The idea of grass-topped rafters isn't new, as any Swiss miss can tell you. But the technology's been updated in recent years to serve specific purposes, like controlling runoff. In hard-paved cities with little or no absorbent ground cover, municipal sewer systems can be overwhelmed by excess flow following a hard rain. A green roof absorbs 50 to 75 percent of the rainfall that strikes it, significantly diminishing the amount of water that reaches the gutter.

Roof pitches of up to 12/12 can be green, although the system's complexity and cost may increase accordingly. Outside Stuttgart, Germany, a contemporary-style house with a verdant roof updates the archetypal thatched cottage (top). A private rooftop garden — also near Stuttgart — puts to rest any argument that a flat roof is an ugly roof (above)...

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