1. To Green Roof Or Not To Green Roof?
Luis Noboa
Environmental Economics
ECON 2505
Prof. Sean P. MacDonald
05/17/2017
What is a green roof ? To put simply, it’s just a rooftop covered in vegetation.

2. History of Green Roofs 500 BC Hanging Gardens of Babylon
1 of the Seven Wonders of the Ancient World.
Real or Myth?
1914, Moos Water Filtration Plant, Zurich
Oldest recorded green roof structure
9 acres of green roof meadows
2013: 20 million square feet installed
2012, 18 million square feet installed
2011, 15 million square feet installed
U.S Coat Guard headquarters in Washington D.C

3. Types of Green Roofs Extensive Intensive Inaccessible
Light weight: lbs/sq. ft
Soil Depth Under 6”
No irrigation
Limited plant options
Less expensive to maintain
Accessible
Heavy weight: up to 150 lbs/sq ft.
Soil Depth Over 6”
Regular irrigation
More plant options: Trees and Shrubs
More expensive to maintain
Intensive green roofs have a much thicker substrate layer in order to accommodate the heavier, higher maintenance plants involved. Trees and shrub-like plants are commonly used and the depth of the substrate often exceeds 1 foot.
This system often requires the installation of artificial irrigation. The depth of the foundation and plant weight bears a much heavier load upon the structure below and therefore must be design accordingly. Though this type of system is higher maintenance, it is the system that is capable of being utilized as a space for public recreation because the building and system is designed to bear the additional weight.
An extensive green roof has a relatively shallow substrate, typically 2-4 inches in depth and the type of plants incorporated grow low and wide, often having broad leaves. Moss and grasses are commonly used as well.
They are designed to be virtually maintenance free. By using hardy plants that can withstand harsh weather conditions ranging from extreme drought, to harsh winds and ice, the system requires only minimal attention.
Another important characteristic of an extensive roof is that the weight in which one bears upon the structure below is minimal. This, in addition to low maintenance and low cost is mainly the reason for its popularity in comparison to the other type, intensive.

4. Anatomy of a Green Roof
Now that you are familiar with the 2 types of systems, I’m going to cover the main functional layers of a green roof. This diagram illustrates the six basic components, and any additionally layer is optional depending on the manufacturer, who is constructing or what type of system is being implemented.
1) Plants (chosen depending on aesthetic desire and/or system types and what is desired to be achieve through their use. Plants have unique qualities)
2) A specially engineered mixture of soil, minerals and nutrients.
3) A filter layer that contains roots and soil.
4) Drainage layer that sometimes has a built in reservoir (water retained can for example be used for watering a yard or for plumbing)
5) Water proofing membrane with a root repellant.
6) Original roof structural material, or what is referred to as the roof deck.

5. Benefits of Green Roofs
Public
Private
Stormwater Management
Increased Biodiversity
Reduction in urban heat island effect
Improved air quality
Waste Diversion
Energy Efficiency
Noise Reduction
Local Job Creation
Tax Incentives
Aesthetics
Energy Efficiency
Increased roof durability
Increase Property Value
Fire Retardation
Reduction of Electromagnetic Radiation
Noise Reduction
Phipps Conservatory, pitssburg. Thus reducing thea mount of stormwater runoff, and delaying the time at which runoffs occur, resulting in decreased stress on sewer systems.
Heat island effect
Green roofs can sustain a variety of plants. This allows high productivity in various season. Also, by having different types of plants and inverterbrates it can provide a habitat for various species of bird. In fact, Jacob Javits center was once the leading killers of birds, ovrer 500 birds a year would smash into the glass walls. Now, after their green roo0f renovations they have 500 bird sigting during the spring and summer that are nesting on the roof.

6. The Not So Good Of Green Roofs
Expensive
$15 to $20 per square feet
$1.20 to $4 per sq ft for Asphalt
Increase in weight load
Requires infrastructure
Extra maintenance
Upkeep, and inspections
City University in Hong Kong June 2016

7. To Green Roof or Not To Green Roof?
The University of Michigan, for instance, compared the expected costs of conventional roofs with the cost of a 21,000-square-foot green roof and all of its benefits, such as stormwater management and improved public health from the absorption of nitrogen oxides. The university found that the green roof would cost $464,000 to install versus $335,000 for a conventional roof in 2006 dollars. Over its lifetime, though, the green roof would save about $200,000. Nearly two-thirds of the savings come from reduced energy needs for the building below it.
As energy prices increase, the energy-related savings also will increase.
The larger the surface area, the greater the stormwater management savings.
Econmy of scale. The more implementation would bring down the costs of green roofs. The larger the surface area the cheaper the sq ft
Government policy.
90% less air conditioning time
The cost-benefit calculations hint that with a higher rate of implementation and realization of public benefits, the green roofs would be a good investment. However, because the private benefits are not high enough to justify a green roof installation for a private decision maker, the rate of implementation can be expected to stay low without corrective policy instruments. Policy instruments could include supportive policies that add incentives for private decision makers to install green roofs, such as storm-water fee reductions (already a reality in Vaasa) or real estate tax abatements.

8. References
Green Roofs for Healthy Cities. (2012). About Green Roofs. Retrieved April 12, 2017, from General Services Administration (2011, May). The Benefits and Challenges of Green Roofs on Public and Commercial Buildings (Publication). Retrieved April 10, 2017, from United States GSA website: ic_and_Commercial_Buildings.action EVSTUDIO. (2014, April 24). Green Roofs – Drawbacks and Benefits. Retrieved April 09, from Green Roofs for Healthy cities. (2015). Green Roofs for Healthy Cities. Retrieved May 01, 2017, from Taylor, M. (2015, May 22). What a Green Roof Costs You on the Way to Saving Everything. Retrieved May 05, 2017, from thestreet.com: saving-everything.html