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CS-2009 SSc6.1:Stormwater Design—Quantity Control

Impervious Calculation

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LEEDuser Basic Member
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Hi,

Just want to clarify the exact meaning of the existing impervious and it's calculation. Below are my questions:

1. Site with more or less 50% existing impervious refers to the area where there was no development or any activity/construction (original site condition)?

2. How to calculate the existing impervious area? (existing impervious area divided by total area) -where total area refers to the total open space within the leed boundary or total site area?

Also, I'm thinking that if the site before (original site condition) is 100% impervious and the project team will construct let's say 50% of the total site area that means 50% impervious and 50% pervious, meaning the post-development site runoff quantity can't make any reduction as it reduce the impervious area? Or that's why we have to provide stormwater harvesting to be an alternative to the lose impervious area? Is my assumption correct?

Thank you in advance!

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