Short answer
Direct roof water at least 6 to 10 feet away from your foundation using solid downspout extensions or a buried solid pipe that slopes to daylight or a pop-up emitter. Regrade the soil so it slopes away from the house at about 5 percent for the first 10 feet, using compactable, clay-rich fill and keeping finished grade 6 to 8 inches below the bottom edge of siding. Combine both measures for the best protection against basement moisture.
Key measurements and specs
Downspout discharge distance: 6–10 feet minimum from foundation
Surface grade: 5 percent slope for first 10 feet (6 inches drop over 10 feet)
Buried pipe slope: 1–2 percent (about 1/8 to 1/4 inch per foot)
Pipe size: 3–4 inch solid pipe for roof leaders
Finished grade clearance: keep soil 6–8 inches below siding or framing
Dry well distance: 10–15 feet away from foundation (only where soils drain well)
How to direct downspouts effectively
1) Choose your discharge method
- Surface extension: Easiest and cheapest. Attach a hinged or rigid extension to the downspout and run it 6 to 10 feet over the lawn or landscaping. Add a splash block at the end if desired.
- Buried to pop-up emitter: Cleaner look and less trip hazard. Run 3 or 4 inch solid pipe underground with a steady slope to a pop-up emitter or daylight. Add a cleanout near the downspout.
- Dry well or infiltration trench: Only if soil percolates well. Use a chamber or rock-filled pit wrapped in fabric, placed 10 to 15 feet from the foundation. Avoid in heavy clay.
2) Size and maintain gutters and downspouts
- Use at least one downspout per 30 to 40 feet of gutter. Consider upsizing to 3 by 4 inch downspouts for high-flow roofs.
- Keep gutters clean. Add downspout strainers or gutter guards to reduce clogging.
3) Materials you will need
- Downspout adapters and elbows, 3 by 4 inch typical
- 3 or 4 inch solid PVC or corrugated polyethylene pipe
- Pop-up emitter, catch basin or cleanout, and fittings
- Compactable fill soil with some clay content, topsoil for the final inch or two
- Mulch, sod, or seed to stabilize
- Landscape fabric and 3 quarter inch drain rock if doing a dry well
4) Tools
- Ladder, gloves, safety glasses
- Tape measure, string line and stakes, 2 or 4 foot level or laser level
- Shovel, trenching shovel, mattock or pick, hand tamper
- Utility knife, PVC saw, PVC cement or rubber couplings
- Wheelbarrow and rake
Step-by-step: Regrade the soil
1) Pull back mulch and plants within 3 to 5 feet of the foundation. Keep wood mulch off the wall.
2) Add clayey fill in 2 to 3 inch lifts, compacting each lift with a hand tamper. Aim for a total drop of 6 inches over the first 10 feet from the foundation.
3) Maintain clearance: keep finished soil at least 6 to 8 inches below siding or wood framing to prevent rot and pests.
4) Shape shallow swales to steer water around window wells and toward safe discharge areas like a driveway or daylight.
5) Top with an inch or two of topsoil and stabilize with sod or seed. Recheck slope after watering; add more fill if settlement occurs.
Time and cost: A basic regrade along one side of a house is a half-day to one-day DIY project. Expect 1 to 3 cubic yards of soil at 20 to 50 dollars per yard plus delivery. Hand tamper 30 to 50 dollars.
Step-by-step: Buried downspout to pop-up emitter
1) Call 811 before you dig to mark utilities. Plan a route that avoids property lines, trees, and hardscape.
2) Set slope: From the downspout outlet, stake a string line to the emitter location and set a 1 to 2 percent fall.
3) Dig a trench 12 to 18 inches deep. Maintain a consistent slope; avoid bellies that hold water.
4) Install a leaf filter or cleanout at the downspout, then run 3 or 4 inch solid pipe to the emitter or daylight. Dry-fit first, then glue PVC or use gasketed couplings.
5) Test with a hose. Fix any sags. Backfill and lightly compact. Keep the emitter top flush with surrounding turf.
Time and cost: A typical 25 to 40 foot run costs 100 to 300 dollars in pipe and fittings, plus 20 to 30 dollars for a pop-up emitter. Expect 3 to 6 hours DIY depending on soil.
Safety and code considerations
- Ladder safety: 3 points of contact, stable footing, and avoid working in wind or rain.
- Digging safety: Call 811, wear boots and gloves, and never enter trenches deeper than 4 feet.
- Do not discharge onto sidewalks or driveways where icing can occur.
- Check local rules on stormwater discharge and neighbor runoff. Avoid directing water across property lines.
Tips for best results
- Use solid pipe for roof leader lines; perforated pipe near the foundation can leak water back into the soil you are trying to dry.
- Clay-rich fill near the house sheds water better than sandy soil. Save topsoil for the top layer only.
- Add a hinged extension that flips up for mowing if you use surface extensions.
- Window wells: Add clear covers and ensure the well drains; do not let downspouts discharge near them.
- Sump pump discharge should run at least 10 to 20 feet from the house and not into foundation drains.
Common mistakes to avoid
- Short or missing downspout extensions that dump right at the foundation
- Flat grades or edging that traps water against the house
- Setting soil too high against siding or covering weep screed on stucco
- No cleanouts on buried lines, leading to clogs
- Expecting mulch or decorative rock to fix slope issues without adding compacted fill underneath
When to call a pro
- Persistent seepage, wall cracking, or hydrostatic pressure signs
- Large-scale regrading, swale construction, or tie-in to municipal storm laterals
- Poor site drainage where the house sits lower than surrounding yards
- If you need a stamped drainage plan or permits
With clean gutters, properly extended downspouts, and a firm positive grade away from the house, most basement water issues improve dramatically. Start with the easy fixes, reassess during a rain, and upgrade to buried piping or site regrading as needed. Check the ToolStash catalog for 4 inch drainage pipe, pop-up emitters, tamps, and laser levels to make the work faster and cleaner.