value of green roofs | SOLARIFY

Costs for city dwellers are worth it

Green roofs, also known as roof gardens or eco-roofs, typically consist of a layer of plants growing in the soil on the roof, along with waterproofing, structural support and insulation materials. a new inLandscape and Urban Planning According to a press release dated May 3, 2022, an open access study by Reed College in cooperation with the University of Illinois (U of I) and Portland State University examined the advantages of green roofs and the question of how much Portland residents are willing to pay to increase the number of green roofs in the city. An example for many other cities.

Green roof in Berlin – Photo © Gerhard Hofmann Agency Future

“Countries around the world are investing significant public funds to reduce the impact of stormwater runoff,” said Amy Ando, ​​professor of agricultural and consumer economics at the U of I and co-author of the study. “Green roofs are part of this solution because they capture some of the rainwater that would otherwise end up in the sewage system. Knowing the benefits of investing in green roofs is important for implementing sound public policy”. Not just since Friedensreich Hundertwasser, who is probably not well known in the state on Lake Michigan.

The study examines how much people would pay for the benefits of reducing sewer overflow events (Combined Sewer Overflow – CSO), the reduction of the urban heat island effect and the increase in pollinators such as bees and butterflies. Like many other cities, Portland’s extreme rainfall can quickly overwhelm old sewage systems, causing flooding that affects water quality, traffic, and real estate.

“Although the number of CSO events in Portland has drastically decreased following a major system buildout ($1.4 billion ‘Big Pipe Project’), they still occur,” said Noelwah Netusil, professor of economics at Reed College and lead author the study. “Our results show that respondents place the highest value on further reducing CSO events and are willing to devote additional resources to do so.”

Since 2018, the City of Portland has required that new downtown buildings with a floor area greater than 20,000 square feet have an eco-roof covering 100% of the area (minus some exceptions such as solar panels and evacuation routes) to further protect the city from flooding. Most of the green roofs are in the city center, where they cover an area of ​​1.4 million square meters.

Respondents indicated how much they would pay for a green roof to get a range of benefits. For example, it would be more expensive to reduce the number of sewage overflows three times a year instead of twice, lower the air temperature by more than a degree instead of half a degree, and attract more bees, birds and butterflies than pollinators to keep the same level.

Respondents were willing to pay $442.40 for green roofs that lower average temperatures by more than 1 degree Fahrenheit, reduce sewage overflows by three per year, and increase pollinators by 150% payable per household. That equates to $116.8 million for the city of Portland. For green roofs, which reduce summer temperatures by less than 0.5 degrees, reduce sewage overflow by one degree, and increase pollinator numbers by 50%, residents were willing to pay $202.40 per household, or $54.4 million in total to pay for Portland. The cost would be added to the wastewater and stormwater bill in monthly installments for a year, and the green roofs would be installed a year after the program was fully funded.

While respondents who had already toured or seen a green roof had the highest estimated willingness to pay for the program outlined in the survey, respondents who did not know anything about green roofs prior to taking the survey still supported the green roof program. In addition, respondents generally preferred a more even distribution of eco-roofs across the city rather than a concentration in the city centre.

“The reduction in CSO events was the most valued for all respondents, whether they had visited, seen, heard, or were unaware of green roofs prior to the survey,” explains Netusil. “The estimated total benefits of the programs we studied would be enough to more than double the number of green roofs on commercial and industrial lots in our study area (Portland).”