Insulated, precast concrete foundation walls need a compacted and leveled gravel footing before the walls can be dropped in place. This type of foundation system often can be set up in only two days: one day for prep work and one day for setting the walls.
But before the foundation crew can set the panels, the contractor’s crew must install a foundation drain and then dump, level and compact the gravel footing. The next day, the foundation crew will regrade the gravel to a more exacting tolerance and then install the wall panels.
The gravel footings must extend below the frost line. For this foundation, which has a daylight basement, that meant digging down along the right side where the foundation won’t be backfilled. In North Carolina, the frost line is 12 in. below the surface. A perforated-pipe perimeter drain outside the foundations wall will run around the inside of the excavation and then down into the front trench where it’ll connect with a drain (barely visible in the corner of the trench).