Overflowing gutters
Why are my gutters overflowing when it rains?
Rain pouring over the front of a gutter has a cause you can find. Here are four causes, and how to tell them apart without leaving the ground.
The short answer
Gutters overflow because something stops the water reaching the downpipe: a choked outlet, a run that dips or slopes the wrong way, brackets that have worked loose, or a gutter too small for the roof feeding it. Watch where the water spills. Spilling at the outlet points to a blockage, while spilling along the run points to a dip or a slope that is wrong.
5 min read · Part of Gutters, soffits & fascias
Reading where the water spills
The place the water leaves the gutter points to the cause, so watch the next heavy shower, or run a hose along the roof edge and watch.
| Where it spills | Likely cause |
|---|---|
| At the outlet | Blocked outlet or downpipe |
| Along one low stretch | A dip between brackets |
| At the stop end | Slope set away from the outlet |
| Everywhere in a downpour | Gutter too small for the roof |
A single cause is not always the whole story. A choked outlet fills the run and makes a slight dip spill as well, so once the outlet is clear you can see what is left. A gutter that spills in two spots has two faults, and they are put right one at a time, outlet first. It is worth clearing first and testing again, rather than assuming the whole run is at fault, and a second test with the hose shows what remains. Keep a note of each result, because it tells us where to start, and send it with your photo.
Blockages at the outlet and in the pipe
Leaves, moss washed from the tiles and grit shed by the roof all drift towards the outlet, because that is where the gutter is sending everything, including the lumps of moss that come down after a roof has been cleaned. Once it is choked, the run fills and spills over its lowest edge. The downpipe can block at its bends or at its foot, and then the water backs up the pipe into the gutter.
Which? Trusted Traders price clearing a property's gutters, front and back, at £75 to £350 (November 2025, excluding VAT), and say the South East is likely to price towards the top of the range.
Clear the outlet first, then check that the downpipe below runs freely. Our answer on a blocked downpipe shows what can safely be done from the ground. Moss on the roof above keeps feeding the gutter after each storm, so look at the roof as well as the run, and note whether the same stretch of tiles sheds into the same stretch of gutter. Overhanging branches do the same job, dropping leaves and seeds straight into the run, so a tree close to the eaves means the clearing has to be repeated.
Slope, brackets and gutter size
Guttering is meant to fall gently towards the outlet. Brett Martin gives the fall as 1 mm for every 600 mm, which is too slight to judge by eye, so we check it with a level laid along the run and mark any dip with a pencil before a bracket is touched.
Three faults follow when the slope or the support goes wrong.
- A dip between two brackets holds a pool that never gets to the outlet.
- A bracket that has lost its grip in the fascia lets the run settle a little further each shower.
- A run set to slope away from the outlet sends its water to the stop end.
On a sound fascia these are repairs: re-set the brackets, add one where the gap between them is wide and correct the slope so the water runs to the outlet. On a long front drained by one outlet at the end, a second outlet halfway can be tidier, and it is worth deciding early.
Size is the fourth cause. A large roof slope feeding a shallow gutter can overshoot it in a downpour although the run is clear and level, and then the cure is a deeper profile or a second downpipe to share the load.
When overflowing means something bigger
A spilling gutter has not necessarily worn out. A choked outlet, or a single bracket that has slipped, makes a good gutter spill just as a worn one does, and neither calls for new guttering. Settling that is the first question we answer at a survey.
Sometimes the cause sits behind the gutter. If water has spilled for years, the fascia can be wet or soft, and brackets pull out of soft timber. Our page on a leaking gutter joint deals with the neighbouring fault in the same run. Where the fascia has failed, the job is different, and our answer on capping over fascias explains why a cover is not the cure.
Send a photo of where the water spills, with a note of how hard it has to rain before it happens, and whether the same place spills every time. We come to look, tell you which of these causes it is and give one written total price. The gutters, soffits and fascias page shows what else we check along the roofline.
More questions
Why do my gutters overflow only in the heaviest rain?
In a downpour the roof sends down more water than a small or part-blocked gutter can carry, so a slight dip, a half-choked outlet or a shallow profile shows up. If it happens only then, a deeper gutter or a second downpipe may be the answer, and the survey tells which.
Can overflowing gutters cause damp inside the house?
They can. Water that runs down the wall instead of down the pipe soaks the brickwork, and a spilling gutter keeps the fascia and rafter feet wet. We look at the wall and the board behind the gutter at the survey, and report what we find before suggesting any work.
Tell us what's wrong with the roof.
You'll get one written total price.