What The Heck Is A 'Green Roof?'

It looks like an open-air rooftop greenhouse. Or perhaps a manicured mini park in the sky.

Green roofs – these secret islands of bucolic beauty that are rarely seen and never heard on the ground – are quietly moving in, blanketing buildings across the country in muted greens and pinks. They're taking over the tops of structures big and small, from the narrow green terraces of the Empire State Building to the country's most massive green roof installation, which sits atop a sprawling Ford truck plant in Michigan.

The Environmental Protection Agency defines a green roof as any “vegetative layer grown on a rooftop.” And while pitching a layer of protective sod on top of buildings and homes is nothing new (the vikings did this, too), what's happening now is a bit more high tech.

The modern 'green roof' concept was introduced in Germany about 40 years ago where more than 10 percent of the country's roofs have gone green. Unlike early Norse techniques, modern green roofing relies more on savvy materials science than grass seed or sod. There is a bed of hearty vegetation on the tippy top of the green roof - but below the green shrubs sits a multi-layered lightweight wind and rain-friendly contraption:

The succulent leafy sedum plants on this green roof are born thirsty. When the rains come, water soaks in to the plants, trickling slowly down to the lightweight mats and fibers below, instead of running directly into gushing storm drains.

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