A downspout extension should carry roof water far enough from the wall that it cannot soak back to the foundation: University of Minnesota Extension says at least 4 feet beyond the wall, and the U.S. Department of Energy's Building America guide says at least 5 feet from the foundation. Which figure fits your house, and which kind of extension, depends on what is under the house and where the water goes next.
How long should a downspout extension be?
Each source sets its own figure, so read each one as that body's rule.
| Source | What it says | Note |
|---|---|---|
| University of Minnesota Extension | Extensions should discharge water "at least 4 feet beyond the wall" | A minimum; the same page sets a grading rule (below) |
| DOE Building America | Downspouts should "terminate at least 5 feet from the foundation" | Or at an underground catchment system at least 10 feet away |
| NC State Extension | Water piped underground goes to a release outlet "at least 10 feet downhill and away from the house" | It says splash blocks "release water too close to the home" |
| City of Portland, detail SW-102 (2024) | The end of an extension at least 6 feet from basement walls, and 2 feet from crawl spaces and concrete slabs | Portland uses this detail only by exception, with its approval; your city may differ |
A house with a basement needs more distance than one on a slab in the Portland rule, and the 4-foot and 5-foot figures are minimums. Where they differ, choosing the longer figure meets all of them.
Where should the extended water land?
On ground that slopes away from the house and can take the water. University of Minnesota Extension says the soil should slope away from the foundation wall "a minimum of 1 inch per foot for at least 6 feet". If the ground falls back toward the house, a longer extension does not fix it; that is grading work. Portland's sheet says not to discharge "onto driveways, hardscape or other impervious areas including public sidewalks and streets", and that the end may need to sit further from a neighbor's property when the ground slopes toward it.
Which kind of extension fits?
| Kind | Where it fits | What to check |
|---|---|---|
| A fixed section of downspout pipe | A clear run of lawn or bed | Portland requires gutter-grade material for its projects |
| A hinged section that lifts | A path that must stay clear for mowing | That it is down again before rain |
| A splash block alone | Little room beside the wall | NC State says splash blocks are not recommended |
| A flexible plastic hose | Temporary use | Portland prohibits flexible hose for its projects |
| A pipe under the ground | Long runs and paved yards | Underground drains are not part of a repair request here |
How do you measure the length you need?
- Note what is under the house: a basement, a crawl space or a slab.
- Measure from the wall along the ground to the first point where the ground slopes away and can take water.
- Check what is at that point: a walkway, a driveway, a neighbor's lot, or a bed or lawn.
- Take the longer of that distance and the source figure that fits your house.
- Write the result and the downspout's place in the request: "back-left downspout, about 6 feet toward the lawn".
Downspout repair covers a downspout that is loose or crushed, and what a visit clears in a downspout covers clogs.
A worked example
A hypothetical house has a basement. Its back-left downspout empties onto a splash block about a foot from the wall, and a patio starts 7 feet out. University of Minnesota Extension asks for 4 feet, DOE for 5, and Portland's basement figure is 6, so the owner aims for about 6 feet across the lawn, short of the patio. The owner chooses Repair, ticks "A downspout loose, crushed, missing or too short", and writes: "Back-left downspout ends 1 ft from the wall; add an extension about 6 ft toward the lawn; patio starts at 7 ft."
Scope and limits
Fitting or lengthening an above-ground extension is part of a gutter repair request. Pipes under the ground, dry wells and regrading are not. The distances above are each source's own rule; your city's code or a drainage contractor may set a different one. If the gutter above overflows, start with do my gutters need cleaning?
Get my price
Start a downspout extension request, tick the downspout box, and give the length and direction you measured. A person confirms the provider, scope and price in writing before payment.
Any US ZIP. No contact details until you have seen the estimate.
Sources
- University of Minnesota Extension, "Moisture in basements: causes and solutions," https://extension.umn.edu/moisture-and-mold-indoors/moisture-basements-causes-and-solutions, verified 2026-11-10.
- U.S. Department of Energy, Building America Solution Center, "Gutters and Downspouts" (last updated 2021-09-26), https://basc.pnnl.gov/resource-guides/gutters-and-downspouts, verified 2026-11-10.
- NC State Extension, "Moisture Control and Prevention: Gutter Management" (April 20, 2022), https://content.ces.ncsu.edu/moisture-control-and-prevention-gutter-management, verified 2026-11-10.
- City of Portland, Bureau of Environmental Services, "SW-102 Downspout Extension" detail (12/10/24), https://www.portland.gov/bes/stormwater/documents/sw-102-downspout-extension/download, verified 2026-11-10.