Impervious area
Understand the numbers.
Learn why lot coverage, paved surfaces, decks and patios can matter to North Carolina residential permit reviews.
Not all lot coverage measures are the same.
A building footprint and an impervious-surface total can be two different numbers for the same property. Local ordinances determine what counts and which limit applies.
Building coverage often measures the portion of a lot covered by buildings as locally defined. Impervious or built-upon area may include roofs, driveways, paved walkways, patios and other surfaces that restrict infiltration.
Be careful with uncovered decks, gravel, permeable pavers and similar materials. Their treatment depends on the local rule, not on what the product is marketed to do.
A site plan may present a calculation when it is part of the required submission. Drainage analysis or stormwater engineering is a distinct professional scope when needed.
A hypothetical lot-coverage example.
Example inputs
- Lot area: 10,000 square feet
- House roof footprint: 2,000 square feet
- Driveway: 900 square feet
- Patio: 300 square feet
- Assume all three surfaces are counted for this example
Illustrative result
32.0%
(2,000 + 900 + 300) ÷ 10,000 × 100 = 32%
This is arithmetic only. It does not establish how any particular NC jurisdiction classifies a surface or calculates allowable coverage.
Information needed to calculate responsibly.
Reliable lot area
Use the correct parcel area from an appropriate source and check whether local calculations exclude any areas.
Existing improvements
Document roof footprints, driveways, walks, patios, decks and other surfaces along with their materials.
Proposed changes
Record dimensions, surface type and what is being removed or added to the property.
Common areas of confusion.
- Different jurisdictions may distinguish building coverage from total impervious coverage.
- Uncovered decks may be handled differently from covered decks or roofed porches.
- Permeable pavers or gravel should not be assumed exempt without explicit local rules.
- Retaining walls, pool surfaces, utility structures and access pavement can trigger unique questions.
- Floodplain, watershed or drainage overlays may require additional review beyond a simple percentage.
Keep an existing-and-proposed area schedule to show what changed. If the project requires stormwater design, coordinate a qualified professional.
How the drawing supports review.
A well-organized site drawing can locate the surfaces used in an area schedule and distinguish proposed improvements from existing work. The numbers are only as accurate as the measurements and classifications supplied.
Learn about reliable property information ↗Have an actual site-plan request?
Tell us the city or county, project size and what property documents you have. We’ll clarify the right drawing scope.