What Is Positive Drainage Around a Building?
Positive drainage means the ground slopes away from the building in all directions — typically 6 inches of fall in the first 10 feet (5%) for landscaped areas and 2% minimum for paved surfaces — so water never ponds against the foundation. It is the cheapest structural protection a building has: most foundation distress, basement leaks, and expansive-soil damage trace back to water collecting where it should not.
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The numbers
IRC requires 6 inches of fall within 10 feet of the foundation; where lot lines or physical barriers prevent it, drains or swales must carry the water away. Impervious surfaces (concrete, pavers) need 2% minimum slope away from the building. These are minimums — expansive clays and high-rainfall regions warrant more aggressive grading. The civil engineer's grading plan shows the drainage patterns; the building section should never show flat ground against the wall.
Gutters, downspouts, and discharge
Roof water is the largest single source: a 2,000 sq ft roof sheds 1,200+ gallons in a 1-inch rain. Gutters must be sized and maintained, downspouts must discharge at least 5-10 feet from the foundation (extensions or buried leaders to daylight), and splash blocks alone are not a drainage strategy. Landscaping that dams water against the house — raised beds, edging, mulch volcanoes — defeats the grading.
When grading is not enough
Tight urban lots, uphill neighbors draining onto you, and high water tables need engineered solutions: area drains and catch basins tied to the storm system, retaining walls with backdrains that double as drainage interceptors, and waterproofing designed for the actual water condition (dampproofing is not waterproofing). The geotechnical report's drainage recommendations are part of the foundation design, not landscaping advice.
The bottom line
Slope ground away from the building — 6" in 10' for landscape, 2% for paving — and get roof water 5-10+ feet out. Most foundation water damage is a grading failure, not a structural one.
Torch Engineering PLLC · (480) 490-0064 · info@torchengineering.com — PE stamping backed by Apex Grid Engineering.