Our project has an elevated second story over an existing ballasted roof (river rock). The new white roof membrane meets the credit requirement with an SRI of 109. The existing roof below is shaded 90% by the structure above. How do I document compliance? Should I take the SRI value of the entire ballasted roof (currently searching - does anyone know the SRI for river rock?) and generate a composite value for both roofs? Since the lower roof is shaded 90% by the roof above, should I only consider that portion of the lower roof visible in plan view?
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Tristan Roberts
RepresentativeVermont House of Representatives
LEEDuser Expert
11478 thumbs up
September 16, 2010 - 3:30 pm
This is a little tricky, but I'll go out on a limb and try to respond.One issue is that you're generally not allowed to take shading of your own building into account with SSc7.2 calculations. However, that generally applies to a vertical part of the building shading a roof—not one roof over another.One question I have for you is how far is the second story over the lower roof? How much sun will actually reach the lower roof, at different times of day? If it's closely covering it, and the sunlight will be minimal, I'd say you'd be more justified in de-weighting this roof in your calculations by using the plan view.I would probably try using the plan view as you suggest, but if I were you I might play around with the calculator in LEED Online and see what happens when you plug in different numbers. You have a cushion because of the large area of the upper roof and its high SRI number—to get a more conservative read on the credit, I might see how much of the lower roof you could include and still earn the credit.By the way, I don't think there is any single established SRI for river rock. Might take testing of your sample.