Monday, December 6, 2010

Green Roofs - Erosion Control - Nature Irrigated

The vegetated roof system here was installed in a roof corner receiving significant amounts of runoff from other sections of the existing roof.

The volume and velocity of the roof runoff was significant, high enough in-fact to consistently erode and wear out the asphalt roll roofing originally installed.

Rob O's Erosion Control Green Roof
The vegetated roof mat is small - only 1 meter by 1 meter, however it is positioned in the location where the most erosion occurs.

Several plant species were chosen for the April 2009 trial installation.

These plants were selected on their ability to withstand large sheet water flows, flowering characteristics and their ability to survive with nature-based irrigation (precipitation, fog and dew).

After 21 months of field testing the Bulbine frutescens flourished more so than any other species.

We are somewhat amazed that the Bulbine frutescens survived better than the allium species for several reasons, including;

1. Bulbine frutescens is more tender to frost and freezing than alliums and during the trial period, Jacksonville endured several straight weeks of sub-freezing temperatures. We assume the particular spot of the roof is a micro-climate, protected somewhat from freezes.

2. The Bulbine frutescens is exposed to significant sunlight intensity during the afternoon hours, with little or no shade, and

3. The application soil depth was shallow, less than 1" - 26 mm and Bulbine frutescens prefers deeper soils.

Interestingly, the Bulbine frutescens survived without additional irrigation. The plants thrived on nature-based irrigation, including extended periods of drought.

Moreover, Bulbine frutescens acted as an excellent water-break and erosion control BMP - effectively stopping unchecked sheet flow during rain events from cascading off the upper roof.

As always - email us with your questions here.

Happy Green Roofing!


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