Impervious surface coverage requirement

[danthonyjr]

I finished my MCRP in May and took a job in economic development, but I'm moving on to a development review position with another city. I'm trying to remember some of what I learned in my lup/luc classes, but I'm stumped on this one. I figure it's pretty simple, and I'm simply overlooking something.

The city I'm going to work for requires that no more than 80 percent of a development site may be impervious surface. The formula the city gives for calculating impervious surface is this:

(GFA + LCA) / Site Area = Percent Impervious Surface

where GFA is gross floor area and LCA is lot coverage area.


Doesn't gross floor area include square footage on each floor of a multi-story building? If so, then the building's coverage could be counted repeatedly. Wouldn't I really want to look at the building footprint to determine the percent impervious surface?

[vagaplanner]

I think these terms get confused sometimes. If you use GFA with a multi-story building, it becomes more of a density ratio.

[mendelman]

If the building is a single story and the LCA includes only walkways, parking areas, etc. then I don't see the issue.

But if the LCA and GFA both include the building, then your definiately doubling counting the building area.

You should consult with your supervisor and make sure that you only have to count the building once.

[danthonyjr]

LCA only includes outdoor amenities such as sidewalks, parking lots, etc. Thus, LCA and GFA are mutually exclusive.

For a single-story building, the formula works fine because the GFA and footprint should be the same. The problem comes when looking at multiple-story buildings.

[mendelman]

For a single-story building, the formula works fine because the GFA and footprint should be the same. The problem comes when looking at multiple-story buildings.

Yes, that is a problem and you should still consult with your supervisor regarding this silly application of the code. It would be. practically speaking, stupid to double count for multi-story buildings.