Growing greenery on roofs brings many benefits. Buildings stay cooler, saving energy. Roofs last longer, saving money and materials. Birds and insects find new habitat, helping ecosystems. And green roofs make urban spaces more aesthetically and spiritually pleasing, as well as reducing heat-island effects for city dwellers.
Whether you venture onto a few wooden planks over a trout stream, a steel colossus over a swift river or a concrete viaduct carrying bumper–to–bumper commuters, you trust the beams and girders to hold you up. This act of faith, made daily by millions of motorists on U.S. highways, was shaken last summer when a steel truss bridge in Minneapolis plunged into the Mississippi River during rush hour.