Why do gutters with guards overflow in heavy rain, and how do you fix it?
Short answer. Guarded gutters that overflow in heavy rain usually have one of five problems: mesh coated with pollen or sap so water sheets across it, valley water shooting over a corner, gutters pitched wrong so water pools, downspouts too small or too few for the roof area, or a clog in a downspout or underground drain below the guard. Watching where the water escapes during a storm tells you which one you have.
Diagnose it during a storm
Watch during the next heavy rain with a raincoat and a flashlight. Note whether water is running across the top of the guard and over the front, or whether the gutter is full underneath and spilling from inside. Note where it happens: everywhere, at corners, or at one end of a run.
Problems and fixes
- Water crossing the guard everywhere: the mesh is coated with pollen, oak tassels or sap film. Brush it with a soft brush and water, and plan on a spring cleaning each year.
- Water overshooting at inside corners: valleys concentrate flow. Add a corner splash diverter and consider a larger downspout near the valley.
- Gutter full and spilling at one end: the pitch is wrong or the downspout is at the wrong end. Rehang the gutter with a steady slope to the outlet.
- Gutter full everywhere: downspouts are too small or too few. Upgrade from 2 by 3 to 3 by 4 inch, or add a downspout on long runs.
- Downspout backing up: a clog in an elbow or underground drain. Disconnect at the bottom and flush, and consider adding a cleanout.
- Water running behind the gutter: missing drip edge or gutter apron, not the guard.
When the gutter is simply too small
Five inch gutters on a large, steep roof can be overwhelmed in intense Georgia storms with or without guards. Moving to 6 inch seamless gutters with larger downspouts is often the lasting fix. See gutter sizing, seamless gutters and guards and drip edge explained.