How to divert water away from the house
Most wet foundations come down to two things: where roof water lands and which way the soil tilts. Fix those first.
To divert water away from the house, move roof runoff well past the foundation and make the soil near the wall slope away from it. Those two changes handle most of the water that reaches a basement or crawl space from outside. Digging and piping come later, if they come at all.
This page prints no prices. Costs vary by region and year. It explains the order of the work so you can judge a plan.
Step one: send roof water far from the wall
Roof water is often the largest load beside a foundation. Each downspout should discharge well clear of the house, onto ground that falls away. A surface extension is a sound first move. If it is in the way, a buried solid pipe does the same job, as explained in downspout drain pipe.
Check where each one empties after a storm. If water pools within a few feet of the wall, it has not gone far enough.
Step two: fix the slope of the soil
The ground around the house should fall away from the wall for the first several feet. Over the years, backfill settles and the slope can flatten or even reverse. Water then runs toward the house and soaks in along the foundation.
Adding compacted soil to rebuild the fall is a basic and effective fix. The grading and downspouts page covers how much fall is typical. Keep the soil below any siding or the top of the foundation wall that is meant to stay exposed.
Step three: look at paved surfaces
Patios, walks and driveways that tilt toward the house send water straight at the wall. If they slope the wrong way, the fix is to redirect the water, not to hope the seam holds. Sealing a crack helps a little, but it does not change the slope.
Step four: only then consider drains
If the yard is still wet after the roof water and slope are fixed, a surface or trench drain may help. Be honest about what it can do. A shallow yard drain moves shallow water, and it needs somewhere to send it. Two pages to read first: French drain without pipe and dry wells.
Skip anything that stores water close to the foundation. A dry well or pit placed too near the wall turns the soil there into a reservoir.
What not to do
- Do not dump water on a neighbor's property or onto a walkway.
- Do not tie roof water into the sump discharge or a foundation drain.
- Do not pile mulch or soil against siding to build a slope.
- Do not dig deep beside a wall that is cracked, bowed or leaning.
If the basement is still wet
Outside water control cuts the load but does not cover every source. Rising groundwater, a cracked floor or a failed drain can all keep a basement damp. The water diagnosis tool helps tell them apart.
Take a position: spend nothing on a membrane or a sump until the downspouts and the slope are right. Both are cheap to check and often make the rest unnecessary.
Where to stop and call someone
A wall that is cracked, bowed or leaning is a question for a licensed structural engineer, and an independent one has no repair to sell you. For rules on discharge points, grading near property lines and digging, ask your building department, because requirements are set locally.
Frequently asked questions
How do I divert water away from my house?
Send downspouts well past the foundation and rebuild the soil slope so it falls away from the wall for the first several feet.
What is the cheapest way to keep water away from a foundation?
Downspout extensions and correct grading. They address the two biggest sources and need no digging near the wall.
Do I need a French drain to divert water?
Often not. Fix roof runoff and slope first. A yard drain only helps with shallow water and needs an outlet.
How far should water drain from the house?
As far as the site allows, past the area where the ground slopes back toward the wall. Local rules can set limits, so check with your building department.
Can I dig beside the foundation to redirect water?
Not if the wall is cracked or leaning. Digging next to a stressed foundation can make it worse, so ask a licensed structural engineer first.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- US EPA. What You Can Do to Soak Up the Rain
- US EPA. Soak Up the Rain. Managing stormwater around a property