Ballasted Roofs and SRI Values
Choosing a ballasted design in lieu of an adhered or mechanically fastened assembly doesn't mean you're giving up the option of having a reflective roof. Pavers can be used to achieve a white, tan, or light gray roof that meets reflectance values for the LEED® rating system and/or California’s Title 24.
Here are some terms we need to understand:
- The solar reflectance index (SRI) value incorporates solar reflectance and thermal emittance values and is expressed in whole numbers from 0 to 122.
- Thermal emittance refers to a material's ability to release heat and is expressed in a decimal number between 0 and 1. For example, most construction materials have an emittance of 0.85.
- A material's solar reflectance is derived from a reflectometer measurement and is expressed by a decimal number between 0 and 1.
One of the standards that measures solar reflectance is ASTM C1549: Standard Test Method for Determination of Solar Reflectance Near Ambient Temperature Using a Portable Solar Reflectometer. This standard is used heavily for conducting in-situ tests of materials that have been weathering in the field. However, the drawback to this and other reflectometer tests is that the surface being tested must be relatively flat and homogenous. This test cannot be used on smooth, river-washed stone ballast because the ballast itself creates shadows on its surface due to the roughness of the stone. This is because most stone ballast is several inches deep, which creates voids in the visual surface.
The two main types of ballast used for roof assemblies are smooth, river-washed stone and concrete roof pavers. We can still design a reflective ballasted roof using certain roof pavers, such as Hanover Pavers' highly reflective Glacier White, which has an SRI of 84.
Ballasted roof pavers aren't just reflective; they can also be reused in future re-roofing projects. The single-ply membrane underneath the ballast also has very little residual adhesive, so it is a prime candidate for recycling (see last month's blog post about Roofing Recycling Programs).
For further reading on the economics of ballasted roofs, check out the Sure-Seal® Economical Sustainability brochure.
For more information about pavers, check out the Plaza Pavers Product Data Sheet.
Please contact Craig Tyler with questions.
Here are some terms we need to understand:
- The solar reflectance index (SRI) value incorporates solar reflectance and thermal emittance values and is expressed in whole numbers from 0 to 122.
- Thermal emittance refers to a material's ability to release heat and is expressed in a decimal number between 0 and 1. For example, most construction materials have an emittance of 0.85.
- A material's solar reflectance is derived from a reflectometer measurement and is expressed by a decimal number between 0 and 1.
One of the standards that measures solar reflectance is ASTM C1549: Standard Test Method for Determination of Solar Reflectance Near Ambient Temperature Using a Portable Solar Reflectometer. This standard is used heavily for conducting in-situ tests of materials that have been weathering in the field. However, the drawback to this and other reflectometer tests is that the surface being tested must be relatively flat and homogenous. This test cannot be used on smooth, river-washed stone ballast because the ballast itself creates shadows on its surface due to the roughness of the stone. This is because most stone ballast is several inches deep, which creates voids in the visual surface.
The two main types of ballast used for roof assemblies are smooth, river-washed stone and concrete roof pavers. We can still design a reflective ballasted roof using certain roof pavers, such as Hanover Pavers' highly reflective Glacier White, which has an SRI of 84.
Ballasted roof pavers aren't just reflective; they can also be reused in future re-roofing projects. The single-ply membrane underneath the ballast also has very little residual adhesive, so it is a prime candidate for recycling (see last month's blog post about Roofing Recycling Programs).
For further reading on the economics of ballasted roofs, check out the Sure-Seal® Economical Sustainability brochure.
For more information about pavers, check out the Plaza Pavers Product Data Sheet.
Please contact Craig Tyler with questions.
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June 02, 2021
Roofing Recycling Programs
A roof replacement with a complete tear-off involves removing the single-ply membrane, cover boards, and insulation boards, all the way down to the roof deck. And for most roof replacements, a lot of that material will be headed directly to a landfill. However, there is another solution for mechanically fastened and ballasted single-ply membranes.