Water sheeting over the guards in a downpour has a cause, and where it escapes usually points straight to it. This post shows you how to read the spill pattern and match each one to a fix.
In This Article
Watch first, then guess
Guessing at the cause wastes money, so watch instead. Stand under a porch or at a window during a heavy downpour and note where the water leaves the eave. Is it one short stretch under a valley, the whole front edge of a run, the corners, or the end nearest the downspout? A short phone video helps, because water behaves differently at different points in a storm.
The rain leaves evidence too. Look for dirt splash marks on the siding under the eaves, a shallow trench in the soil along the drip line, or a wet patch at the foundation where a downspout should have discharged. Do not climb a ladder in the rain to look closer.
Reading the spill pattern
| Where it spills | Likely cause | First move |
|---|---|---|
| One short stretch under a roof valley | Fast, concentrated valley water jumping the guard | Ask about a valley diverter or a larger trough at that spot |
| Along the whole front edge of a run | A matted or filmed guard surface, or too little trough for the roof area | Brush the surface, then have the trough size reviewed if it recurs |
| Near the downspout end, with water backing up | A blocked outlet or downspout below the guard | Flush the downspout and check the bottom elbow |
| At a corner | Debris packed in the corner, or a gap at the joint | Inspect and clear it, and reseal or replace the corner piece |
| At the low end of a run, with a pool of water | The trough is not sloping toward the downspout | Have the run re-hung to the right slope |
| Only in the biggest storms, from a long roof | More water than the system can take, so it skips past | Discuss another guard design or an extra downspout |
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The usual causes, explained
A blocked downspout. Grit and seeds pass through most guards and pack the outlet or the bottom elbow. Water then backs up in the trough and spills over the top. Run a hose into the downspout: a strong flow at the bottom is good, a trickle is not.
A matted or filmed surface. A wet leaf mat or a film of pollen and fine grit can stop water passing through the guard. It then sheets over the edge instead. A soft brush on a pole often fixes it.
Too much roof for the trough. A large roof area can outrun a small trough, or too few downspouts. Read our eavestrough sizing guide to see how size and downspout count work together.
Valleys and long runs. Where two roof planes meet, or where a long slope funnels water into one place, the flow is fast enough to jump a guard. A diverter or a second downspout can help.
Slope. A trough that pools instead of draining toward the downspout leaves less room for the next surge. See why gutter pitch matters.
Fixes to try, and fixes to book
Reasonable to try from the ground or a low ladder in dry weather:
- brush the guard surface with a soft brush on a pole
- flush each downspout with a hose and check the outlet
- trim overhanging branches that drop debris straight onto the guard
- add or lengthen downspout extensions so discharge is carried away from the wall
Better booked with a crew:
- valley diverters, a larger trough or an extra downspout
- re-hanging a run to the right slope
- changing the guard design if the current one keeps skipping water
- anything involving soft fascia or second-storey work
What not to assume about an overflow
An overflow does not automatically mean guards are useless, and it does not automatically mean the guard is defective. It means one part of the system is being outrun, and finding which part is the whole job. Show the installer your video and your notes on where the water left the roof, and ask them to look at that spot first. Photograph the site and keep the paperwork in case a warranty question comes up.
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Key Takeaways
- Watch a downpour from a window or porch and note exactly where the water leaves the roof edge before you decide on a fix.
- A blocked downspout, a matted guard surface, an undersized trough, fast valley water and poor slope cause most overflows.
- Brush the surface, flush the downspouts and trim branches yourself in dry weather, but book valley diverters, re-hanging and design changes.
- An overflow points to one part of the system being outrun, so show the installer the exact spot.
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