Clogged Underground Downspout? How to Find, Clear and Fix It

A buried downspout line is one of the best drainage fixes for a Jacksonville house — until it stops taking water. Then the roof's water backs up in the downspout, spills out at the connection and lands right where the line was supposed to keep it away from: at the foundation. Here is how to tell your line is clogged, why it happens, what you can try, and when the line has to be replaced.

Signs the underground line is blocked

• Water overflows at the top of the buried connection, or the downspout leaks at the seams during a storm.
• The gutter above that downspout overflows even though the gutter itself is clean.
• The pop-up emitter or the outlet at the curb stays dry in a storm.
• A wet patch or sinkhole appears along the route of the line — a sign it has cracked or separated rather than clogged.

Why buried downspouts clog here

• Leaves and needles. Oaks drop leaves and pines drop needles from fall through winter, and whatever gets past the gutter goes down the downspout.
• Roof grit. Shingle granules settle in the low points of the line.
• Roots. Live-oak roots find the joints of old lines and close or crush them. This is common on older streets in Mandarin and Orange Park.
• No fall, or a sag. A line laid without steady fall to the outlet, or one that settled, holds water and silt in the low spot.
• A blocked outlet. A pop-up emitter buried by mulch or grown over by sod cannot open.

How to find where an underground downspout goes

Start at the downspout and look for the outlet: a pop-up emitter in the lawn, an opening at the curb, or a grate in a swale. Cleanouts — capped pipes sticking up at the turns — show the route. Running a hose into the downspout and watching where water comes out, or where the ground turns soft, tells you the rest. On older houses the lines were often never mapped, and finding them is part of what we do on the inspection.

What you can try yourself

1. Clear the gutter and the outlet first. Make sure the gutter drains into the downspout and the emitter or curb outlet is not buried.
2. Flush from the top. Disconnect the downspout at the buried adapter and run a garden hose into the line. If water flows freely at the outlet, a gutter or downspout clog was the problem.
3. Flush through a cleanout. If there is a cleanout, flushing from there pushes debris toward the outlet in shorter steps.
4. Stop if it does not move. A line that will not take a hose is usually crushed, root-bound or separated, and pushing harder will not open it.

When the line has to be replaced

Crushed corrugated pipe, joints full of roots and lines with no fall cannot be flushed back to working. We dig out the failed section or the whole line and replace it with solid pipe, laid with steady fall to a legal outlet — the street, a swale on your lot or a dry well — and put cleanouts at the turns so it can be flushed instead of dug up the next time. Near big oaks we route around the root zone. The sod goes back.

Clogged line or crushed line?

The difference decides the fix. A clogged line takes some water from a hose and slowly gets better as you flush it; debris comes out at the outlet. A crushed or root-bound line takes almost nothing, and water backs up at the downspout within seconds. A line that takes water but never delivers it to the outlet has separated underground, and the wet patch along its route shows where. Only the first can be flushed back to working.

How to keep a new line from clogging

• Keep the gutters clear, or add guards where oaks and pines overhang the roof.
• Keep mulch and sod off the emitter lid.
• Flush through the cleanouts once a year, ideally after the leaves are down.

What it costs

Replacing or installing an underground downspout line runs $300 to $800 per point in our area, depending on the distance to the outlet and what is in the way; a line that crosses a driveway or a paver walk needs a bore or a cut. A house with four downspouts is typically $1,500 to $3,000. See downspout & underground drainage and gutter repair, or call (904) 561-1816 for a free inspection within 48 hours.