Why water matters so much
Water changes soil. Clay swells when wet and shrinks when dry, so uneven moisture moves slabs and footings. Saturated soil weighs more and pushes harder on basement walls, and freezing water in wet soil adds frost pressure. Sandy soil can wash out from under slabs when water is concentrated. In karst areas, concentrated runoff speeds up sinkhole formation. Whatever your region, water management is the foundation of foundation care.
1. Gutters and downspouts
A single roof can shed thousands of gallons of water in a heavy storm, and gutters concentrate it at a few downspouts. If those downspouts empty right next to the foundation, the soil there gets far more water than anywhere else around the house.
- Keep gutters clean so they do not overflow along the wall.
- Extend downspouts well away from the foundation; many builders and inspectors recommend several feet at minimum, and some guidance suggests up to 10 feet where the yard allows.
- Use splash blocks, extensions or underground lines that discharge to daylight, a swale or an approved drain.
- Check that underground downspout lines are not cracked or clogged; broken lines can dump water right at the footing.
2. Grading
The International Residential Code, which many US jurisdictions adopt, requires lots to be graded to drain surface water away from foundation walls, with a fall of at least 6 inches within the first 10 feet. Where that is not possible, the ground must slope at least 5 percent away and water must be directed to drains or swales, and impervious surfaces within 10 feet of the foundation must slope at least 2 percent away. Over time, soil settles and landscaping builds up, so grades that were right when the house was built often slope back toward it decades later.
- Add soil to rebuild a slope away from the house, keeping it below siding and weep holes.
- Keep mulch and planting beds from trapping water against the wall.
- Make sure patios, walks and driveways slope away, not toward the house.
3. French drains and swales
A French drain is a gravel-filled trench with a perforated pipe that collects groundwater and surface water and carries it to a lower discharge point. A swale is a shallow, grassed channel that guides surface runoff around the house. Both are useful on sloped lots where water runs toward an uphill wall, common in Atlanta, Birmingham, Knoxville, Chattanooga and the West Hills of Portland. They need a place to discharge and a proper slope, so they are usually worth a professional design.
4. Footing drains and interior drainage
Many basements have footing drains (drain tile) around the outside of the footing that collect groundwater and send it to a sump or to daylight. In older homes these are often clogged or collapsed. Replacing exterior drains means excavation; the alternative is interior drainage along the inside of the footing to a sump pump. Interior systems relieve water pressure on the floor and wall joint but do not reduce soil pressure on the outside of the wall, so they are often combined with wall stabilization for bowing walls. See bowing basement walls.
5. Sump pumps
Where groundwater is high, a sump pump removes water collected by footing or interior drains. A battery or water-powered backup protects against power outages during storms, exactly when the pump is needed most. Discharge must go well away from the house, not back toward the foundation.
Drainage by region
| Region | Main drainage concern |
|---|---|
| Texas clay (Dallas, Houston, San Antonio, Austin) | Even moisture around slabs; avoid ponding and dry gaps |
| Northeast and Mid-Atlantic basements | Runoff and groundwater pressure on block and stone walls |
| Hillside homes (Atlanta, Birmingham, Tennessee, Portland) | Runoff toward uphill walls; retaining wall drainage |
| Florida and coastal areas | Washout of sandy soil under slab edges and pool decks |
| Karst areas | Avoid concentrating water in one spot |
When drainage is enough and when it is not
Better drainage can stop minor, seasonal movement and slow ongoing problems. It will not lift a settled slab, straighten a bowed wall or replace failed footings. If cracks keep growing, doors keep sticking or walls keep moving after drainage is fixed, have the foundation evaluated. Many foundation contractors include drainage work in their plans; see the foundation repair process.
Retaining walls and drainage
Retaining walls hold back soil next to driveways, patios and yards on sloped lots. Without drainage behind them, water builds up, pushes the wall forward and keeps soil near the house wet. Signs of trouble include leaning, bulging, cracks and water seeping through the face. Good walls have gravel backfill, a drain pipe at the base and weep holes. A failing wall close to the house can affect the foundation, so it is worth having both looked at together.
Costs in context
Drainage improvements range from very low cost, such as downspout extensions and regrading a few low spots, to larger projects such as French drains, footing drain replacement or interior drainage with a sump pump. Compared with structural foundation repair, drainage is usually the less expensive part of a plan, and it protects the structural work. Ask contractors to price drainage and structural items separately so you can see both.
Common drainage mistakes
- Downspouts connected to buried pipes that are clogged or broken, dumping water at the footing.
- Landscape edging and raised beds that hold water against the wall.
- Sump pump discharge that runs back toward the house.
- Irrigation heads spraying the foundation every day.
- Gutters sized too small for the roof, so they overflow in every heavy storm.
A simple yearly check
- Walk around the house during a heavy rain and watch where water goes.
- Clean gutters in spring and fall.
- Check downspout extensions and underground lines.
- Look for low spots next to the foundation and refill them.
- Test the sump pump before storm season.