Online Tools Makes The Cost-Effective Case For Green Roofs

With its green-building focus, abundant annual rainfall, and vested interest in preserving the water quality of the Willamette River, it’s not surprising that Portland, Ore., is a leader among cities when it comes to green roofs. But developers in other areas of the country have yet to be sold on the benefits of such roofs, according to Archinect’s Sherin Wing, who writes,”Trying to persuade a client about the benefits of relatively inexpensive, passive, more sustainable building strategies is difficult enough, and honestly, a green roof is anything but.”

So when it comes to getting more greenery on the nation’s rooftop’s, it’s the numbers that need to do the talking — specifically, about how much energy a building stands to save by incorporating a green roof. That’s where Portland State University‘s (PSU’s) online Green Roof Energy Calculator comes in. The product of PSU’s Green Building Research Laboratory — developed via a collaboration involving researchers from the University of Toronto, and Green Roofs for Healthy Cities — this free tool allows users to compare the annual energy performance of a building with a vegetative green roof to the same building with either a dark roof or a white roof.


green roof, Portland

image via City of Portland

The tool works via either in US or international SI units of measure , and offers present-time simulations for new construction (ASHRAE 90.1-2004) and old construction (pre-ASHRAE 90.1-2004) office and residential buildings driven by typical precipitation and weather data for the area in which the building is located. The team that maintains the website also provides answers to questions as best they can, which means that architects and building planners can count on support when using to the Green Roof Energy Calculator to sell their clients on the benefits of including a green roof.

The research behind PSU’s Green Roof Energy Calculator (and the online tool itself) was funded by the US Green Building Council with additional financial and in-kind support from the University of Toronto, Portland State University, GRHC, and Environment Canada.

Susan DeFreitas has covered all manner of green technology for EarthTechling since 2009. She is a graduate of Prescott College for the Liberal Arts and the Environment, and has a background in marketing green businesses. Her work on green living has been featured in Yes! Magazine, the Utne Reader and Natural Home.


  • Reply September 28, 2012

    Earl the Pearl

    If you want to save energy why not just add more insulation below the membrane? Green roofs are very expensive to install (one here in Lincoln on a new building cost over 4 times the cost per square foot as other areas on the same building), they are very expensive to find and repair leaks, and in dry times they use precious water. They are very much like the IRMA (Inverted Roof Membrane Assembly) roofs that are no longer installed because no one likes them for the same reasons as seen above. They are fine for those who want to pay for them, but those who say things such as seen above are not telling the whole truth. P.S. Just for your info. I have been in roofing for 34 years and have inspected thousands of roofs over a seven state area of the upper midwest.

    • Reply November 6, 2012

      Karen Morby

      You make some very good points but a vegetated roof is more than insulation. In fact I have been doing green roofs for 12 years and have always thought that the ‘energy’ saving was one of the poorest reasons for a green roof.

      Green roofs serve as heat sinks. they absorbe and use the energy of the sun and convert co2 onto o2. Now who much effect will one say, 10,000 sq ft roof have in a city, minuscule but if there were millions of sq ft the effect is real. Also the primary reason green roofs started in Europe was to control run off. A green roof can slow and use rainwater that would otherwise wind up on storm sewers, floods etc. Again a green roof won’t save you from a Sandy kind of rain but over time green roofs absorbe and respire normal rainfall. they also clean up run off water.
      Green roofs were and are often oversold as a magic bullet. They aren’t they are one of a combination of ways to make the urban environmental work with nature not against. they are not for every building.
      But they are getting cheaper and easier and can ultimately be a big factor in improving how cities exist in nature.

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