Grading and foundation drainage
Summary: The building code requires the ground to fall at least 6 inches in the first 10 feet away from a new house, and hard surfaces to slope at least 2%. Roof water should discharge 5 feet or more from the foundation; Indianapolis requires at least 3 feet[2][1][4].
Why does grading matter?
The ground around a house decides where water goes after it leaves the downspout or falls straight on the yard. The U.S. Department of Energy’s building science guidance warns that water not drained away “can rapidly saturate the soil surrounding the building and wick through the foundation to the interior”, leading to mold, rot, poor indoor air and reduced durability[1]. It lists the defenses: sloping grade away from the house, gutters, perimeter drain pipe, a capillary break, and free-draining soils or a drainage mat.
What does the code require?
The International Residential Code, the model code behind Indiana’s residential code, says lots “shall be graded to drain surface water away from foundation walls” and that the grade “shall fall a minimum of 6 inches within the first 10 feet”[2]. Where lot lines, walls or other barriers make that impossible, the code allows drains or swales to carry water away instead. Impervious surfaces within 10 feet of the foundation must slope at least 2% away from the building. Those rules apply to new construction; existing houses are not usually required to be regraded, but the numbers are a good target.
| Surface | Minimum fall away from foundation |
|---|---|
| Soil (first 10 ft) | 6 in (5%) |
| Impervious surfaces such as patios (within 10 ft) | 2% |
What about roof water?
Where expansive or collapsible soils are known, the IRC requires a controlled method of roof drainage that discharges at least 5 feet from foundation walls or to an approved drainage system[3]. The DOE guidance makes a similar recommendation for all houses: pipe downspout water to a sloping grade more than 5 feet from the foundation, or to an underground catchment more than 10 feet away that is not connected to the foundation drain[1]. In Indianapolis, Citizens Energy Group sets a minimum of 3 feet and bans connections to the sanitary sewer[4].
How can I check my own grading?
- Tie a string to a stake at the foundation and another stake 10 feet out, level it with a line level, and measure from the string to the ground at the outer stake. You want 6 inches or more of drop.
- Walk the house in a heavy rain and note where water stands, where downspouts discharge and where splash hits the wall.
- Look for settled backfill, which often sinks next to foundations in the years after a house is built and leaves a dip that collects water.
- Check that mulch and soil in flower beds do not slope toward the house or bury the siding.
Small corrections, such as adding compacted soil to fill a settled strip, are often enough. Where the yard is flat or slopes toward the house, a swale, a French drain or a buried downspout line to a lower point may be needed.
Does frost depth matter for drainage?
Yes, for anything buried. The Indianapolis homeowner permit guide lists a frost line depth of 30 inches[5]. Downspout lines are usually shallower than that, so they must slope continuously to an outlet and drain dry between storms; a line that holds water can freeze, crack or block. Celtic Rainwater Systems’ drainage page stresses PVC lines designed not to clog[6].
See also
Common questions
How much should the ground slope away from a house?
The IRC requires a fall of at least 6 inches within the first 10 feet for new construction.
How far should water be discharged from a foundation?
At least 5 feet under the IRC where soils are expansive or collapsible; DOE guidance recommends more than 5 feet for all houses; Citizens requires at least 3 feet in Indianapolis.
What is the frost line in Indianapolis?
30 inches, per the city’s homeowner permit guide.
References
- ^ a b c Foundation Drain, Gutters and Downspouts. U.S. Department of Energy, Building Science Education Solution Center. Accessed 9 November 2026.
- ^ a b 2021 International Residential Code, Section R401.3 Drainage. International Code Council. Accessed 9 November 2026.
- ^ 2021 International Residential Code, Section R801.3 Roof drainage. International Code Council. Accessed 9 November 2026.
- ^ a b Our Wastewater Correct Connect Initiative. Citizens Energy Group. Accessed 9 November 2026.
- ^ Homeowner’s Building Permit Guide (work exempt from permitting; local design criteria). City of Indianapolis and Marion County, Department of Business and Neighborhood Services. Accessed 9 November 2026.
- ^ Drainage (PVC downspout drainlines, French drains, basement drainage and sump pumps). Celtic Rainwater Systems (celticrainwater.com). Accessed 9 November 2026.