n. The project has exceeded the 25% minimum, thus earning1 point. Table 2. Design Case Imperviousness Surface Type Runoff Coefficient Area (sf) Impervious Area _m_ (d) Pavement. Asphalt 0.95 5.075 4,821 Pavement, Pervious 0.60 1,345 807 Roof, Garden Roof (4 - 8 in) 0.30 8,240 2,472 Vegetation,