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.
More recently, voters in Denver approved a green roof initiative that requires newly built buildings larger than 25,000 square feet to dedicate a portion of their rooftops to vegetation or solar panels. The green roofs are intended to help reduce Denver’s urban heat island effect, which is the third worst in the nation.
And this July, the so-called ecoroof requirement went into effect in Portland, Ore. It mandates that vegetation must cover 100 percent of the roofs on buildings in the central city over 20,000 square feet (with some exceptions). Roughly 25 cities in North America have some sort of program to encourage green roofs, but, says Peck, “lately we’re seeing more of a move to make them mandatory.”
Part of the reason green roofs have been slow to take root is cost. A study by the University of Michigan found that a 21,000-square-foot green roof, for example, cost about $100,000 more to install than a conventional roof. Of course, the same study found that over its lifetime, the green roof would save about $200,000 thanks mostly to reduced energy needs. To help with the upfront costs, the firm Counterpointe Sustainable Real Estate announced last year that it will start offering property assessed clean energy financing. Through the PACE program, loans are repaid with long-term, fixed rates through an additional line item on the property tax statement. PACE is available in 21 states.
Another reason for their slow adoption is that installing green roofs is complicated. Peck’s organization has developed a toolkit to help. The Living Architecture Performance Tool (LAPT) is a rating system and best practice guide. While its ultimate goal is to certify that green roofs and walls are planned to achieve certain measurable and replicable performance benefits, its more immediate focus is offering guidance. The tool is free to policymakers in particular, who can use it to maximize public benefits and create effective policies. “Not everyone can be an expert,” says Peck, “but with LAPT you don’t have to be. This can help policymakers incentivize green roofs.”