Downspout Not Draining: How a St. Louis Gutter Contractor Finds the Block

The outlet at the top

The hole in the bottom of the gutter where the downspout connects is the narrowest point in the whole system. Everything in the trough heads there. In late April the silver maples drop their seeds by the bucket, and they wedge into that opening like corks.

Oak tassels arrive a few weeks later and bind it all together. Shingle granules settle underneath and turn the mess into something close to mud. Clearing it by hand from a ladder takes a few minutes. Leaving it for a season means the gutter fills and spills in every storm.

Elbows catch what the outlet lets through

Most downspouts don't run straight. There's an offset near the top to kick the pipe in from the eave to the wall, and another elbow at the bottom to turn the water out into the yard. Each bend is a place for a clump of leaves to stop.

Tap along the downspout with a screwdriver handle. A clear pipe rings hollow. A packed one sounds dull right where the clog sits. Upper elbows can usually be cleared from the top with a plumber's snake or by taking the offset apart, and we'll reattach it with fresh screws so it doesn't sag afterward.

If clogs come back every few months, the outlet may be undersized for the roof above it. A 3x4 downspout carries noticeably more water than a 2x3 and is far harder to plug.

Buried pipe that quit years ago

Lots of St. Louis houses have downspouts tied into a pipe underground. Older homes may have clay tile lines. Houses from the last few decades usually have black corrugated plastic, the flexible ribbed kind. Both fail, just differently.

Clay tile cracks at the joints, and tree roots find the cracks. Corrugated pipe crushes under a mower or a car, and its ridges trap silt until the line is half full of dirt. Neither shows any sign from above until water starts backing up the downspout or bubbling out of the lawn a few feet away.

We run water through the line and see where it comes out, if anywhere. A drain camera settles the question when the hose test can't. Our downspout drainage solutions page lays out the replacement options once you know the line is done.

Clay soil changes the plan

Here's the honest part. Much of the St. Louis area sits on heavy clay that barely takes on water. A pop-up emitter at the end of a buried line only works if the pipe has somewhere lower to go. On a flat lot in the Metro East or a yard that slopes back toward the house, that lower spot may not exist.

In those cases a buried line just becomes an underground holding tank. Water sits in it, then seeps back toward the foundation. Sometimes the better answer is a longer extension above ground, or re-routing the downspout to a different corner where the grade falls away. We'd rather tell you that than dig a trench that won't drain.

Frozen solid in January

Freeze-thaw weather does a number on downspouts. Snow melts off the roof on a sunny afternoon, runs down the pipe, and freezes in the bottom elbow after dark. The next melt has nowhere to go. In a bad week the whole downspout can fill with ice, and a seam may split as it expands.

Usually the ice thaws on its own and everything works again. But a downspout that freezes every winter is often sitting in shade, or it's emptying into a buried line that holds water. Fixing the drainage below it tends to fix the freezing too. Our ice dams and gutters page covers the roof side of winter water.

Why this one's worth the trouble

A blocked downspout isn't just a gutter problem. Every bit of water it was supposed to carry away ends up spilling at the foundation. On clay, that water swells the soil, pushes on the walls, and finds its way into the basement. See basement flooding from gutters if you're already seeing it inside.