What is “impervious surface” and what are the impervious surface requirements in the Critical Area?
An impervious surface is one composed of any material that significantly impedes or prevents natural infiltration of water into the soil. Impervious surfaces include roofs, buildings, paved streets and parking areas and any concrete, asphalt, or compacted gravel surface. Generally, the requirements for sites in LDAs or RCAs are that no more than 15% of the total land area of any parcel may be developed with impervious surfaces. There are exceptions however. If your parcel is one-half acre or smaller and was in residential use, or so-zoned, before December 1, 1985, then impervious surfaces associated with that parcel are limited to 25% of the parcel or lot. Your local government may allow you to add 500 square feet to this total. If your lot is greater than one half acre and less than one acre, then impervious surfaces may exceed the 15% limit up to 5.445 square feet. If your lot is one acre or smaller and is part of a subdivision approved after December 1, 1985, then impervious surface
