Why are my gutters overflowing? 6 common causes and fixes

The quick answer

In almost every case, a gutter that overflows is a gutter that's blocked. Water can't reach the downpipe, so it backs up and spills over the front edge instead. Around Greater Manchester that's usually leaves, moss and silt, and it gets worse from October onwards, once the leaves are down and the rain arrives properly.

There are a few other causes, though, and each one needs a different fix. Here are the six we come across most, and what each of them actually needs.

1. Leaves, moss and silt in the gutter run

This is the most common cause by a long way. Leaves collect first, then moss washed off the roof, then grit and general dirt. Together they form a silt that holds water like a sponge. The gutter fills, and the next heavy shower sends water straight over the front.

Homes with trees close to the roof are worst. So are roofs on the Pennine side of Greater Manchester — Rochdale, Littleborough and Oldham — which shed more moss than most, and that moss ends up in the gutter.

A straightforward clear-out is all this needs.

2. A blocked downpipe

This one catches people out, because the gutter itself can look perfectly clean. If the outlet or the downpipe is blocked, water backs up along the run and overflows at the nearest low point — often directly above a front door, which is how a lot of damp patches get started.

You can usually spot it during rain: a downpipe that stays dry while the gutter above it is pouring over. Clearing the gutter without flow-checking the downpipe just moves the problem a few feet along the wall.

3. Gutters that have lost their fall

Gutters are meant to run very slightly downhill towards the downpipe. If brackets have dropped or the run has been pushed out of line, water sits in the low spots instead of draining away, and the gutter overflows at that point even when it's empty of debris.

Overflow at one point, with a dry downpipe below it, is the classic sign. This isn't a cleaning job — it needs the run re-set and re-fixed.

4. Joints and brackets that have failed

The joints between gutter sections, and the brackets holding the run up, take a lot of weight when a gutter is full of wet debris. A joint that's pulled apart or a bracket that's snapped lets water escape — usually as a steady drip or a streak down the wall rather than a full overflow.

5. Gutters too small for the roof or the rain

Older narrow gutters on a large roof can struggle in a genuine downpour even when they're spotless. If your gutters are clear, the downpipes are flowing, and they still overflow in the worst weather, capacity is the more likely explanation than a blockage.

6. Water shooting over from a valley or steep roof

On a steep roof, or where two roof slopes meet in a valley, rainwater arrives at the gutter in a rush. In a cloudburst it can overshoot the gutter completely. This tends to happen on the same stretch of roof every time, and only in heavy rain.

Overflowing gutter, or leaking joint?

Worth knowing the difference, because the two need different things. An overflowing gutter sends water over the front edge, usually in sheets and usually during heavy rain. A leaking joint drips from one specific point, often for a while after the rain has stopped. The first is nearly always a blockage. The second is usually a joint that's failed, and it's worth catching early before it stains the wall or soaks into the brickwork.

What you can safely check from the ground

You can learn a lot without going up a ladder:

• Look for plants, grass or moss growing out of the gutter.
• Watch it in the rain and note whether the overflow runs along the whole gutter or comes from one spot.
• Check that each downpipe is actually running in heavy rain.
• Look for dark tide marks or green staining on the wall under the gutter line.
• Look for gutters that sag, or visible gaps opening at the joints.

We don't recommend going up a ladder to look. Falls from ladders cause a lot of serious injuries at home, and the view from the top is rarely better than the view from the ground.

When to call a professional

If the gutter is blocked, the downpipe is blocked, or you've spotted damage, it's time to get someone out. Overflowing water does real damage over time: damp patches inside, rotten fascia boards, blown render, stained brickwork. Clearing a gutter costs far less than repairing what it damages.

With our gutter clearing service we clear every accessible gutter run from the ground using a high-reach vacuum, flow-check the downpipes, and send you before and after photos. If we find damage — a failed joint, a snapped bracket, a gutter that's lost its fall — we'll tell you and show you in the photos.

If you're still not sure whether it's a blockage or something else, our guide to the signs your gutters are blocked walks through it. And when you're ready, you can see your fixed price and book a clear online in about a minute.