Monday, November 15, 2010

Harvesting Rainwater for Green Roofs - Underground Storage Systems

EcoRain Tank Modular Rainwater Harvesting for Green Roofs
We've talked about water crises and irrigation of green roofs many times before.  Designing a green roof irrigation system to run off of rainwater instead of potable water is easy.

One of the biggest disadvantages of large rainwater tanks before has been the freight expense of bringing a large tank from the manufacturer to the site.

Many times the cost of freight exceeded the cost of the tank - and there are not many tank manufacturers so the tanks may have had to been hauled across the country.  Long freight hauls create large carbon footprints.

However, several new structural Rainwater Harvesting Systems are now available on the market that are collapsable and can easily be assembled on-site.  For a video of a very large underground rainwater collection system in Dallas, Texas click here (opens in a new window).

EcoRain Tanks Rainwater Harvesting System
One of the more green subdivisions in Gainesville, Florida, the Madera Subdivision, utilizes underground collection and storage of stormwater in several of their homes.

Collection of rainwater and subsequent irrigation of green roofs can be a valid method for allowing larger buildings on Urban Core lots previously designed with much smaller impervious allotment.  This applies also to historic residential areas where renovations are occurring.

Importantly, the Green Roof design needs to anticipate periods of natural drought where stored rainwater may be depleted.

The use of potable water should be only used in certain instances, and the green roof plant selection should reflect species that can utilize the stored rainwater, however are also drought tolerant.

EcoRain Tanks Rainwater Harvesting System
Typical Underground Rainwater Storage Systems for Green Roof irrigation are designed and installed with little effort.

First the seasonal high groundwater level should be determined.  This can be accomplished with the civil engineer or geotechnical expert.  For the homeowner, simply take a shovel, I prefer a set of post hole-diggers, and dig a small hole down until wet soil or water appears.

The Green Roof Underground Stormwater Harvesting System should be primarily installed above the Seasonal High Ground Water Level.

Size your storage system to hold a 24-hour storm event quantity for the surface area of the roof you are collecting from.  ARCSA has a great website about sizing and designing systems - click here - opens in a new window.

Modular EcoRain Tank Unit
You can use solar pumps to pump the water back up from the rainwater harvesting cistern to the green roof.

Unpackage your EcoRain Tanks and assemble on site, placing them inside the liner within the excavated cistern area (refer to the video above for illustrations).

Detailed design information is available from the EcoRain Tank websites - and at

Remember, we a growing population on this globe and conservation of all water resources is important.  Ensure your green roof plant designer is using species that are friendly to conservation of water!

As always, feel free to contact us with your questions!

Happy Green Roofing!

1 comment:

Rainwater Harvesting said...

Rainwater harvesting is essential for any society aiming for sustainability. Rain is clean, free and has a zero carbon footprint - why waste it?