Grading and Drainage: How to Slope Your Yard Away from the House

Water Goes Downhill. Make Sure “Downhill” Is Away from Your House.

Foundation damage, flooded basements, mold, erosion, and soggy yards — all caused by water going where it shouldn't. Proper grading is the first line of defense, and it's the one that gets ignored most often. Builders grade the lot before construction, then landscapers, homeowners, and time undo the work. Soil settles. Mulch piles up against the foundation. Garden beds get raised without thinking about drainage. Within a few years, water flows toward the house instead of away from it.

What the Code Requires

The International Residential Code (IRC) Section R401.3 requires the ground to slope away from the foundation at a minimum of 6 inches of fall within the first 10 feet. That works out to roughly 1/2″ per foot, or about a 5% grade.

Where lot lines, walks, or other constraints prevent achieving the full 6 inches in 10 feet, the IRC allows an alternative: a 5% slope for at least 5 feet, combined with a drainage system (like a French drain or swale) to handle the rest. The intent is clear — get water moving away from the structure by whatever means necessary.

Measuring Your Existing Grade

You don't need a surveyor for basic grade checks. Here are two methods:

1. String line and level method. Drive a stake at the foundation wall and another 10 feet out. Tie a string between them and level it with a line level. Measure the distance from the string to the ground at the far stake. That distance should be at least 6 inches less than at the foundation. If the ground is higher at the far stake than at the foundation, water is flowing toward the house.
2. 4-foot level method. Place a 4-foot level on the ground starting at the foundation, with one end at the wall. Lift the far end until the bubble reads level. Measure the gap between the level and the ground at the far end. You want at least 2 inches of drop over those 4 feet (that's 1/2″ per foot).

Check all four sides of the house. Grading problems often exist on one or two sides while the others are fine. Pay special attention to areas where additions were built, driveways meet the foundation, or planting beds abut the house.

Cut and Fill: Moving Dirt

Regrading means moving soil — cutting high spots and filling low spots. For most residential corrections:

• Building up at the foundation. Add compacted fill dirt (not topsoil — it's too soft and settles too much) against the foundation to create the slope. Maintain at least 6 inches of clearance between the soil and any wood framing or siding. Soil touching wood causes rot.
• Cutting at the perimeter. If the yard is relatively flat, removing soil at the 10-foot mark and beyond can create the slope without building up at the house. This works well when you need to maintain existing landscape features.
• Compaction matters. Fill dirt must be compacted in lifts (layers of 4–6 inches, tamped down before adding the next layer). Loose fill will settle within a year and you'll be back where you started. A hand tamper works for small areas; rent a plate compactor for larger jobs.

Swales

A swale is a shallow, wide depression in the landscape that channels water. Think of it as an open ditch with gentle slopes — it looks like a natural contour of the yard but actually directs runoff to a safe discharge point.

For residential work, swales should have a minimum cross-slope of 1% along their length (so water keeps moving) and side slopes no steeper than 3:1 (3 feet horizontal for every 1 foot of drop) so they're easy to maintain with a mower. Line the swale with grass or erosion control fabric. Bare soil in a swale erodes quickly.

French Drains

When grading alone can't solve the problem — flat lots, constraints from property lines, hardscape that can't be moved — a French drain provides an underground path for water.

A French drain is a trench filled with gravel and a perforated pipe, wrapped in filter fabric. Water seeps through the gravel, enters the perforations, and flows through the pipe to a discharge point (daylight opening, storm drain, or dry well).

• Trench depth: 12–18 inches for yard drainage, deeper if intercepting subsurface water
• Trench width: 6–12 inches
• Pipe: 4″ perforated corrugated or rigid PVC, holes down (this is debated, but holes-down with gravel surround is the most common practice)
• Slope: minimum 1% (1/8″ per foot), ideally 1–2%
• Filter fabric: Wrap the entire gravel-and-pipe assembly to prevent soil from migrating into the gravel and clogging the system over time

Downspout Extensions and Discharge

Roof runoff is the single largest source of water near a foundation. A 1,000 square foot roof section in a 1-inch rainstorm produces about 620 gallons of water. If that water dumps at the foundation from a short downspout, no amount of grading will save you.

• Minimum extension: Downspouts should discharge at least 4–6 feet from the foundation. The IRC recommends 6 feet minimum. 10 feet is better.
• Underground extensions: Solid (not perforated) pipe running underground to a pop-up emitter at the yard's low point is the cleanest solution. Use 4″ PVC or corrugated drain pipe at a minimum 1% slope.
• Splash blocks: A minimum solution, not a great one. They slow the water and spread it slightly, but 620 gallons concentrated at one spot overwhelms a splash block in a heavy storm.

Retaining Walls and Grade Changes

When the lot has significant elevation changes, retaining walls hold the higher grade in place. For walls under 4 feet, most jurisdictions don't require an engineer's design (check local codes). Above 4 feet, you typically need an engineered design and a building permit.

Drainage behind a retaining wall is critical. Without it, hydrostatic pressure builds behind the wall after every rain, pushing the wall outward until it fails. Every retaining wall needs:

• Gravel backfill (at least 12 inches) behind the wall face
• A perforated drain pipe at the base, sloped to daylight
• Filter fabric between the gravel and native soil
• Weep holes or drainage aggregate at regular intervals

Erosion Control

Regraded soil is vulnerable until vegetation establishes. A single heavy rain on bare graded soil can undo hours of work. Protect your grade:

• Seed and straw immediately. Grass seed with straw mulch or erosion control blanket is the standard for residential work. Hydroseed for larger areas.
• Silt fence or erosion logs at the downhill edge of disturbed areas to catch sediment before it reaches storm drains or neighboring properties.
• Temporary ground cover. If you can't seed immediately (wrong season, ongoing work), cover bare soil with erosion control blankets, plastic sheeting, or at minimum a layer of straw.

When to Hire a Surveyor

For most residential regrading, a homeowner or landscaper with a level and some common sense can handle the job. But certain situations call for a professional:

• The lot drains toward the house from multiple directions and simple regrading won't fix it
• Water is entering the basement or crawlspace and you need to determine whether the source is surface runoff or a high water table
• You're changing grade significantly (more than 12 inches) near property lines
• Local code requires a grading permit and a grading plan
• The property has easements, utility lines, or septic systems that constrain where you can move dirt

Common Drainage Mistakes

• Mulch volcanoes against the foundation. Thick mulch beds that contact the siding create a moisture pathway into the wall assembly and can reverse the grade within 2–3 years as mulch decomposes and builds up. Keep mulch at least 6 inches below siding and sloped away from the house.
• Directing water to the neighbor. Your grading solution can't create a problem for adjacent properties. If regrading changes where water goes, make sure it goes to a storm drain, swale, or public right-of-way — not into the neighbor's yard.
• Forgetting about window wells. Basement window wells are bowls next to the foundation. Without proper drainage (gravel fill and a drain tied to the footing drain or a sump), they collect water and funnel it directly into the basement.
• Flat patios against the house. Concrete patios, stoops, and walks that abut the foundation must slope away at 1/4″ per foot minimum. A patio that has settled and now slopes toward the house is a guaranteed moisture problem.

Use our Concrete Volume Calculator to estimate material for drainage structures like French drain fill or retaining wall footings. Pair it with the Mulch Calculator to plan your landscape restoration after regrading work is complete.