Gutters
Downspout Drainage: Keep Roof Water Off Your Foundation
Downspouts should drop roof water well away from your house, onto ground that slopes away from the foundation. University of Minnesota Extension says extensions should discharge water at least 4 feet beyond the wall. EPA building guidance goes farther and calls for drain lines that extend at least 10 feet from the foundation.
Gutters only catch the water. The downspout decides where it lands. When we look at a wet basement or a cracked walk, the trouble often starts at the bottom of a downspout, not at the top of the gutter.
Why does downspout water matter so much?
A roof collects a lot of water. UMN Extension figures that a 1-inch rain puts 1,250 gallons of water on the roof of a 2,000-square-foot house. Your gutters gather most of that water and send it down a few downspouts. Each downspout dumps its share in one small spot.
If that spot is right next to the foundation, the soil there stays soaked. Water then finds the easiest path. That can be a crack in the basement wall, the joint where the wall meets the floor, or a window well. UMN Extension says a great number of basement water problems can be solved by handling rainwater with gutters, downspouts, extensions, and proper grading.
Early summer is when this shows up. Our June storms can drop a lot of rain in a short time. A downspout that seemed fine in a light spring rain can flood a corner of the yard in a thunderstorm.
How far should a downspout drain from the house?
Different sources set different targets. Here is what each one says.
| Source | What it says |
|---|---|
| UMN Extension | Extensions should discharge water at least 4 feet beyond the wall |
| EPA Moisture Control Guidance | Connect downspouts to leaders sloped at least 6 inches per 10 feet that extend at least 10 feet from the foundation, or farther if local code requires |
| 2018 IRC R801.3 | Where expansive or collapsible soils are known to exist, roof drainage must discharge at least 5 feet from foundation walls or to an approved drainage system |
The International Residential Code (IRC) is the model code. Ohio's residential code is based on the 2018 IRC, with Ohio changes. Your city or township building department has the final word on local rules.
My plain advice: 4 feet is the minimum. Go farther if your yard allows it. Never let the water turn back toward the house.
Does the ground around your house slope the right way?
Distance alone is not enough. If the ground slopes toward the house, the water comes right back.
The 2018 IRC, in section R401.3, says lots shall be graded so the ground falls at least 6 inches within the first 10 feet from the foundation. Hard surfaces such as walks and patios within 10 feet of the foundation must slope at least 2 percent away from the building. UMN Extension suggests a slope of at least 1 inch per foot for at least 6 feet.
Soil settles over time, especially along new foundations and over old trenches. Flower beds get built up against the house. Mulch piles grow. A yard that drained well when it was built may not drain well now.
Try this on a dry day. Lay a straight board on the ground out from the foundation. Put a level on it. The end near the house should be higher. If it is lower, water is running toward your basement.
What are your downspout drainage options?
Pick the simplest option that gets water far enough away.
- Splash blocks. These concrete or plastic trays sit under the downspout and spread the water. They work on short runs where the ground already slopes away. They do little on flat ground.
- Above-ground extensions. A straight section or a hinged piece that flips up for mowing. They are cheap and easy to change. The downside is that people trip on them, mowers hit them, and they get left flipped up.
- Flexible extensions. These bend around beds and corners. They crush easily and can hold standing water, so check them often.
- Buried drain lines. A solid pipe runs underground to a spot downhill, often ending at the surface or at a pop-up outlet. EPA guidance says to use solid pipe, not perforated pipe, for these lines and to keep the joints watertight. Buried lines can clog with leaves and are hard to clear, so they need a clean gutter above them.
- Rain barrels. A barrel collects some water for the garden. When it fills, the overflow still has to go somewhere. Point the overflow away from the house too.
Check with your city or local sewer district before you connect a downspout to any underground pipe. Rules on where roof water may go vary from place to place.
How do you check your downspouts during a rain?
The best test is a real storm. Put on a rain jacket and walk around the house. Here is what to look for.
- Water comes out of every downspout. A downspout that stays dry while the gutter overflows is clogged.
- Water does not spill over the gutter edge, especially at inside corners and below valleys.
- Each extension is attached and pointed downhill.
- Water flows away across the yard, not along the foundation.
- No puddles form within a few feet of the walls.
- Nothing drains onto a walk or drive that will freeze and become slick in winter.
- Nothing drains toward your neighbor's foundation.
Write down what you see. If you have a basement leak, note which corner is wet and which downspout is closest. That link is often the answer.
Do you have enough downspouts?
Sometimes the problem is not where a downspout drains but how much water it has to carry. UMN Extension recommends at least one downspout per 50 linear feet of roof eave. Berger, a gutter maker, also treats 50 feet as the practical limit for one downspout because of how the metal expands.
A long run with one downspout at the end can overflow in a heavy rain even when it is clean. Adding a downspout, or moving one to a better spot, can fix that. Our gutter installation guide covers sizing and slope in more detail.
How Shamrock can help
We install, replace, and repair seamless gutters across northern Cincinnati, and we size and pitch them to the roof. If water is overflowing or landing in the wrong place, we can look at gutter size, pitch, and downspout placement during a free estimate. Learn more on our gutter services page. If water has already reached your basement, see our water damage restoration page.
FAQ
Can a downspout cause a basement leak? Yes. A downspout that dumps water right at the foundation keeps the soil there soaked. That water can push through cracks and joints in the basement wall. Fixing the downspout is often the first and cheapest step.
Are buried downspout lines better than extensions? They look cleaner and stay out of the mower's path. They also cost more and can clog where you cannot see them. If you choose them, use solid pipe, slope it downhill, and keep the gutters clean.
Should a downspout drain into a window well? No. Water in a window well has nowhere to go but against the window and wall. Move the downspout outlet so it drains away from the well.
What if my lot is too flat to slope 6 inches in 10 feet? The IRC allows for this. Where lot lines or other barriers prevent that fall, it calls for drains or swales to move water away from the house. A swale is a shallow, grassy channel that guides water downhill.