Why the extension matters
A downspout concentrates the rain from a whole roof section into one stream. Without an extension or splash block, that stream lands right against the foundation, soaks the backfill and finds cracks, window wells and crawl-space vents. The City of Naperville, Illinois puts it plainly in its homeowner brochure: a downspout without an extender or splash block is worse than no downspout at all. See downspouts and your foundation.
How far should water go?
Recommendations vary by source and soil, but they cluster in a narrow band:
- At least 4 feet: Naperville’s seepage brochure says extensions and splash blocks should discharge at least four feet beyond the wall, and the University of Minnesota Extension gives the same 4-foot minimum in its basement moisture guidance.
- 5 feet: Arlington County, Virginia suggests 5 feet for downspouts that discharge onto the ground, and the City of Aurora, Colorado’s building code amendment calls for a five-foot splash block or hinged section.
- 10 feet with a basement: Arlington County recommends 10 feet where a basement is present, and Naperville asks for 10 feet for sump pump discharge.
The common thread: farther is better, water must land on ground that slopes away, and the discharge must not create a problem for a neighbor or a walkway.
Types of extensions
Splash blocks
Concrete or plastic pads that spread the stream and carry it a foot or two from the wall. Cheap and simple, but they move, tilt and rarely reach the 4-foot mark on their own. Best on lots with a good slope away from the house.
Fixed rigid extensions
Lengths of downspout, usually 2x3 or 3x4 inch, attached to the bottom elbow and run along the ground. They are durable and keep their slope but sit in the way of mowing and foot traffic.
Flip-up (hinged) extensions
A hinged section lets you swing the extension up for mowing and back down afterward. The weak point is human: extensions left up through a storm or a winter thaw send water straight to the foundation. At seasonal homes they are a poor choice. See gutters for seasonal and vacation homes.
Roll-out and flexible extensions
Vinyl sleeves that unroll under pressure, and corrugated flexible pipe that bends around beds. Flexible pipe clogs more easily because debris catches in the ridges, and vinyl roll-outs wear out. Useful as a quick fix, not a permanent solution.
Buried lines with pop-up emitters
Smooth-wall pipe buried a few inches down carries water to a pop-up emitter in the lawn or a dry well. Clean looking and mower-proof, but it needs a steady slope so water drains fully, a cleanout for debris and a discharge point that does not freeze shut or flood the neighbor. See underground downspout drainage.
Rain barrels and cisterns
A barrel catches the first part of each storm; the overflow still needs one of the extensions above. See rainwater harvesting from gutters.
What cities require or forbid
Local rules on downspouts come in three kinds. First, discharge distance and direction: Aurora’s amendment bars downspouts from draining across primary walkways or onto adjacent properties, and Overland Park, Kansas sets a 5-foot setback from property lines for discharges. Second, sewer connections: many cities, among them Skokie and Evanston in Illinois and Marietta in Georgia, prohibit or require removal of downspout connections to sanitary or combined sewers. Third, incentives: Arlington County gives a stormwater credit for redirection systems with storage, and Round Rock, Texas rebates part of the cost of rainwater collection gutters. Our city pages list the local rules where we have official sources: Naperville, Aurora, Overland Park, Arlington, Evanston, Marietta and Round Rock.
Common mistakes
- Extension points uphill or onto a flat spot, so water pools and flows back.
- Discharge next to a window well or a crawl-space vent. See gutters and window wells.
- Onto a walk or driveway, where it freezes in winter. See downspouts and icy walkways.
- Onto a septic drainfield or toward a well. See gutters on rural homes.
- Flexible pipe left buried without a cleanout, which clogs within a few seasons.
- Too few downspouts, so each extension carries more than it can spread. The University of Minnesota Extension suggests at least one downspout per 50 feet of eave; many installers use 30 to 40 feet. See downspout size and placement.
Grading goes with it
An extension only works if the ground beyond it slopes away. The University of Minnesota Extension recommends a slope of at least 1 inch per foot for the first 6 feet from the foundation; Naperville asks for a 6-inch drop over the first 10 feet. Settled backfill along a foundation often creates a trough that needs filling before any extension will help. See gutters and landscaping.
Cost
Splash blocks and rigid extensions cost little and are usually included when gutters are installed; buried lines cost more because of digging and fittings. HomeGuide puts downspouts themselves at about $2 to $4 per foot installed. Ask the installer to list the discharge method for each downspout in the quote. See how to compare gutter quotes and our cost guide.
A quick check after installation
During the next heavy rain, walk around the house. Water should leave every extension and keep moving away. Pooling at the outlet, flow back toward the wall or a stream across a walk means the extension or grading needs adjusting. Doing this once saves a wet basement later. See wet basement? check gutters first.
Sources
- City of Naperville: Protecting your home, preventing seepage problems (brochure)
- University of Minnesota Extension: Moisture in basements, causes and solutions
- Arlington County: Conservation landscaping guidance (2023)
- City of Aurora, CO: Council study session notice with building code amendments (gutters and downspouts)
- City of Overland Park: Sump pump discharge policy (Resolution No. 3690, 2008)
- HomeGuide: Seamless gutters cost