Grading & Surface Drainage
~12 min read · Spot negative slope at the foundation and know how far and how fast grade must fall away.
Water is the house's oldest enemy, and grading is the first defense: grade must fall away from the foundation — the benchmark is 6 inches in the first 10 feet — and every site inspection starts by asking where the water goes when it rains.
The slope standard
The stable benchmark: finished grade falls at least 6 inches within the first 10 feet from the foundation (about a 5% slope); impervious surfaces (patios, walks, driveways) within 10 feet slope at least 2% away. Where lot lines or physical barriers prevent 10 feet of fall, swales and drains must carry water off. Negative slope — ground pitching TOWARD the house — is the finding that predicts wet basements, hydrostatic pressure, and settlement.
- 6 in of fall in 10 ft (soil); 2% for paving
- Swales/drains substitute where space is short
- Negative slope = the headline site defect
Reading the site
Field evidence outranks a level: erosion channels and splash marks show flow paths; sediment against the foundation, staining on the stem wall, and moss/algae bands mark standing water; interior confirmation comes from efflorescence and dampness on the matching basement wall. Check downspout discharge (part of the same system), window wells, and low spots that pond. Mulch and landscaping built up ABOVE siding clearance creates a second problem while 'fixing' the first.
- Erosion, sediment, staining: the water's autograph
- Match exterior low spots to interior damp walls
- Raised beds against siding trade drainage for rot and pests
Reporting the finding
The inspection framing: report the CONDITION and its implication, not a code citation — 'grade slopes toward the foundation at the north wall; evidence of moisture intrusion on the interior side; recommend regrading to direct water away.' Cheap dirt-moving now prevents expensive structural and mold remediation later — the classic high-consequence, low-cost correction.
Worked example
At a 12-year-old house, the rear yard tilts visibly toward the foundation; soil touches the siding's bottom edge; the basement's rear wall shows a white crystalline band 18 inches up. The buyer asks: 'is this a foundation problem?'
Chain the evidence: negative slope delivers roof and surface water to the rear wall; the soil-to-siding contact violates the clearance principle (wood siding wants 6 inches to earth) and hides the top of the foundation; the white band inside is efflorescence — minerals left by water migrating through the concrete, proof of chronic moisture, not necessarily structural failure. The report: negative grading (condition) → chronic moisture intrusion (implication) → regrade to achieve fall away from the foundation, restore siding clearance, extend downspouts (action); monitor for structural movement. It is a WATER problem today; left alone, hydrostatic pressure and saturated soils make it a foundation problem eventually.
Common exam pitfalls
Measuring slope only where it's convenient.
Walk all four sides — one negative-slope wall is enough to wet a basement, and additions/patios often break the original grading.
Calling efflorescence 'just cosmetic salt.'
Efflorescence is evidence of water movement through the wall — the finding is the moisture path, not the powder.
Ignoring where downspouts dump.
Perfect grading loses to a downspout discharging at the foundation corner — the system is graded soil PLUS controlled roof water.
Six in ten, two percent paved, water walking away — or it's walking in.
Recap
- Grade falls 6 in over the first 10 ft; paving slopes 2% away
- Negative slope predicts wet basements and pressure damage
- Erosion, sediment, efflorescence: read the water's tracks
- Match exterior findings to interior wall evidence
- Report condition → implication → regrade recommendation
- Downspouts and window wells are part of the grading system
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