measurement of imperviousness

Jean Marais

b.i.g. Bechtold DesignBuilder Expert

LEEDuser Basic Member

581 thumbs up

May 7, 2010

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Amy Rider

Sustainability Manager

KEMA Services

LEEDuser Basic Member

110 thumbs up

Sat, 05/22/2010 - 00:09

Keep in mind that this credit looks at the site as a whole not a single paving material. Your pre-development runoff rate should answer the question of whether case 1 or case 2 is applicable by giving you a ratio of runoff to rainfall; thus the perviousness of your site.

Jean Marais

b.i.g. Bechtold DesignBuilder Expert

LEEDuser Basic Member

581 thumbs up

Wed, 05/26/2010 - 09:16

What you're saying is that Run-off Coeffient RC = Imperviousness right? This would be a clear quantifiable definition that is not found in the reference guide. I can work with this.

Amy Rider

Sustainability Manager

KEMA Services

LEEDuser Basic Member

110 thumbs up

Wed, 06/02/2010 - 20:41

Just to clarify: Run-off coefficients are for specific materials under specific circumstances (e.g. turf with 1-2% slope) whereas imperviousness is typically applied to an area, or in this case a site, as a whole. Yes, in this case where your site seems to be of a uniform nature, they are roughly equivalent.

Jean Marais

b.i.g. Bechtold DesignBuilder Expert

LEEDuser Basic Member

581 thumbs up

Thu, 06/03/2010 - 07:10

Run-off coefficients are also area weighted when calculating the RC for the whole site. This is standard practice. Thanks for the tips.