Downspout Extensions and Underground Downspout Drainage: When They Work & How They Are Installed

What it is

Roofs collect a large amount of water during a storm, and gutters concentrate it at a few downspouts. When downspouts dump next to the house, that water can pool against the foundation, wash out beds and flood side yards.

Above-ground extensions or splash blocks move water a short distance. Underground downspout drainage connects each downspout to buried solid pipe that carries roof water to an outlet such as a pop-up emitter, ditch or curb outlet where allowed. It is often the simplest first fix for water near a house.

When it is a good fit

Water pooling where a downspout discharges
Soil or mulch washing out below downspouts
Wet side yards between houses
Downspouts that empty onto walkways or driveways

When something else may work better

Groundwater or soggy soil from other sources (French drains or grading may be needed too)
Clogged gutters, which must be cleaned first

How it is usually installed

Check gutters and downspouts for clogs and leaks
Choose an outlet lower than the downspout and away from the house and neighbors
Trench from the downspout, keeping steady slope
Connect the downspout with an adapter and lay solid pipe
Install the outlet (pop-up emitter, curb outlet or other) and test with a hose

Every property is different. A drainage professional confirms the design onsite. Call 811 before any digging.

What a drainage professional checks first

Roof area draining to each downspout
Whether lines can share a pipe or need separate runs
Distance and fall to the outlet
Clay soils and tree roots along the route
Rules about piping to the curb or street

Maintenance

Keep gutters clean so debris does not enter the pipe
Check that pop-up emitters open and close freely
Flush lines if water backs up at the downspout

What affects the cost

Pricing pending verification

Drainage.net does not publish prices until they have been checked against sourced data. See what drives the cost of downspout extensions and underground downspout drainage, or request an onsite evaluation for a real quote.

Example drainage photos

Red clay trench beside a shrub with green drain pipe sections and a white tee fitting on the lawn — Drain pipe and fittings ready to lay in a clay trench.

White drain pipe laid in a lawn trench, ending at a concrete edge — White drain pipe in a lawn trench, before backfill.

Grey drain pipe in a trench running across a front lawn and under a sidewalk — Drain pipe routed across a front lawn and under the sidewalk.

Green drain pipe in a trench running along a sidewalk and curb — Drain line running along a sidewalk toward the street.

Photos show drainage work in progress and are included for illustration only. They are general examples, not customer reviews.

Frequently asked questions

How far should a downspout drain from the house?

Far enough that the water cannot flow back toward the foundation. The right distance depends on the slope of the yard, and buried pipe to a lower outlet is often more reliable than a short extension.

Why is water bubbling out at my downspout?

The underground line may be clogged, crushed or flat, or the outlet may be blocked. See underground downspout clogged.

This page is educational and does not replace an onsite evaluation. Conditions, codes and HOA rules vary by property.

Downspout Extensions and Underground Downspout Drainage