What is the impervious surface ratio (ISR)?

The Impervious Surface Ratio (ISR) is the portion of a lot that is covered by impenetrable materials, such as concrete. The ISR is dictated by the Future Land Use designation of a property. The table shows the permitted ISR for each Future Land Use designation:

Future Land UseMaximum Density/Intensity
OfficeLess than or Equal to 65% ISR
Restricted CommercialLess than or Equal to 65% ISR
CommercialLess than or Equal to 65% ISR
IndustrialLess than or Equal to 65% ISR
Downtown Development DistrictLess than or Equal to 90% ISR
Public/Semi-PublicLess than or Equal to 65% ISR
RecreationLess than or Equal to 65% ISR
High Intensity Planned Development -Target Industry18 DU/1 Acre, Maximum 65% ISR and 35% Minimum Open Space
High-tech / Industrial Corridor Protection AreaLess than or Equal to 65% ISR
Transit Oriented Development OverlayLess than or Equal to 90% ISR
Downtown Economic Policy Initiative OverlayLess than or Equal to 90 %ISR

Show All Answers

1. How can I find the zoning designation of a property?
2. Can I operate a business from my home?
3. Do you have a survey on file of my property, if not, where can I get one?
4. What uses are allowed in a zoning district?
5. What is the impervious surface ratio (ISR)?
6. What are the setbacks for commercial development?
7. What are the lot sizes and setbacks for a single family home?
8. Why do P.U.D's have different zoning requirements?
9. Where am I allowed to put my swimming pool and pool enclosure?