranes, helping them to last longer before repair or replacement.
- Keeps roofs cooler in summer, reducing stress on the air conditioning system by up to 75 percent.
- Insulates better in winter, reducing the amount of heat needed to warm the building.
- Helps reduce fire damage if the building should catch on fire.
- Blocks low-frequency noises that may bother humans inside the building, leading to increased productivity.
Crunching the Numbers
The added costs of installing a green roof may be more, but may pay for themselves. According to the U.S. Environmental Protection Agency (EPA), a green roof costs between $10 and $25 a square foot to install, depending on complexity. Maintenance is $0.75–$1.50 per square foot.
The same EPA review looked at a 21,000-square-foot commercial roof as an example. With all the possible benefits installed, a green roof would cost $464,000 (compared to a traditional roof at $335,000). However, over its lifetime, the green roof would save nearly $200,000 in maintenance and reduced energy costs.
Looking at the increased lifespan and durability of green roofs is harder to do because they haven't been around very long. A traditional commercial roof can last 15 to 25 years. In contrast, many green roofs are doing well at 40 years; a building in Portland, Oregon hasn't had any leaks since 1975.
Other Benefits to Green Roofs
There are other, more subtle benefits to installing a green roof, as well as benefits that come when multiple buildings in an area all have green roofs. When many buildings are covered in vegetation, the entire area reflects more of the sun's rays and stays cooler. Also, green roofs can:
- be pleasant areas for people to engage in gardening or recreation, as opposed to traditional roofs.
- filter carbon dioxide and other gases, making the air cleaner.
- allow a wide range of plants to live, which can attract birds, butterflies and other beneficial insects; this increases biodiversity.
When considering a new building, or replacing the roof on an existing commercial building, green modern roofing can save money over time and should be a consideration of an owner or builder.