Rooftops aren’t just for shingles and solar panels anymore. Increasingly, they’re for the birds, the bees and the trees. Green roofs, which have been common in Europe for more than 40 years, are slowly catching on in the U.S. Since the mid-aughts, there’s been a small but growing effort -- particularly in the last two years -- to turn rooftops over to all kinds of vegetation.
The focus comes as cities are setting ever more ambitious energy efficiency and renewable energy goals. Green or living roofs are an obvious solution because they’ve been found to reduce energy costs and absorb stormwater. What’s more, green roofs improve air quality and help reduce the urban heat island effect, a condition in which cities absorb and trap heat at higher rates than rural areas. A study commissioned by the Washington state Department of Energy and Environment found that every dollar invested in green roofs generated $2 in benefits. “There is more of a mindset today that the roofs of buildings are an infrastructure asset,” says Steven Peck, founder and president of Green Roofs for Healthy Cities. “It makes sense then to use those assets to reduce stormwater, filter the air and reduce the urban heat effect.”
That’s why several cities have begun implementing policies to promote green roofs, starting with San Francisco’s Better Roofs Ordinance, which launched in January 2017. The ordinance made San Francisco the first major U.S. city to mandate solar and living roofs on between 15 percent and 30 percent of most new construction. “We should treat real estate on the top of our buildings as valuable,” says Barry Hooper, green building specialist for the city’s Department of the Environment.