Why does water pour over the gutter at a roof valley?
A valley is where two roof planes meet. Rain that falls across both planes runs toward that one line and leaves the roof at one narrow spot. Speed, roof material, roof pitch, the valley flashing and where the gutter sits under the roof edge all decide whether the water drops into the gutter or flies past it. Valleys also carry leaves, pine needles and shingle granules toward the same outlet.
How much water comes off a roof valley?
Roof runoff demand is about 0.0104 x rainfall intensity (in/hr) x roof area (sq ft). If two roof planes send 1,200 sq ft of roof to one valley, a 6 in/hr downpour delivers about 74.8 gallons per minute to that spot. That is water arriving, not proof any gutter will catch it.
| Roof area feeding the valley | At 4.5 in/hr | At 6 in/hr | At 8 in/hr |
|---|---|---|---|
| 500 sq ft | 23.4 gpm | 31.2 gpm | 41.6 gpm |
| 1,000 sq ft | 46.8 gpm | 62.3 gpm | 83.1 gpm |
| 1,200 sq ft | 56.1 gpm | 74.8 gpm | 99.7 gpm |
| 1,500 sq ft | 70.1 gpm | 93.5 gpm | 124.7 gpm |
| 2,000 sq ft | 93.5 gpm | 124.7 gpm | 166.2 gpm |
What are the 5 causes of gutter overflow at a valley?
Before anyone sells a bigger gutter, we find which of these is happening. It is often more than one.
| Cause | What you see | Usual fix | Will a 7-inch gutter help? |
|---|---|---|---|
| Overshoot | Water sheets past the front lip, gutter not full | Reposition the gutter relative to the roof edge; wider opening; check splash guard options | Sometimes; the wider opening catches more |
| Outlet bottleneck | Gutter brims near the downspout; downspout not keeping up | Larger outlet, 4x5 downspout or added downspout | Not by itself |
| Clog | Overflow after leaf or pollen season | Clean; review outlet, elbows and guards | No |
| Poor slope or low spots | Standing water, overflow mid-run | Re-pitch toward outlets; re-hang | No |
| Not enough gutter for the water | Gutter full along the run in heavy rain, outlets clear | Larger gutter plus matching downspouts | Yes |
When does a 7-inch gutter actually fix valley overflow?
A 7-inch gutter fixes it when the gutter is too small for the water reaching that run and the outlets and downspouts are upgraded with it. Using one maker's reference profiles, a 7-inch trough holds about 27% more standing water than a 6-inch (about 1.42 vs 1.12 gallons per foot). That is storage, not flow. If the outlet is the tight spot, a bigger gutter still backs up there. Learn more in our 7-inch seamless gutters guide.
Do valley splash guards stop overflow?
A splash guard can redirect some water that overshoots at a valley. Used in the wrong place, it can back water up, trap debris or hide the real problem. We check the gutter's front lip, the roof edge, the slope, where the valley ends and outlet capacity first, and we never fasten through roofing or valley flashing without the roofing system's approval. See valley splash guards on tile roofs and can rain shoot over gutters.
Will a bigger downspout fix an overflowing valley?
Only if the outlet or downspout was the restriction. If water overshoots before it reaches the gutter, a larger downspout won't catch it. When the outlet is the problem, a larger outlet, a 4x5 downspout or an extra downspout near the valley usually helps. See 3x4 vs 4x5 downspouts for 7-inch gutters and add a downspout or a larger gutter?.
Do gutter guards stop valley overflow?
No guard is clog-proof, and every guard still needs upkeep. Guards reduce some debris, but in heavy rain, sheets of fast water can run over some guard surfaces at a valley. Valleys and guard tops still need checking after storms. Read gutter guards in heavy Florida rain.
How does PrimeFlow assess a valley that overflows?
Our overflow correction service: Orlando and Sarasota.
- Record the roof type, pitch and roughly how much roof drains to the valley.
- Photograph the valley, the roof edge, the gutter position and any overflow stains or splash marks.
- Decide which cause applies: overshoot, backup, blocked outlet, poor slope, discharge, or a mix.
- Check the fascia angle and condition before choosing hangers.
- Find the nearest downspout and check the outlet opening and elbows.
- Recommend a fix and where the water should go once it leaves the downspout.
Book a roof-valley overflow assessment
We find the real cause before recommending a size. Call (407) 902-7639 in Orlando or (941) 404-3901 in Sarasota for a free estimate.