Economic Benefits of a Green Roof

Some of the Economic Benefits of a Green Roof:

Increases the Life Expectancy of the roofing system to 40 yrs or more

• Reduces the weathering/damage from extreme heat and freezing
• Reduces the UV exposure and degradation
• Reduces the stress from expansion/contraction in the building

Lowers the Surface Temperature of the Roof by 70 degrees

Conventional roofs store radiation from the sun and re-radiate it back into the atmosphere as heat.  But plants convert that radiation through photosynthesis and evapotranspiration into biologically useful energy, and don’t store it as heat. So, rather than being a blistering 170 degrees on a hot summer day, the green roof temperature will be about the same as the ambient air temperature.  (see attached drawings illustrating Urban Heat Island Effect)

Improves Air Quality at the Outside Air Intakes

Because of the plant growth on the roof, makeup air inside the building contains more oxygen and less carbon dioxide than air taken off a convention, hard surfaced roof.  (see illustrations)

Reduces the Energy Used for Air Conditioning by 75%

In a study done at the Field Roof Facility in Ottawa, a roof was divided equally, and one part was covered with an extensive green roof, while the other remained a standard modified bitumen membrane.  The green roof showed a decrease in daily energy demand for air conditioning of over 70%.  (see graph sheet)

Increases the Efficiency of AC Systems in Hot Weather

HVAC systems are designed to be most efficient when air temperatures at the Outside Air intakes are 90 degrees or less.  Since OA intakes are generally only about 30” above the roof surface, the temperature of the intake air is directly related to the surface temperature of the roof.  Studies have shown that when the intake air temperature reaches 115 degrees, the energy required to cool the coils rises by 12%, and the cooling capacity of the system drops by 10%.  In summer, conventional roof surface temperatures in Georgia regularly reach 170 degrees.

Reduces Stormwater Runoff Quantity while Improving Quality

85% of the first 1” of rainfall is retained by a Green Roof, and all the runoff is filtered for pollutants such as rainwater pollutants and roof surface contaminants.