Gutter refers to the concave part between the two spans of the roof of a building. Roof drainage is divided into organized drainage and unorganized drainage (free drainage). Organized drainage generally collects rainwater into the gutter and then drains it through the rainwater pipe. The ditch that collects rainwater is called the gutter. Gutters are divided into internal gutters and external gutters. Internal gutters refer to gutters inside the outer wall, which usually have parapets; external gutters are gutters that extend out of the outer wall, which usually do not have parapets.