Solar Reflectance and SRI Measurements

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.
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.

Table 1. SRI Report

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

Heat Island Reduction Credit Changes in LEED v4

Project teams are allowed to register for either LEED v4 or LEED 2009 until June 1, 2015, after which LEED v4 will be the required rating system. USGBC has made some changes to the Heat Island reduction credit requirements for 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

1. U.S. Green Building Council (2009). Heat island effect – roof. Retrieved May 29, 2014, from http://www.usgbc.org/node/1731100?return=/credits/new-construction/v2009
2. U.S. Green Building Council (2012, October 4). LEED Reference Guide for Green Building Design and Construction with Global Alternative Compliance Paths. Retrieved June 3, 2014, from http://www.usgbc.org/sites/default/files/LEED%202009%20RG%20BD+CSupplement_GLOBAL_12_2013_Heat_Island_Update.pdf

Solar Reflectance of Hardscape for LEED

\ Surface Optics does not perform aged SRI testing.

Table 1. Minimum SRI for Cool Roof Materials in LEED 2009 vs. LEED v4
		Slope	Initial SRI	3 year aged SRI
LEED 2009	Low sloped roof	≤ 2:12	78	—
	Steep-sloped roof	> 2:12	29	—
	Parking Cover	—	29	—
LEED v4	Low sloped roof	≤ 2:12	82	64
	Steep-sloped roof	> 2:12	39	32
	Parking Cover	—	39	32

The impact of hardscape 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 SRI asked for in LEED 2009.

Table 2. Minimum Solar Reflectance for Hardscape in LEED 2009 vs. LEED v4
	Metric	Initial	3-year aged
LEED 2009	Solar Reflectance Index	29	—
LEED v4	Solar Reflectance	0.33	0.28