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Foundation "Protective Zone"

Engineers refer to the ten feet around a foundation as the "protective zone."  The industry standards and criteria dictate that precautions are taken during the design and construction of grading in this protective zone to ensure proper drainage.  These precautions are critical to avoid damage from water infiltration into the backfill material around the foundation.

The Residential Building Code (IRC) states the following in Section R401.3-Drainage regarding slope around a foundation:

Surface drainage shall be diverted to a storm sewer conveyance or other approved point of collection that does not create a hazard.  Lots shall be graded to drain surface water away from foundation walls.  The grade shall fall a minimum of 6 inches within the first 10 feet. 

Exception: Where lot lines, walls, slopes, or other physical barriers prohibit 6 inches of fall within 10 feet, drains or swales shall be constructed to ensure drainage away from the structure.  Impervious surfaces within 10 feet of the building foundation shall be sloped a minimum of 2 percent away from the building.

The optimum slope away from a foundation is 12 inches of vertical drop for the first ten feet.  In cases where ten feet of distance is not available, for example, where houses are very close together, 6 inches vertical drop for the first 5 feet may be used.

Slope at Foundation
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