Walk around your house and look at where each downspout ends. On a lot of homes, it's a short elbow aimed at the corner of the stoop, the edge of the driveway, or a strip of mulch that has turned into a little canyon.
That elbow handles more water than you'd think. An inch of rain on 1,000 square feet of roof adds up to roughly 600 gallons, and one downspout often drains a big share of the roof. All of it lands a foot or two from the foundation, right beside your concrete.
When a stoop, patio, or garage apron sinks, there's very often a downspout or sump outlet within a few feet of the low corner. Fixing that is cheap, and you can do it this weekend.
What That Water Does to a Slab
Concrete doesn't sink on its own. The soil under it goes somewhere. Concentrated roof water washes fine soil out from under slab edges, soaks the loose backfill that surrounds every foundation, and feeds frost heave when that wet soil freezes in winter. More on the first one in voids under concrete.
How Far Should Downspouts Extend?
The guidance lands in a fairly tight range:
- University extension guidance for homes with wet basements says to release downspout water 5 to 10 feet from the house.
- The International Residential Code, a national model code, calls for at least 5 feet from foundation walls where soils are expansive or collapsible, unless the water goes to an approved drainage system.
- Some Wisconsin cities set their own. Mequon tells homeowners to extend downspouts 6 feet.
Our advice: 6 feet is a good minimum and 10 is better. But distance isn't the whole test:
- 1The water has to keep movingAn extension that ends in a low spot just builds a puddle that drains back toward the house. For new homes, that same model code calls for at least 6 inches of fall in the first 10 feet from the foundation, which is a good target for any yard.
- 2It has to clear the concreteNext to a stoop, walk, or patio, the extension should end past the far edge of that slab, on grass that slopes away. Dumping onto the slab just moves the problem to its other side.
Downspout Extension Options Compared
| Option | Relative cost | In a Wisconsin winter | Watch out for | Good fit when |
|---|---|---|---|---|
| Hinged (flip-up) extension | Low | Flipped up for snow removal, it dumps at the foundation every thaw | Mower and snowblower damage | The outlet has to clear a walk or driveway |
| Flexible or accordion extension | Lowest | Fills with ice and freezes to the ground | Cracks in the cold; sags into low spots | You need a quick fix, or have to curve around something |
| Splash block | Lowest | Ices over and heaves out of place | Spreads water instead of moving it; tips toward the house as soil settles | Under the end of an extension, on ground that slopes away |
| Buried line to daylight | Moderate to higher | The most freeze-tolerant buried option, if it drains empty | Needs steady fall, a cleanout, and a Diggers Hotline call | There's a slope or low area away from the house to send water to |
| Buried line to a pop-up emitter | Moderate to higher | Water sitting below the emitter can freeze and back up to the house | Clogs with shingle grit and leaves | The lot is flat with no place to daylight |
| Rain barrel | Low to moderate | Must be drained and disconnected in fall or it can crack | Fills fast; the overflow still needs to go 6+ feet away | You want garden water, with an extension on the overflow |
A rain barrel isn't a drainage plan. A typical 55- to 60-gallon barrel under a downspout that drains 250 square feet of roof is full before half an inch of rain falls. The rest comes out the overflow.
If You Bury It, Build It to Drain Empty
A buried line is the neatest option and the one most likely to fail quietly here. Frost runs deep in northeast Wisconsin, and getting a downspout line below it isn't practical for most homeowners. So the line has to empty itself between storms.
A buried line that holds up has:
- Solid pipe, not perforated. Perforated pipe near the house leaks water right back into the backfill you're trying to keep dry.
- Fall the whole way. At least 1/8 inch of drop per foot, with no dips where water can sit.
- A cleanout. Shingle grit and leaves are what clog buried lines. A debris trap near the downspout lets you flush it with a hose.
- An outlet that drains. Daylighting onto a slope is the most reliable. Pop-up emitters hold water in the line below them, and that's the part that freezes.
- A route that stays out from under slabs. A cracked pipe under a walk or driveway washes soil out from below, where you can't see it.
- A winter fallback. When a buried line ices up, water spills out at the downspout, right at the foundation. Some homeowners switch to a surface extension from late fall until spring.
Before you trench, contact Diggers Hotline. Wisconsin law (Statute 182.0175) requires anyone digging, homeowners included, to contact them at least three working days ahead. Dial 811. It's free.
Winter Problems to Plan Around
- Ice dams. Ice at the roof edge makes meltwater spill over the gutter instead of going down the downspout, so no extension helps. Ice dams usually trace back to attic heat loss, which is a roofer or insulation contractor's call.
- Thaw days. On sunny February and March afternoons, roof snow melts and runs down the downspouts while the ground is still frozen. Water that crosses a driveway or sidewalk refreezes overnight. Then come the deicers, and salt plus freeze-thaw is hard on concrete (more on that here).
- Snow piles. Snow shoveled against the house or onto an extension outlet melts right where you don't want it. Pile it downhill from the house, and flip hinged extensions back down on thaw days.
Where Not to Send the Water
- Onto a neighbor's property. It's a classic source of disputes.
- Across a public sidewalk or street. It becomes ice for everyone who walks by.
- Into the sanitary sewer. Pumping sump or downspout water into a floor drain, laundry tub, or sewer line is prohibited in many Wisconsin communities, because clear water overloads the sanitary system and contributes to basement backups.
Local rules vary. Nearby, the Village of Greenville bars sump discharge onto public walkways, onto a neighbor's property without an easement, or within 10 feet of the property line. Check with your own municipality.
Don't Forget the Sump Pump
In a wet spring, a sump pump can run over and over on snowmelt and groundwater, even when the roof isn't dripping. Discharge that lands along the foundation can soak back toward the drain tile, so the pump runs again. Same rules as downspouts, plus two for winter:
- Add a relief point. If a long or buried discharge line freezes, an overflow or freeze-relief fitting near the house lets water escape at the surface instead of backing up.
- Keep the outlet clear. A discharge buried under a snowbank is about to freeze.
The After-Rain Walk: Is Water Already Under Your Concrete?
Walk the whole house during or right after a heavy rain, or on a thaw day.
| What you see | What it probably means | What to do |
|---|---|---|
| Water running along a slab edge or disappearing under it | It's carrying soil out from under the slab | Extend that downspout now |
| A gully or washed-out mulch at an outlet | The outlet is too close or aimed wrong | Lengthen or redirect it |
| A gap under a slab edge you can slide fingers into | Soil is gone from under that edge | Check for sinking; foam fills voids as it lifts |
| A slab tipped toward the house, or an open joint where it meets the house | Water is being sent straight down along the foundation | Lift the slab to pitch away, then seal the joint |
Then step on each slab corner near a downspout. If it rocks, or sounds hollow when you tap it with a hammer handle, there's likely a void underneath.
What's DIY, and Where We Come In
Extending downspouts is a homeowner job, and the most useful thing you can do for your concrete. You don't need a contractor, and we don't install gutters, extensions, or drain lines.
Where we come in is the damage the water already did:
- Foam lifting raises sunken slabs and fills the voids under them as it lifts, through 5/8" holes about the size of a dime. Cured foam is waterproof, so it won't wash out the way the soil did. Here's how concrete lifting works.
- Joint and crack caulking closes the gaps where surface water gets under slabs, including the joint where concrete meets the house. We seal after lifting, once the holes are patched.
Fix the water before the lift or right after it. Leave the downspout dumping beside a lifted slab, and next spring's melt starts digging a new void.