In the New Construction v.4 Guide, the calculation of stormwater storage volume for runoff control, does not mention the conditions before the project. I understand that the same should be considered the conditions of impermeability and permeability before, or in version 4 only the post project condition is considered? In my project it would make a big difference, since currently (pre project) there is a lot of impervious area.

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David Posada

Integrated Design & LEED Specialist

SERA Architects

LEEDuser Expert

1361 thumbs up

Wed, 07/10/2019 - 21:00

For Option 1, Percentile of rainfall events, only the post-project condition is considered. For Option 2, Natural land cover conditions, you are comparing the post-project conditions to the natural conditions of the land (before any kind of development happened) and managing the difference in run off. For either option, we don't use the current or previously developed condition like we did in earlier versions of LEED, so that impervious area you have unfortunately isn't considered in version 4.

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