Solar Reflectance Index Green Roof

Leed version 2 2 is the first national specification to use a relatively new measure of reporting a cool roof s properties.

Solar reflectance index green roof.

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. The solar reflectance of green roofs varies depending on the plant types generally 0 3 0 5. By lessening the demand for energy it decreases carbon emissions that cause pollution. 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.

The guide to choosing a cool roof. California s building energy efficiency standards for residential and nonresidential buildings title 24 part 6 contains requirements for the thermal emittance three year aged reflectance and solar reflectance index sri of roofing materials used in new construction and re roofing projects. The sr value is a number from 0 to 1 0. The sri is a calculation method using solar reflectance and thermal emittance values to determine the roof s overall capacity to refuse solar heat.

The us department of energy defines the solar reflectance index sri as a measure of the roof s ability to reject solar heat as shown by a small temperature rise. Solar reflective index sri is important to understand when selecting a highly reflective roof coating that will help lower energy cooling costs. Solar reflectivity r solar reflectance index sri by color. Sri measures the roof s ability to reject solar heat defined such that a standard black reflectance 0 05 emittance 0 90 is 0 and a standard white reflectance 0 80 emittance 0 90 is 100.

Solar reflectance index sri. Leed 2 2 sustainable sites credit 7 2 states that to receive one point building owners should use a roof with a solar reflective index sri of 78 over at least 75 percent of the roof s surface for roofs with slopes. A value of 0 indicates that the material absorbs all solar energy and a value of 1 0 indicates total reflectance. Incorporates both solar reflectance and thermal emissivity in a single value.

Green roofs may not reflect as much as a cool roof but do have other benefits such as evapotranspiration which cools the plants and the immediate area around the plants aiding in lowering rooftop. Furthermore it doesn t store as much thermal energy as an ordinary roof. It is defined so that a standard black reflectance 0 05 emittance 0 90 is 0 and a standard white reflectance 0 80 emittance 0 90 is.