Best Practice Guide

Commercial Office Buildings

Introduction

Planning an Energy Program

Funding and Approval

Lighting

Building Envelope

Cool Roofs

Office Buildings

Central HVAC System

Distributed Generation

Demand Response

Commissioning

Procurement Policy

Water Use

Education

Energy Efficiency in Telecommuting

Resources and Appendices

Lessons Learned


Adobe Systems Incorporated and Cushman & Wakefield

Arden Realty and next>edge

Cypress Semiconductor

Equity Office Properties

Glenborough Realty Trust

Natural Resources Defense Council

Qualcomm

Swinerton, Inc.

Transwestern Commercial Services


View the Glossary

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.

Urban Heat Island Profile, courtesy of U.S. EPA.View Details.


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. 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.

Business Examples

The Natural Resources Defense Council applied TOPCOAT MB Plus, a water-based, sprayable liquid membrane coating that has an emissivity rating of 0.95, to their 1917 retrofitted office in Santa Monica. The cool roof reflects nearly 100 percent of solar radiation hitting the rooftop. The cool roof shares real estate with photovoltaic panels, native plants and overhangs that provide shade, further reducing solar heat from radiating into interior spaces.

Swinerton, Incorporated, explored dozens of ENERGY STAR-certified roofs for high albedo (i.e., reflectance) and low emissivity (i.e., radiation) to lower indoor temperatures and reduce the urban heat island effect, but none met its high-traffic resistance criteria. Swinerton convinced 3M Company, maker of an elastomeric roofing product, to add a white, high albedo admixture. The resulting experimental product was then tried and tested at 260 Townsend, Swinerton's headquarters in San Francisco. The trial was so successful, 3M is conducting further tests of the new product in order to qualify for ENERGY STAR certification, and hopes to make it available to the building industry.


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.