Energy Savings From Cool Roofs

How Much Energy Can Cool Roofs Save?

In-field monitoring of over 10 buildings in California and Florida demonstrates that cool roofs save residents and building owners between 20-70% in annual cooling energy use.

These year-round energy savings are calculated by comparing decreased summertime costs (from lowered air conditioning demand) with any observed increases in wintertime heating expenditures. The results of research studies indicate that in most US climates summertime air-conditioning energy savings significantly exceed this winter penalty.

Researchers have determined that the penalty is usually of little consequence because winter days are short and the sun is low in the sky. These factors cause a proportionately small quantity of solar radiation to strike the rooftop, causing minimal heat loss.

What Factors Affect the Amount of Energy a Cool Roof Will Save?

Determining whether a cool roof will result in annual energy savings requires a careful consideration of the following factors:

• Air conditioning must be present to save cooling energy. While comfort in an un-air conditioned building can be improved with a cool roof, no energy savings are achieved.
• The higher the level of roof insulation, the less effective a cool roof will be at reducing the air conditioning load of a building. Therefore, cool roofs save more energy when installed on buildings with little roof insulation.
• Buildings with an attic radiant barrier have already minimized the ability of heat to transfer through the roof. This greatly reduces the energy-saving potential of cool roofs.
• A high level of attic ventilation brings the attic temperature closer to the outside temperature. Buildings with low ventilation will see greater benefit from a reflective roof.
• Considerations of climate and geographic location also affect energy savings. This is discussed at greater length below.

For more information on reflective roofs, go to the cool roofs section of this website or visit EPA's ENERGY STAR Roof Products site.

Results of UHIPP 11-City Energy Savings Study

LBNL also conducted an analysis of energy savings (from cool roofs only) in 11 metro areas. City-wide results are shown in 1993 dollars. In the City of Chicago, for example, LBNL estimated savings of approximately $10 million for a high rate of cool roof implementation over the metropolitan statistical area.

More information on heat island reduction in Chicago is available in the Research and Implementation section of this site.

What are Some Examples of How States and Localities are Saving Energy From Cool Roofs?

• California has implemented the Cool Savings Program providing a rebate for construction with reflective roofing materials. The program goal is a peak electricity demand savings of approximately 62 MW at an overall cost of $24.5 million (or $395/kW). Information about the Program is available through the California Energy Commission (CEC).
• The City of Chicago's energy codeincludes a standard requiring light-colored roofs on certain categories of buildings to reduce urban heat island effect.
• Georgia instituted the "Georgia White Roof Amendment" altering its energy code. The Amendment goes beyond a 1994 congressional provision (which requires ASHRAE 90.1 energy efficiency standards) by mandating the use of additional insulation for roofing systems that do not achieve 75% solar reflectivity and emissivity.