Sustainability History Project

[This post was written by Michael Aitchison, Donovan Jackson, and Stephanie McCarthy. The post is in response to our tour of the Jean Vollum Natural Capital Center and complements previous students’ analysis of the question What is Sustainability?]

Jean Vollum Natural Capital Center

On June 30, 2011 our class conducted a self-guided of the Jean Vollum Natural Capital Center, also known as the Ecotrust Building, located at 721 NW 9th Avenue, in Portland. One of the building’s many ecofriendly features is its ecoroof. Unfortunately, we were unable to view the roof, but the information in our field guide piqued our interest. Ecoroofs are not only beautiful to look at but they also make real environmental and economic sense. Ecoroofs greatly extend the lifespan of a roof, reduce stormwater runoff, and also reduce energy consumption by decreasing rooftop heat loss. The vegetation planted on the ecoroof at the Jean Vollum Natural Capital Center was carefully selected from Pacific Northwest native plants and seeds. These native plants, a mix of grasses, wildflowers, and succulents, are drought tolerant and once established need very little watering and maintenance. The ecoroof is part of the sites stormwater management system that helps to minimize rainwater runoff, including pollutants and sediment, from flowing into the Willamette River. This stormwater system, which also includes bioswales, captures at least 90% of the rainwater falling at this location. The system is funded in part by the City of Portland’s Bureau of Environmental Services.

What is a green roof?

Green Roofs should probably be referred to more appropriately as eco-roofs as many are not “green” at all. To start this particular discussion it’s useful to run through a few items:

There are two generally accepted terms used to classify these roof systems

1. Intensive Roofs can support a complex variety of planting species and is characterized as having the need for additional structural support elements and a substrate depth of 20 cm (7.87 inches) or greater. These roofs often require irrigation support.

2. Extensive Roofs are generally planted with low growing, stress tolerant vegetation that requires little if any irrigation support. Characterized by the lack of addition support structure and substrate depths of less then 20 cm (7.87 inches).

However, other systems have been used to achieve some of the same end results that are not green at all, such as small pools and other water features. So it seems that the characterization of intended uses are more the determining factor. If you are creating a space such as a park or other recreational purposes than an intensive roof is going to probably be your best design selection. However if your looking to achieve some of the positive benefits but not create a habitat for human recreation than one might consider a more economically based solution of an extensive roof design.

What are the advantages?

The eco-roofs can have various advantages and we will attempt to list them with a brief explanation below:

• Reduction of the Heat Island Effect. Primarily the aspect in consideration is the ability for a rooftop to maintain some moisture content whether in pools of water, or moisture content in soils. This creates a heat sink during hot days and allows for passive work of solar energy to create vapor thus actually cooling the regional airspace.

• Reduction of impervious water run-off—a two fold prospect:

• In an area such as Portland, OR where the sewer and rain drain systems are not separated the increased water flow created by the impervious surface run-offs can overload our system causing the unwanted actions of deliberate dumping of untreated sewage directly into the river.

• In areas where system separation is in place there are still imposed harms done in areas of large urbanization where impervious surfaces cause higher levels of nitrogen and phosphorus. This is then carried to the streams and causes unwanted effects from urbanization commonly referred to as urban stream syndrome.

So why aren’t we doing this on every roof?

While there are certainly benefits to the use of said systems there are still many unknowns. Culturally we are a bit more aware of unintended consequences, and while we have studied the benefits, quantitative research of negative effects has not yet been completed. In places such as Switzerland and Germany where governance has been progressive in establishing required uses for such systems, they may have also been negligent in respect to establishing building code requirements, as there are still undetermined variables to be determined.

Some recent research one of us learned about at a PSU seminar on green roofs suggested that the micro-ecosystems varied by changes in substrate depths as little as 0.65 cm (1/4 inch). If confirmed than we could be looking a wide realm of impact possibilities not previously considered.

The study of topographical effects should also be considered as a factor as deviation from the natural surroundings could again cause unwanted or unpredicted influences. Further the couple between causes could manifest into larger upsets in the otherwise natural balance. One need not think back far to recall instances in our own culture both of agriculture and industrial to see the devastating effects of understudied breakthroughs in technology and materials.

Locality as well influences in implementation where the applicability of extensive roof designs are not practical in the southern hemisphere and thus create the need for the use of already short supply of potable water resources.

Ecoroofs at Portland State University

Upon further research, we discovered that Portland State University is home to five ecoroofs, including the largest ecoroof in Portland, located on the Broadway Housing Building (certified LEED Silver), which features an impressive 18,000 sq. ft. ecoroof. Another magnificent ecoroof is located on The Native American Student Center. The building highlights native plants on its rooftop gardens. There are also small ecoroofs located on Portland State University’s Natural Buildings. Two of these small ecoroofs can be found on Cob Oven, a community gathering space, and on a PSU informational kiosk between Smith Hall and Neuberger Hall. In 2005 PSU was awarded the BEST Award for the Broadway Housing Building’s ecoroof. Visit sustainability@pdx.edu to take a self-guided Sustainability Tour to see how and where PSU is incorporating sustainability into campus operations.

Sources:

Ecotrust. www.ecotrust.org (Accessed July 2011)
Sustainability at PSU. sustainability@pdx.edu (Accessed July2011)

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