Intent
To reduce heat islands1 to minimize impacts on microclimates and human and wildlife habitats.
Requirements
Option 1
Use roofing materials with a solar reflectance index2 (SRI)equal to or greater than the values in the table below for a minimum of 75% of the roof surface.
Roofing materials having a lower SRI value than those listed below may be used if the weighted rooftop SRI average meets the following criteria:
|
Area Roof Meeting Minimum SRI ———————————————— Total Roof Area |
x |
SRI of Installed Roof —————————— Required SRI |
≥ | 75% |
Alternatively, the following equation may be used to calculate compliance:
| [ | Area of Roof A | x |
SRI of Roof A ——————— Required SRI |
] | + | [ | Area of Roof B | x |
SRI of Roof B ——————— Required SRI |
] | + | ... | Total Roof Area | ||
| 0.75 | |||||||||||||||
| Roof Type | Slope | SRI |
| Low-sloped roof | ≤ 2:12 | 78 |
| Steep-sloped roof | > 2:12 | 29 |
OR
Option 2
Install a vegetated roof that covers at least 50% of the roof area.
OR
Option 3
Install high-albedo and vegetated roof surfaces that, in combination, meet the following criteria:
|
Area Roof Meeting Minimum SRI ———————————————— 0.75 |
+ |
Area of Vegetated Roof —————————— 0.5 |
≥ | Total Roof Area |
| Roof Type | Slope | SRI |
| Low-sloped roof | ≤ 2:12 | 78 |
| Steep-sloped roof | > 2:12 | 29 |
Alternatively, a weighted approach may be used to calculate compliance for multiple materials:
2 The solar reflectance index (SRI) is a measure of the constructed surface's ability to reflect solar heat, as shown by a small temperature rise. It is defined so that a standardblack surface (reflectance 0.05, emittance 0.90) is 0 and a standard white surface (reflectance 0.80, emittance 0.90) is 100. to calculate the SRI for a given material, obtain the reflectance value and emittance value for the material. SRI is calculated according to ASTM E 1980. Reflectance is measured according to ASTM E 903, ASTM E 1918, or ASTM C 1549. Emittance is measured according to ASTM E408 or ASTM C 1371.
3 For the purposes of this credit, under cover parking is defined as parking underground, under desk, under roof, or under a building.
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