Grading: How to Slope Water Away From Your Foundation

The grade — the slope of the soil around your foundation — determines where rainwater goes when it falls near your house. Proper grading routes water away from the foundation. Improper grading (flat, or sloping toward the house) routes water toward the foundation, where it collects, exerts hydrostatic pressure, and eventually enters the basement or crawl space. This is one of the most common and most correctable causes of foundation water problems in Seattle.

How Do I Fix Grading That Slopes Toward My House?

The problem: Over decades, soil around the foundation settles. Original grading that sloped away from the house may now be flat or slightly toward the house. Combined with Seattle’s annual rainfall, flat or adverse grading concentrates water at the foundation.

The fix — adding soil to restore slope:

1. Measure the current grade: Use a level and a long board, or a line level on a string. Measure the slope from the foundation outward over 6–10 feet. Note where it’s flat or sloping in.

2. Choose the right fill material: Use a mix of topsoil and fill that drains well — not pure clay (holds water). A mix of 30% topsoil and 70% composted materials or clean fill works well.

3. Apply soil and establish slope: Starting at the foundation, add fill to create a minimum 1-inch drop per foot over the first 6 feet. Slope should be gradual and consistent — not a steep mound immediately adjacent to the foundation.

4. Avoid mounding against the foundation: Keep soil at least 2 inches below any wood framing, siding, or mudsill. Soil in contact with wood creates rot conditions.

5. Compact and settle: The new soil will settle over the first 1–2 rainy seasons. Plan to add another thin layer after settlement.

6. Seed or plant: Re-establish grass, ground cover, or landscape fabric and mulch to prevent erosion of the new grade.

How Much Slope Do I Need Away From My Foundation?

Code requirement: The International Residential Code (IRC) and Seattle’s residential code require a minimum of 6 inches of fall over the first 10 feet from the foundation. In practical terms, this is 0.6 inches per foot.

Recommended minimum for Seattle: 1 inch per foot for the first 6 feet. This is more than the code minimum and is appropriate for Seattle’s rainfall intensity.

How to measure:
– Place a long level (6 feet or longer) with one end at the foundation wall
– Raise the far end until the level reads level
– Measure the distance from the far end of the level to the soil surface
– This is the drop — you want at least 6 inches of drop at 6 feet (1 inch per foot)

More slope is generally better up to a practical limit — very steep grades near the foundation erode quickly and may be difficult to maintain. Slopes greater than 2 inches per foot close to the foundation are typically unnecessary.

What Is the Correct Grade Around a House Foundation?

The standard: 6 inches of fall in the first 10 feet (IRC minimum). Seattle conditions benefit from 1 inch per foot in the first 6 feet.

The extended slope: Beyond the first 6–10 feet, the grade should continue to drain away from the house — at whatever slope the lot permits. Water should drain to the street, to a catch basin, or to the yard’s perimeter — not back toward the house.

Special situations:

Uphill side of the house: If the lot slopes toward the house on one side (common on Seattle’s hillsides), a swale or catch basin on the uphill side intercepts water before it reaches the foundation. Grading alone is insufficient when the lot’s overall slope directs water toward the house.

Flat lots: In flat areas, achieving positive drainage may require raising the foundation side above an existing concrete path or driveway. French drains or catch basins may be necessary to provide drainage when grade alone can’t direct water away.

After adding soil: The added soil takes 1–2 seasons to compact and settle. Plan to add a topping layer the following spring to restore slope after settlement.

Can I Regrade My Own Yard to Fix Drainage?

Yes — for most grading corrections near the foundation:

What’s involved:
– Purchasing topsoil or fill (typically 1–4 cubic yards for a foundation perimeter)
– Spreading and grading with a shovel, rake, and hand tamper or plate compactor (rental)
– Re-establishing the lawn or ground cover

Tools needed:
– Shovel and wheelbarrow
– Landscape rake
– Long level for grade checking
– Plate compactor rental (for larger areas) — $60–$100/day

When professional help adds value:
– Large areas requiring significant earth moving
– Uphill-side drainage problems requiring swales or catch basins
– Situations where downspout re-routing is involved
– When the fix involves navigating retaining walls or complex landscaping

DIY cost: $100–$500 in materials (topsoil, seed, landscape fabric) plus rental equipment. Labor is 2–8 hours of physical work.

How Much Does It Cost to Regrade Around a Foundation?

Seattle area (2026):

What drives cost:
– Area of the regrading project
– Whether existing landscaping or hardscape must be removed
– How much fill needs to be imported
– Complexity of drainage routing to an outlet point
– Whether a swale, catch basin, or French drain is part of the project

Water Pooling Against Foundation Wall — What to Do

Pooling water against the foundation is one of the most damaging ongoing conditions for a Seattle home. It saturates the soil, exerts hydrostatic pressure against the foundation wall, and eventually enters through cracks, the cove joint (wall-floor joint), or porous concrete.

The sequence of problems:
1. Water pools against foundation → soil is continuously saturated
2. Saturated soil → hydrostatic pressure increases against foundation wall
3. Hydrostatic pressure → water enters through any available crack or gap
4. Basement or crawl space becomes wet → wood rot, mold, structural deterioration begin

Immediate steps:
1. Improve grading — add soil and restore 1-inch/foot slope away from the house
2. Extend downspouts — if downspouts terminate near the foundation, extend them 8–10 feet or connect to underground discharge
3. Check for blocked foundation drains — if the foundation has a perimeter drain that’s blocked, clear or replace it

If pooling persists after grading correction:
A French drain along the foundation perimeter intercepts water and routes it away before it can pool against the wall. This is the next step when grading improvement alone isn’t sufficient.

How to Tell If My Yard Is Graded Correctly

Simple visual test: After a significant rain, observe where water collects. If water visibly moves away from the house within minutes of rain stopping, grading is adequate. If water collects against the house for hours, grading is insufficient.

Level test:
– Run a string line or long level from the foundation wall extending outward 6–10 feet
– Note the change in elevation
– The far end of the 6-foot measurement should be at least 6 inches lower than the foundation end

Soil type effect: Clay soil holds water and drains slowly regardless of grade — water may pool temporarily even on a correct grade. The distinction is whether water is pooling against the foundation or in the yard: foundation pooling is the critical concern.

Professional assessment: A drainage contractor or landscape contractor can assess grade with a transit or laser level and give you precise measurements, which is useful when the problem is ambiguous.

How to Add Soil Around Foundation to Improve Slope

Choosing the right soil: Avoid pure clay — it holds water and expands when wet. Use a free-draining blend:
– 70% clean fill (loam or sandy fill) + 30% compost
– Commercial topsoil blend from a landscaping supply company
– Avoid fine soils or pure organic material that compacts excessively

How much soil:
– A 6-foot wide strip around a 50-foot foundation perimeter, 3–4 inches average depth: approximately 4 cubic yards
– A cubic yard covers roughly 80–100 square feet at 3 inches depth

Application:
1. Remove or pull back existing plants, landscape fabric, or mulch
2. Spread fill in layers of 3–4 inches; compact each layer before adding the next
3. Check grade with a level as you work
4. Keep soil at least 2–4 inches below siding, any wood trim, and at least 6 inches below any mudsill or floor framing
5. Re-establish ground cover — seed, sod, or replant with low plants that don’t retain water against the foundation

When to use a retaining structure: If adding enough soil to achieve proper grade would create a steep slope that erodes, a low retaining edge (landscape timber, stone, or concrete edge) at the 6-foot mark stabilizes the grade change.

Does Poor Grading Cause Basement Water Problems?

Yes — frequently. Of all the causes of basement water in Seattle homes, poor grading (combined with inadequate downspout management) is among the most common and most correctable.

The mechanics:
– Poor grade collects water at the foundation
– That water exerts pressure against the foundation wall
– The foundation wall has micro-cracks, porous areas, and the cove joint — all potential entry points
– Water enters and appears in the basement

How to confirm grading is the cause:
– If basement water appears specifically after rain events (not from groundwater rising)
– If the wet areas in the basement correspond to the side of the house with the worst grade
– If correcting downspout extensions and grade reduces or eliminates the water entry

What grading improvement can achieve:
– Eliminating basement water entry in cases where surface water is the source
– Reducing hydrostatic pressure against foundation walls
– Reducing saturated soil conditions that support foundation movement over time

How Far Should Grading Slope Away From the House?

The minimum: 1 inch per foot for the first 6 feet (achieving 6 inches of fall in 6 feet).

The ideal: Maintain a consistent downward slope away from the house for the full distance to the next drainage outlet (street, catch basin, yard perimeter). The first 6 feet is the critical zone; the grade beyond should not slope back toward the house.

The complicating reality: Many Seattle lots are narrow, hilly, or have hardscape that limits where water can go. On narrow urban lots, grading improvement close to the foundation may be limited by the property line — drainage infrastructure (French drains, catch basins) supplements grading in these situations.

For houses on hillside lots: The uphill side requires different treatment than the downhill side. On the uphill side, a swale (shallow channel running across the slope) intercepts hillside runoff before it reaches the foundation. Grading alone is insufficient on the uphill side of a hillside property.

FAQ

Q: How do I fix grading that slopes toward my house?
A: Add a free-draining soil mix (loam + compost, not pure clay) around the foundation to restore a downward slope of at least 1 inch per foot for the first 6 feet. Keep the new soil at least 2 inches below any wood siding or framing. Compact the soil, re-establish ground cover, and plan for a second application after settlement.

Q: How much slope do I need away from my foundation?
A: Code minimum is 6 inches of fall in the first 10 feet. In Seattle’s rainfall conditions, aim for 1 inch per foot in the first 6 feet — 6 inches of fall over 6 feet. This is typically enough to route surface water away from the foundation before it pools.

Q: Does poor grading cause basement water problems?
A: Yes — frequently. When grading slopes toward the foundation, rainwater collects against the house, saturates the soil, and exerts hydrostatic pressure that forces water through any crack or gap. Grading correction is often the cheapest fix for basement water entry.

Q: Can I regrade my own yard?
A: Yes for most foundation perimeter regrading. Purchase topsoil/fill, spread to restore slope, compact, and re-establish ground cover. Materials cost $100–$500; physical labor 2–8 hours. Professional help adds value for larger areas, uphill drainage problems, or when drainage infrastructure (French drains, catch basins) is part of the solution.

Q: How far should grading slope away from the house?
A: The critical zone is the first 6 feet — aim for 1 inch per foot of drop. Beyond 6 feet, the grade should continue to move water away from the house toward a drainage outlet, not slope back toward the house. Hillside lots on the uphill side need a swale or catch basin to intercept runoff before it reaches the foundation.