Why is my eavestrough overflowing?

Where and when does it overflow?

Two questions narrow it down faster than anything else. Does the water come over in one spot, or along the whole run? And does it happen in every rain, or only in a downpour? Put the two answers together and you are most of the way there:

• One spot, every rain. Something is holding the water at that point: a blocked outlet or downspout, or a low spot where the run has sagged.
• One spot, heavy rain only. Usually a roof valley or a steep section dropping more water on one short stretch than it can take.
• The whole run, every rain. The slope is wrong, or the trough is packed with debris along its length.
• The whole run, heavy rain only. Too few downspouts, or a run too small for the roof it serves.

The best time to look is a steady rain. Walk around the house and take a photo or a short video of each spot that spills. It helps whoever comes to look, and it lets you check that what they quote matches what you saw.

What does it mean if it overflows in one spot?

Water coming over at one place means the water is being held up at that place.

A blocked outlet or downspout. The outlet is the hole in the bottom of the trough where water drops into the downspout. Leaves, seeds and shingle grit collect there first, and once it plugs, the stretch beside it fills and spills. If the overflow is right next to a downspout, start here.

A sag. A run that has dropped between its fasteners holds water in the low spot instead of draining it, and in a heavy enough rain that low spot is where it comes over. A sag usually leaves standing water behind after the rain stops, too. If a stretch of yours is dipping or pulling away from the house, our guide to sagging or pulling-away eavestrough goes through why it happens.

A corner or an end. Corners collect debris, and an inside corner takes water from two directions at once. If it is always the same corner, that corner is holding water.

One thing to rule out: a drip is not an overflow. Water dripping from underneath, at a joint or a corner, is a leak. Water coming over the front edge is an overflow. In a downpour the two look the same from the driveway, so stand where you can see the front lip.

What does it mean if it overflows along the whole run?

When a whole side of the house spills, the problem is the run itself, not one point in it.

Slope. Eavestrough is not hung level. It needs a steady fall toward the downspout so the water runs to the outlet instead of sitting in the trough. A run hung flat, or one that has shifted so it now falls the wrong way, fills along its length and comes over the front. Two giveaways: standing water along the run a day after the rain, and overflow that is worst at the end farthest from the downspout.

Too few downspouts. Each downspout can only carry so much water away. A long run with one downspout at the far end can spill along its length in a heavy rain even when the slope is perfect, because the water reaches the outlet faster than the downspout can take it.

Too small for the roof. A big or steep roof sends more water into the eavestrough, faster, than a small one. If the run is undersized for the roof above it, it overflows in every downpour. More downspouts is often the answer, so each one serves less of the roof. On some roofs, a larger size of eavestrough is.

Debris along the length. Under mature trees, which describes a lot of London, the whole trough can fill, and water runs over the top of the debris instead of along the bottom.

Does it overflow every rain, or only in a downpour?

The timing tells you whether something is stopping the water or the eavestrough simply cannot carry it.

Every rain, even a light one. A light rain should never fill a working eavestrough, so overflow in a drizzle means something is in the way: a blockage, a sag or a backwards slope.

Heavy rain only. The eavestrough works, but it is at its limit, from too few downspouts, an undersized run, or a roof valley. A valley is where two roof slopes meet and funnel their water into one short stretch. In a downpour, water comes off a valley fast enough to shoot past the trough or swamp that one section, while the rest of the run copes fine.

Winter. Icicles building along one stretch usually mark where water sits in a low spot or spills over the front. A run full of ice cannot drain at all, so meltwater on a mild day goes straight over the edge. If your trouble is mostly in winter, read our guide to ice dams and eavestrough, because the cause can start on the roof above, not in the trough.

What can you check safely from the ground?

More than you might expect, and none of it needs a ladder. Leave second-storey eavestrough to a crew with the right equipment.

In a steady rain:

• Note every spot where water comes over the front, and whether it is one spot or a whole side.
• Look at the bottom of each downspout. A trough spilling above a downspout that is barely running points to a blockage in the outlet or the downspout.
• Check where each downspout empties. Water landing against the foundation is its own problem, and our guide on where downspouts should drain covers it.

On a dry day:

• Stand at a corner of the house and sight along the eavestrough. A sag shows up as a dip in the line.
• Look for a gap between the eavestrough and the house, where a run is pulling away.
• If an upstairs window looks down into the trough, check for standing water or a build-up of debris.
• Look at the board behind the eavestrough, and the window sills below it, for stains, peeling paint or soft wood.

That last check matters more than it looks. Water that spills over the front lands on whatever is below, and water that gets behind the trough soaks the board it hangs on. That board is the fascia, and once it goes soft the fasteners lose their grip, the run sags, and the overflow gets worse. Our guide to the signs of rotted fascia and soffit shows what to look for.

Is overflowing eavestrough a repair or a sign to replace it?

Overflow on its own does not mean new eavestrough. It depends on the cause and the shape of the rest of the run.

These are usually a repair:

• One sag on a sound board. The run is refastened and its slope reset so it drains to the downspout again.
• A downspout in the wrong place, or not enough of them. Downspouts can be added, moved, extended or rerouted.
• One corner or section that holds water.

These lean toward replacement:

• The slope is wrong along most of the run, or it sags in several places.
• The board behind it has gone soft along long stretches. Rotted wood cannot hold a fastener, so the board has to be replaced first, and the eavestrough has to come down for that anyway.
• Overflow plus leaking seams, rust or splits. Then the overflow is one symptom of eavestrough that is failing overall.

A blocked outlet on an otherwise sound run is neither. That is debris, not a fault in the eavestrough, and it is no reason to replace anything.

We look for the cause first and tell you which it is. If a repair will not hold, we say so before you pay for one. Our page on eavestrough repair in London lists the fixes we do. For the rest of the decision, including age and condition, see whether to repair or replace your eavestrough.

Will a leaf guard stop my eavestrough overflowing?

Often not. A guard changes what gets into the eavestrough. It does nothing for a sag, a backwards slope, too few downspouts or a run too small for the roof, and those cause most overflow. Where a valley or a steep roof sheds water fast and heavy, the water can run straight across the guard and over the front.

We are not fans of guards in general, and we would rather fix the cause than cover it. Debris still builds up on a guard, and in a London winter ice can build up in it. If you are weighing one anyway, our guide on whether leaf guards are worth it covers the few cases where one earns its place.

Common questions

Why does my eavestrough overflow when it isn’t clogged?

Then the run itself is usually the problem: a sag, a flat or backwards slope, too few downspouts, or a run too small for the roof. Watch where and when it spills to tell which.

Why does my eavestrough overflow at the corner?

An inside corner takes water from two roof slopes at once, often right below a valley. If one corner spills in every heavy rain, more water is arriving there than that stretch can move to a downspout.

Is water coming over the back of the eavestrough a problem?

Yes, and it is worse than water over the front. Water going behind the eavestrough runs down the board it hangs on and can rot it. If you see staining behind the trough or on the board, have it looked at soon.

Will new seamless eavestrough stop overflowing?

Only if the cause is fixed with it. New seamless eavestrough still needs the right slope, enough downspouts and a sound board behind it. A new run hung flat will overflow like the old one.

Can you tell me what’s causing mine?

Yes. When we come out to quote, we look at the slope, the downspouts, the roof above and the board behind the eavestrough, and tell you what is causing the overflow and whether it is a repair. The inspection is free. We serve London, Ingersoll, St. Thomas, Strathroy-Caradoc, Stratford and Aylmer. Call or text (548) 488-3206, or ask for a free quote.