The number of green roofs in North American is estimated to have grown by 15 percent since 2013. It’s common to call anything that’s more sustainable than standard practices “green.” But a green roof, sometimes called a living roof, is not just any sustainable roofing material. A green roof is a specific type of roofing system that supports living plants. Green roofs have been around in the form of sod roofs since at least the middle ages.
But a modern green roof involves more than just plants. It needs high quality water-proofing and protection against root damage, a drainage system, filter cloth, and a lightweight growing medium. The plants may be small, drought-tolerant ones like sedums, or larger grasses. The system can be modular or site-built, and depending on the planting medium depth, may even resemble a natural meadow or a garden with shrubs and trees.
Green roofs have been used on private residences very successfully. Although the high cost of design and installation has slowed their adoption as a standard roofing option, they can provide lifetime savings.
Single-family homes made up less than 2 percent of the green roofs in the U.S. in 2015. Multifamily homes, on the other hand, have the efficiencies of scale to justify the expense (and sometimes, have the square footage to trigger green roof requirements) and made up 22 percent of green roof projects. That still leaves the vast majority of green roofs to industrial and commercial buildings.
But private homeowners need not despair. Many of the incentives available for green roof construction are available for single-family residences, too.
Toronto became the first city to require green roofs in 2009; in 2019, New York City became the latest. In between, at least 20 U.S. cities have passed some sort of green roof policy. The list includes cities you might expect – like Portland, Denver, and San Francisco. But it also includes some you might not expect – Baltimore and Nashville.