5-Inch or 6-Inch? The One Decision That Outlasts the Paint

Why this question matters more in Wilmington than in Raleigh

Gutter sizing is a rate problem: can the trough carry water to the outlets as fast as the roof delivers it? Our rainfall is what engineers politely call "high intensity" — the design storms that size drainage here assume more inches per hour than almost anywhere inland in the Carolinas. A gutter that never overflows in Charlotte can regularly overflow on the same house rebuilt in Carolina Beach. When a properly clean gutter still sheets over the edge in July downpours, capacity is the culprit, and no amount of cleaning or resealing fixes arithmetic.

The actual decision factors

• Roof area feeding each run. The bigger the plane draining to one gutter, the more it argues for 6-inch. Big open ranch roofs and two-story rear planes are the classic offenders.
• Pitch. Steep roofs fire water into the gutter faster — same volume, less time. Steep + large = 6-inch, almost automatically.
• Valleys. A valley concentrates two planes into one firehose aimed at a few feet of gutter. Runs fed by valleys either get 6-inch, a splash diverter, or both.
• Downspout count. Sometimes the honest fix is another downspout on a 5-inch run rather than an upsize — cheaper, and we'll say so when it's true.

The mixed answer is a real answer

Houses aren't uniform and quotes shouldn't be either: 6-inch on the two big planes that actually flood, 5-inch on the porch and dormers where it's plenty. That's how we quote when the roof calls for it — sized by plane, itemized by the foot, no rounding everything up to the expensive number.