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Five inch, six inch, and the number that actually matters
Most overflowing gutters are not undersized. They are under-drained, back-pitched, or full.
This works out an answer as you change the controls, which needs JavaScript. Without it, the reference section below covers the same ground, and we are happy to talk it through.
Why downspouts matter more than size
A gutter is a holding trough on the way to a downspout. Once water arrives faster than the outlets can take it away, the trough fills and the surplus goes over the front edge regardless of whether it is five inches or six. Adding an outlet is usually cheaper and always more effective than replacing a run.
- Put outlets at the ends of runs, and add one wherever a valley discharges into the gutter.
- A valley concentrates two planes of water into a few feet of trough. That is the spot that overflows first.
- Downspouts need somewhere to go. A downspout discharging against the foundation moves a roof problem into a basement problem.
- Check the pitch of the run. Gutters hung flat or back-pitched hold water, and standing water is what pulls a run off a fascia.
The drawing below puts the troughs and the two downspout outlets side by side, which is where the difference in capacity actually shows.
When the answer is not a bigger gutter
| What you see | What it usually is | What fixes it |
|---|---|---|
| Overflow at one spot every time | A valley discharging into a run with no outlet near it | An outlet where the water arrives |
| Overflow along the whole run | Too few downspouts, or blocked ones | More outlets, or clearing the ones you have |
| Water behind the gutter | Missing or reversed drip edge | Correct edge metal at the eave |
| A sagging run | A rotten fascia that will not hold a spike | Carpentry first, gutter second |
| Staining down the cornice on an old house | A failed box gutter lining | Relining, not replacing with a hung gutter |
On the pre-1940 stock in Hyde Park, Mt. Adams, Clifton, Norwood, Over-the-Rhine and Columbia-Tusculum, the gutter is frequently built into the cornice. Sizing does not apply in the usual way, and swapping it for a hung gutter changes a historic elevation and is often the wrong repair. Box gutters.
Gutters, fascia and drip edge are one system, and they are usually diagnosed together.
Have them looked atAll work is performed by licensed and insured local roofing professionals.