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Extensive Green Roof Project
Transcript of Extensive Green Roof Project
“If our aim is to build low-maintenance green roofs, we must imitate natural ecosystems,”- Sergio Andri
What type of green roof are you planning? What is the substrate involved? What types of plants will you be using? Why is this type suited for this building?
Explain the purpose of the green roof and its benefits.
The Purpose of Green Roof is to increase energy efficiency by reducing temperatures and offering insulation. The benefits of a green roof include: being aesthetically pleasing, energy reduction (insulates and cools), increase in market value of the building, ability to earn up to 34 LEED certification points, a reduction of the urban heat island effect, reduced air pollution, saved cost (especially for extensive because it is low maintenance), helping with storm water management by delaying run-off and allowing for evaporation, and financial incentives (tax breaks, Better Building Challenge, Green Building Incentives).
Discussion of the environmental benefits of a green roof.
The cost-effectiveness of an extensive green roof.
How much does a typical extensive green roof costs?
Installation cost: an average of $10.00 per square foot, and for the Buhl Hall roof above the Atrium it costs about $1,080.
Maintenance cost: $0.75- $1.50 per square foot, and for the Buhl Hall it costs about $80 - $160.
How much upkeep is involved?
We are planning to build an extensive green roof on top of Buhl.
We believe that it is best to begin by creating a green roof that is relatively simple and low-cost. Intensive green roofs are basically parks that are built on the tops of buildings. The depth of the planting mediums for intensive green roofs range from 6 inches to a couple of feet. These roofs are planted with grasses, flowers, shrubs, and even trees, and they often include walking path and benches to encourage people to spend time on the roof and interact with the plants. These roofs can weigh as much as 150 pounds per square foot. In contrast, extensive green roofs are designed with much simpler plants and do not require the planting mediums to be very deep. They also much more light-weight.
Layers of an Extensive Green Roof
The bottom layer of the roof is the membrane, which separates the green roof from the structural support beneath it. The membrane must be strong to keep water from seeping through.
The layer above the membrane is the membrane protection, and this can be made of lightweight concrete, insulation, thick plastic, or copper foil. This layer is important in preventing the deterioration of the membrane layer.
The next layer is the insulation layer, whose function is protecting everything below it, especially the membrane, from being damaged by the weight of the green roof.
A drainage layer will exist above the insulation. The purpose of the drainage layer is to adequately remove excess water from the green roof.
The fifth layer consists of the growing medium. For extensive green roofs, this layer will be between 1.6 inches and 6 inches. Because of the plants that will be grown on the top layer, succulents and grasses, the soil needs to be a little less rich than a regular planting soil. The right mix is about 50% compost combined with humus and perlite and some sand.
The top layer is the vegetation layer.
Types of Plants Growing on Green Roof
-These plants have parts that are thick and fleshy to help retain water. They are very good at storing water.
Why is an extensive green roof a good option?
Extensive roofs are a good option for an existing building because the fact that they are lightweight means that there does not need to be a lot of structural changes made to the building. Extensive roofs only add between 10 and 35 pounds per square foot to a roof's load. Still, the design gives high performance to water use and thermal advantage. Extensive green roofs are the simplest to install, and at a base cost of $10 per square foot, they are significantly cheaper than other forms of green roofs. Extensive roofs also require less maintenance than other green roofs, so those who would be in charge of maintaining the roof on top of Buhl would not have to check on the plants frequently.
Traditional Roof Maintenance
- Inspection for Drainage
- Inspection for Leaks
- Inspection for Damage
Green Roof Maintenance
Green roofs can contribute to the reduction of what’s put in our landfills in several ways. One of which is in the use of recycled materials in construction. Composted materials can also be applied to the vegetation on the green roof. Green roofs also prolong the service life of ventilation, HVAC, and air cooling/heating systems through decreased usage and therefore prevent how often such machinery is thrown away or, ideally, recycled for parts. Also the presence of a green roof decreases the exposure of waterproofing membranes to large temperature fluctuations that can cause micro tearing and the need for replacing your roof. Micro tearing that goes untreated will lead to water damage and therefore structural issues.
Long Term Green Roof Maintenance
- Re-Waterproofing Membrane
In addition to traditional roof maintenance
Improved Water Quality
With green roofs, water is stored by the substrate and then taken up by the plants from where it is returned to the atmosphere through transpiration and evaporation, which keeps the water from flooding the surrounding area in times of heavy storms. The roofing not only reduces the amount of storm water runoff, but also delays the time at which runoff occurs, resulting in decreased stress on sewer systems at the peaks of rainy seasons—good for use in cities such as Pittsburgh. In summer, depending on the plants and depth of growing medium, green roofs retain 70-90% of the precipitation that falls on them; in winter they retain between 25-40%. Green roofs; however, not only retain rainwater, but also moderate the temperature of the water and act as natural filters for any of the water that happens to run off working like a constructed wetland. Depending on the thickness of the various layers of the roof garden, a green roof is able to filter out heavy metals and nutrients present in rainwater. This advantage would be beneficial in urban areas where precipitation is collected for domestic usage in addition to treated potable water supply from the utility provider (there are several water treatment facilities within Allegheny county and close to the Pittsburgh area).
Moderation of Urban Heat Island Effect
The Urban Heat Island effect is caused by the absorption and retention of solar heat in buildings in highly urbanized cities resulting in the air temperature in such areas becoming significantly warmer than in the rural areas. This higher temperature means that the buildings in the city will need to increase the air-conditioning load and therefore uses more energy than otherwise would. This in turns discharges warm exhaust air from the air-conditioners into the outdoor air thus the cycle continues. On a macro level, the increase in energy consumption means that more fossilized fuel will be used to generate the extra electricity and this increases the emission of greenhouse gases and other pollutants, which directly impacts the issue of global warming and higher pollution level. The use of roof gardens has been proven to lower the surface temperature by as much as 86°F. These reductions in temperature are due mainly to the shading of the heat absorbing roof surfaces as well as through the daily dew and evaporation cycle, plants on vertical and horizontal surfaces are able to cool cities during hot summer months and reduce the Urban Heat Island effect. Green roofs provide shade and remove heat from the air through evaporation, reducing temperatures of the roof surface and the surrounding air. On hot summer days, the surface temperature of a green roof can be cooler than the air temperature, whereas the surface of a conventional rooftop can be up to 90°F warmer. The light absorbed by vegetation would otherwise be converted into heat energy. UHI is also mitigated by the covering some of the hottest surfaces in the urban environment (black tar rooftops).
Improved Air Quality
The plants on green roofs can capture airborne pollutants and atmospheric deposition and filter noxious gases. The temperature moderating effects of green roofs can also reduce demand on power plants, and potentially decrease the amount of CO2 and other polluting by-products being released into the air from the high population of vehicles within cities. Green roofs can also help reduce the distribution of dust and particulate matter throughout the city. A higher temperature at roof level tends to create a thermal draft drawing up dust particles from street level. Roof greening has been found to be effective in moderating the thermal draft by reducing the temperature differences between rooftop and street level and subsequently the traveling of dust particles. As well, this roofing system reduces the production of smog, as it is highly sensitive to air temperatures—the higher the temperature, the greater the concentration of smog; the lower the temperature the cleaner the air. This can play a role in reducing greenhouse gas emissions and adapting urban areas to a future climate with warmer summers. As well green roofs have a substantial thermal mass and so can provide moderate insulation. This means that air conditioning usage can be significantly reduced, thus reducing carbon dioxide emissions. A good example of energy saving remains Paradise Park in London. Due to the thermal mass of the green roof, no air conditioning was installed during construction. This has led to a reduction of 3,800 kilowatts per hour and prevented some 1.6 tons of CO2 from being emitted into the atmosphere. It is important to note; however, that these calculation were complied during the summer months. Heavy amounts of snow, for example experienced in London (and Pittsburgh), affect the insulation created by the thermal mass as its effectiveness varies depending on how wet the roof is. As well the plants on the roof themselves, through the process of photosynthesis, can absorb and diminish carbon dioxide; however, not to the same scale as cutting back the use of air conditioning. Vegetation can also remove air pollutants and greenhouse gas emissions through dry deposition and carbon sequestration and storage.
The greater insulation offered by green roofs can reduce the amount of energy needed to moderate the temperature of a building, as roofs are the sight of the greatest heat loss in the winter and the hottest temperatures in the summer. By lowering air conditioning demand, green roofs can decrease the production of associated air pollution and greenhouse gas emissions. For example, research published by the National Research Council of Canada found that an extensive green roof reduced the daily energy demand for air conditioning in the summer by over 75%. As well green roofs work well with solar panels, as they increase their efficiency by regulating temperatures—something already employed here at Chatham to reduce dependency on fossil fuels.
Water's Edge at the Pittsburgh Zoo & PPG Aquarium (its the tiger shark, sea otter, and polar bear exhibit)
Green roofs can sustain a variety of plants and species, acting as a habitat for various species of bird and insect especially if you include nest boxes, logs and water features, and plant native species. Research in London and Basel has shown that well-designed extensive green roofs can provide an important refuge for rare invertebrates associated with brownfield sites*. By acting as a “stepping stone” habitat for migrating species they can link species together that would otherwise be fragmented and allow ecosystems to better maintain high levels of productivity during periods of environmental variation. In Pittsburgh, green roofs could be hosts to various local creatures.
*A brownfield site is land previously used for industrial purposes or some uses left undeveloped, yet not entirely reclaimed by the wilderness.
‘Summers by 2050 will be 34-39 degrees (Fahrenheit) hotter. The Tyndall Centre for Climate Change has found that an urban area will need to increase the amount of vegetation by 10 percent to combat climate change. In the majority of cities there is limited space at ground level for vegetation and soil, so green roofs are an ideal solution. It is expected that rainfall patterns will change, leading to more short intensive rainfall events, especially in summer. This will lead to an increase in local flash flooding – green roofs can help reduce this.
Adapting To Climate Change
Using green roofs as the site for an urban agriculture project can reduce a community’s urban footprint through the creation of a local food system as well as creating an example in a community for a more environmentally friendly way of living. These projects can serve as a source of community empowerment, give increased feelings of self-reliance, and improve levels of nutrition.
Thank you, Colleen!
Thank you, Colleen!
Have a good Holiday!
Is there any short-term incentive for installing the extensive green roof?
The federal Energy Policy Act of 2005 allowed a tax credits up to $1.80 per square feet for green building projects that meet ASHRAE standards.
The ASHRAE standards regarding green roof has regulations for the types of vegetation, R-values for high mass walls, planting medium, filter layer, drain layer, vapor restrictions, and irrigation requirements,
How long will it take to see the return on the investment?
It takes about 15 to 25 years for the extensive green roof, and the payback period is becoming shorter and shorter through improved techniques and maintenance.