Why Green Roofs
Keeping the Mississippi Mighty: Mississippi River corridor pollution is mostly attributed to storm runoff, making stormwater management an important issue for downtown Minneapolis.
In Open, Green Areas: Stormwater is absorbed and filtered by the ground. In Urban Areas:
- Rain falls only on hard surfaces such as concrete and buildings and can only run into storm sewers. That water goes straight into the river, which negatively affects river water and pollution levels.
- Over time, the riverbanks become unstable and it’s hard for plants to grow there. Banks begin to collapse into the river.
- Rain that falls on a green roof soaks into the “ground” where it falls. The green roof helps filter out pollutants in the rain and air.
7 Key Water Quality Issues/Pollutants Prevented by Green Roofs
- Excess Peak Runoff Volume
- Suspended Solids
Saving Operating Costs
Lower Energy Costs: The insulation provided by a green roof reduces energy costs for heating and cooling.
Longer Roof Life: Soil and plants protect the roof from ultraviolet radiation and extreme temperatures, which can double or triple the life of the roof.
Urban Wildlife: Green rooftops provide habitat for beneficial birds, butterflies, spiders and beetles. Endangered species have even been found to live on green roofs.
Climate Control: Green rooftops can be much cooler than standard roofs. On a 90-degree day, temperatures reached:
- 170 degrees on a typical black roof
- 145 degrees on gravel ballast
- 125 degrees on a white reflective roof; and
- Only 92 on the green roof – just 2 degrees warmer than the ambient temperature
Improves urban air quality-reduces dust and smog levels
Lessens urban heat island effect
Provides sound insulation
Improves aesthetics which produces psychological benefits
Green roofs are most beneficial for volume and rate control in areas with precipitation patterns like those found in Minneapolis:
- Low annual precipitation
- Short, high intensity storms (i.e. cloudbursts) that occur during dry weather periods
Green Roofs support up to 8 LEED-NC credits :
LEED Credit Categories
- Sustainable Sites – 3 out of 14 possible credits
- Water Efficiency – 1 out of 5 possible credits
- Energy & Atmosphere – 1 of 17 possible credits
- Materials & resources – 2 of 13 possible credits
- Indoor Environmental Quality – 0 of the 15 possible credits
- Innovation & Design Process – 1 of 5 possible credits
*The LEED Green Building Rating System™, developed by the USGBC, is the only nationally recognized green building rating system. LEED evaluates the performance of buildings from a “whole building” perspective, over the course of a building’s lifecycle, which provides a definitive standard for what constitutes a green building.
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