D.C. Mun. Regs. tit. 11, § 3402
3402.1 The GAR shall be calculated using the following formula:
$$GAR = \frac{(\text{area of landscape element 1} \times \text{multiplier}) + (\text{area of landscape element 2} \times \text{multiplier}) + \dots}{\text{Lot Area}}$$
3402.1 For the purposes of the above formula and the remainder of this chapter:
3402.3 The process for calculating a property’s GAR under the formula is as follows:
3402.4 The total points for all permeable paving and enhanced tree growth credits may not count for more than one-third (1/3) of the GAR score for a lot.
3402.5 If multiple landscape elements occupy the same area, for example groundcover under a tree or trees and shrubs on an intensive green roof, the full square footage or equivalent square footage of each element may be counted.
3402.6 A landscape element must meet the eligibility conditions of § 3403.
3402.7 Equivalent square feet of tree canopy and large shrubs are identified in the table below.
| GREEN AREA RATIO LANDSCAPE ELEMENTS | EQUIVALENT SQUARE FOOTAGE |
|---|---|
| Plants, not including grasses, at least 2 feet tall at maturity | 9 s.f. per plant |
| Tree canopy for trees 2.5 inches to 6 inches in diameter | 50 s.f. per tree |
| Tree canopy for trees 6 inches to 12 inches in diameter | 250 s.f. per tree |
| Tree canopy for trees 12 inches to 18 inches in diameter | 600 s.f. per tree |
| Tree canopy for trees 18 inches to 24 inches in diameter | 1300 s.f. per tree |
| Tree canopy for trees larger than 24 inches in diameter | 2000 s.f. per tree |
3402.8 Landscape elements of the GAR shall be measured in the following ways:
(h) All trees shall be measured for diameter at a height four feet, six inches (4 ft. 6 in.) above grade when planted and the square footage equivalent based on diameter shall be as established in the table in § 3402.7;
(i) For vegetated walls, use the vertical square footage of the portion of the wall covered by vegetation; and
(j) For all other elements other than trees, large shrubs, perennials, and vegetated walls, square footage is determined by the area of a horizontal plane that is over the element.
3402.9 Eligible landscape elements are identified in the table below:
| GREEN AREA RATIO LANDSCAPE ELEMENTS | MULTIPLIER |
|---|---|
| Landscaped area (select one of the following for each area) | |
| Landscaped areas with a soil depth of less than 24 inches | 0.3 |
| Landscaped areas with a soil depth of 24 inches or more | 0.6 |
| Bioretention facilities | 0.4 |
| Plantings | |
| Ground covers, or other plants less than 2 feet tall at maturity | 0.2 |
| Plants, not including grasses, at least 2 feet tall at maturity | 0.3 |
| Tree canopy for all trees 2.5 inches to 6 inches in diameter | 0.5 |
| Tree canopy for new trees 6 inches in diameter or larger | 0.6 |
| Tree canopy for preservation of existing trees 6 inches to 24 inches in diameter | 0.7 |
| Tree canopy for preservation of existing trees 24 inches diameter or larger | 0.8 |
| Vegetated wall, plantings on a vertical surface | 0.6 |
| Vegetated roofs | |
| Extensive vegetated roof over at least 2 inches but less than 8 inches of growth medium | 0.6 |
| Intensive vegetated roof over at least 8 inches of growth medium | 0.8 |
|---|---|
| Permeable paving | |
| Permeable paving over at least 6 inches and less than 2 feet of soil or gravel | 0.4 |
| Permeable paving over at least 2 feet of soil or gravel | 0.5 |
| Other | |
| Enhanced tree growth systems | 0.4 |
| Renewable energy generation (area of) | 0.5 |
| Water features (using at least 50% recycled water) | 0.2 |
| Bonuses | |
| Native plant species listed in §3403.9 | 0.1 |
| Landscaping in food cultivation | 0.1 |
| Harvested stormwater irrigation | 0.1 |
SOURCE: Final Rulemaking published at 60 DCR 10077 (July 12, 2013).