Saving For A Drainy Day: Drainage Systems For Green Roofs

If you own a commercial building onto which you're installing a green roof, listen up: El Nino is looking more and more likely for the winter of 2015-2016, and that means a lot of rain in much of the country. If you are going to install a permanent green roof -- in other words, those plants are staying outside no matter what -- you must ensure that the drainage systems are working well. The alternative is to see your plants drown and your roof overrun by flooding. Here's a look at some of the more common green roof drainage systems that are available.

Conduit Plus Aggregate

One form of drainage system has a layer of aggregate or stones over a conduit or channel that leads water to wherever you want it to go. The aggregate layer is integrated with the layers of other planting materials. Typically, you'll find the plants and soil, then a special fabric that lets the water filter down, then the aggregate and possibly a special mat to catch some of that water for reuse with the plants, and then the drainage channel.

If these layers are less than 4 inches thick all together, don't plan on being able to retain much moisture. Also, ensure that the stones are easy to get to so you can clean them (and the system in general) occasionally.

Panels, Plates, and Cores

These are sheets of plastic or other materials that allow water to sit in channels imprinted into the plates, waiting to be soaked back up by the soil. If too much water drains into the channels, the extra water washes away. The sheets lie under layers of filtering fabric and soil or other growing media. A retaining edge is set down around the perimeter of the mass of sheets.

Sometimes the channels for letting extra water drain away are on the underside of the sheets, so be sure that the roof's surface can handle that water draining away. Before having a green roof installed, have the roof inspected and even replaced if necessary.

Maintenance and Upkeep

Never assume that the roof will work perfectly for years without inspections. You have to be sure that growing media or aggregate aren't being washed away. If you install the green roof and experience a very strong storm or a lengthy series of storms, talk to the roofing contractor about having the system checked out to ensure that nothing has become clogged or has been moved by heavy rainfall.

Remember that green roofs rely on a strong basic roof for support, so if you are still going to have that green roof installed, contact a roofing contractor today. Ensure that the roof is in great shape, can handle the drainage, and is strong enough to support what should be a very pretty addition to your building. For more information, contact a professional like those at All American Roofing Incorporated.


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