An impervious surface is a hard surface that does not allow rain to absorb into the ground. Impervious surfaces increase stormwater runoff. Examples of impervious surfaces considered for the utility are roofs, paving (including gravel driveways), sidewalks internal to the site (not along the streets), sheds, paved patios, and pool decks. Surfaces not considered impervious: planting beds/landscaping features, the surface area of pools and decks (unless the area under the deck is paved).
To better understand how impervious surfaces are mapped and calculated view the impervious calculation document.