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Heat Island Mitigation with Cool Walls

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Pilot-Credits SSpc154: Heat Island Mitigation with Cool Walls 1 point

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Credit language

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© Copyright U.S. Green Building Council, Inc. All rights reserved.

Requirements

Surface at least 75% of the building’s gross exterior wall area (including vertical fenestration) with a “cool-wall material”. For the purposes of this pilot credit, a “cool-wall material” must be opaque to sunlight, exhibit an initial solar reflectance of at least 0.60, and exhibit an initial thermal emittance of at least 0.75. Vegetated walls may qualify as “cool walls” for the purposes of pilot credit compliance.

To avoid disproportionate placement of cool-wall materials on the building face that receives the least sun, no more than 25% of the building’s total cool-wall area may be sited on the wall facing away from the equator; that is, on the north wall in the northern hemisphere, or on the south wall in the southern hemisphere.

Report for each cool-wall material its manufacturer, model, description, initial solar reflectance, initial thermal emittance, and wall area covered as shown in Table 1.

Table 1. Sample documentation of cool wall materials
Material # Manufacturer Model Description Initial solar reflectance1 (must be ≥ 0.60) Initial thermal emittance2(must be ≥ 0.75) Wall area covered (m²)
1 Acme Vanilla White White acrylic paint field applied to fiber-cement walls at a dry film thickness of ~100 µm 0.61 0.90 800
2 - - - - - -
1 Solar reflectance shall be measured in accordance with (a) ASTM Standard E903-20 (https://doi.org/10.1520/E0903-20), weighting solar spectral reflectance with the solar spectral irradiance for a sun-facing vertical surface specified by ASTM Standard G197-14 (https://doi.org/10.1520/G0197-14); (b) ASTM Standard C1549-16 (https://doi.org/10.1520/C1549-16), using instrument output AM1.5GV (labeled "1.590") based on the aforementioned solar spectral irradiance; or (c) Appendix 9 of the CRRC-1 Program Manual (https://coolroofs.org/documents/CRRC-1_Program_Manual.pdf), using instrument output “G197GT90” of the Surface Optics 410-Solar-i directional-hemispherical portable reflectometer (also based on the aforementioned solar spectral irradiance).
2 Thermal emittance shall be measured in accordance with ANSI/CRRC Standard S100-2021 (https://coolroofs.org/product-rating/ansi-crrc-s100).


In addition, report gross wall and cool wall areas as shown in Table 2.

Table 2. Sample documentation of cool wall coverage
(A) Whole-building gross exterior wall area (m²) 1,000
(B) Whole-building cool-wall area (m²) 800
(C) Whole-building cool-wall area on equator-opposing wall (m²) 200
(D) Fraction of gross exterior wall area surfaced with cool-wall materials (D=B/A; must be ≥ 75%) 80%
(E) Fraction of cool-wall area sited on equator-opposing wall (E=C/B; must be ≤ 25%) 25%

Submittals

General
Register for the pilot credit Feedback Survey
Documentation/Compliance
  • Report for each cool-wall material its manufacturer, model, description, initial solar reflectance, initial thermal emittance, and wall area covered as shown in Table 1.
  • Report gross wall and cool wall areas as shown in Table 2.
Changes
  • 4/9/21 - Original Publication
See all forum discussions about this credit »

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Documentation toolkit

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USGBC logo

© Copyright U.S. Green Building Council, Inc. All rights reserved.

Requirements

Surface at least 75% of the building’s gross exterior wall area (including vertical fenestration) with a “cool-wall material”. For the purposes of this pilot credit, a “cool-wall material” must be opaque to sunlight, exhibit an initial solar reflectance of at least 0.60, and exhibit an initial thermal emittance of at least 0.75. Vegetated walls may qualify as “cool walls” for the purposes of pilot credit compliance.

To avoid disproportionate placement of cool-wall materials on the building face that receives the least sun, no more than 25% of the building’s total cool-wall area may be sited on the wall facing away from the equator; that is, on the north wall in the northern hemisphere, or on the south wall in the southern hemisphere.

Report for each cool-wall material its manufacturer, model, description, initial solar reflectance, initial thermal emittance, and wall area covered as shown in Table 1.

Table 1. Sample documentation of cool wall materials
Material # Manufacturer Model Description Initial solar reflectance1 (must be ≥ 0.60) Initial thermal emittance2(must be ≥ 0.75) Wall area covered (m²)
1 Acme Vanilla White White acrylic paint field applied to fiber-cement walls at a dry film thickness of ~100 µm 0.61 0.90 800
2 - - - - - -
1 Solar reflectance shall be measured in accordance with (a) ASTM Standard E903-20 (https://doi.org/10.1520/E0903-20), weighting solar spectral reflectance with the solar spectral irradiance for a sun-facing vertical surface specified by ASTM Standard G197-14 (https://doi.org/10.1520/G0197-14); (b) ASTM Standard C1549-16 (https://doi.org/10.1520/C1549-16), using instrument output AM1.5GV (labeled "1.590") based on the aforementioned solar spectral irradiance; or (c) Appendix 9 of the CRRC-1 Program Manual (https://coolroofs.org/documents/CRRC-1_Program_Manual.pdf), using instrument output “G197GT90” of the Surface Optics 410-Solar-i directional-hemispherical portable reflectometer (also based on the aforementioned solar spectral irradiance).
2 Thermal emittance shall be measured in accordance with ANSI/CRRC Standard S100-2021 (https://coolroofs.org/product-rating/ansi-crrc-s100).


In addition, report gross wall and cool wall areas as shown in Table 2.

Table 2. Sample documentation of cool wall coverage
(A) Whole-building gross exterior wall area (m²) 1,000
(B) Whole-building cool-wall area (m²) 800
(C) Whole-building cool-wall area on equator-opposing wall (m²) 200
(D) Fraction of gross exterior wall area surfaced with cool-wall materials (D=B/A; must be ≥ 75%) 80%
(E) Fraction of cool-wall area sited on equator-opposing wall (E=C/B; must be ≤ 25%) 25%

Submittals

General
Register for the pilot credit Feedback Survey
Documentation/Compliance
  • Report for each cool-wall material its manufacturer, model, description, initial solar reflectance, initial thermal emittance, and wall area covered as shown in Table 1.
  • Report gross wall and cool wall areas as shown in Table 2.
Changes
  • 4/9/21 - Original Publication
See all LEEDuser forum discussions about this credit » Subscribe to new discussions about Pilot-Credits SSpc154