Foundation Drainage in Heavy Rain: French Drains, Gutters, and Negative Slope Risks
Water always follows the path of least resistance. If your yard slopes toward your house, thousands of gallons of winter runoff will pool beneath your foundation. Here is how to engineer water away from your home.
Zachary Bradley
Licensed Home Inspector · WA Lic #26014533
Key Inspector Takeaways
- ✓Building code requires ground to slope away from the foundation at least 6 inches in the first 10 feet (5% positive slope).
- ✓A standard roof catches over 60,000 gallons of rain annually; discharging downspouts next to foundation walls guarantees crawl space flooding.
- ✓Perimeter French drains intercept subsurface groundwater before it penetrates foundation stem walls.
- ✓Sump pumps must discharge water out to daylight drainage swales, never back onto the foundation.
Surface Water vs Subsurface Groundwater
Managing wet Washington winters requires two separate drainage defenses: surface water control (gutters, slope grading, swales) and subsurface drainage (footing drains, interior French drains, sump basins).
The 6-Foot Downspout Rule
Never let gutter downspouts dump water at the foundation corners. Install smooth-wall PVC piping underground to discharge rainwater at least 10 feet away or into an approved municipal storm catch basin.
Frequently Asked Questions
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