A 100% vegetated roof coverage best addresses both heat island effect and rainwater runoff from the roof only. A vegetated roof, also known as a green roof, is a layer of living plants thatcovers the roof surface. A vegetated roof reduces the heat island effect by providing shade, evapotranspiration, and insulation, lowering the roof temperature and the surrounding air temperature. A vegetated roof also reduces rainwater runoff by retaining and absorbing precipitation, decreasing the volume and peak flow of stormwater leaving the roof. The other options are not as effective as a 100% vegetated roof coverage in addressing both heat island effect and rainwater runoff from the roof only. A 100% high-albedo roof reflects more solar radiation than a conventional roof, reducing the heat island effect, but it does not reduce rainwater runoff. A 20% high-albedo and 80% conventional roof has a lower reflectance than a 100% high-albedo roof, resulting in a higher heat island effect, and it does not reduce rainwater runoff either. A 50% standing seam copper and 50% vegetated roof has a lower vegetated area than a 100% vegetated roof, resulting in less shade, evapotranspiration, insulation, retention, and absorption, leading to a higher heat island effect and more rainwater runoff. References: LEED Green Associate Candidate Handbook, page 27; USGBC, [Sustainable Sites], page 3.