Table 4: Permitted Impervious Surface Coverage
| |||
---|---|---|---|
Zoning District
|
Permitted Maximum Impervious Surface Coverage
| ||
R-1
|
50%
| ||
R-1A
|
60%
| ||
R-2
| |||
Detached or duplex
|
60%
| ||
Townhouse
|
65%
| ||
Apartment or other multifamily
|
75%
| ||
C-1
|
80%
| ||
C-2
|
65%
| ||
Institutional
|
75%
| ||
Industrial (I)
|
80%
| ||
Village Overlay
|
100%
| ||
OMU
|
90%
|
Table 5: Impervious Surface Ratings
| ||
---|---|---|
Surface Materials
|
Rate of Imperviousness1
(% impervious)
| |
Asphalt, rubber or metal roofing roof; conventional concrete
pavement; conventional asphalt pavement; open water body; gravel roof
|
0.95
| |
Stone, concrete or brick pavers with grouted joints on concrete
base; compacted angular aggregate pavement; wood or composite wood
deck
|
0.75
| |
Green roof less than or equal to 4-inch depth; stone, concrete
or brick pavers with ungrouted joints on sand and/or aggregate base
|
0.50
| |
Uncompacted nonangular aggregate pavement; Green roof greater
than 4-inch to 8-inch depth; open-celled concrete grid with lawn or
nonangular aggregate fill
|
0.30
| |
Open-celled plastic grid with lawn or nonangular aggregate fill;
lawn; green roof great than 8-inch depth; permeable concrete pavement;
permeable asphalt pavement; field
|
0.20
| |
Woodland
|
0.15
|
Notes:
| ||
---|---|---|
1
|
Based on slopes between 0 and 3%. Reduce the impervious rating
of each surface material by 0.05 for surfaces located on slopes >
3% to 10%. Reduce the impervious rating of surface material by 0.15
for surfaces on slopes > 10%.
|
Table 6: Impervious Surface Coverage Worksheet
| ||||
---|---|---|---|---|
Column A
|
Column B
|
Column C
|
Column D
| |
Surface Material
|
Total Square Feet of Surface
|
Rate of Imperviousness
(see Table 5)
|
Adjusted Square Feet of Surface Material
(Column B x C)
| |
Line 1
|
Asphalt, rubber or metal roofing roof; conventional concrete
pavement; conventional asphalt pavement; open water body, gravel roof
|
_____ x
|
0.95
|
=_____
|
Line 2
|
Stone, concrete or brick pavers with grouted joints on concrete
base; compacted angular aggregate pavement; wood or composite wood
deck
|
_____ x
|
0.75
|
_____
|
Line 3
|
Green roof less than 4-inch depth; stone, concrete or brick
pavers with ungrouted joints on sand and/or aggregate base
|
_____ x
|
0.50
|
= _____
|
Line 4
|
Uncompacted nonangular aggregate pavement; green roof greater
than 4-inch to 8-inch depth; open-celled concrete grid with lawn or
nonangular aggregate fill
|
_____ x
|
0.30
|
=_____
|
Line 5
|
Open-celled plastic grid with lawn or nonangular aggregate fill;
lawn; green roof greater than 8-inch depth; permeable concrete pavement;
permeable asphalt pavement; field
|
_____ x
|
0.20
|
=_____
|
Line 6
|
Woodland
|
_____ x
|
0.15
|
=_____
|
Line 7
|
Sum of Lines 1 + 2 + 3 + 4 + 5 + 6
|
_____
Total Lot Area
|
_____
Adjusted Impervious Surface Total
| |
Maximum Permitted Impervious Surface Coverage (per Table 4)
|
= _____
| |||
Percent of Impervious Surface Coverage (Adjusted Surface Area/Total
Lot Area)
|
= _____
|
Table 7: Permeability Enhancement
| ||
---|---|---|
Permeability Enhancement
|
Increase to Permitted Impervious Surface Coverage
| |
Installation of a cistern
|
15%
| |
Installation of a rain garden or series of rain gardens
|
10%
| |
Installation of a bioswale
|
5%
|