Building Residential Occupancies on Hillsides or Slopes
R401.3 Drainage - Surface drainage shall be diverted to a storm sewer conveyance or other approved point of collection so as to not create a hazard. Lots shall be graded so as to drain surface water away from foundation walls. The grade away from foundation walls shall fall a minimum of 6" (152 mm) within the first 10’ (3,048 mm). One exception is where lot lines, walls, slopes, or other physical barriers prohibit 6" (152 mm) of fall within 10’ (3,048 mm), drains or swales shall be provided to ensure drainage away from the structure.