A pervious surface is a surface that allows the percolation of water into the underlying soil. Pervious surfaces include grass, mulched groundcover, planted areas, vegetated roofs, permeable paving as well as porches and decks erected on pier foundations that maintain the covered lot surface’s water permeability. Pervious surfaces do not include any structure or building, any porch or deck that limits the covered lot surface from absorbing water, or any outdoor stairs, on-grade surface sports court, swimming pool, artificial turf, sidewalk or patio constructed of concrete, asphalt, brick, compacted gravel or other material that impedes the infiltration of water directly into the subsurface of the lot.
Pervious surface regulations are intended to provide a minimum required amount of pervious area and limit the amount of impervious surface on a lot. The minimum pervious surface percentage shall be as required by the development standards for the Residential and Residential Flat zones.
The minimum pervious surface percentage requirement shall be applicable only in conjunction with the following:
- The construction of a new principal structure;
- An addition to a principal or accessory structure, other than a historic resource, that increases the existing lot occupancy at the time of a building permit application by 10% or more;
- The construction of a new accessory structure that increases the existing lot occupancy at the time of a building permit application by 10% or more; or
- An addition to a historic resource that increases the existing lot occupancy at the time of building permit application by 25% or more.
Only the following shall be considered pervious surfaces for the purposes of calculating the pervious surface area:
- Grass, mulched groundcover, all areas of a vegetated roof planted with a growing medium, and other planted areas;
- Permeable or pervious pavers or paving that facilitate the infiltration of water into the soil; and
- Decks or porches constructed above the surface of the lot that are erected on pier foundations, and that maintain a permeable surface underneath that can facilitate the infiltration of water into the soil.
Pervious surfaces on a lot shall not include:
- On-grade surface treatments used for purposes of recreation (e.g. patios), outdoor stairways, walking, driving and parking areas made of concrete, brick, asphalt, decorative pavers, compacted gravel or other material that does not facilitate the infiltration of water directly into the subsurface of the lot;
- The building footprint based on its foundation perimeter, whether located below grade or at grade;
- Where a building does not have a foundation, the area of the roof; and
- The area dedicated to a below or above grade swimming pool.
The percent of pervious surface area shall be calculated by dividing the total area of pervious surfaces on the lot by the total area of the lot.
For more information on the following topic, please see the corresponding referenced chapter:
- Pervious Surfaces– Subtitle C, Chapter 5