A gutter has one job: take the water that lands on a roof and walk it to a downpipe. In ordinary rain it manages without anyone noticing. In a downpour the whole roof delivers at once, and any weakness shows up as water pouring over the front lip, down the wall or past a corner. Autumn adds leaves, which clog outlets, and winter adds ice, which blocks, splits and weighs things down.
The leaking guide covers faults such as perished seals and sagging runs. This one is about weather load, so it starts from the question of how much water arrives and where it goes. We do not quote rainfall figures for Stroud or Gloucestershire, because the reasoning works without them and we would rather not guess. Where a number appears, it comes from a manufacturer or a published price guide. For faults, see leaking gutters; for the full service, gutters, soffits and fascias.
How a downpour overwhelms a gutter that is otherwise fine
Think of the gutter as a channel with a limited flow. Its capacity depends on its width and depth, its fall towards the outlet, how many outlets it has and how far the water must travel to reach one. The load depends on how much roof drains into it. A broad roof slope feeding a long, single-outlet run gives the water far to go and a lot of it at once.
Where it spills first
Overflow tends to begin at the same few places. The first is a stop end or internal corner, where flow changes direction and piles up. The second is the foot of a roof valley, where two slopes tip their water into one point on the gutter. The third is the stretch just before an outlet that is partly blocked. A gutter that is perfectly adequate along most of its length can fail at one of these, and the staining on the wall below shows which.
Fast water and the front lip
Rain running off a steep roof arrives with speed. It can shoot over the front lip of a shallow gutter even though the channel is not full. A gutter that is set too low relative to the roof edge, or tilted out of position by a loosened bracket, will catch less of that stream.
Fall, brackets and the levels that keep water moving
A gutter that is dead level holds water in the run, and one with a back-fall sends it away from the outlet. Both lose capacity before the storm even starts. Manufacturers give a gentle slope towards the outlet. FloPlast's guide for its small-building gutters recommends 1:350 where a fall is fitted, and Brett Martin's guidance is a drop of 1 mm for every 600 mm of run, which is 1:600. Taken together, the typical range is about 1:600 to 1:350 depending on the system, and you can follow your own product's data sheet.
Why bracket spacing matters in rain
A full gutter is heavy. Water weighs a lot, and a run that sags between brackets forms a shallow dip where water sits and the lip drops below the rest. FloPlast says brackets on straight runs of its small gutter should be no more than 500 mm apart. Brett Martin's guide gives a maximum of 900 mm for its system and advises supports spaced more closely, down to 600 mm, where heavy snow is expected. Those are different products, so the number to follow is the one for the gutter on your house.
What we check
We look along each run for sagging, for brackets that have pulled or rusted, for joints that have opened and for the fall itself. Our guide to leaking gutters deals with the joints. Fall and brackets matter in this guide for a simpler reason: they decide how much of the gutter's capacity is actually available when the weather arrives.
Sizing, outlets and downpipe positions
When a roof has changed, the gutter may no longer suit it. An extension feeding an old run, a dormer dropping its water into one corner or a larger slope after a loft conversion all add to the load. The gutter that coped before may now be the weak point.
Options for a gutter that is too small
A wider or deeper section carries more. An extra outlet and downpipe shortens the distance the water must travel. Moving an outlet closer to the point where the roof delivers most of its water, such as a valley, removes the pile-up at its source. Often a combination is right: a larger section and an additional downpipe.
Downpipes and the drain
A gutter can be generous and still back up if the downpipe is narrower than the flow or the ground drain cannot take it. If water overflows only when it has been raining for a while, the problem may be at the bottom of the system. Our guide to fascias, soffits and gutters explained shows how the parts connect.
Pricing a change of size
MyBuilder's 2026 price guide puts guttering at £30 to £70 per metre, with scaffold at £20 to £40 per m². These are national ranges, not our figures. A wider section or an extra outlet goes into the written quote after the survey, so the upgrade can be weighed against like-for-like replacement. Our roofline cost guide covers what moves the price.
Autumn leaf fall: the slow blockage
Leaves behave differently from rain. They collect in the low points of the gutter and at the outlet, and a few can start a dam. Once water backs up behind them, a modest shower is enough to overflow, and the wet mass of leaves adds weight to the run. A gutter beneath overhanging trees can go from clear to blocked in a single stormy week.
Moss, grit and the roof itself
Leaves are not the only debris. Moss and grit wash off the roof covering into the gutter, particularly from a roof that has been cleaned or from tiles that are shedding granules. A gutter is a catchment for everything the roof loses, and the silt that builds up can fill the channel and sprout plants.
Clearing and checking
Clearing should happen when the leaves have come down, not when the first storm shows the problem. Do it from a safe position. We cover methods in our gutter cleaning guide. After clearing, pour water in and watch the flow: standing water at one point means a fall problem, a slow drain means a blocked outlet or pipe.
Never lean a ladder on a plastic gutter or climb onto a wet roof edge. If a gutter is overflowing in the middle of a storm, note where from the ground and call us instead.
Gutter guards: what they help with and what they do not
Guards are covers or meshes that sit over the channel to keep leaves out. They can reduce how often a gutter needs clearing, which is the reason people fit them under trees.
The benefits
A well-fitted guard keeps larger leaves and twigs out of the run, so the water stays free to flow. Over a long gutter with a hard-to-reach section, that cuts the number of ladder visits.
The limits
Guards do not make a gutter maintenance-free. Fine debris, moss and grit can settle on top of or pass through a mesh. In heavy rain a guard can also act as a shelf, with fast water skimming over the top and past the lip, and a badly fitted one can lift in wind or catch a gutter's edge. Some guard types restrict access for checking the channel, so rot or a blocked outlet beneath goes unnoticed.
Where we would suggest one
Under overhanging trees, or over a section feeding a single awkward downpipe. On a gutter that is sagging or sloping the wrong way, we fix the gutter first, because a guard hides the fault and does not cure it. Our gutter guard answer weighs the options in more detail.
Winter ice and snow load
Freezing weather changes the gutter in several ways. Water standing in the run freezes and expands, and that can split joints in plastic and crack cast iron, particularly at the bends. Ice in an outlet or at the top of a downpipe blocks it, so that melt water or the next rainfall has nowhere to go but over the lip.
Weight on the brackets
Snow slides from a roof into the gutter in a heavy lump. Ice-filled gutters weigh far more than the system was designed for in ordinary use, and brackets that are already loose or corroded give way. That is why the bracket spacing in the manufacturer guidance tightens for snow country, and why we check fixings before the cold sets in.
Thaw is the risky moment
Overflow often shows up when the ice starts to melt: the gutter is still partly frozen while the roof is shedding water, so the melt cannot clear. Streaks of ice or green staining on a wall below a gutter are worth a look on a dry day.
Preparing
The best preparation is the same as for rain: a clear channel, working outlets and sound brackets. A leak at a joint also turns into an icicle in cold weather, so what looks like a winter problem may be a repair that could have been done earlier. We do not give frost or snowfall figures, only the order of work: clear, check the fixings, and look again after the first hard frost.
Reading your own gutters in a downpour
You can learn a great deal by watching from the ground, dry and safe, during a heavy shower. Note where the water leaves the gutter and how. A sheet over the front lip along a straight run points to a fall or capacity problem. A spout at a corner suggests a stop end or joint. A stream pouring from one point under the eaves, or down the wall, suggests a blocked outlet.
What to send us
Photographs and a short note: which elevation, how the water behaved and whether it happens in every storm or only the heaviest. With that, we can usually say whether the answer is clearing, resetting the fall, a bracket repair, an extra outlet or a bigger section before we visit.
What follows
At the survey we take pictures of the gutters, the roof edge and the downpipes on your own house. The written quote covers scaffold, removal, new goods and making good, and the work comes with a 10-year workmanship guarantee, in writing. Rainwater goods that are sized for the roof and kept clear tend to give the least trouble, so the steps above tend to cost less than repeated emergency visits.