Green roofs replace or obscure asphalt shingles, black cladding, or other materials with plants. They’re aesthetically advantageous, of course: green roofs are near-universally considered attractive. When accessible to office workers, they’re a recreational hit. But these systems also have some serious environmental benefits. Plants, for example, slow rainwater’s descent to street level, reducing the chance of small-scale flooding, while filtering notoriously dirty stormwater.