Water Running Behind Gutters? Usually It's the Roof Edge
If you see water running behind gutters on your house — streaks down the fascia, drips between the gutter and the board, a wet band of paint along the eave — the gutter itself is often fine. The roof above it is putting water in the wrong place. A lot of what gets reported as a "gutter leak" in St. Louis is really a roof-edge problem, and that matters for two reasons: resealing a corner won't help, and the fix may belong to a roofer rather than a gutter contractor. Here's how to tell which is which before anyone gets on a ladder.
Water running behind gutters: the drip edge
A drip edge is an L-shaped strip of metal that sits under the first course of shingles at the eave and hangs over the back of the gutter. Its job is to carry water from the shingle edge into the gutter instead of letting it wick back under the shingle and run down the fascia. Current model residential codes call for it on new roofs, and it has been standard practice for decades, though what's actually required and enforced on a re-roof depends on your city or St. Louis County. It's also the first thing skipped on a fast roof replacement.
St. Louis has a particular version of this problem. The metro gets hail most springs, and a lot of roofs in the county have been replaced after storms, sometimes twice in fifteen years. Storm work is often done quickly, and if the original roof had no drip edge the new one often doesn't either. So there are plenty of 1960s–90s houses in Florissant, Affton, Ballwin and O'Fallon with a newer roof and no drip edge, and the fascia behind the gutter has been wet ever since.
How to spot it: from the ground, look at the eave. You should see a strip of metal, usually white or brown, just under the shingle edge and behind the gutter. If you see shingle, then a gap, then gutter, there's no drip edge. Fascia that's stained or peeling in a continuous band along the roof edge, rather than just below the corners, is the other tell.
The fix: a roofer slips drip edge under the first course, or a gutter contractor adds a gutter apron — a wider flashing that does the same job from the gutter side — when re-hanging. Either is a few hundred dollars for a whole side. Getting drip edge and gutters to work together is mostly about the overlap: the metal has to end inside the gutter, not behind it.
Shingle overhang
Shingles should extend past the drip edge by about a quarter to three-quarters of an inch, so water drops cleanly into the gutter. Cut them flush with the fascia and water clings to the underside and runs back. Cut them two inches long and they droop, break, and in a wind-driven storm water blows past the outside of the gutter altogether.
How to spot it: flush shingles show as a clean, straight roof edge with the gutter well below it. Long shingles curl down over the gutter's front lip. Both show up as wet fascia or water on the ground right below the eave during a moderate rain, with the gutter not particularly full.
Valleys and the splash guard
A roof valley — where two roof planes meet in a V — concentrates water. On a two-story hip-roofed home in Chesterfield or Wildwood, a single valley can deliver water from 400 square feet of roof to one spot on the gutter at a rate the gutter can't absorb, and it shoots over the front lip or, in wind, past the gutter entirely. It looks like an overflow. The gutter is clean and pitched right.
How to spot it: water pouring over the gutter at one specific point directly below a valley, in the first minutes of a storm, while the rest of the run is fine.
The fix: a splash guard — a small bent piece of aluminum screwed to the front lip below the valley — for $40–$80, or a 6-inch gutter on that run if the roof area is big enough. Sometimes a diverter on the roof above spreads the flow.
Roof problems that show up as gutter symptoms
| What you see | Looks like | Actually is |
|---|---|---|
| Wet fascia in a long band, gutter not full | Gutter leaking along the back | Missing drip edge |
| Water on the ground under the eave in light rain | Gutter overflow | Shingles cut flush |
| Overflow at one spot under a V in the roof | Clogged gutter | Valley surge |
| Water behind the gutter only at one end | Failed end cap | Step flashing at a wall or chimney failed above |
| Granules and grit filling the gutter | Debris | Shingles shedding; the roof is aging |
| Ice forming behind the gutter | Gutter pitch | Ice dam from attic heat loss |
The last row is the winter version. Ice that forms behind the gutter, against the fascia, is meltwater from a warm roof deck refreezing at the cold eave — an attic problem, covered in ice dams in gutters.
What a good contractor does about it
A sound gutter repair or replacement estimate includes a look at the roof edge from the ladder, because there's no point hanging a new gutter behind an eave that's sending water down the fascia. If it's a drip edge problem, a good gutter contractor will say so and either add a gutter apron as part of the job or suggest you have a roofer look at it first. If it's a valley, the splash guard or the 6-inch run belongs on the estimate. Some roof and gutter contractors handle both trades, which can make the edge detail simpler to coordinate; if yours doesn't, ask who owns the flashing before work starts.
What nobody should do is reseal the same corner three times because the water keeps coming. If the gutter has been "fixed" twice and the fascia is still wet, look up.
Why it's worth catching early
Fascia that stays wet behind a gutter rots, and rotten fascia is what the hangers are screwed into. A roof-edge problem left for a few winters turns a few hundred dollars of flashing into new fascia boards plus a re-hang. If you're also seeing overflow at the corners, why gutters overflow in St. Louis rain covers the capacity side, and how to find a gutter leak has the hose test that separates the two.
Common questions
Should drip edge go over or behind the gutter?
The drip edge sits under the shingles and its lower flange should end inside the gutter, over the back edge, so water drops into the trough. If the gutter was hung low and the flange ends behind it, water runs down the fascia instead. A gutter apron can bridge that gap without re-roofing.
Who fixes a missing drip edge, a roofer or a gutter contractor?
Either can, depending on the approach. A roofer installs true drip edge by lifting the first course of shingles; a gutter contractor usually fits a gutter apron from below while the gutters are off or being re-hung. If the roof is new and under a roofer's workmanship coverage, ask the roofer first.
Why does my gutter leak only in heavy rain?
A gutter that drips only in a downpour is usually overflowing at a valley or a long run rather than leaking through a seam. A true seam or corner leak shows up in light rain and in a slow hose test. If the drip appears only in the first heavy minutes of a storm and only below a valley, look at a splash guard or a bigger gutter on that run.
Can short shingles be fixed without a new roof?
Often, yes. A roofer can add drip edge or a flashing extension under the existing first course, and a gutter apron can carry water past a flush-cut edge. Shingles that are too long and curling usually need trimming or a section replaced, which is a small roofing repair.
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