General Questions about Cool Roofing

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1.) Are cool roofs affordable? 

Yes.  Many cool roof varieties cost the same amount as other comparable roofing materials, and for those that cost slightly more, the difference can usually be quickly recovered in savings from reduced energy costs.

2.) Can you tell me which product is best for me?

No. While we can answer many general questions about the radiative properties of roofs, we cannot recommend specific products or types.  Once you have looked at our Rated Products Directory we encourage you to contact the manufacturers of the products in which you are interested, or contact a private contractor or roof consultant to assist in choosing the “coolest” product for your home or project.

3.) Are there other “cool” options besides  white roof coatings?

Yes.  Cool roofs are available in almost every common product type and come in an unlimited range of colors – including “cool” black in some cases.  Take your pick!

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4.) Will Cool roofs significantly increase my heating bills in the winter months?

No. The roof is an insignificant source for heat gain in winter.  While cool roof owners may pay slightly more to heat their homes, this amount is usually insignificant compared to the cooling energy savings during the summer. Why?

• In the wintertime, the sun is much lower in the sky and less intense.  (Passive solar heating usually occurs from sunshine streaming through windows this time of year).
• There is a higher incidence of cloudy days, and in some regions the roof is covered in snow for long periods.
• Winter days are shorter (fewer hours of sunshine)
• A cool roof will not shed more heat proportionate to other types of roofing materials at night or on cloudy days.  It will simply limit the amount of heat entering the building on hot summer days

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5.) What are Solar Reflectance and Thermal Emittance?
Solar reflectance and thermal emittance are the two radiative properties used to measure the "coolness" of a roof.

6.) What is SRI and how is it measured?

The Solar Reflectance Index (SRI) is a measure defined by the Lawrence Berkeley National Laboratory as the roof's ability to reject solar heat, as shown by a small temperature rise. It is defined so that a standard black (reflectance 0.05, emittance 0.90) is 0 and a standard white (reflectance 0.80, emittance 0.90) is 100. Due to the way SRI is defined, particularly hot materials can even take slightly negative values, and particularly cool materials can even exceed 100.

The CRRC directory will list an initial SRI value and an aged SRI value, both calculated with CRRC initial and aged reflectance and emittance values using ASTM standard E1980 with medium wind speed. If the CRRC aged values are not yet available, the Directory will state "pending". In acknowledgement that SRI values are dependent on the test method employed to measure reflectance and emittance, the CRRC will also note on the Directory which test method was conducted to produce the reflectance and emittance values. The SRI values listed in the CRRC Rated Product Directory were calculated using an application developed by the Lawrence Berkeley National Laboratory and can be found here. The SRI is a measurement that is referenced by an increasing number of code bodies and voluntary green programs, including LEED NC Version 3, ASHRAE 0.1-2007, and California Title 24 Standards.

7.) Which reflectance and emittance values are used to calculate the SRI values?

The SRI values for initial SRI are based on the initial reflectance and emittance values listed for each product in the CRRC Rated Product Directory. The aged (three year) reflectance and emittance values listed in the Rated Product Directory are used to determine the aged SRI value. This differs from the California Energy Commission (CEC) SRI value for Title 24 compliance, which is calculated by using only the aged radiative properties' values. If the aged values are not available, the CEC SRI value is calculated using the calculator found here. Thus, the CRRC initial SRI value may NOT correlate with the California Energy Commission (CEC) SRI value.

8.) How do I compute the Solar Reflectance Index (SRI) of a roofing product?

SRI is an alternative method for considering the radiative properties of roofing materials. SRI is defined by ASTM Standard E1980-01 and is a calculation that uses solar reflectance and thermal emittance.  EPA summarizes SRI as “the relative steady-state surface temperature with respect to the standard white (SRI=100) and standard black (SRI=0) under the standard solar and ambient conditions.”  SRI is often used as an alternative for products that have a low thermal emittance but a very high solar reflectance—the theory is that the higher solar reflectance will outweigh the impact of a low thermal emittance.

The CRRC Product Directory includes SRI for all rated products. Unknown SRI values can be calculated using solar reflectance and thermal emittance values.  Lawrence Berkeley National Laboratory has developed an easy-to-use SRI calculator in Excel format. It can be downloaded at http://coolcolors.lbl.gov/assets/docs/SRI%20Calculator/SRI-calc10.xls. Enter the solar reflectance and thermal emittance values in the appropriate cells and then click to red button to calculate.

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If you have a question that has not been answered on this page, see CRRC-1 (the CRRC's Program Manual) or contact us.