Gutters prevent water from seeping into the interior of the building by channeling the water away from the exterior of the walls and the foundations. Water running down the walls will cause dampness in the affected rooms and creates a favorable environment to host mold, and wet rot in timber. A roof must be designed with a suitable fall to allow the rainwater to discharge in order to work.
The water drains into a gutter which channels into a downpipe. A flat roof should be equipped with a watertight surface. They can drain internally or to an eaves gutter. The pitch of a pitched roof is determined by the construction material of the covering. For slate roofing this will be at 25%, and for machine made tiles it will be 35%. Water then falls towards a parapet gutter, a valley gutter or an eaves gutter. Also when two pitched roofs meet at a certain angle, they form a pitched valley gutter and the join can be sealed with valley flashing. Parapet gutters and valley gutters flow into internal rainwater pipes or directly to external down pipes at the very end of the run.