Overflowing gutters
Why do conservatory gutters overflow?
The short answer
Conservatory gutters overflow for a handful of reasons: leaves and debris blocking the outlet, a gutter that has sagged or lost its fall, split or loose joints, and too much water arriving from the house roof above. A small gutter and a single downpipe cope badly with a big catchment. Most causes can be found by watching the gutter in heavy rain, then put right with cleaning, refixing or a larger outlet.
The usual reasons a conservatory gutter spills over, how to tell them apart from the ground, and what puts each one right.
Blocked outlets and debris
The commonest cause is the plainest. Leaves, moss, grit from the roof and the occasional ball settle in the gutter, and the outlet to the downpipe chokes. Water then backs up and runs over the front edge, often at the lowest point or at the far end. Conservatory gutters are small and tucked under overhanging branches or against a house wall, so they fill faster than people expect and are easy to forget.
Clearing is simple in principle, but the access is not. Many conservatory gutters sit above fragile roofing, and a ladder leant on the panes can crack them. A reach from a stable platform or a proper access tower is safer. After clearing, pour water in with a hose and watch the downpipe at ground level. If water pours out freely, the blockage was in the gutter. If it trickles, the downpipe or the drain at the bottom is also blocked, and that needs rodding. A leaf guard or mesh can slow the build-up, though it still needs checking.
Gutters that have lost their fall
A gutter has to slope gently towards the outlet so water keeps moving. Manufacturers give figures for it. Brett Martin's installation guidance says 1 mm for every 600 mm, and FloPlast gives 1 in 350 for its MiniFlo system, so roughly 1 in 600 to 1 in 350 depending on the system. Brackets should be no more than 900 mm apart on the Brett Martin system. Over time brackets loosen, fascia boards move, and the gutter sags between supports, leaving a pool of standing water that spills over in a downpour.
A standing puddle after rain is the sign. Lay a straight edge or watch how the water sits after a shower. The cure is to refix the brackets and set the run back to a proper fall, and sometimes to add a bracket in the middle of a long span. If the fascia behind is rotten, the gutter will not hold its line however many brackets are added, and the fascia needs replacing first. Our guttering, soffit and fascia page explains that work.
Joints, brackets and stop ends that have failed
If water is coming out of the gutter but not over the top edge, look for the joints. Plastic gutters are joined with push-fit unions that hold a rubber seal. The seal hardens and splits over time, and the joint begins to drip, often only in heavy rain when the flow is high. Stop ends at either end of the run can come away from the gutter body. Cracked brackets let one section drop below the next and create a step where water pools.
Fresh drips and tide marks on the fascia or the wall behind show where the water has been running. Wet patches under a joint tell the story even when the weather is dry. A replacement seal or a new union is often all that is needed, which is far less expensive than a new run. Silicone smeared on from the outside is a poor fix, since it seldom lasts and it hides the failure. If the gutter is old, brittle and sagging along its length, replacing the lot is more sensible than patching joint after joint.
Too much water for a small gutter
Conservatory gutters often serve more than the conservatory. Where the roof of the house comes down onto the conservatory roof, or a valley sends a long run of water across it, the little gutter at the edge catches a catchment it was never sized for. In heavy rain it simply cannot carry the flow, and the gutter overtops even though it is clean, level and well jointed. A single outlet at one end makes this worse, because the water has to travel the length of the gutter before it can leave.
The tell-tale is overflow only in downpours, at the same point each time. The fixes include a larger gutter section, a second outlet and downpipe, or a better way of taking the house roof water away. Sometimes the answer is a downpipe on the house roof that stops the upper water arriving at all. Our guide to a leaking conservatory roof covers cases where the problem is the roof and not the gutter, and the two are easy to confuse.
Tracing the cause and getting it fixed
The quickest test is to watch the gutter in heavy rain, or to run a hose along it from the highest end while someone watches the outlet. Note where the water leaves, whether it is over the front, out of a joint or behind the gutter into the wall. Photograph it. That tells a roofer far more than a description does, and it saves a wasted call-out.
We survey the roof, take photographs of each fault and tell you whether cleaning, refixing or replacing will fix it. That gives you a written quote with a single total price. If the gutter overflow is a symptom of something larger, such as a ridge that leaks or a roof that has failed, we tell you, and our page on conservatory roof rain noise and the other guides in the conservatory roof replacement section explain what comes next.
Related questions
Gutter overflow checks
Why does my conservatory gutter only overflow in heavy rain?
Usually because the gutter or outlet is too small for the water arriving, often with extra run-off from the house roof. A clean, level gutter can still overtop in a downpour. A bigger section or a second outlet is the normal cure.
Can I stop overflow by fitting a leaf guard?
It helps with leaves but not with a poor fall, a failed joint or a catchment that is too big. Find the cause first, because a guard over a sagging gutter simply hides the problem.