Best Practice Guide

Local Governments

Introduction

Planning an Energy Program

Funding and Approval

Education

Lighting

Central HVAC System

Procurement Policy

Building Envelope

Commissioning

Office Buildings

Cool Roofs

Demand Response

Distributed Generation

Water Use

Motors

Food Service

Resources and Appendices

Lessons Learned


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Building Envelope

Cool Roofs

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Cool roofs are roofs with special coatings or surfaces that reflect heat. While this seems simple in concept, the cooling benefits can be quite dramatic. Consider that dark surfaces in the sun are up to 70ºF hotter than white ones - this means that when normal rooftop temperatures are peaking at 190ºF during the hot summer months, cool roofs only reach about 120ºF. The ability of your rooftop to reflect solar radiation and reduce surface temperatures is related to how hard cooling equipment needs to work to condition indoor spaces.

Besides lowering HVAC operating costs, cool roofs help others in the local community. In cities, building rooftops and paved surfaces collectively create urban heat islands. Researchers at Lawrence Berkeley National Laboratories and the U.S. EPA have found that these heat islands raise outdoor temperatures 6 to 8ºF above surrounding areas, which can lead to a higher incidence of smog.

Cool roofs make sense when:

  • A building has high air conditioning loads and/or is located in a hot, sunny climate.
  • The roof has a large surface area as compared to the overall building size.
  • Re-roofing or other roof maintenance is scheduled as part of routine operations and maintenance.
  • Constructing a new building.
  • Installation is part of a wider effort to reduce cooling loads; cool roofs and good insulation levels go hand in hand.

Cool roofs are most effective during the hottest part of the day and the hottest time of year, coinciding with peak energy demand. By allowing you to turn down the HVAC - without sacrificing the comfort of employees or tenants - cool roofs reduce energy costs while ensuring that California has reliable energy during the critical summer months.

Remember that a cool roof is only one surface, and that any rooftop retrofit should be part of a wider effort to improve insulation of the building envelope. Installing proper levels of insulation provides year round benefits by preventing heat gain in the summer and blocking cold air infiltration in the winter.

Most Californian properties will benefit from the savings resulting from cool roofs. However, in a few regions, additional winter heating costs may outweigh summer benefits. This is especially true for mild climates with cool, cloudy summers, like San Francisco.

Temperature, Energy and Smog

Temperature, Energy and Smog

Temperature affects energy in a few important ways. First and foremost, high temperatures cause people to turn on their air conditioners, one of the most intensive uses of energy in home or office. Peak use of air conditioners contributes to peak energy demand in California, the time when higher energy surcharges and shortages are likely to occur.


Temperature also affects pollution in urban areas. All other things being equal, the higher the temperature, the worse the air quality is. Pollution is like a chemical stew that changes as temperatures rise. In Los Angeles, for example, pollution rises by three percent for every degree increase above 70ºF. One study conducted by the Lawrence Berkeley National Laboratory suggested that if all buildings in L.A. had cool roofs, the total savings from reductions in energy use and pollution prevention would reach about $500 million per year.

Cool Roof Calculator

Cool Roof Calculator

The Department of Energy has developed a useful calculator for small- and medium-size businesses that estimates annual cost savings resulting from the installation of a cool roof. The calculator provides information based on location (climate, average temperatures), including 10 urban areas in California.


Resources

Flex Your Power Product Guide Cool Roofs.

Lawrence Berkeley National Laboratory, Heat Island Group, Cool Roof information.

U.S. Environmental Protection Agency, Heat Island Reduction Initiative,Cooling Summertime Temperatures: Strategies to Reduce Urban Heat Islands.

California Energy Commission, Information on Cool Roof Information.

The Cool Roof Rating Council provides accurate radiative property data on roof surfaces.