Saturday, February 26, 2011

Green Roof Drainage, Use of Natural Materials, Arundo Donax Reeds

Per the University of Maryland, Typical Green Roof Soil Media is made from;

  • Expanded Slate
  • Expanded Shale
  • Expanded Clay
  • Volcanic Pumice
Amended with;
  • Synthetic Fibers
  • Fly Ash
  • Rubber Foam
  • Tire Crumbs
The study goes on to point out that producing 1 cubic meter of expanded slate, clay or shale in the kiln embodies 1.7 million BTU's, producing 110 kg Carbon Dioxide.

Obviously not an ecologically friendly process for a supposedly 'green' product.

The note goes on to point out that during the 2008-2009 time period there were 290,000 square meters of green roofs installed in the three cities of New York, Chicago and D.C., representing a green roof soil media carbon footprint of;

1,148 Metric Tons of CO2

from green roofs.

I thought green roofs were supposed to be at least carbon neutral, and this does not even take into account the carbon footprint of the fertilizers added or the potable water pumped up to and used for supplemental irrigation.

Seemingly, portions of the green roof industry are not so green anymore, possibly hiding behind corporate profits as many other industries are.

But not all green roof professionals are focused solely on profits.  We think there is a strong grassroots effort to move the industry back towards sustainability, focusing on renewable and sustainable building materials and practices.

However there is much established industry pressure to not only continue using high carbon footprint materials, but formalize those materials into required 'standards' - the ultimate monopolizing practice.

ASTM is developing green roof soil media standards as we speak.  There is significant pressure to use these kiln processed, mined earth materials as the basis for all future green roof soils.

Unfortunately, if one looks past profits, there is a real problem with mined earth products treated via heat to make green roof soil media.  The problem is not so apparent in our limited view of seemingly expansive time and space unless we consider the scale.

Using the Galapagos Islands as an example we can see how unsustainable natural resource use has impacted ecology.

Here in the states it is hard to understand ecological impacts from mining because most of us never see what strip mines look like.  There is so much available land that the impact of mined earth products stays out of sight and out of mind.

But in the Galapagos, where real estate is limited in quantity and population pressures increase daily, the problem is easily discernible.


Hopefully we can learn from the Galapagos' near environmental tragedy.

Importantly, other green roof leaders from around the world are also looking to use of alternative materials for soils components.

Drainage is an important function expanded mined earth products help facilitate.

A recent project on the south coast of France is utilizing hard native reeds for the drainage components.

The native reeds are used locally for roofing materials and have been proven to last thirty years or longer, about the normal life of a typical roof.

Granted, thirty years life span is not the millennia expanded shale will last, but rather than a strip-mine approach or petro-fired kiln approach, the reeds represent sustainability.

And sustainability is what green roofs are really supposed to be about - creation of habitat for wildlife in the urban core, cleaning of stormwater, sequestering of carbon (instead of creating huge carbon footprints), and offering a sense of place for inhabitants.

Big industry can afford a powerful counter argument as to why strip mined and kiln fired products are really eco-friendly.  But I am not big industry, nor am I an industry organization who is influenced by big industry advertising money.

I can and I will say that green roofs should be based on sustainable practices, using rapidly renewable materials, native plants and ultimately helping the world we live in rather than contributing to a Galapagos like tragedy.

Otherwise, lets just use TPO white roofing to cure heat island effect.  TPO is a whole lot more cost-effective.

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