When you think of a “dry basement” the first thing that comes to mind is the waterproofing. This is a common misconception.
Although quality waterproofing is an essential part of the drainage system in a basement, it's only one part. The waterproofing provides a barrier that stops water from penetrating the foundation wall.
With the help of drainage board and some granular fill in the overdigs, water is forced to the footing level. By providing a minimum of eight inches of granular fill and a row of four inch perforated tile on each side of the footing, water easily travels to the sump pit or gravity drain where it is then removed from the foundation.
Also, the granular fill serves as a barrier covering the tile and reducing the chances of concrete damaging or covering the tile when the walls are poured.