A building's construction displaces rainwater, and a gutter system uses gravity to move this displaced water away from the building. Without a gutter, the water falls from the roof in heavy sheets, in many cases striking the ground with enough force to cause significant ground erosion. Improperly installed gutters can cause basement flooding, rotting wood, siding staining and foundation problems. A proper gutter slope ensures that the water properly exits the gutter and enters the drains as designed.
Installers attach gutters to the fascia board of the building with spikes, screws or gutter hangers. The installer then cuts a hole into the bottom of the gutter and inserts an outlet to attach the downspout. The downspout carries the water from the roof line to the ground. An elbow at the bottom of the gutter attaches the system to a splash block, underground drains or water collection systems.
When the installer hangs the gutter with a slope down toward the downspout, the water will naturally flow in that direction without any other propulsion methods. Without a slope, the water will collect in the guttering instead of exiting the system through the downspouts. The correct slope prevents overflowing and forces the system to empty quickly, even during heavy rains.
The recommended gutter slope is 1/8 inch for every 10 feet of gutter, or 1/4 inch for each foot. Any gutter should have a minimum of a 1/16-inch slope per foot of gutter. Use a greater slope in areas with heavy rainfall, and a lower slope where rainfall is usually light. The rate of the slope controls the speed with which the water travels through the gutter toward the downspout. A greater slope speeds the water's exit so the system can handle larger amounts of water.
Standing water in a gutter system from an improper slope causes many problems, including insect infestations, odor, mold and mildew. In cold temperatures, standing water freezes and may become too heavy for the fasteners to hold, which can cause the gutter to fall from the building. Since the gutter attaches to the fascia board, the size of the board also affects the slope. On long gutter runs, the fascia board may not be wide enough to accommodate the desired slope. In this situation, simply install the gutter consistently with as much slope as possible, or install a center downspout to break the gutter run.