Drainage Around Driveways and Patios

How much water there is to move

NOAA's 1991–2020 normals for Wichita list about 34.3 inches of precipitation a year, peaking in May at about 5.2 inches and June at about 4.9 (NOAA NCEI 1991–2020 monthly normals, Wichita Eisenhower airport station). Rain often comes in bursts: the annual normals count about 10.7 days a year with an inch or more of precipitation (NOAA NCEI 1991–2020 annual normals, Wichita Eisenhower airport station), and NWS Wichita lists about 53 thunderstorm days a year (NWS Wichita, annual climate normals for Wichita, Salina and Chanute). A patio that drains fine in a light shower can pond badly in a spring storm.

Slope away from the house

K-State Research and Extension's guide to dry basements recommends sloping the ground away from the foundation about one inch for every foot for 15 feet as ideal, with at least six inches of fall in the first ten feet maintained over time (K-State Research and Extension, MF2809 Dry Basements and Crawl Spaces). Patios and walks next to the house should follow the same idea: pitched away so water leaves the foundation and the slab edge.

Concrete slabs themselves are usually pitched gently, enough to shed water without feeling tilted. The exact slope is part of the design; ask how it will be set before forms go in.

Slope the base too

NRMCA's cracking guidance says the slab, and therefore the subgrade, should be sloped for proper drainage (NRMCA, CIP 4: Cracking Concrete Surfaces). Water that gets under a slab through joints or edges should have somewhere to go rather than sitting on the clay beneath. A compacted granular base helps water move and gives the slab more even support.

Downspouts are the usual suspect

Roofs collect a lot of water. A downspout that empties at the corner of a patio or the edge of a driveway soaks the same spot every storm. On clay that leads to heaving or settling; in winter it creates ice and scaling. Extensions, splash blocks pointed the right way, or underground drain lines carried past the slab solve most of these problems.

Where water meets the house

Gaps where a patio or walk meets the foundation funnel water down beside the house. Over time the soil under that edge washes out and the slab tips toward the house, which makes it worse. Sealing that joint with flexible sealant and correcting the slope stops the cycle. NRMCA recommends an isolation joint where slabs meet walls and other fixed points so each can move independently (NRMCA, CIP 6: Joints in Concrete Slabs on Grade); that joint still needs to be sealed against water.

Clay and water

K-State notes that clay swells when wet and shrinks when dry, with enough force to move concrete sidewalks (K-State Research and Extension, Clay Soil: It Shrinks and Swells). Uneven wetting is the problem. One wet corner and one dry corner give one slab two different foundations. Good drainage keeps moisture under a slab more even. See expansive clay soil under slabs.

Signs of a drainage problem

• Puddles that remain hours after rain
• Scaling or flaking in one area while the rest is fine
• A slab tipped toward the house
• Soil washed out from under an edge
• Ice forming in the same spot every winter
• Algae or dark staining in a low spot
• Wet basement walls next to a patio

Fixes, from simple to involved

1. Redirect water. Downspout extensions and sprinkler adjustments.
2. Seal joints. Especially along the house.
3. Regrade soil. Rebuild the slope along the edges of slabs and the foundation.
4. Add drains. Channel or trench drains across a driveway, or a surface drain at a patio low point.
5. Lift the slab. If a slab settled toward the house, lifting can restore the pitch. See slab lifting.
6. Replace with a better design. New concrete with corrected slope, base and drainage.

Driveways on slopes

Driveways that slope toward the garage collect water at the door. A trench drain across the driveway in front of the garage, and a slight crown or swale to steer water to the sides, can help. Driveways that slope toward the street mostly drain themselves but may wash out the soil along their edges.

Patios in the backyard

Backyards in many Wichita-area subdivisions are graded to drain along lot lines to swales. A new patio should not block that path. Look at where water goes in a heavy storm before deciding the patio's size and shape.

See concrete patios and the estimate factors page for how drainage work affects scope.

Planning a new backyard slab? See concrete patios and what shapes a patio scope.

Sources: K-State Research and Extension, MF2809 Dry Basements and Crawl Spaces; NOAA NCEI 1991–2020 monthly normals, Wichita Eisenhower airport station; NOAA NCEI 1991–2020 annual normals, Wichita Eisenhower airport station; NWS Wichita, annual climate normals for Wichita, Salina and Chanute; NRMCA, CIP 4: Cracking Concrete Surfaces; NRMCA, CIP 6: Joints in Concrete Slabs on Grade; K-State Research and Extension, Clay Soil: It Shrinks and Swells.