Green roof construction continues to grow in popularity in North America due to the environmental benefits they provide, an increase in interest in green building and the enactment of regulations and the offer of incentives by various governmental bodies.

Aesthetics aside, the benefits of green, or vegetated roofs include better stormwater management, reduction of the urban heat island effect, removal of carbon from, and release of oxygen into, the atmosphere, added habitat for birds and insects, decreased energy costs for the building's tenants and increased life of the building's roof membrane. Of these, stormwater management seems to be the main impetus for the regulations and incentives.

In the book, The Green Roof Manual by Edmund C. Snodgrass and Linda McIntyre, the authors note "stormwater management infrastructure is overburdened in many cities, and green roofs are one way to take some of the pressure off by mitigating runoff into those systems."

Green Incentives
Chicago, an early supporter of green roofs (its city hall, under the directive of then-mayor Richard Daley, had plants installed on its topside in 2000), not only offered an expedited permitting process to developers who incorporated green roofs in their plans, they also allowed the square footage of the roof to be counted toward any pervious surface area requirement.

Portland was another early adopter, officially recognizing vegetated roofs as a stormwater best management practice in 1999. To promote their inclusion on commercial and residential structures, the city began, in 2008, offering grants of up to $5 per square foot, which amounted to about 50% of a project's overall cost according to industry specialists.

The Regional Green Roof Initiative in Milwaukee provided funding for up to $5 per square foot of approved green roofs on properties that were within the city's sewerage district.

Government entities in Ohio received below market rate loans for the design and construction of green infrastructure on economic development projects.

Expedited permitting and low rate loans with longer payback periods were made available, through the Properly Assessed Clean Energy program, to San Francisco commercial developments that included vegetated roofs.

And in Washington, D.C., rebates for eligible green roof construction ranged from $7 to $10 per square foot.

Mandating Green Construction
San Francisco was the first place in the U.S. to enact a law calling for green roofs - requiring between 15 to 30 percent of a roof's area on most new building projects to be planted with vegetation, installed with solar panels, or a combination of both.

In 2017, voters in the city of Denver passed an initiative that required green roofs on new buildings of 25,000 square feet or more of floor area, and vegetated roof and solar panel combinations on existing buildings of that size when replacing their roofs. The city council however revised that ordinance; adding compliance options that would produce environmental benefits at less cost.

And other places have building code requirements that the inclusion of a green roof can help satisfy. For instance:

All projects receiving financial or zoning assistance from the city of Chicago must fulfill certain green building conditions, and all new city buildings must be LEED certified.

Seattle requires 30% of plant coverage in commercial and neighborhood commercial zones and 50% coverage in multi-family residential zones.

Through the State Green Building Construction Act, all new government buildings and major renovation projects in New York must meet green building standards set by the state's Office of General Services.

San Francisco's Green Building Ordinance sets criteria for stormwater runoff amounts.

And legislative efforts continue: last year members of the New York City Council introduced various proposals that would require that the roofs of certain buildings have all or part of their available space covered with environmentally-friendly solutions such as a green roof system.