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Why do the requirements focus on 1-year and 2-year, 24-hour storms?

Why include the 1-year storm in the credit requirements? Won't management practices for the 2-year storm be effective?

How can green roofs count as a stormwater control measure?

How can I achieve compliance if my project's stormwater control measures are outside the LEED project boundary?

I have 100-year data—how do I convert to 2-year?

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The calculations for this credit are always a headache! While our projects are usually awarded the credit, the equations in the LEED Reference Guide are helpful mostly for sizing a reservoir or cistern, but don't help you get to the final results. Does US

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NC-2009 SSc6.2:Stormwater Design—Quality Control

green roof

We will install an extensive green roof in our project. Does anyone know what the runoff rarte is and how much TSS are captured by 2.7 inches of substrate?

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Profile picture for user tristanroberts
Tristan Roberts
Representative
Vermont House of Representatives
LEEDuser Expert
7780 thumbs up

Thu, 03/31/2011 - 21:32

Emmanuel, I am not a stormwater expert so I wouldn't be able to tell you how to get this value. However, I would be cautious about assuming standard values for green roofs. This article in Environmental Building News shared some interesting data on this: Green Roof Study Finds Big Variation in Stormwater Retention.
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Michael DeVuono
Regional Stormwater Leader
Arcadis North America
LEEDuser Expert
144 thumbs up

Sat, 03/03/2012 - 14:34

This is a credit that the CEs should worry about, and unless you have PondPack, HydroCAD, or something similar in your office (and know how to use it) you should pass this work on to the CE. You can get a VERY rough estimate using the rational method (this method isnt really accepted for SWM any more because it is so rough), but it will get you in the ballpark. Q=CIA Q=Rate of runoff C=Runoff Coefficient I=Rainfall Intensity A=Area C=I would use .6 for your green roof, .95 for any impervious areas (walks, parking, etc). Get their areas and calculate a weighted C value. I=Local rainfall intensity can be obtained from NOAA, use 5min Tc A=Area of the site/building/whatever

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