Throughout the warmer months, employees at DC-area anti-poverty nonprofit Bread for the City take time out of the day to relax, eat lunch, or teach classes on the roof of their building, surrounded by nature. Bread for the City has one of the hundreds of green roofs in Washington, D.C., that the city is encouraging as an alternative to traditional “gray” water management infrastructure. Green infrastructure isn’t just another way to comply with building codes or qualify for incentives, though; there is a host of peripheral benefits that make it an attractive option.
It’s easy to understand the intangible benefits up on Bread for the City’s roof, surrounded by greenery. The tomato vines in one patch are a tempting shade of red. Next to them, bees are buzzing in a patch of flowers not far from the currently out-of-use bee colonies. Cacti, eggplants, and dozens of other crops round out the display.
“Staff eat lunch up there, do yoga up there sometimes, we have open hours in the garden,” Kristen Kozlowski, associate director of development for Bread for the City, told Aquicore. “It’s a beautiful, safe, green space.”
As beautiful as green roofs are, there would be fewer without policies that support them and other green infrastructure. Understanding why cities commit to these policies takes an appreciation of how difficult it is to manage city infrastructure.
Here’s the bottom line: Cities deal with a lot of rain. A lot of rain. That’s an easy fact to forget when the weatherman predicts an inch of rain and almost all of it disappears in an instant down storm drains and gutters. Rain seems like something that just deals with itself. In reality, like so many invisible processes in cities and buildings, stormwater management is a massive engineering challenge that continues to cause problems in cities across the country.
So, how much water is in that inch of rain?
Every inch of precipitation deposits about 27,154 gallons of water per acre – the equivalent of almost 680 bathtubs full of water. If you live in Washington, D.C., which has an area of 43,737.6 acres, that inch of rain means your city has to find a way to divert or drain about 1.2 billion gallons of water. To put that in perspective, that’s just shy of 1,800 Olympic swimming pools.
And that’s just a single inch. The rainiest recorded storm to hit America, Hurricane Amelia, deposited roughly 48 inches on its route across Texas.
The capital gets over 40 inches of precipitation every year on average. Even more of a challenge – some storms drop several inches of rain in just a few hours. As a result, 860 communities in the U.S., D.C. among them, are affected by sewage runoff due to the increased strain on combined stormwater-sewage systems during heavy rains. These communities have “combined” systems for storm water and sewer drainage. That means that they’re generally separate but run through the same pipes. When there is too much rainwater for the system to handle, mixed sewage and rainwater overflow into nearby rivers. This pollutes natural environments and drinking water.
Usually, combined drainage systems work fine. It’s only during heavy storms that the system is overwhelmed. In theory, cities could pay the astronomical sum needed to dig up their existing pipes and put in modern designs. In practice, most cities have found that it’s more cost effective to incentivize building owners to retain rainwater during storms and release it over time.
Among the distributed options for water management, there are “green” and “gray” options. Grey options, like holding tanks that feed into sewers after the storm is open for example, are generally much more affordable up front than green equivalents.
So, at first glance, it would be easy to assume that developers would avoid green infrastructure. However, tangible and intangible benefits of the green approach to stormwater management mean that, in many cases, it provides more long-term value for a commercial space. Incentives from local governments and other initiatives also often nudge the math in the right direction.
Katharine Burgess, Senior Director of Urban Resilience at the Urban Land Institute, told Aquicore about her and her team’s findings in a recently released report titled Harvesting the Value of Water: Stormwater, Green Infrastructure, and Real Estate. The institute looked at cases in which commercial developers made use of green infrastructure to create value beyond the initial goal of managing stormwater.
“The very best projects use stormwater management as a way to create inviting, enticing green spaces,” Burgess told Aquicore. “We also saw a number of projects that used innovative approaches to stormwater management to essentially increase their development yield and develop a larger portion of the site than would have been possible with a more traditional approach, like a retention pond.”
Burgess cited the Tampa Housing Authority’s Encore Project, a mixed-use redevelopment adjacent to Tampa’s downtown. There, THA used an expansive stormwater vault as the centerpiece of a park. The approach paid off. THA gained three developable lots in comparison to using a retention pond and were able to create a more dense, urban product. And, they gained an amenity for the park at the same time, having positioned their stormwater infrastructure as a feature. This is a common approach with green infrastructure. Green roofs, rain gardens, and bioswales help manage storm water and work as attractive reliefs in urban environments.
Government incentives and pleasant intangibles aside, there are financial reasons why a developer might invest in green infrastructure.
Colin Hood, the property manager for Cushman & Wakefield in charge of World Wildlife Fund headquarters in downtown D.C., helped to explain why the organization had opted for a green roof.
“Energy-wise, it reduces heat gain and cooling loss for the building,” Hood told Aquicore. He explained that the soil acts as an insulator in the winter, preventing heat from escaping through the roof. In the summer, the plants create a small pocket of cool, moist air through a process called evapotranspiration. This reduces heat gain and provides a source of cooler air for the air intake vents to draw from.
“It [also] provides sound insulation,” said Hood. “The medium the plants are in basically works on the low-frequency sound and then the plants work on the high-frequency sound.”
Green infrastructure projects also help buildings to net LEED points, which create value for tenants. The WWF headquarters is LEED Platinum certified, for example, which fits with the nonprofit’s values. Hood also mentioned that the building’s green roof fulfills another of the organization’s goals. It provides a habitat for local wildlife, including the bees from a nearby rooftop apiary.
Finally, green roofs like WWF’s can extend the life of the underlying roof membrane – sometimes doubling its effective lifetime. That alone provides one of the clearest financial cases for developers and asset owners. “That’s probably the biggest financial benefit,” Hood agreed.