Wednesday, September 1, 2010

Green Roofs, Tropical Storms, Green Roof Plants and Hurricanes

Its that time of year again.  There are three cyclones in the Atlantic and another wave forming.

If your roof has a parapet then you are lucky.  Most testing has shown parapets minimize wind damage to a green roof - though in a large hurricane, all bets are off.

Even if your green roof does not have a parapet it can still be designed to withstand significant tropical storm wind damage.

The video here is of a small green roof in Jacksonville, Florida on August 25th, 2008 when Tropical Storm Fay pummeled the northeast Florida area with over twenty inches of rain.  The video shows how the roof reacted to gusts up to 50 mph.  Wind speed was recorded using an ExTech anemometer.

The roof shown in the video does not have a parapet.  The video illustrates how the irregular surface of he vegetated roof interrupts wind generated uplift that can damage asphalt shingle roofs.  The plants range in height from two inches to six inches and can be seen moving back and forth in response to the wind.

Wind racing across a flat surface can create lift - or a vacuum - and literally lift the shingles or roll roofing up off the decking below.

The plant habit acts to break the shear flow of air, creating turbulence and working against damaging uplift.

Another important quality of a well designed green roof is the drainage factor.  The roof here is allowing a rapid drain of roughly 18" of rain over a 24 hour period without washing out.

Monolithic mats used as the basis of the planting system allow for quick drainage of the stormwater.

Moreover, the engineered soil, though primarily held to the mat by extensive root systems, is also considered erosion resistant due to an embedded natural, low VOC tackifier.

We will always deal with the 5 H's here in Florida - High Heat, High Humidity, Hard Frosts, Hurricanes and Hard Desiccating Winds, but with good green roof design your Florida Green Roof can withstand a severe storm, including tropical storms!

Email me with your Questions or Comments!

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