If your gutters overflow even when they are clean, the system cannot move water as fast as your roof sends it. The usual causes are gutters or downspouts that are too small for the roof area, too few downspouts, gutters pitched the wrong way or sagging, or a valley that dumps a flood of water into one corner. A blocked underground drain line can also back water up the downspout and out the top. Where the water spills over tells you which problem you have.
Where is your gutter overflowing?
Watch the gutters during a steady rain, from the ground or from inside the house. The location of the overflow is the best clue you will get.
| Where it overflows | Most likely cause |
|---|---|
| At an inside corner below a valley | Valley water overshooting or overwhelming the gutter |
| In the middle of a run | Sagging section or loose hangers creating a low spot |
| Along the entire length in heavy rain | Gutter or downspouts too small for the roof area |
| At the end farthest from the downspout | Pitch running the wrong way, or the run is too long for one outlet |
| Right at the downspout | Clogged outlet, elbow or underground drain line |
| Behind the gutter, down the fascia | Missing drip edge or gutter mounted too low |
| Off the front edge with guards installed | Guard shedding water instead of letting it in |
Are your gutters too small for your roof?
Many homes around Pittsburgh still have the 5 inch K style gutters and 2 by 3 inch downspouts that were standard when they were built. That size works on a modest ranch. It often falls short on a large, steep roof, a two story colonial with a big back slope, or any roof where several planes drain into one run.
Steep pitch makes it worse. Rain picks up speed on a steep roof and can shoot right over the front lip of a small gutter in a downpour. Our summer thunderstorms can drop rain at several inches per hour for short bursts, and that peak intensity is what a gutter has to handle, not the average rainfall.
Upgrading to 6 inch gutters gives you noticeably more capacity, and a 6 inch gutter fits a larger 3 by 4 inch downspout. A 3 by 4 inch downspout has twice the opening of a 2 by 3, so it drains water much faster and is far less likely to clog. Our comparison of 5 inch vs 6 inch gutters explains when the larger size is worth it.
Do you have enough downspouts?
A gutter can only empty as fast as its outlets let it. A common rule is one downspout for every 30 to 40 feet of gutter, with long runs pitched toward downspouts at both ends or split in the middle. If you have a 50 foot run with a single downspout at one end, the far end will overflow in heavy rain even with a perfectly clean gutter.
Adding a downspout is often the cheapest fix for overflow. Converting existing downspouts to 3 by 4 inch at the same time can solve the problem without replacing the whole gutter.
Is the gutter pitched correctly?
Gutters need a slight slope toward each downspout, usually about 1/4 to 1/2 inch of fall for every 10 feet. Too little slope and water sits. Too much and the gutter looks crooked and the low end can overload. On older homes, hangers loosen as the wood fascia ages, and heavy snow, ice and ladders leaned against the gutter pull sections out of line.
From the ground, look for standing water a day or two after rain, a gutter that visibly dips in the middle, or a gap between the gutter and the fascia. Old spike and ferrule hangers are a frequent culprit. Rehanging with hidden hangers screwed into solid fascia every 2 feet or so, and replacing any rotted fascia board behind them, fixes most sagging gutters.
Why do gutters overflow at roof valleys?
A valley collects water from two roof planes and sends it down a single channel. By the time it reaches the eave, it is moving fast and concentrated in one spot, usually an inside corner of the gutter. That water can jump the gutter entirely or fill the corner faster than it drains.
Two fixes help. A valley splash guard, a small piece of metal fastened to the front of the gutter at the corner, catches water that would otherwise overshoot. Placing a downspout close to the inside corner, or upsizing that corner to 6 inch, gives the water somewhere to go.
Could the problem be underground or in your gutter guards?
Many western Pennsylvania homes have downspouts tied into buried clay or plastic drain lines. Over decades those lines fill with silt and leaves, get crushed, or are invaded by roots. When the line cannot drain, water backs up the downspout and out the top of the gutter, even though the gutter itself is clean. Our guide to downspout drainage covers your options, from cleaning the line to redirecting water above ground.
Gutter guards can also cause overflow. Some solid cover designs rely on water curling around a rounded nose, and in a hard rain on a steep roof the water can sail past. Fine mesh guards clogged with pollen, oak tassels or shingle granules can shed water like a roof. If overflow started after guards were installed, the guards are the first suspect. See whether gutter guards are worth it for your roof.
Finally, winter overflow is often ice. A frozen downspout or ice built up in the gutter stops flow completely, and meltwater runs over the front and can refreeze as icicles.
What simple tests can you do safely?
- Watch it rain. Note exactly where water spills over and whether it happens in every rain or only downpours.
- Check for standing water. From the ground or a window, look for water sitting in the gutter a day after rain.
- Test the underground drain. Where the downspout meets the drain pipe at ground level, disconnect it if you can and run a garden hose into the pipe. If water backs up quickly, the line is blocked.
- Test the downspout. Run a hose into the bottom of the downspout or tap it along its length. A dull sound or no flow means a clog in an elbow.
- Look at the hangers. From the ground, look for gaps between the gutter and fascia or hangers that have pulled loose.
Leave anything above a first story ladder height to a professional, especially on wet or icy days.
Frequently Asked Questions
Why do my gutters overflow only in heavy rain?
Usually because the gutters or downspouts are undersized for the roof area, or there are too few downspouts. Light rain drains fine, but peak storm flow exceeds capacity. Upsizing downspouts to 3 by 4 inch or adding outlets is often the fix.
Will 6 inch gutters stop overflow?
They hold and carry more water than 5 inch gutters and accept larger downspouts, which solves most capacity problems. They will not fix a blocked underground drain, a sagging section or a pitch problem, so those should be checked first.
Is gutter overflow a serious problem?
It can be. Water spilling at the same spot erodes soil, splashes siding and can soak into foundation walls, which is a common cause of wet basements. Water running behind the gutter can rot fascia and roof decking.
Can I just add a downspout instead of replacing my gutters?
Often, yes. If the gutters are in good shape and properly pitched, adding a downspout or upsizing existing ones can be the most cost effective fix. If the gutters are old, leaking at the seams or sagging, replacement with seamless gutters may make more sense.
If your gutters overflow and you cannot figure out why, call Bella Construction at (724) 515 5163 for a free inspection. We will check sizing, pitch, downspouts and drainage and recommend the simplest fix that works. Learn more about our seamless gutter installation, and book soon because fall schedules fill before winter.