Green Roof Drainage Question

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Author Message Colin Gilboy Senior Member Username: colin Post Number: 409 Registered: 09-2005 Posted on Friday, July 17, 2015 - 10:25 am:    I have a question for the deeper green roofs using a drainage mat for drainage. This is not about planted tray designs. The drain industry has created designs that enclose the drain in perforated stainless steel. The perforated S/S is the primary drainage path for the water. If the S/S plugs there will be no way for the water to drain from the green roof. With ponding water under the surface of the green roof, problems will not be obvious. Ponding water is not a membrane’s friend and accelerates its failure. I am presently aware of a green roof project in FL. that failed at 5 years due to this problem. I spent time at a testing facility flow testing the perforated S/S and in what we considered as laboratory conditions we had the first inch of the S/S plug in 20 minutes of testing. T green roof is a debris creator so the risk of debris plugging the S/S is very high. Does everyone out there feel safe with the drainage mat delivering the water to the outside of a S/S drain enclosure that the water must pass to get to the drain or do you feel as I do that a green roof box should be installed that is separate from the drain and sits on top of the drainage mat allowing the water to flow freely to the drain throughout the life of the green roof. In the green roof box configuration the perforated S/S is secondary drainage path and basically media barrier. The industry started with the boxes and progressed to the totally enclosed drains. Not everything progresses in the correct direction but they will usually sort themselves out overtime, but this one is going to carry a extremely high price tag if it is not sorted out early. Craig J. Froeter Froet Industries [edited with Craig's permission - Colin] Colin Gilboy Publisher, 4specs.com 435.200.5775 - Utah 800.369.8008