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Up on a (Green) Roof

In a sunny corner of Manoa, Leyla Cabugos, a master's candidate in botany at the University of Hawaii, is conducting one of only two research projects that are studying green-roof applications in the Islands. Currently, she is carefully monitoring the growth of five different native Hawaiian ground covers and sedges in 28 planter boxes, 576 square feet in all. She is growing each species individually and in different combinations to determine the most effective mix for a green roof.

Photo by Scott T. Kubo
Vegetation - Cabugos selected a variety of native Hawaiian ground covers and sedges that have a high tolerance to drought, high wind, shallow soil and salt spray – general conditions characteristic of roofs in the drier parts of Hawaii. The plants include ilima, akulikuli, aki aki, pohinahina and Carx wahunesis. Pohinahina, ilima and akulikuli are plants often used in lei-making.

Photo by Scott T. Kubo
Growing medium - The project’s growing medium is a mixture of coconut fiber, Big Island cinder and locally produced compost. The right combination is crucial, because the medium must be able to meet the nutritional and drainage needs of the plants without adding unnecessary weight to the roof.


green roof

Photo by Scott T. Kubo

The benefits of a green roof can vary widely depending on the environmental conditions of a particular area and the architectural characteristic of each building. However, according to, a grass roof with 3.9 inches of growing medium will reduce a building’s cooling needs by 25 percent. A roof with 6 inches of growing medium will reduce heat gains by 95 percent. Green roofs, which can last twice as long as conventional roofs, also insulate buildings from sound, reducing it by as much as 60 decibels.

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Sep 26, 2009 03:53 am
 Posted by  geoie

thanks a lot for the great information and discussion on the green roofs project ... i hope that this would be adopted by all so that we can all help in sustaining our world and be ecologi9c and cosmic-friendly ... more powers and keep well ...

Nov 12, 2009 10:42 pm
 Posted by  jere

I am interested in green roofs for residential applications on sloped roofs. You would obviously need to make sure the roof it is being installed on is water tight and will be in good shape for a long time, but I suppose that once installed, it would reduce the weathering of your existing roof. I would like to know how this might work in areas where you collect your catchment water for household use. Is there a way to develop a roof system that would work for this application.

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Nov 12, 2009 10:48 pm
 Posted by  jere

So the main benefits would be Insulating, Sound Reduction, water filtration for catchment purposes? Controlling storm water run-off? Increase life due to reduced weathering of your existing roof? Reducing levels of carbon in our atmosphere? Would these all be legitimate benefits of a green roof and are there any other benefits?

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