Building designers and developers that are pursuing the Heat island reduction credit for LEED certification require documentation of the Solar Reflectance Index (SRI) for their project’s roofing materials, shade giving structures, and paving materials.
Under the U.S. Green Building Council’s LEED 2009 rating system, credits SSc7.1 and SSc7.2 (combined as credit SSc5 in LEED v4) are intended to minimize effects on microclimates and human and wildlife habitats by reducing heat islands. To satisfy the requirements of the Heat Island reduction credits, a certain percentage of the hardscape and roofing must have a high solar reflectance index.
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 standard black surface (reflectance 0.05, emittance 0.90) is 0 and a standard white surface (reflectance 0.80, emittance 0.90) is 100. See: SSc7.2: Heat Island Effect – Roof,LEED 2009 BD+C: New Construction
How Do I obtain SRI Values for My Building Materials?
LEED requires specific SRI values for your individual product or material. Many roofing manufacturers have already obtained independent laboratory testing of the SRI of their product catalog. Your desired roofing or hardscape SRI specifications may be readily available in the form of a manufacturer datasheet, which can be used as LEED documentation.
In cases where the manufacturer can not provide the SRI of a material, or the manufacturer is unknown, the USGBC allows for SRI values to be obtained from a laboratory following the appropriate ASTM standards for reflectivity and emissivity testing.
Laboratory Testing Service for SRI
By sending in a small sample of your building material, the Surface Optics Measurements Lab can perform SRI testing in accordance with ASTM and LEED requirements. Our lab will provide a report that includes the values shown in Table 1 for the provided sample(s). The SRI Report for your material can be submitted as documentation for LEED heat island reduction credit.
| Value | Test Method |
|---|---|
| Solar Reflectance | ASTM C1549 – Standard Test Method for Determination of Solar Reflectance |
| Thermal Emittance | ASTM E408 – Standard Test Method for Total Normal Emittance of Surfaces Using Inspection-Meter Techniques |
| Solar Reflectance Index | ASTM E 1980 – Standard Practice for Calculating Solar Reflectance Index of Horizontal and Low-Sloped Opaque Surfaces |
Surface Optics does not perform aged SRI testing.
Heat Island Reduction Credit Changes in LEED v4
USGBC made some changes to the Heat Island reduction credit requirements in version 4, which are:
- Combined Sustainable Sites credits 7.1: Heat Island Effect — Non-Roof and 7.2: Heat Island Effect – Roof into a single credit SSc5: Heat Island Reduction.
- Increased the SRI requirements for cool roofing materials
- Included 3-year aged SRI/ SR values as an alternative option for product qualification
- Incorporated a weighted average SRI calculation methodology
- Changed the metric by which hardscape paving materials are measured from SRI to Solar Reflectance (SR)
- Increased minimum percent of parking spaces under cover from 50% to 75% to qualify
| Slope | Initial SRI | 3-year Aged SRI |
| Low sloped roof ≤ 2:12 | 82 | 64 |
| Steep-sloped roof > 2:12 | 39 | 32 |
| Parking Cover | 39 | 32 |
Solar Reflectance of Hardscape
The impact of hardscapes such as roads, sidewalks, courtyards, and parking lots is an important element in earning the Heat Island reduction credit. Table 2 shows the requirements for hardscape and shade-providing architectural devices and structures. In LEED version 4, paving materials require documentation for Solar Reflectance only, not the full SRI previously asked for in LEED 2009.
Initial SR |
3 year Aged SR |
0.33 |
0.28 |