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 that covers 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. Reference: LEED Green Associate Candidate Handbook, page 27; USGBC, [Sustainable Sites],

page 3.