Water Shooting Over the Gutters on a Metal Roof: Causes and Fixes
Why Metal Roofs Overshoot Gutters
A shingle roof has a rough, granular surface and overlapping courses. A metal roof is smooth panel from ridge to eave. In a heavy downpour, water on a metal roof arrives at the edge as a fast, continuous sheet, and if the gutter's front edge is low or the trough is narrow, the water clears it and lands on the ground below.
When a home switches from shingles to metal, the existing gutters were sized and hung for the old roof, so it is worth checking them as part of the job.
Steep pitches make it worse. A University of Illinois guide to gutters and downspouts notes that "a steeper pitch needs a bigger gutter," which is why it bases gutter size on actual roof area rather than the footprint of the house.
Gutter Size for a Metal Roof
Residential gutters are usually 5 or 6 inches wide. The University of Illinois guide gives a simple rule:
| Condition for a 5-inch gutter | If not met |
|---|---|
| Downspouts are less than 30 feet apart | Use a 6-inch gutter |
| Roof pitch is 9 in 12 or less | Use a 6-inch gutter |
| Roof area drained is less than the gutter length in feet times 30 | Use a 6-inch gutter |
All three conditions have to be true for a 5-inch gutter. In the guide's words, "Most other cases require six-inch gutters."
Steep metal roofs and large unbroken roof planes often fail at least one of those tests, so upsizing to 6-inch gutters is a common fix for overshooting.
Gutter Position and Panel Overhang
Where the gutter sits relative to the roof edge matters as much as its size.
- Back edge under the drip edge. The University of Illinois guide says "the back edge of the gutter should be placed under the front edge of the metal gutter apron or drip edge," and if the gutter sits lower, a strip of matching metal should be added behind the drip edge so water runs into the gutter and not behind it.
- Panel overhang into the gutter. Metal panels should extend past the eave and over the gutter, but only so far. One panel manufacturer, Allsteel, recommends 2 to 3 inches of overhang where there is no gutter, "while only 1-inch overhang is necessary where gutters are used." Your panel manufacturer's eave detail is the governing reference.
- Gutter height. A gutter mounted too high on the fascia, or tilted forward, leaves a shallow front lip for fast water to clear.
Downspouts Matter Too
A gutter that cannot drain fast enough overflows even if it is the right size. The University of Illinois guide recommends one square inch of downspout per 100 square feet of roof: a 2 x 3 downspout can handle about 600 square feet of roof, and a 3 x 4 about 1,200. It also recommends an extra downspout when the run between corners is longer than 50 feet. Upsizing from 2 x 3 to 3 x 4 downspouts, or adding one in the middle of a long run, is often part of the fix.
Where two roof planes meet at a valley, water concentrates on a short stretch of gutter. That is a related but separate problem, usually solved with a splash guard at that corner.
Fixes, From Simplest to Most Complete
- Clean and check the pitch. Debris or a gutter sloped away from its downspout makes overflow worse in any storm.
- Add splash guards at spots where water clears the gutter, such as below valleys and at inside corners.
- Add or upsize downspouts so the gutter empties faster.
- Re-hang the gutter lower and tight to the drip edge, with the back edge under it, so the panel overhang lands in the trough.
- Replace with 6-inch gutters sized for the roof area and pitch. This is often the complete fix after a switch from shingles to metal.
If you are planning a new metal roof, it is the right time to size gutters for it. Our gutter installation service can size and position gutters for a metal roof, and our metal roof repair page covers the roof side of the eave.
Why It Is Worth Fixing
Water that overshoots the gutter falls along the foundation, splashes the lower siding and can erode beds and walkways. The 2024 International Residential Code takes roof runoff seriously where soils are a concern: "In areas where expansive soils or collapsible soils are known to exist," homes must have a controlled method of roof drainage that discharges at least 5 feet from foundation walls or to an approved drainage system (R801.3). If your home sits on expansive clay, ask your builder or a foundation professional whether that applies to your lot. Either way, gutters that actually catch the water are what make that possible.
Sources: University of Illinois Small Homes Council-Building Research Council, Council Notes F13.1, "Gutters and Downspouts for the Home" (1990); Allsteel metal roofing FAQ; International Residential Code (2024) R801.3.
Frequently Asked Questions
Why does rain shoot over my gutters on a metal roof?
Water runs off smooth metal quickly, so in heavy rain it can clear a gutter that is too small, hung too high or too far back, or that sits under panels hanging too far out.
What size gutters do I need for a metal roof?
A University of Illinois guide says 5-inch gutters work only when downspouts are under 30 feet apart, the pitch is 9 in 12 or less and the roof area is modest. Most other cases call for 6-inch gutters.
How far should a metal roof overhang into the gutter?
Follow your panel manufacturer’s eave detail. One manufacturer, Allsteel, says about 1 inch of overhang is enough where gutters are used, versus 2 to 3 inches without gutters.
Do gutter splash guards work on metal roofs?
They help at specific spots where water concentrates, such as valleys and inside corners. They do not fix a gutter that is undersized or hung in the wrong position.
Do I need new gutters when I get a metal roof?
Not always, but the existing gutters should be checked for size, position and downspout capacity, because they were set up for the old roof.
