Why is water flowing over my gutter guards?
Short answer. Water flows over gutter guards for one of five reasons: a mat of pollen, needles or grit on top of the guard, a hood-style guard overshooting in heavy rain, a guard set at the wrong angle, a clogged downspout backing water up under the guard, or a gutter too small for the roof above it. Watching where and when it happens usually points to the cause.
Diagnose by pattern
- Along the whole run in moderate rain. Surface clog. Pine pollen, oak tassels and fine grit form a film on mesh that water skims across. Brush and hose the surface.
- Only in cloudbursts, guards look clean. Overshoot. Common with hood and reverse-curve guards, and with any guard below a steep plane. Mesh designs and splash diverters help.
- At inside corners. Valley water concentrates there and hits the guard at speed. Add a valley splash guard or diverter, and check that corner panels are mitered tight.
- Near a downspout, with water standing under the guard. The downspout is clogged and the gutter has filled. Clear the outlet and elbows.
- Everywhere, even when clean. The gutter or downspouts are undersized for the roof area and pitch.
Check the installation angle
Many mesh guards are meant to sit nearly in line with the roof slope so water runs onto them and drops through. A guard tilted back toward the house, or bowed down in the middle, can pond debris; one tilted steeply outward can shed water off the front. Under-shingle installs that pushed the shingle edge up can also redirect water past the gutter.
Quick test
On a dry day, run a hose on the roof above the problem area, starting slow and increasing flow. If water passes through at low flow but overshoots at high flow, the guard type is the limit. If it overshoots even at low flow, the surface is clogged or the angle is wrong.
For size and capacity, see gutter sizing and guards; for what overflow does to the house, common causes of roof leaks.