Gutters for a Metal Roof: Size, Placement and Snow

Gutters for a metal roof need to be bigger and mounted a little differently than gutters under shingles. Water comes off smooth metal panels faster, it can overshoot a small gutter in a hard rain, and snow slides off in sheets that can tear a gutter right off the fascia. A 6-inch gutter with 3x4 downspouts, hung slightly lower on the fascia and paired with snow guards in snow country, solves most of it.

Size up

Smooth metal has almost no friction, so a cloudburst arrives at the gutter all at once. Most roofers put 6-inch K-style or larger gutters under metal, even on houses that would get by with 5-inch under shingles. Pair them with 3x4 downspouts. If the roof plane is long and steep, consider 7-inch or extra downspouts. Sizing details are in our downspout guide.

Placement on the fascia

Two measurements matter:

1. Panel overhang. Metal panels usually extend about 1 to 1.5 inches past the drip edge into the gutter. Too little and water curls back along the underside of the panel; too much and it shoots past the gutter.
2. Gutter height. Hang the gutter so that a straight line continuing the roof slope passes above the front lip. In snow country, many installers hang it a bit lower than they would under shingles so sliding snow clears the gutter instead of hitting it.

Snow and ice

On a metal roof, snow doesn't melt off slowly. It lets go as a sheet. Without protection, that sheet can:

• rip gutters and hangers off,
• crush shrubs, railings and anything below,
• injure someone standing at the drip line.

Snow guards (clamped to standing seams or fastened to the panels) hold the snow on the roof so it melts in place. They're the single most important add-on for gutters under metal in snowy climates. Use hangers every 16 to 24 inches and screw them into the rafter tails, not just the fascia board.

Match the metals

Metal roofs and gutters can corrode each other:

• Copper roof: use copper gutters only. Copper runoff corrodes aluminum, galvanized and Galvalume.
• Galvalume or painted steel roof: aluminum, Galvalume or painted steel gutters all work. Galvalume gutters are a common match.
• Fasteners: stainless or coated fasteners made for the metal; avoid mixing copper and steel fasteners.

Gutter guards under metal roofs

Metal roofs shed leaves well, so more debris ends up in the gutter. Guards help, but hood-style guards can be overshot by fast water off steep metal. Mesh guards that sit flat, attached to the front lip and the fascia, work better. Don't slide guards under metal panels or fasten through the panels.

Do you need gutters at all?

Some metal-roofed barns and cabins skip gutters and let water fall onto a gravel drip trench. That works where the ground slopes away and there's no basement. On a house with a basement or crawlspace, or anywhere the drip line is near a door or walkway, use gutters.