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CNA Blog — From the Experts

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Published Wednesday, June 8, 2016

It’s Not Easy Being Green – Or, Is it? Weighing the Benefits and Risks of Green Roofs

With today's focus on being green, businesses are looking up – to their roofs, that is. According to the 2015 Annual Green Roof Industry Survey, the green roof and wall industry grew 18.5% from 2014, with 1,595,957 square feet of green roofs installed in 2015. In Shanghai, "vertical greening" rules were approved in 2015, which mandate that 50 percent of new roofs get covered in plants. France passed a law this year that will require all new commercial buildings to be equipped with either green roofs or solar panels. Tokyo, Toronto, Zurich and Copenhagen also require new buildings to have some or all of their roofs covered in plants1

So why is there so much emphasis on installing green roofs? 

Aside from the aesthetic improvements and additional work/leisure space, these roofs can cool cities, clean the air, help regulate internal building temperature and even prolong a roof's life.

A phenomenon called the Urban Heat Island Effect contends that urban areas tend to be warmer than in surrounding rural areas due to the heavy concentration of buildings and people. Greenery absorbs carbon and keeps the air cool, not to mention providing a sanctuary for birds, bees and other species that are helpful to the ecosystem and need space to call home in a dense city.


Furthermore, green roofs can reduce the amount of air conditioning necessary to cool a building by up to 75 percent2. Boasting a green roof also can help your company's reputation and marketability. But it's important to weigh the risks before calling your roofing contractor to get started on your business' green roof. Keep these things in mind to ensure you are getting the maximum benefit while neutralizing potential risks:

  • Make sure your roofing company is familiar with all green roof construction and maintenance. You may need to hire specialized personnel to install and maintain roof plants.
  • It's much more difficult to find and fix a leak in a green roof, as you'd have to move soil or install a wired grid that detects moisture.
  • If your roof is not built to withstand heavy loads, it may not be able to support the weight of a green roof.
  • An old roof should be inspected and possibly replaced before going green, as it may be out of code and not as robust as it once was.

If your business needs a green roof to comply with local laws, be sure to thoroughly prepare your building to carry the weight, and be prepared to maintain it.

For businesses hesitant to build a green roof due to costs, there's good news. In order to retrofit buildings more quickly, and with a lower cost, architecture firms are experimenting with more nimble ways to build green roofs. Dutch architect Neville Mars has developed a low-cost roof mat pre-planted with seeds, which can be unrolled on corrugated tin rooftops. These mats grow naturally as long as there is rain, and they absorb much of the sun's heat, making building interiors cooler1.

Remember, each roof installation is unique. Your business' green roof's success and stability will depend on your region, climate, building and green roof type and design. The National Roofing Contractors Association (NRCA) offers "Green Roof Construction and Maintenance," a technical resource that presents information you need to skillfully design, construct and maintain green roofs. To learn how to best protect your business from roof-related risks, visit www.cna.com/NRCA

1 Why We're Still Up in the Air About Green Roofs, accessed June 7, 2016.

2 Looking Up: How Green Roofs and Cool Roofs Can Reduce Energy Use, Address Climate Change, and Protect Water Resources in Southern California, accessed June 7, 2016.

One or more of the CNA companies provide the products and/or services described. The information is intended to present a general overview for illustrative purposes only. Read CNA’s General Disclaimer.
One or more of the CNA companies provide the products and/or services described. The information is intended to present a general overview for illustrative purposes only. Read CNA’s General Disclaimer.