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C402.3 Roof Solar Reflectance and Thermal Emittance
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Low-sloped roofs directly above cooled conditioned spaces in Climate Zones 1, 2 and 3 shall comply with one or more of the options in Table C402.3.
Exceptions: The following roofs and portions of roofs are exempt from the requirements of Table C402.3:
- Portions of the roof that include or are covered by the following:
- Photovoltaic systems or components.
- Solar air or water-heating systems or components.
- Roof gardens or landscaped roofs.
- Above-roof decks or walkways.
- Skylights.
- HVAC systems and components, and other opaque objects mounted above the roof.
- Portions of the roof shaded during the peak sun angle on the summer solstice by permanent features of the building or by permanent features of adjacent buildings.
- Portions of roofs that are ballasted with a minimum stone ballast of 17 pounds per square foot [74 kg/m2] or 23 psf [117 kg/m2] pavers.
- Roofs where not less than 75 percent of the roof area complies with one or more of the exceptions to this section.
| Three-year aged solar reflectanceb of 0.55 and 3-year aged thermal emittancec of 0.75 | |
| Three-year-aged solar reflectance indexd of 64 | |
- The use of area-weighted averages to comply with these requirements shall be permitted. Materials lacking 3-year-aged tested values for either solar reflectance or thermal emittance shall be assigned both a 3-year-aged solar reflectance in accordance with Section C402.3.1 and a 3-year-aged thermal emittance of 0.90.
- Aged solar reflectance tested in accordance with ASTM C 1549, ASTM E 903 or ASTM E 1918 or CRRC-1 Standard.
- Aged thermal emittance tested in accordance with ASTM C 1371 or ASTM E 408 or CRRC-1 Standard.
- Solar reflectance index (SRI) shall be determined in accordance with ASTM E 1980 using a convection coefficient of 2.1 Btu/h • ft2 • °F (12W/m2 • K). Calculation of aged SRI shall be based on aged tested values of solar reflectance and thermal emittance.
Where an aged solar reflectance required by Section C402.3 is not available, it shall be determined in accordance with Equation 4-3.
where:
| Raged | = | The aged solar reflectance. |
| Rinitial | = | The initial solar reflectance determined in accordance with CRRC-1 Standard. |
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