Sourced from House Method
An aerial view of most cities will show you swathes of black asphalt or gravel-filled roofs—utilitarian spaces that have traditionally been underutilized. But some cities, like Chicago and Indianapolis, have come up with a solution to reimagine these spaces: green roofs.
What is a green roof?
According to the EPA, a green roof, also called an eco-roof or rooftop garden, is a vegetative layer grown on a rooftop. There are two main types of green roofs: intensive and extensive. Intensive green roofs are essentially elevated parks that sustain trees, walkways, and benches with their complex structural support, irrigation, drainage, and root protection layers. About a foot of growing medium is needed for an intensive green roof, creating a load of 80–150 pounds per square foot.
Extensive green roofs typically exist solely for environmental benefits—unlike intensive green roofs, extensive roofs don’t function as accessible rooftop gardens or parks. They are made up of a thin but hardy two-inch growing medium and are relatively light, weighing about 15–50 pounds per square foot.
Green roof costs and installation
The estimated cost of installing a green roof starts at $10 per square foot for extensive roofs and $25 per square foot for intensive roofs. Annual maintenance for either type of roof can range from $0.75–$1.50 per square foot. Though the initial cost of green roofs is higher than roofs with conventional materials, building owners can offset the difference through reduced energy and storm management costs.