Quantifying the Financial Value of the Soft Benefits of Green Roofs

6 05 2011

Steven Peck, Hon. ASLA, and Founder and President of Green Roofs for Healthy Cities was recently interviewed by The DIRT while in Washington D.C. for the Living Architecture Symposium, (“Despite the Economy, Green Roofs Bloom“). In the interview, Mr. Peck quoted a recent survey of the green roof industry  which reported that 8-9 million square feet of green roofs were built last year. This figure represented a 30% increase in market growth. Most of this expansion was focused in cities that have public policies in place that encourage and support green roof installation. The most intriguing statements in the article are those that helped quantify the economic impact of green roofs.

The post included some assertions that quantified the financial value of some of the soft benefits of green roofs. These included

“…average stormwater mitigation benefit is $4.26/sf” and  a view of a green roof improves property values of nearby buildings by 11%”

These figures are based on research by Smart Cities Research Services, Montreal.  “The Monetary Value of the Soft Benefits of Green Roofs” report prepared by Ray Tomalty, Ph.D. and Bartek Komorowski, MUP with the assistance of Dany Doiron, published last year. The report includes research on developing heuristic methods for quantifying seven soft benefits of green roofs: including: change in property values, marketing benefits, food production and food security, sound attenuation, stormwater retention, air quality, and green house gas (GHG) sequestration. The following is a summary of their findings:

I did not include the marketing figures in the table above, due the complexity of their findings.

Since there is little to no research specific to green roofs, the heuristic methods described in the report rely on other related research. Examples include:

Supply and demand play a critical role in determining one values and this is not any different for green infrastructure. For urban areas that may incorporate little to no green infrastructure (i.e. parks, green roofs, street trees) and are predominantly unsightly parking lots and roofs, projects that include green roofs should be more valuable and those properties surrounding it should benefit in some way as well. The report provides a great starting point for financially quantifying the soft benefits of green roofs. Over time, data specific to green roofs will eventually become available and we will be able to more accurately quantify their specific benefits.

-Brian Phelps


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Categories : Green roof, Plans and studies, Uncategorized

Valuing Green Infrastructure

23 03 2011


Earlier this year the Center for Neighborhood Technology (CNT) released the publication “ The Value of Green Infrastructure: A Guide to Recognizing Its Economic, Environmental and Social Benefits”. The publication is a great summary of the benefits of Green Infrastructure and goes a step further by providing data to help communities quantify many of its benefits.

The document includes two example demonstration projects. The first is for a green roof project on a single site and the other seeks to illustrate the benefits of the green roof site if expanded to a neighborhood scale. The authors point out that full life-cycle analysis was not a part of the scope of the analysis included in these demonstrations.

In addition, they offer a series of considerations and limitations of the data included. These points are helpful to consider when applying the information within the report. These include considering the full life-cycle analysis, local performance and level of benefits realized, spatial scaling and thresholds, temporal considerations and scale discounting, operation and maintenance, price variability, and double counting.

The concept of “discounting” described in the report was interesting. It recognizes that society typically values present benefits over future benefits. The following is an excerpt describing this concept:

“The term “discounting” refers to the adjustment one makes to account for future uncertainty (or the opportunity cost of money: a dollar today is not worth the same as a dollar five years down the road). Our society generally values what an investment gives us in the present more than what we might get for it in the future. The reason for this is future uncertainty, and as such, the future value or benefit of an investment must be adjusted or discounted. It is a technique widely used in benefit-cost analyses to understand and compare a project’s implications (its rate of return) over a given temporal scale.”

Overall the report is a helpful resource in quantifying the benefits of green infrastructure. The additional external links and resources provide additional tools and are worth exploring. You can find the full report on CNT’s website.

-Brian Phelps


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Categories : Bioretention, Green roof, Pervious Pavement, Sustainable Site Strategies

Funding Green Infrastructure: Understanding A Project’s “Benefit Fingerprint”

20 09 2010

Last week I attended the American Society of Landscape Architect’s (ASLA) annual meeting in Washington D.C. It was invigorating to hear about promising green infrastructure related projects being plan and constructed across the United States. One favorite was Herbert Dreiseitl’s presentation on the promise of water. His approach and sensitivity to water was inspiring.

Many of the conference sessions reinforced the multiple benefits of green infrastructure projects and the importance of continuing to build the data supporting these benefits. In addition, it was clear that green infrastructure projects are addressing multiple political agendas and problems facing our cities.  As a result, municipalities are able to seek funding from a variety of traditional and non-traditional sources. When considering these sources, it is critical to understand and quantify the benefits of a project.

While all green infrastructure projects have multiple benefits, depending on the approach, site, and its context, each project will have a unique combination and varying impact.  Understanding this “benefit fingerprint” is helpful in successfully targeting funding sources. It also opens up the possibilities of non-traditional sources and helps others see the project with a broader perspective.

-Brian Phelps


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Categories : Sustainable Site Strategies

Triple Bottom Line of Green Infrastructure

18 11 2009

Before and After of Green Infrastructure Improvements
(Source:“Green Cities Clean Waters” Plan)

In an earlier post titled “Making Green Infrastructure Common Place” we discussed the recent release of Philadelphia’s $1.6 billion dollar “Green Cities Clean Waters” Plan. Its thrust is to transform over 4,000 acres of impervious areas within the City’s Combined Sewer System to green space over the next 20 years through the use of green infrastructure strategies. This would involve converting over 34% of all existing impervious areas. Of this, the conversion will primarily be made on public property and right-of-ways. Green streets, the most widely used management tool, will comprise nearly 38% of these improvements (see graphic). The report claims this is “the largest green stormwater infrastructure program ever envisioned in this country”. While green infrastructure has been utilized and proven in many parts of the country, the sheer magnitude and commitment of the city is a radical departure from the conventional approach to stormwater management practices.

Map of Green Street Locations
(Source:“Green Cities Clean Waters” Plan)

So why did Philadelphia decide to rely so heavily on green infrastructure as a means of reducing overflows in their CSO system? Quite simply it was cheaper, significantly cheaper. The plan estimates over the next 20 years the plan is to be implemented, the “triple bottom line” benefits (social, environments, economic) of the plan alone will add up to a present value of $2.2 billion dollars. The following is a breakdown of the benefits that comprise this figure.

  • Heat Stress Mortality Reduction (35%)
  • Recreation (22%)
  • Property Value Added (18%)
  • Water Quality and Habitat (14.5%)
  • Air Quality (4.6%)
  • Avoided Social Costs from Green Jobs (3.7%)
  • Energy Savings (1.0%)
  • Carbon Footprint Reduction (0.6%)
  • Reduction in Construction- Related Disruptions (0.2%)

So instead of employing conventional underground infrastructure that is one-dimensional, and is estimated to cost $16 billion, the city has decided that implementing a multi-dimensional strategy with multiple benefits made more sense. But not only is it more desirable, it is politically easier to implement because it makes the city a more beautiful and healthy place. So if you are going to have to spend the money anyway, why not make it count.

The shortcomings of the conventional “tanks and tunnels” approach were not only that it exceeded the EPA’s affordability standard for stormwater management (2% of median household income), but it also did not address water quality issues and could require green infrastructure tools anyway to meet these requirements. In addition, the report points out that the conventional solution isn’t aligned with the EPA’s broader goals of sustainability, reduces streams baseflow thereby damaging the resources that is designed to protect, and doesn’t offer any secondary triple bottom line benefits. Furthermore, since the conventional solution is not delivered incrementally it is not flexible and does not offer any benefits immediately.

Green infrastructure on the other hand offered the city the opportunity to revitalize and restore the city’s streams and rivers, enhance the quality of the built environment throughout the city, improve air quality, reduce the heat island effect, and sequester carbon. While accumulating these benefits, the approach was more flexible, offered immediate benefits, and, most importantly, the cost of implementation was offset by the dollar value of the benefits. (see Volume 2: Triple Bottom Line Analysis of the plan for specifics)

While conventional infrastructure has its place, the combination of the two can play a significant role in addressing many of the issues facing our cities. It is critical that we continue to move toward making these strategies common place. By doing so we can make our cities healthier and more beautiful for all of us to enjoy, while at the same time responsibly managing our stormwater.

-Brian Phelps


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Categories : Bioretention, Green roof, Green Street, Pervious Pavement, Sustainable Site Strategies

Green Roofs Address D.C.’s Environmental Problems

30 10 2009

asla green roofPhoto Source: ASLA

It has been three years since the American Society of Landscape Architects (ASLA) finished the 3,000sf green roof on top of the their headquarters building in Washington D.C. The green roof is unusual in that it is sloped to cover the mechanical units on the roof. An informative video (link to video) was posted on Youtube this month highlighting the stormwater benefits of the ASLA roof. Nancy Somerville, ASLA’s CEO was interviewed during the video and she stressed the important role green roofs could play in helping address Washington D.C.’s and the nation’s difficult stormwater issues (i.e. water pollution, Combined Sewer Overflows). An EPA report estimated 850 billion gallons of untreated sewage and stormwater are discharged nationally each year as combined sewer overflows. (EPA Fact Sheet [pdf]) As Ms. Somerville points out, green roofs can filter the stormwater falling on the roof as well as act as a sponge and significantly reduce the amount of stormwater coming off of the roof. A green roof with 4″ deep planting media has been shown to retain 63% of the rain fall hitting the roof.

During the first year, ASLA conducted a study (link to ASLA green roof website) to quantify the specific benefits of the their green roof. The data showed that 74% of the water was retained on the roof. Interestingly, the water quality of the stormwater discharge leaving the roof included an increase in pH and temperature as compared to the rain fall. In addition, the test results showed a significant increase over the concentration originally present in rain water for Chemical Oxygen Demand (COD), phosphate, total phosphorus, total suspended solids, and total dissolved solids. According to the report most of these contaminants were within the allowed freshwater chronic concentration values established by the E.P.A. and none of the concentrations were above the acute level. Unfortunately, the study did not compare the green roof with a conventional roof. The report concluded that “Green roofs have significant potential for reducing stormwater carried pollutants in major metropolitan areas such as Washington DC. However, more comprehensive and extensive monitoring studies are needed to evaluate specific performance measures of specific designs and develop accurate predictive tools.” The following are a few specific findings highlighted in their press release (.doc):

  • The roof typically retained 100 percent of a one-inch rainfall.
  • The heaviest rainfall during the monitored period was March 16, 2007. A total of 2.48 inches of rain fell during the 24-hour period with the roof retaining 51 percent, the equivalent of 1.3 inches of rain.
  • The green roof did not add any nitrogen to the runoff. Because of the amount of water retained, the roof provided a significant reduction in the amount of nitrogen introduced back into the watershed.
  • Typical of “young” green roofs, the analysis showed higher amounts of some other nutrients such as phosphorus, as well as heavy metals in the runoff—all below EPA standards and below levels expected from street runoff. Based on other green roof research, nutrient levels are expected to decrease in a few years. The heavy metals may be coming from the roof materials or from settled particulate matter/pollutants.
  • It is important to note that this study did not look at runoff from a conventional roof compared to the green roof runoff—and the results would be expected to look different. Water quality testing will be repeated in two years to see how the results change over time with a goal of comparing the green roof runoff to conventional roof runoff.
  • The green roof has been as much as 32 degrees cooler than conventional black roofs on neighboring buildings.
  • Engineering analysis showed that the green roof created a 10 percent reduction in building energy use during winter months and negligible difference in the summer.

On a city wide level, the Casey Tree, a non-profit dedicated to restoring, enhancing and protecting the tree canopy of the Nation’s Capital, conducted a study (link to study) of the Washington D.C. area that examined the impact of green roofs and tree plantings. They concluded that if 55 million square feet of green roofs were installed throughout the Washington D.C. area, they would reduce the reduce CSO discharges by 435 million gallons or 19% each year.

These studies illustrate the effectiveness of including green infrastructure within the overall strategy for cleaning up our nation’s stormwater.

-Brian Phelps


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