Why Is My Gutter Overflowing? 6 Common Causes

An overflowing gutter is one of the most common calls we get, and the good news is that the cause is usually easy to identify once you know what to look for. Here are the six most common reasons, roughly in order of how often we see them.

1. A blocked gutter

A blocked gutter is by far the most common cause of overflow. Leaves, moss and general debris build up over time, and once a section is blocked, water simply spills over the front rather than running along to the downpipe. If you can see debris sitting in the gutter, or plants growing out of it, this is almost certainly your answer. See our gutter cleaning service, or if it has not been touched in years, our full clearance service.

2. A blocked downpipe

A blocked downpipe causes overflow even when the gutter itself is clear, but the downpipe it feeds into is blocked further down, so water backs up and overflows at the top. This often shows up as overflow concentrated at one specific point rather than along the whole run. Our downpipe unblocking service clears this without digging.

3. Incorrect fall (pitch)

Incorrect fall means the gutter was not fitted with the right slope. Gutters need a slight pitch so water runs to the downpipe; with a very slight slope so water runs towards the downpipe. If a section has dropped or was fitted incorrectly, water can pool in the middle of a run and overflow there even when the gutter is clean. This usually needs a bracket adjustment rather than a clean.

4. The gutter is pulling away from the fascia

A gutter pulling away from the fascia is usually caused by old or corroded brackets can let a gutter sag or tilt outward. Water then runs along the front lip instead of staying inside the channel. You will often see this as a visible gap or dip in the line of the gutter.

5. Undersized gutters

Undersized gutters are a less common cause, but on some extensions or larger roof areas the original gutter simply is not sized for the volume of water it now has to carry, especially during heavy downpours. This is worth investigating if overflow only happens in the heaviest rain despite the gutter being clear and well-fitted.

6. Genuinely heavy rainfall

Heavy rainfall can overwhelm even a well-maintained, correctly sized gutter will still overflow briefly during an exceptionally heavy downpour. If it only happens in the worst weather and clears up afterwards, this may simply be the system reaching its limit rather than a fault.

What to do next

If you are not sure which applies to you, the quickest way to find out is to have it looked at. We check gutters, downpipes, brackets and fall as standard on every visit, and will tell you honestly which of these is causing the problem rather than just booking a clean regardless. See our gutter repairs page if the issue turns out to be structural.