A downspout extension in Sioux Falls should carry roof water at least 5 feet from the foundation, farther if the house has a basement, and set it down on ground that falls away from the wall. It also can’t send water across a public sidewalk, which city code forbids. Most extensions cost about $33 to $40 installed. A buried line to a pop-up emitter in the lawn runs about $150 to $350 per downspout.
How long should a downspout extension be?
Five feet is the minimum. A 600-square-foot roof plane sends about 375 gallons down one downspout in a one-inch rain, and without an extension all of it lands a foot from the wall.
With a basement, go farther. The soil against a basement wall is usually backfill packed looser than the ground around it, so it settles and soaks up water. A buried line should end 10 feet or more from the house.
Length only helps if the ground keeps the water moving. Building code wants the soil to fall at least 6 inches in the first 10 feet from the foundation. If the yard levels off or tips back toward the house 4 feet out, an 8-foot extension just drops the water into a puddle that drains back. Walk the line in a rain and end the extension where the ground is still falling away.
A splash block on its own moves water 1 to 3 feet. Set one under the end of the extension to keep the stream from digging a hole in the lawn.
Which type of extension works best?
| Type | Best for | Weak point |
|---|---|---|
| Rigid section, aluminum or vinyl | Most yards, and the easiest to keep draining in winter | In the mower’s path, and easy to knock loose |
| Flexible corrugated plastic | Bending around a shrub, a step or a corner | The ridges hold water and grit, and cold plastic cracks |
| Roll-out sleeve | Short runs that need to stay out of the way | Thin plastic that freezes flat, so it comes off before winter |
| Flip-up hinge on a rigid section | A lawn that gets mowed every week | Only works if someone flips it back down |
| Buried pipe to a pop-up emitter | Long runs, paths to cross, two downspouts on one line | Costs the most and needs a cleanout |
A rigid section the same size as the downspout is the right default. It drains fastest, holds nothing, and a hinge at the downspout lets it swing up for the mower. Flexible tubing earns its place where the water has to bend around something. A roll-out sleeve unrolls when water fills it and rolls back when it dries, which keeps the lawn clear in summer and makes it the first thing to fail in January.
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Can a downspout extension cross a sidewalk or driveway?
Not a public sidewalk. Sioux Falls code bars any pipe from the eaves placed so that its water flows onto or over a public sidewalk. The rule goes back to the 1957 ordinances, and it matters most in winter, when water across a walk is ice by morning.
The city does let a flat, collapsible sump pump hose cross a sidewalk toward the street. That exception covers sump pumps only.
Your own driveway and walks aren’t under that rule, but the same ice forms on them. The fixes, from cheapest up: turn the extension to run along the house to open lawn, bury a line under the lawn to a pop-up past the paving, or move the downspout to another corner, which a contractor does by re-pitching that run of gutter. Digging under a public sidewalk is work in the city right of way, so ask the city before planning a route there.
Where is the water allowed to go?
Onto your lawn, to the street or into a storm sewer. City code keeps roof runoff out of the sanitary sewer unless the city engineer approves it, so an extension can’t feed a floor drain, a cleanout or a sewer connection. That is one of several rules on where downspout water can go in Sioux Falls.
Aim it away from the neighbor’s yard too. The city’s rule against water flowing onto adjoining property is written for sump pumps, and water running onto a neighbor’s lot starts the same argument whatever pipe it came from. Nearby towns set their own drainage rules, so check the rules in your town before running water to the street.
What happens to downspout extensions in winter?
They freeze from the end back. On a sunny February afternoon, snow melts off the roof, runs down the downspout and slows in the flat extension, which sits in the shade at ground level. It freezes there. The next melt backs up behind the ice and fills the downspout, and a full downspout can split at a seam.
Before the first hard freeze:
- Take roll-out sleeves and thin flexible tubes off and store them, and set a splash block under the downspout for the winter.
- Leave rigid extensions on, pointed downhill with no dip, so melt water runs out instead of pooling.
- Keep the end clear of the pile from shoveling the driveway.
- Check that buried lines drain at the pop-up. A buried downspout line sits well above the 42-inch frost depth Sioux Falls builds to, so water left standing in it freezes. A pop-up with a small weep hole drains between storms, and an overflow fitting near the downspout lets water out if the line is blocked.
A downspout that freezes solid is usually part of a bigger winter problem, and frozen gutters and ice dams begin up at the roof.
When is it worth burying the line?
Bury it when an above-ground extension keeps getting knocked off or mowed over, when the water has to cross a walk or driveway, when it needs to reach 10 feet or more, or when two downspouts can share one line.
Ask for smooth solid PVC, a slope of at least 1/8 inch per foot, a pop-up emitter at least 10 feet out and a cleanout where downspouts join. Anyone digging, homeowners included, calls South Dakota 811 two business days first. Regrading or landscaping in or within 100 feet of the regulated floodplain needs a $75 city floodplain permit, and the city can say whether a buried line counts.
How much do downspout extensions cost?
| Job | Price, 2026 |
|---|---|
| Above-ground extension, installed | About $33 to $40 each |
| Buried line to a pop-up emitter | $150 to $350 per downspout |
| Underground drainage for the whole house | $1,500 to $7,000, about $2,800 on average |
The length of each run, what it has to pass under and how many downspouts join decide your price, and a measured quote settles it.
What if the extension isn’t the problem?
If water still stands at the wall with a long extension on, look up and down. A gutter that overflows over the front drops water along the whole wall, nowhere near the downspout. A downspout that clogs every fall may need to be a 3×4 instead of a 2×3. A yard that tips toward the house needs regrading, and a basement that stays wet after all of that points to the causes of water in the basement after rain.
Questions about downspout extensions
How far should a downspout extension go from the house?
At least 5 feet, farther with a basement, and onto ground that falls away from the wall. A buried line should end 10 feet or more out.
Is a splash block enough?
No. A splash block moves water 1 to 3 feet, which leaves it in the soil against the foundation. Use one under the end of an extension.
Can a downspout drain across the sidewalk in Sioux Falls?
No. City code bars any pipe from the eaves placed so its water flows onto or over a public sidewalk. The flat hose the city allows across a sidewalk is for sump pumps only.
Should downspout extensions come off for winter?
Roll-out sleeves and thin flexible tubes should, because they freeze and crack. Rigid extensions can stay on if they point downhill with no dip.
Can a downspout drain into the sewer?
Not the sanitary sewer. City code keeps roof runoff out of it unless the city engineer approves. The lawn, the street and the storm sewer are the allowed routes.
How much does a downspout extension cost?
About $33 to $40 each installed, or $150 to $350 per downspout for a buried line to a pop-up emitter in 2026.
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