http://www.expressmilwaukee.com/blog-5602-the-green-alternative-to-asphalt-roofs.html

The Green Alternative to Asphalt Roofs

In Section: Green Life Posted By: Kathleen Wills

For centuries, it hasn’t seemed like much of a problem to dig out the earth, erect structures and cap them with impervious asphalt roofs. But with population growth and ensuing urban development, it has become extremely problematic. Storm-water runoff, flooding, polluted watersheds, violent temperature contrasts, increased heating and cooling energy consumption and costs, gusting winds and stripped habitats are all by-products of the replacement of earth with concrete.
Of these complications, storm-water runoff has been the most challenging. When rain falls on our waterproof concrete jungles it picks up pollutants as it flows off roofs, walls and gutters and runs straight into storm drains and on to its final destination – our lakes, rivers and oceans. With nothing to slow down heavy downpours, wastewater systems flood, dumping raw sewage into local bodies of water.

The other major problem to contend with is the urban heat-island effect. Asphalt rooftops can reach 150oF, contributing to warmer temperatures in cities than their surrounding regions – a 10o difference in some areas. This translates to higher energy consumption and costs to cool buildings.

How to mitigate these environmental extremes is something city planners and architects worldwide have been grappling with for years. The solution? Green roofs!

Green roofs, also called living roofs, solve the flooding and water pollution problems by mimicking meadows. Soil composites and vegetation absorb water, filter and cleanse it, slow it down, and even store some of it for use during dry spells. They help the energy consumption quandary by acting as insulation thus reducing energy costs by as much as 20%. They even improve air quality by absorbing carbon dioxide. Water savings also come in to play in buildings where rainwater is collected and reused for watering exterior plants or flushing water for toilets.

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More next week.

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