Green roofs have been proven to bring about significant energy savings, particularly during the summer cooling season in which single story buildings can experience a reduction of greater than 25% energy use for air conditioning. Green roof soils insulate the roof from heat, and green roof plants transform heat and soil moisture into humidity, to create natural evaporative cooling. Each gallon of water transpired by the plants or evaporated from the soil surface liberates 8000 BTU of thermal energy.