When a gutter overflows, almost everyone assumes it is full of leaves. Sometimes it is. Just as often the gutter is doing exactly what it was built to do and the system was never sized for the roof above it.
The Part People Get Wrong
A gutter does not overflow because the trough is too small to hold water. Water is not supposed to sit in it. It overflows because water is arriving faster than the downspouts can take it away.
That means downspout count and size matter more than gutter width. A 6-inch gutter with one undersized downspout at the end of a 50-foot run will overflow. A 5-inch gutter with two properly placed 3x4 downspouts on the same run usually will not.
Contractors upsell gutter width because it is visible and easy to quote. Downspouts are the cheaper fix and the more effective one.
When 6-Inch Is Genuinely Worth It
Move to 6-inch gutter with 3x4 downspouts if any of these apply:
- Steep roof pitch, 8/12 or greater. Water arrives at the eave fast and with momentum, and a 5-inch trough lets it shoot over the front edge.
- Large roof area draining to one short run. A long, wide plane dumping into 20 feet of gutter needs capacity.
- Valleys discharging onto a gutter. A valley concentrates the runoff of two roof planes into a stream a few inches wide. That point overwhelms a 5-inch gutter in heavy rain regardless of how clean it is.
- Metal roofing. Snow and water shed faster off metal than off asphalt.
On a standard Milwaukee ranch or bungalow with moderate pitch and no valley dumping, 5-inch with adequate downspouts is genuinely fine. We do not upsell 6-inch as a default.
Downspout Rules We Work To
- One downspout per 30–35 feet of gutter run, minimum.
- 3x4 rather than the older 2x3 on anything with real roof area above it. A 3x4 moves roughly twice the water.
- An outlet at any point where a valley discharges, not just at the ends of the run.
- Never drain an upper roof downspout directly onto a lower roof surface. That concentrated stream will strip granules off the shingles below and cut a visible track in a few seasons. Run it into the lower gutter or carry it down the wall.
Where the Water Goes Next
This is the step that actually protects the house, and the step most commonly skipped.
A downspout that ends at the foundation is not solving a drainage problem, it is relocating it. Water discharging at the wall goes straight down beside the footing. In Milwaukee's clay soils, that is how you get a wet basement, and over enough freeze cycles it is how you get foundation movement.
Extensions should carry water 6–10 feet away from the wall, and the grade should fall away from the house for at least the first 6 feet. Buried drain lines work well when they are pitched correctly and daylight somewhere sensible. They fail badly when they are buried flat, because they silt up and you cannot see that it has happened.
If you have a wet basement and you have not checked where your downspouts terminate, check that before you spend money on interior waterproofing. We have seen a lot of basements dried out by $200 of extensions and regrading.
Ice Load, the Wisconsin Variable
A 6-inch gutter full of ice weighs substantially more than a 5-inch one. If you are going wider, the hanger spacing has to come with it, 24 inches on center with hidden hangers screwed into solid fascia. Wide gutter on old spike-and-ferrule hardware is how you end up with a gutter hanging off the front of the house in February.
How We Size It
We measure the roof area draining to each run, look at pitch and valley discharge points, then size the trough and place downspouts against that. It takes a few extra minutes on the estimate and it is the difference between a gutter system that works in a hard August downpour and one that only works in light rain.
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