412.1 The minimum pervious surface percentage requirement stated below shall be applicable only in conjunction with the following:

1. (a) The construction of a new principal structure;
2. (b) An addition to a principal or accessory structure, other than a historic resource, that increases the existing lot occupancy at the time of building permit application by ten percent (10%) or more;
3. (c) The construction of a new accessory structure that increases the existing lot occupancy at the time of building permit application by ten percent (10%) or more; or
4. (d) An addition to a historic resource that increases the existing lot occupancy at the time of building permit application by twenty-five percent (25%) or more.

412.2 For the purposes of § 412.1 a historic resource is a building or structure listed in the District of Columbia Inventory of Historic Sites or a building or structure certified in writing by the State Historic Preservation Officer as contributing to the character of the historic district in which it is located.

412.3 Except as provided in §§ 412.1 and 412.4 or as otherwise required by this title, the minimum percentage of pervious surface of a lot in a Residence District listed in the table below shall be as set forth in the following table:

ZONE DISTRICT AND STRUCTURE	MINIMUM PERCENTAGE OF PERVIOUS SURFACE
R-1 through R-4 Public recreation and community centers	30%
R-1-A, R-1-B All other structures	50%
R-2 All other structures	30%
R-3 All other structures	20%

412.4 Except as required in § 412.3 for public recreation and community centers or as otherwise required by this title, in the R-4 zone a minimum pervious surface requirement for structures other than those listed in § 412.2 shall be based on lot size as set forth in the following table:

MINIMUM LOT SIZE	MINIMUM PERCENTAGE OF PERVIOUS SURFACE
Less than 1,800 square feet	0%
1,801 to 2,000 square feet	10%
Larger than 2000 square feet	20%

412.5 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.

412.6 Only the following shall be considered pervious surfaces for the purposes of calculating the pervious surface area:

1. (a) Grass, mulched groundcover, all areas of a vegetated roof planted with a growing medium, and other planted areas;
2. (b) Permeable pavers or paving that facilitate the infiltration of water into the soil; and
3. (c) 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.

412.7 The Board of Zoning Adjustment may grant, by special exception, a full or partial reduction in the minimum pervious surface requirement required by this section if, in addition to meeting the general requirements of § 3104, the applicant demonstrates that complying with the minimum pervious surface requirement is impractical because of size of lot, or other conditions relating to the lot or surrounding area that would tend to make full compliance unduly restrictive,

prohibitively costly, or unreasonable, or as a result of equivalent measures being implemented on the property that provide the same minimum pervious surface amount.

SOURCE: Final Rulemaking published at 60 DCR 10077 (July 12, 2013).