This type of roof tends to see a significant amount of moss growth. Although they are flat like torch-on roofs, tar & gravel roofs hold a lot of moisture within the gravel instead of freely draining. This allows moss to grow, often in abundance and resembling a green carpet, further trapping moisture and debris, as well as adding a lot of weight to the roof. Moss removal and a roof cleaning are helpful in allowing this type of roof to drain better and decreasing the potential risks of clogged drains and excessive weight on the roof.