Most gutter overflow isn’t a clogging problem — it’s a sizing problem. A standard 5-inch gutter has a fixed water capacity per linear foot, and a large or steep roof can exceed that capacity during a heavy storm even when the gutter is completely clean.
Sizing a gutter correctly means calculating the roof’s drainage area, not just its footprint — a steep pitch sheds water faster than a shallow one, which increases peak flow. In areas with high-intensity rainfall, a 6-inch gutter with oversized downspouts is often the right call even on a moderately sized roof.