Plain-English glossary · Zoning & land use
Impervious surface ratio (ISR)
Impervious surface ratio is the share of a lot covered by surfaces that don't absorb water — roofs, driveways, patios, pool decks. Florida jurisdictions cap ISR to control stormwater runoff, separately from building lot coverage, so a design can pass one limit and fail the other.
In plain English
ISR is the limit builders discover last, usually when the pool deck and driveway get added to a plan that was fine without them. It interacts with drainage and stormwater review, which on larger sites can pull in state and environmental permits.
We run ISR alongside lot coverage in the same tabulation pass during zoning verification — one number wrong in either column is the same rejection.
Why it matters on a Florida build
Hardscape added after approval — a bigger deck, a wider drive — can push a compliant lot over its ISR cap and stall the final inspection. Cheap to check on paper; expensive to discover in the field.