In Portland Oregon it is nearly impossible to find a roof not covered in plants as the city is a leader in bringing green infrastructure. Green roofs or whatever you refer to them as (some people say rooftop gardens others say ecoroofs) typically have a layer of plants growing in solin on on top of the roof. There is an added layer of waterproofing, structural support, and even insulation.

Studies done with Reed College, the University of Illinois, and Portland State University has explored how much residents are willing to pay to increase the amount of green roofs seen across the city and why they would be willing to pay those amounts.

"Countries around the world are investing significant public resources to reduce the impact of stormwater runoff. Green roofs are part of that solution because they capture some of the rain that would otherwise end up in sewage systems. Knowing the benefits from investing in green roofs is important for implementing sound public policies."

Amy Ando, professor of agricultural and consumer economics at the Univeristy of Illionois and a co-author on the study, explains.

The benefits individuals would be paying for include sewer overflow events, reduced urban heat island effect, and increase presence of pollinators such as bees and butterflies. The overflow events (CSOs) occur often as extreme rainfall is a common occurrence in Portland and old sewer systems continuously become flooded.

"Although CSO events have declined dramatically in Portland after a major system upgrade ($1.4 billion "Big Pipe Project"), they still happen. Our findings show that survey respondents place the largest value on reducing CSO events further and are willing to support additional funding for this."

Says Noelwah Netusil, professor of economics at Reed College and the lead author for the paper.

To further protect the city from flooding, Portland has required new buildings in the central city with a footprint over 20,000 square feet to have an ecoroof covering 100% of the area. Most of the green roofs in reference are concentrated in the city center and cover more than 1.4 Millio square feet.

Respondents to the survey claimed they were willing to pay upwards of $442.40 per household in terms of reducing the average temperatures, reducing sewer over flows, and increasing pollinators. The is nearly $116.8 Million for the entire city. When asked about reducing temperatures by less than 0.5 degrees, reducing overflow by one, and increasing pollinators by 50%, residents then claimed they were willing to pay an average of $202.40 per household which totals to nearly $54.4 Million for the city.

Individuals with a past of visiting or seeing a green roof had the highest willingness to pay up for support of the program. Those who knew nothing were still very supportive of the program and people generally preferred ecoroofs to be equally spread throughout the city rather than concentrated in the center.

"Reducing CSO events had the largest value for all survey respondents—whether they had visited, seen, heard, or knew nothing about green roofs prior to taking the survey. The total estimated benefits from the programs we examined would be sufficient to more than double the number of green roofs on commercial and industrial properties in our study area (Portland)."

Netusil explained further.

"When municipalities in Illinois contact us because they're interested in applying green infrastructure, they want to know how the public will benefit from their investment. This new research on green roofs goes beyond Portland, giving gives stormwater professionals more tools to advocate for practices that are valuable for communities across Illinois and elsewhere."

Eliana Brown, University of Illinois Extesnion and Illinois-Indiana Sea Grant water specialist, said as she mentioned inclusion of the study to a new green stormwater infrastructure website.

The paper, "Valuing the public benefits of green roofs," is published in Landscape and Urban Planning. Authors include Noelwah Netusil, Lauren Lavelle, Sahan Dissanayake, and Amy Ando.