PROBLEM TO BE SOLVED: To provide a greened construction on a rooftop, etc., of a building, without providing the weight load to the building, capable of being readily constructed, and excellent in water retainability and exhausting ability of surplus water. SOLUTION: A water-impermeable, water-intercepting and root-preventing seat 34, a drainage layer 36 consisting of a nonwoven structural mat composed of a synthetic resin fiber having 750-2500 de size and discharging water along the surface of the water-intercepting and root-preventing seat 34, a water- retaining layer 38 consisting of a nonwoven-structural mat composed of a synthetic resin fiber having <=100 de size and retaining the water, and a soil dressing layer 40 are accumulated successively on a rock surface 32 of a building. A drainage pipe 50 is convened with a filtration cylinder 46 made of a nonwoven structural mat of a synthetic resin fiber having 50-100 de size to prevent the outflow of the soil dressing.
